The Electromagnetic Spectrum

Electromagnetic spectrum

From Wikipedia, the free encyclopedia

Class				Freq uency	Wave length	Energy
				300 EHz	1 pm	1.24 MeV
	γ	Gamma rays
				30 EHz	10 pm	124 keV
	HX	Hard X-rays
				3 EHz	100 pm	12.4 keV
	SX	Soft X-rays
				300 PHz	1 nm	1.24 keV
				30 PHz	10 nm	124 eV
	EUV	Extreme ultraviolet
				3 PHz	100 nm	12.4 eV
	NUV	Near ultraviolet
Visible				300 THz	1 μm	1.24 eV
	NIR	Near Infrared
				30 THz	10 μm	124 meV
	MIR	Mid infrared
				3 THz	100 μm	12.4 meV
	FIR	Far infrared
				300 GHz	1 mm	1.24 meV
Radio waves	EHF	Extremely high frequency
				30 GHz	1 cm	124 μeV
	SHF	Super high frequency
				3 GHz	1 dm	12.4 μeV
	UHF	Ultra high frequency
				300 MHz	1 m	1.24 μeV
	VHF	Very high frequency
				30 MHz	10 m	124 neV
	HF	High frequency
				3 MHz	100 m	12.4 neV
	MF	Medium frequency
				300 kHz	1 km	1.24 neV
	LF	Low frequency
				30 kHz	10 km	124 peV
	VLF	Very low frequency
				3 kHz	100 km	12.4 peV
	VF / ULF	Voice frequency
				300 Hz	1 Mm	1.24 peV
	SLF	Super low frequency
				30 Hz	10 Mm	124 feV
	ELF	Extremely low frequency
				3 Hz	100 Mm	12.4 feV
Sources: File:Light spectrum.svg [1] [2] [3]

The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation.^[4] The "electromagnetic spectrum" of an object has a different meaning, and is instead the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object.

The electromagnetic spectrum extends from below the low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency) end, thereby covering wavelengths from thousands of kilometers down to a fraction of the size of an atom. The limit for long wavelengths is the size of the universe itself, while it is thought that the short wavelength limit is in the vicinity of the Planck length.^[5] Until the middle of last century it was believed by most physicists that this spectrum was infinite and continuous.

Most parts of the electromagnetic spectrum are used in science for spectroscopic and other probing interactions, as ways to study and characterize matter.^[6] In addition, radiation from various parts of the spectrum has found many other uses for communications and manufacturing (see electromagnetic radiation for more applications).

 

 

 

 

 

 

 

 

 

 

History of electromagnetic spectrum discovery

For most of history, visible light was the only known part of the electromagnetic spectrum. The ancient Greeks recognized that light traveled in straight lines and studied some of its properties, including reflection and refraction. Over the years the study of light continued and during the 16th and 17th centuries there were conflicting theories which regarded light as either a wave or a particle.^{[citation needed]}

The first discovery of electromagnetic radiation other than visible light came in 1800, when William Herschel discovered infrared radiation.^[7] He was studying the temperature of different colors by moving a thermometer through light split by a prism. He noticed that the highest temperature was beyond red. He theorized that this temperature change was due to "calorific rays" which would be in fact a type of light ray that could not be seen. The next year, Johann Ritter worked at the other end of the spectrum and noticed what he called "chemical rays" (invisible light rays that induced certain chemical reactions) that behaved similar to visible violet light rays, but were beyond them in the spectrum.^[8] They were later renamed ultraviolet radiation.

Electromagnetic radiation had been first linked to electromagnetism in 1845, when Michael Faraday noticed that the polarization of light traveling through a transparent material responded to a magnetic field (see Faraday effect). During the 1860s James Maxwell developed four partial differential equations for the electromagnetic field. Two of these equations predicted the possibility of, and behavior of, waves in the field. Analyzing the speed of these theoretical waves, Maxwell realized that they must travel at a speed that was about the known speed of light. This startling coincidence in value led Maxwell to make the inference that light itself is a type of electromagnetic wave.
Maxwell's equations predicted an infinite number of frequencies of electromagnetic waves, all traveling at the speed of light. This was the first indication of the existence of the entire electromagnetic spectrum.

Maxwell's predicted waves included waves at very low frequencies compared to infrared, which in theory might be created by oscillating charges in an ordinary electrical circuit of a certain type. Attempting to prove Maxwell's equations and detect such low frequency electromagnetic radiation, in 1886 the physicist Heinrich Hertz built an apparatus to generate and detect what is now called radio waves. Hertz found the waves and was able to infer (by measuring their wavelength and multiplying it by their frequency) that they traveled at the speed of light. Hertz also demonstrated that the new radiation could be both reflected and refracted by various dielectric media, in the same manner as light. For example, Hertz was able to focus the waves using a lens made of tree resin. In a later experiment, Hertz similarly produced and measured the properties of microwaves. These new types of waves paved the way for inventions such as the wireless telegraph and the radio.

In 1895 Wilhelm Röntgen noticed a new type of radiation emitted during an experiment with an evacuated tube subjected to a high voltage. He called these radiations x-rays and found that they were able to travel through parts of the human body but were reflected or stopped by denser matter such as bones. Before long, many uses were found for them in the field of medicine.

The last portion of the electromagnetic spectrum was filled in with the discovery of gamma rays. In 1900 Paul Villard was studying the radioactive emissions of radium when he identified a new type of radiation that he first thought consisted of particles similar to known alpha and beta particles, but with the power of being far more penetrating than either. However, in 1910, British physicist William Henry Bragg demonstrated that gamma rays are electromagnetic radiation, not particles, and in 1914, Ernest Rutherford (who had named them gamma rays in 1903 when he realized that they were fundamentally different from charged alpha and beta rays) and Edward Andrade measured their wavelengths, and found that gamma rays were similar to X-rays, but with shorter wavelengths and higher frequencies.

Range of the spectrum

Electromagnetic waves are typically described by any of the following three physical properties: the frequency f, wavelength λ, or photon energy E. Frequencies observed in astronomy range from 2.4×10²³ Hz (1 GeV gamma rays) down to the local plasma frequency of the ionized interstellar medium (~1 kHz). Wavelength is inversely proportional to the wave frequency,^[6] so gamma rays have very short wavelengths that are fractions of the size of atoms, whereas wavelengths on the opposite end of the spectrum can be as long as the universe. Photon energy is directly proportional to the wave frequency, so gamma ray photons have the highest energy (around a billion electron volts), while radio wave photons have very low energy (around a femtoelectronvolt). These relations are illustrated by the following equations:

where:

• c = 299,792,458 m/s is the speed of light in vacuum and
• h = 6.62606896(33)×10⁻³⁴ J s = 4.13566733(10)×10⁻¹⁵ eV s is Planck's constant.^[9]

Whenever electromagnetic waves exist in a medium with matter, their wavelength is decreased.

Wavelengths of electromagnetic radiation, no matter what medium they are traveling through, are usually quoted in terms of the vacuum wavelength, although this is not always explicitly stated.

Generally, electromagnetic radiation is classified by wavelength into radio wave, microwave, terahertz (or sub-millimeter) radiation, infrared, the visible region is perceived as light, ultraviolet, X-rays and gamma rays. The behavior of EM radiation depends on its wavelength. When EM radiation interacts with single atoms and molecules, its behavior also depends on the amount of energy per quantum (photon) it carries.

Spectroscopy can detect a much wider region of the EM spectrum than the visible range of 400 nm to 700 nm. A common laboratory spectroscope can detect wavelengths from 2 nm to 2500 nm. Detailed information about the physical properties of objects, gases, or even stars can be obtained from this type of device. Spectroscopes are widely used in astrophysics. For example, many hydrogen atoms emit a radio wave photon that has a wavelength of 21.12 cm. Also, frequencies of 30 Hz and below can be produced by and are important in the study of certain stellar nebulae^[10] and frequencies as high as 2.9×10²⁷ Hz have been detected from astrophysical sources.^[11]

Rationale for spectrum regional names

Electromagnetic radiation interacts with matter in different ways across the spectrum. These types of interaction are so different that historically different names have been applied to different parts of the spectrum, as though these were different types of radiation. Thus, although these "different kinds" of electromagnetic radiation form a quantitatively continuous spectrum of frequencies and wavelengths, the spectrum remains divided for practical reasons related to these qualitative interaction differences.

Region of the spectrum	Main interactions with matter
Radio	Collective oscillation of charge carriers in bulk material (plasma oscillation). An example would be the oscillatory travels of the electrons in an antenna.
Microwave through far infrared	Plasma oscillation, molecular rotation
Near infrared	Molecular vibration, plasma oscillation (in metals only)
Visible	Molecular electron excitation (including pigment molecules found in the human retina), plasma oscillations (in metals only)
Ultraviolet	Excitation of molecular and atomic valence electrons, including ejection of the electrons (photoelectric effect)
X-rays	Excitation and ejection of core atomic electrons, Compton scattering (for low atomic numbers)
Gamma rays	Energetic ejection of core electrons in heavy elements, Compton scattering (for all atomic numbers), excitation of atomic nuclei, including dissociation of nuclei
High-energy gamma rays	Creation of particle-antiparticle pairs. At very high energies a single photon can create a shower of high-energy particles and antiparticles upon interaction with matter.

Types of radiation

The electromagnetic spectrum

Boundaries

A discussion of the regions (or bands or types) of the electromagnetic spectrum is given below. Note that there are no precisely defined boundaries between the bands of the electromagnetic spectrum; rather they fade into each other like the bands in a rainbow (which is the sub-spectrum of visible light). Radiation of each frequency and wavelength (or in each band) will have a mixture of properties of two regions of the spectrum that bound it. For example, red light resembles infrared radiation in that it can excite and add energy to some chemical bonds and indeed must do so to power the chemical mechanisms responsible for photosynthesis and the working of the visual system.

Regions of the spectrum

The types of electromagnetic radiation are broadly classified into the following classes:^[6]

1. Gamma radiation
2. X-ray radiation
3. Ultraviolet radiation
4. Visible radiation
5. Infrared radiation
6. Terahertz radiation
7. Microwave radiation
8. Radio waves

This classification goes in the increasing order of wavelength, which is characteristic of the type of radiation.^[6] While, in general, the classification scheme is accurate, in reality there is often some overlap between neighboring types of electromagnetic energy. For example, SLF radio waves at 60 Hz may be received and studied by astronomers, or may be ducted along wires as electric power, although the latter is, in the strict sense, not electromagnetic radiation at all (see near and far field).

The distinction between X-rays and gamma rays is partly based on sources: the photons generated from nuclear decay or other nuclear and subnuclear/particle process, are always termed gamma rays, whereas X-rays are generated by electronic transitions involving highly energetic inner atomic electrons.^[12][13][14] In general, nuclear transitions are much more energetic than electronic transitions, so gamma-rays are more energetic than X-rays, but exceptions exist. By analogy to electronic transitions, muonic atom transitions are also said to produce X-rays, even though their energy may exceed 6 megaelectronvolts (0.96 pJ),^[15] whereas there are many (77 known to be less than 10 keV (1.6 fJ)) low-energy nuclear transitions (e.g., the 7.6 eV (1.22 aJ) nuclear transition of thorium-229), and, despite being one million-fold less energetic than some muonic X-rays, the emitted photons are still called gamma rays due to their nuclear origin.^[16]

The convention that EM radiation that is known to come from the nucleus, is always called "gamma ray" radiation is the only convention that is universally respected, however. Many astronomical gamma ray sources (such as gamma ray bursts) are known to be too energetic (in both intensity and wavelength) to be of nuclear origin. Quite often, in high energy physics and in medical radiotherapy, very high energy EMR (in the >10 MeV region) which is of higher energy than any nuclear gamma ray, is not referred to as either X-ray or gamma-ray, but instead by the generic term of "high energy photons."

The region of the spectrum in which a particular observed electromagnetic radiation falls, is reference frame-dependent (due to the Doppler shift for light), so EM radiation that one observer would say is in one region of the spectrum could appear to an observer moving at a substantial fraction of the speed of light with respect to the first to be in another part of the spectrum. For example, consider the cosmic microwave background. It was produced, when matter and radiation decoupled, by the de-excitation of hydrogen atoms to the ground state. These photons were from Lyman series transitions, putting them in the ultraviolet (UV) part of the electromagnetic spectrum. Now this radiation has undergone enough cosmological red shift to put it into the microwave region of the spectrum for observers moving slowly (compared to the speed of light) with respect to the cosmos.

Radio frequency

 

Radio waves generally are utilized by antennas of appropriate size (according to the principle of resonance), with wavelengths ranging from hundreds of meters to about one millimeter. They are used for transmission of data, via modulation. Television, mobile phones, wireless networking, and amateur radio all use radio waves. The use of the radio spectrum is regulated by many governments through frequency allocation.

Radio waves can be made to carry information by varying a combination of the amplitude, frequency, and phase of the wave within a frequency band. When EM radiation impinges upon a conductor, it couples to the conductor, travels along it, and induces an electric current on the surface of that conductor by exciting the electrons of the conducting material. This effect (the skin effect) is used in antennas.

Microwaves

 

Plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation.

The super-high frequency (SHF) and extremely high frequency (EHF) of microwaves are on the short side of radio waves. Microwaves are waves that are typically short enough (measured in millimeters) to employ tubular metal waveguides of reasonable diameter. Microwave energy is produced with klystron and magnetron tubes, and with solid state diodes such as Gunn and IMPATT devices.
Microwaves are absorbed by molecules that have a dipole moment in liquids. In a microwave oven, this effect is used to heat food. Low-intensity microwave radiation is used in Wi-Fi, although this is at intensity levels unable to cause thermal heating.

Volumetric heating, as used by microwave ovens, transfers energy through the material electromagnetically, not as a thermal heat flux. The benefit of this is a more uniform heating and reduced heating time; microwaves can heat material in less than 1% of the time of conventional heating methods.

When active, the average microwave oven is powerful enough to cause interference at close range with poorly shielded electromagnetic fields such as those found in mobile medical devices and poorly made consumer electronics.^{[citation needed]}

Terahertz radiation

Terahertz radiation is a region of the spectrum between far infrared and microwaves. Until recently, the range was rarely studied and few sources existed for microwave energy at the high end of the band (sub-millimeter waves or so-called terahertz waves), but applications such as imaging and communications are now appearing. Scientists are also looking to apply terahertz technology in the armed forces, where high-frequency waves might be directed at enemy troops to incapacitate their electronic equipment.^[17]

Infrared radiation

The infrared part of the electromagnetic spectrum covers the range from roughly 300 GHz (1 mm) to 400 THz (750 nm). It can be divided into three parts:^[6]

• Far-infrared, from 300 GHz (1 mm) to 30 THz (10 μm). The lower part of this range may also be called microwaves. This radiation is typically absorbed by so-called rotational modes in gas-phase molecules, by molecular motions in liquids, and by phonons in solids. The water in Earth's atmosphere absorbs so strongly in this range that it renders the atmosphere in effect opaque. However, there are certain wavelength ranges ("windows") within the opaque range that allow partial transmission, and can be used for astronomy. The wavelength range from approximately 200 μm up to a few mm is often referred to as "sub-millimeter" in astronomy, reserving far infrared for wavelengths below 200 μm.
• Mid-infrared, from 30 to 120 THz (10 to 2.5 μm). Hot objects (black-body radiators) can radiate strongly in this range, and human skin at normal body temperature radiates strongly at the lower end of this region. This radiation is absorbed by molecular vibrations, where the different atoms in a molecule vibrate around their equilibrium positions. This range is sometimes called the fingerprint region, since the mid-infrared absorption spectrum of a compound is very specific for that compound.
• Near-infrared, from 120 to 400 THz (2,500 to 750 nm). Physical processes that are relevant for this range are similar to those for visible light. The highest frequences in this region can be detected directly by some types of photographic film, and by many types of solid state image sensors for infrared photography and videography.

Visible radiation (light)

Above infrared in frequency comes visible light. The Sun emits its peak power in the visible region, although integrating the entire emission power spectrum through all wavelengths shows that the Sun emits slightly more infrared than visible light.^[18] By definition, visible light is the part of the EM spectrum to which the human eye is the most sensitive. Visible light (and near-infrared light) is typically absorbed and emitted by electrons in molecules and atoms that move from one energy level to another. This action allows the chemical mechanisms that underly human vision and plant photosynthesis. The light which excites the human visual system is a very small portion of the electromagnetic spectrum. A rainbow shows the optical (visible) part of the electromagnetic spectrum; infrared (if it could be seen) would be located just beyond the red side of the rainbow with ultraviolet appearing just beyond the violet end.

Electromagnetic radiation with a wavelength between 380 nm and 760 nm (400–790 terahertz) is detected by the human eye and perceived as visible light. Other wavelengths, especially near infrared (longer than 760 nm) and ultraviolet (shorter than 380 nm) are also sometimes referred to as light, especially when the visibility to humans is not relevant. White light is a combination of lights of different wavelengths in the visible spectrum. Passing white light through a prism splits it up into the several colors of light observed in the visible spectrum between 400 nm and 780 nm.

If radiation having a frequency in the visible region of the EM spectrum reflects off an object, say, a bowl of fruit, and then strikes the eyes, this results in visual perception of the scene. The brain's visual system processes the multitude of reflected frequencies into different shades and hues, and through this insufficiently-understood psychophysical phenomenon, most people perceive a bowl of fruit.

At most wavelengths, however, the information carried by electromagnetic radiation is not directly detected by human senses. Natural sources produce EM radiation across the spectrum, and technology can also manipulate a broad range of wavelengths. Optical fiber transmits light that, although not necessarily in the visible part of the spectrum (it is usually infrared), can carry information. The modulation is similar to that used with radio waves.

Ultraviolet radiation

 

The amount of penetration of UV relative to altitude in Earth's ozone

Next in frequency comes ultraviolet (UV). The wavelength of UV rays is shorter than the violet end of the visible spectrum but longer than the X-ray.

UV in the very shortest range (next to X-rays) is capable even of ionizing atoms (see photoelectric effect), greatly changing their physical behavior.

At the middle range of UV, UV rays cannot ionize but can break chemical bonds, making molecules to be unusually reactive. Sunburn, for example, is caused by the disruptive effects of middle range UV radiation on skin cells, which is the main cause of skin cancer. UV rays in the middle range can irreparably damage the complex DNA molecules in the cells producing thymine dimers making it a very potent mutagen.

The Sun emits significant UV radiation (about 10% of its total power), including extremely short wavelength UV that could potentially destroy most life on land (ocean water would provide some protection for life there). However, most of the Sun's most-damaging UV wavelengths are absorbed first by the magnetosphere and then by the atmosphere's oxygen, nitrogen, and ozone layer before they reach the surface. The higher ranges of UV (vacuum UV) are absorbed by nitrogen and, at longer wavelengths, by simple diatomic oxygen in the air. Most of the UV in this mid-range is blocked by the ozone layer, which absorbs strongly in the important 200–315 nm range, the lower part of which is too long to be absorbed by ordinary dioxygen in air. The range between 315 nm and visible light (called UV-A) is not blocked well by the atmosphere, but does not cause sunburn and does less biological damage. However, it is not harmless and does cause oxygen radicals, mutation and skin damage. See ultraviolet for more information.

X-rays

After UV come X-rays, which, like the upper ranges of UV are also ionizing. However, due to their higher energies, X-rays can also interact with matter by means of the Compton effect. Hard X-rays have shorter wavelengths than soft X-rays. As they can pass through most substances with some absorption, X-rays can be used to 'see through' objects with thicknesses less than equivalent to a few meters of water. One notable use in this category is diagnostic X-ray images in medicine (a process known as radiography). X-rays are useful as probes in high-energy physics. In astronomy, the accretion disks around neutron stars and black holes emit X-rays, which enable them to be studied.
X-rays are also emitted by the coronas of stars and are strongly emitted by some types of nebulae. However, X-ray telescopes must be placed outside the Earth's atmosphere to see astronomical X-rays, since the atmosphere of Earth is a radiation shield with areal density of 1000 grams per cm², which is the same areal density as 1000 centimeters or 10 meters thickness of water.^[19] This is an amount sufficient to block almost all astronomical X-rays (and also astronomical gamma rays—see below).

Gamma rays

After hard X-rays come gamma rays, which were discovered by Paul Villard in 1900. These are the most energetic photons, having no defined lower limit to their wavelength. In astronomy they are valuable for studying high-energy objects or regions, however like with X-rays this can only be done with telescopes outside the Earth's atmosphere. Gamma rays are useful to physicists thanks to their penetrative ability and their production from a number of radioisotopes. Gamma rays are also used for the irradiation of food and seed for sterilization, and in medicine they are occasionally used in radiation cancer therapy. More commonly, gamma rays are used for diagnostic imaging in nuclear medicine, with an example being PET scans. The wavelength of gamma rays can be measured with high accuracy by means of Compton scattering. Gamma rays are first and mostly blocked by Earth's magnetosphere then by the atmosphere.

Absorption spectroscopy

From Wikipedia, the free encyclopedia

   

An overview of electromagnetic radiation absorption. This example discusses the general principle using visible light as a specific example. A white beam source – emitting light of multiple wavelengths – is focused on a sample (the complementary color pairs are indicated by the yellow dotted lines). Upon striking the sample, photons that match the energy gap of the molecules present (green light in this example) are absorbed in order to excite the molecule. Other photons transmit unaffected and, if the radiation is in the visible region (400-700nm), the sample color is the complementary color of the absorbed light. By comparing the attenuation of the transmitted light with the incident, an absorption spectrum can be obtained.

An example of applying Absorption spectroscopy is the first direct detection and chemical analysis of the atmosphere of a planet outside our solar system in 2001. Sodium filters the alien star light of HD 209458 as the hot Jupiter planet passes in front. The process and absorption spectrum are illustrated above. Image Credit: A. Feild, STScI and NASA website.

Absorption spectroscopy refers to spectroscopic techniques that measure the absorption of radiation, as a function of frequency or wavelength, due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum. Absorption spectroscopy is performed across the electromagnetic spectrum.

Absorption spectroscopy is employed as an analytical chemistry tool to determine the presence of a particular substance in a sample and, in many cases, to quantify the amount of the substance present. Infrared and ultraviolet-visible spectroscopy are particularly common in analytical applications.
Absorption spectroscopy is also employed in studies of molecular and atomic physics, astronomical spectroscopy and remote sensing.

There are a wide range of experimental approaches to measuring absorption spectra. The most common arrangement is to direct a generated beam of radiation at a sample and detect the intensity of the radiation that passes through it. The transmitted energy can be used to calculate the absorption. The source, sample arrangement and detection technique vary significantly depending on the frequency range and the purpose of the experiment.

Absorption spectrum

Solar spectrum with Fraunhofer lines as it appears visually.

A material's absorption spectrum is the fraction of incident radiation absorbed by the material over a range of frequencies. The absorption spectrum is primarily determined^[1][2][3] by the atomic and molecular composition of the material. Radiation is more likely to be absorbed at frequencies that match the energy difference between two quantum mechanical states of the molecules. The absorption that occurs due to a transition between two states is referred to as an absorption line and a spectrum is typically composed of many lines.

The frequencies where absorption lines occur, as well as their relative intensities, primarily depend on the electronic and molecular structure of the sample. The frequencies will also depend on the interactions between molecules in the sample, the crystal structure in solids, and on several environmental factors (e.g., temperature, pressure, electromagnetic field). The lines will also have a width and shape that are primarily determined by the spectral density or the density of states of the system.

Basic theory

Absorption lines are typically classified by the nature of the quantum mechanical change induced in the molecule or atom. Rotational lines, for instance, occur when the rotational state of a molecule is changed. Rotational lines are typically found in the microwave spectral region. Vibrational lines correspond to changes in the vibrational state of the molecule and are typically found in the infrared region. Electronic lines correspond to a change in the electronic state of an atom or molecule and are typically found in the visible and ultraviolet region. X-ray absorptions are associated with the excitation of inner shell electrons in atoms. These changes can also be combined (e.g. rotation-vibration transitions), leading to new absorption lines at the combined energy of the two changes.

The energy associated with the quantum mechanical change primarily determines the frequency of the absorption line but the frequency can be shifted by several types of interactions. Electric and magnetic fields can cause a shift. Interactions with neighboring molecules can cause shifts. For instance, absorption lines of the gas phase molecule can shift significantly when that molecule is in a liquid or solid phase and interacting more strongly with neighboring molecules.

Observed absorption lines always have a width and shape that is determined by the instrument used for the observation, the material absorbing the radiation and the physical environment of that material. It is common for lines to have the shape of a Gaussian or Lorentzian distribution. It is also common for a line to be characterized solely by its intensity and width instead of the entire shape being characterized.

The integrated intensity—obtained by integrating the area under the absorption line—is proportional to the amount of the absorbing substance present. The intensity is also related to the temperature of the substance and the quantum mechanical interaction between the radiation and the absorber. This interaction is quantified by the transition moment and depends on the particular lower state the transition starts from and the upper state it is connected to.

The width of absorption lines may be determined by the spectrometer used to record it. A spectrometer has an inherent limit on how narrow a line it can resolve and so the observed width may be at this limit. If the width is larger than the resolution limit, then it is primarily determined by the environment of the absorber. A liquid or solid absorber, in which neighboring molecules strongly interact with one another, tends to have broader absorption lines than a gas. Increasing the temperature or pressure of the absorbing material will also tend to increase the line width. It is also common for several neighboring transitions to be close enough to one another that their lines overlap and the resulting overall line is therefore broader yet.

Relation to transmission spectrum

Absorption and transmission spectra represent equivalent information and one can be calculated from the other through a mathematical transformation. A transmission spectrum will have its maximum intensities at wavelengths where the absorption is weakest because more light is transmitted through the sample. An absorption spectrum will have its maximum intensities at wavelengths where the absorption is strongest.

Relation to emission spectrum

Emission spectrum of iron

Emission is a process by which a substance releases energy in the form of electromagnetic radiation. Emission can occur at any frequency at which absorption can occur, and this allows the absorption lines to be determined from an emission spectrum. The emission spectrum will typically have a quite different intensity pattern from the absorption spectrum, though, so the two are not equivalent. The absorption spectrum can be calculated from the emission spectrum using appropriate theoretical models and additional information about the quantum mechanical states of the substance.

Relation to scattering and reflection spectra

The scattering and reflection spectra of a material are influenced by both its index of refraction and its absorption spectrum. In an optical context, the absorption spectrum is typically quantified by the extinction coefficient, and the extinction and index coefficients are quantitatively related through the Kramers-Kronig relation. Therefore, the absorption spectrum can be derived from a scattering or reflection spectrum. This typically requires simplifying assumptions or models, and so the derived absorption spectrum is an approximation.

Applications

The infrared absorption spectrum of NASA laboratory sulfur dioxide ice is compared with the infrared absorption spectra of ices on Jupiter's moon, Io credit NASA, Bernard Schmitt, and UKIRT.

Absorption spectroscopy is useful in chemical analysis^[4] because of its specificity and its quantitative nature. The specificity of absorption spectra allows compounds to be distinguished from one another in a mixture, making absorption spectroscopy useful in wide variety of applications. For instance, Infrared gas analyzers can be used to identify the presence of pollutants in the air, distinguishing the pollutant from nitrogen, oxygen, water and other expected constituents.^[5]

The specificity also allows unknown samples to be identified by comparing a measured spectrum with a library of reference spectra. In many cases, it is possible to determine qualitative information about a sample even if it is not in a library. Infrared spectra, for instance, have characteristics absorption bands that indicate if carbon-hydrogen or carbon-oxygen bonds are present.

An absorption spectrum can be quantitatively related to the amount of material present using the Beer-Lambert law. Determining the absolute concentration of a compound requires knowledge of the compound's absorption coefficient. The absorption coefficient for some compounds is available from reference sources, and it can also be determined by measuring the spectrum of a calibration standard with a known concentration of the target.

Remote sensing

One of the unique advantages of spectroscopy as an analytical technique is that measurements can be made without bringing the instrument and sample into contact. Radiation that travels between a sample and an instrument will contain the spectral information, so the measurement can be made remotely. Remote spectral sensing is valuable in many situations. For example, measurements can be made in toxic or hazardous environments without placing an operator or instrument at risk. Also, sample material does not have to be brought into contact with the instrument—preventing possible cross contamination.

Remote spectral measurements present several challenges compared to laboratory measurements. The space in between the sample of interest and the instrument may also have spectral absorptions. These absorptions can mask or confound the absorption spectrum of the sample. These background interferences may also vary over time. The source of radiation in remote measurements is often an environmental source, such as sunlight or the thermal radiation from a warm object, and this makes it necessary to distinguish spectral absorption from changes in the source spectrum.

Astronomy

Absorption spectrum observed by the Hubble Space Telescope

Astronomical spectroscopy is a particularly significant type of remote spectral sensing. In this case, the objects and samples of interest are so distant from earth that electromagnetic radiation is the only means available to measure them. Astronomical spectra contain both absorption and emission spectral information. Absorption spectroscopy has been particularly important for understanding interstellar clouds and determining that some of them contain molecules. Absorption spectroscopy is also employed in the study of extrasolar planets. Detection of extrasolar planets by the transit method also measures their absorption spectrum and allows for the determination of the planet's atmospheric composition, temperature, pressure, and scale height, and hence allows also for the determination of the planet's mass.^[6]

Atomic and molecular physics

Theoretical models, principally quantum mechanical models, allow for the absorption spectra of atoms and molecules to be related to other physical properties such as electronic structure, atomic or molecular mass, and molecular geometry. Therefore, measurements of the absorption spectrum are used to determine these other properties. Microwave spectroscopy, for example, allows for the determination of bond lengths and angles with high precision.

In addition, spectral measurements can be used to determine the accuracy of theoretical predictions.
For example, the Lamb shift measured in the hydrogen atomic absorption spectrum was not expected to exist at the time it was measured. Its discovery spurred and guided the development of quantum electrodynamics, and measurements of the Lamb shift are now used to determine the fine-structure constant.

Experimental methods

Basic approach

The most straightforward approach to absorption spectroscopy is to generate radiation with a source, measure a reference spectrum of that radiation with a detector and then re-measure the sample spectrum after placing the material of interest in between the source and detector. The two measured spectra can then be combined to determine the material's absorption spectrum. The sample spectrum alone is not sufficient to determine the absorption spectrum because it will be affected by the experimental conditions—the spectrum of the source, the absorption spectra of other materials in between the source and detector and the wavelength dependent characteristics of the detector. The reference spectrum will be affected in the same way, though, by these experimental conditions and therefore the combination yields the absorption spectrum of the material alone.

A wide variety of radiation sources are employed in order to cover the electromagnetic spectrum. For spectroscopy, it is generally desirable for a source to cover a broad swath of wavelengths in order to measure a broad region of the absorption spectrum. Some sources inherently emit a broad spectrum. Examples of these include globars or other black body sources in the infrared, mercury lamps in the visible and ultraviolet and x-ray tubes. One recently developed, novel source of broad spectrum radiation is synchrotron radiation which covers all of these spectral regions. Other radiation sources generate a narrow spectrum but the emission wavelength can be tuned to cover a spectral range.
Examples of these include klystrons in the microwave region and lasers across the infrared, visible and ultraviolet region (though not all lasers have tunable wavelengths).

The detector employed to measure the radiation power will also depend on the wavelength range of interest. Most detectors are sensitive to a fairly broad spectral range and the sensor selected will often depend more on the sensitivity and noise requirements of a given measurement. Examples of detectors common in spectroscopy include heterodyne receivers in the microwave, bolometers in the millimeter-wave and infrared, mercury cadmium telluride and other cooled semiconductor detectors in the infrared, and photodiodes and photomultiplier tubes in the visible and ultraviolet.

If both the source and the detector cover a broad spectral region, then it is also necessary to introduce a means of resolving the wavelength of the radiation in order to determine the spectrum. Often a spectrograph is used to spatially separate the wavelengths of radiation so that the power at each wavelength can be measured independently. It is also common to employ interferometry to determine resolve the spectrum—Fourier transform infrared spectroscopy is a widely used implementation of this technique.

Two other issues that must be considered in setting up an absorption spectroscopy experiment include the optics used to direct the radiation and the means of holding or containing the sample material (called a cuvette or cell). For most UV, visible, and NIR measurements the use of precision quartz cuvettes are necessary. In both cases, it is important to select materials that have relatively little absorption of their own in the wavelength range of interest. The absorption of other materials could interfere with or mask the absorption from the sample. For instance, in several wavelength ranges it is necessary to measure the sample under vacuum or in a rare gas environment because gases in the atmosphere have interfering absorption features.

Dalai Lama

From Wikipedia, the free encyclopedia

 

Dalai Lama
Gendun Drup, 1st Dalai Lama
Reign	1391–1474
Tibetan	ཏཱ་ལའི་བླ་མ་
Wylie transliteration	taa la'i bla ma
Pronunciation	[taːlɛː lama]
Conventional Romanisation	Dalai Lama
Pinyin Chinese	Dálài Lǎmā
Royal house	Dalai Lama

Dalai Lama
Chinese name
Traditional Chinese	達賴喇嘛
Simplified Chinese	达赖喇嘛
[show]Transcriptions Mandarin Hanyu Pinyin Dálài Lǎmā
Tibetan name
Tibetan	ཏཱ་ལའི་བླ་མ་
[show]Transcriptions Wylie taa la'i bla ma

The Dalai Lama /ˈdɑːlaɪ ˈlɑːmə/^[1][2] is a high lama in the Gelug or "Yellow Hat" school of Tibetan Buddhism, founded by Tsongkhapa (1357–1419). The name is a combination of the Mongolic word dalai meaning "ocean" and the Tibetan word བླ་མ་ (bla-ma) meaning "guru, teacher, mentor".^[3]

The Dalai Lama is traditionally thought to be the rebirth in a line of tulkus who are considered to be manifestations of the bodhisattva of compassion, Avalokiteśvara. The Dalai Lama is often thought to be the leader of the Gelug School, but this position belongs officially to the Ganden Tripa, which is a temporary position appointed by the Dalai Lama who, in practice, exerts much influence. The line of Dalai Lamas began as a lineage of spiritual teachers; the 5th Dalai Lama assumed political authority over Tibet.

For certain periods between the 17th century and 1962, the Dalai Lamas sometimes directed the Tibetan government, which administered portions of Tibet from Lhasa. The 14th Dalai Lama remained the head of state for the Central Tibetan Administration ("Tibetan government in exile") until his retirement on March 14, 2011. He has indicated that the institution of the Dalai Lama may be abolished in the future, and also that the next Dalai Lama may be found outside Tibet and may be female.^[4] The Chinese government rejected this and asserted that only it has the authority to select the next Dalai Lama.^[5]

History

 

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v t e

Kublai Khan

Güshi Khan

During 1252, Kublai Khan granted an audience to Drogön Chögyal Phagpa and Karma Pakshi, the 2nd Karmapa. Karma Pakshi, however, sought the patronage of Möngke Khan. Before his death in 1283, Karma Pakshi wrote a will to protect the established interests of his lineage, the Karma Kagyu, by advising his disciples to locate a boy to inherit the black hat. His instruction was based on the premise that the Buddhist Dharma is eternal, and that the Buddha would send emanations to complete the missions he had initiated. Karma Pakshi's disciples acted in accordance with the will and located the reincarnated boy of their master.
The event was the beginning of the teacher reincarnation (Tulku) system for the Karma Kagyu Lineage of Tibetan Buddhism. During the Ming Dynasty, the Yongle Emperor bestowed the title Great Treasure Prince of Dharma, the first of the three Princes of Dharma, upon the Karmapa. Other
Tibetan Buddhist lineages responded to the teacher reincarnation system by creating similar systems.

Unification of Tibet

In the 1630s, Tibet became entangled in power struggles between the rising Manchu and various Mongol and Oirat factions. Ligden Khan of the Chakhar, retreating from the Manchu, set out to Tibet to destroy the Yellow Hat sect. He died on the way to Qinghai (Koko Nur) in 1634.^[6] His vassal Tsogt Taij continued the fight, even having his own son Arslan killed after Arslan changed sides. Tsogt Taij was defeated and killed by Güshi Khan of the Khoshud in 1637, who would in turn become the overlord of Tibet, and act as a "Protector of the Yellow Church."^[7] Güshi helped the Fifth Dalai Lama to establish himself as the highest spiritual and political authority in Tibet and destroyed any potential rivals. The time of the Fifth Dalai Lama was, however, also a period of rich cultural development.^{[citation needed]}

The Fifth Dalai Lama's death was kept secret for fifteen years by the regent (Tibetan: སྡེ་སྲིད།, Wylie: sde-srid), Sanggye Gyatso. This was apparently done so that the Potala Palace could be finished, and to prevent Tibet's neighbors taking advantage of an interregnum in the succession of the Dalai Lamas.^[8]

Tsangyang Gyatso, the Sixth Dalai Lama, was not enthroned until 1697. Tsangyang Gyatso enjoyed a lifestyle that included drinking, the company of women, and writing love songs.^[9] In 1705, Lobzang Khan of the Khoshud used the sixth Dalai Lama's escapades as excuse to take control of Tibet. The regent was murdered, and the Dalai Lama sent to Beijing. He died on the way, near Koko Nur, ostensibly from illness. Lobzang Khan appointed a new Dalai Lama who, however was not accepted by the Gelugpa school. Kelzang Gyatso was discovered near Koko Nur and became a rival candidate.

The Dzungars invaded Tibet in 1717, and deposed and killed Lobzang Khan's pretender to the position of Dalai Lama. This was widely approved. However, they soon began to loot the holy places of Lhasa, which brought a swift response from the Kangxi Emperor in 1718; but his military expedition was annihilated by the Dzungars in the Battle of the Salween River, not far from Lhasa.^[10][11]

A second, larger, expedition sent by the Kangxi Emperor expelled the Dzungars from Tibet in 1720 and the troops were hailed as liberators. They brought Kelzang Gyatso with them from Kumbum to Lhasa and he was installed as the seventh Dalai Lama in 1721.^[12]

After him [Jamphel Gyatso the eighth Dalai Lama (1758–1804)], the 9th and 10th Dalai Lamas died before attaining their majority: one of them is credibly stated to have been murdered and strong suspicion attaches to the other. The 11th and 12th were each enthroned but died soon after being invested with power. For 113 years, therefore, supreme authority in Tibet was in the hands of a Lama Regent, except for about two years when a lay noble held office and for short periods of nominal rule by the 11th and 12th Dalai Lamas.

It has sometimes been suggested that this state of affairs was brought about by the Ambans—the Imperial Residents in Tibet—because it would be easier to control the Tibet through a Regent than when a Dalai Lama, with his absolute power, was at the head of the government. That is not true. The regular ebb and flow of events followed its set course. The Imperial Residents in Tibet, after the first flush of zeal in 1750, grew less and less interested and efficient. Tibet was, to them, exile from the urbanity and culture of Peking; and so far from dominating the Regents, the Ambans allowed themselves to be dominated. It was the ambition and greed for power of Tibetans that led to five successive Dalai Lamas being subjected to continuous tutelage.^[13]

Thubten Jigme Norbu, the elder brother of the 14th Dalai Lama, described these unfortunate events as follows:

It is perhaps more than a coincidence that between the seventh and the thirteenth holders of that office, only one reached his majority. The eighth, Gyampal Gyatso, died when he was in his thirties, Lungtog Gyatso when he was eleven, Tsultrim Gyatso at eighteen, Khadrup Gyatso when he was eighteen also, and Krinla Gyatso at about the same age. The circumstances are such that it is very likely that some, if not all, were poisoned, either by loyal Tibetans for being Chinese-appointed impostors, or by the Chinese for not being properly manageable.^[14]

Throne awaiting Dalai Lama's return. Summer residence of 13th Dalai Lama, Nechung, Tibet.

Thubten Gyatso, the 13th Dalai Lama, assumed ruling power from the monasteries, which previously had great influence on the Regent, during 1895. Due to his two periods of exile in 1904–1909, to escape the British invasion of 1904, and from 1910–1912 to escape a Chinese invasion, he became well aware of the complexities of international politics and was the first Dalai Lama to become aware of the importance of foreign relations. After his return from exile in India and Sikkim during January 1913, he assumed control of foreign relations and dealt directly with the Maharaja and the British
Political officer in Sikkim and the king of Nepal rather than letting the Kashag or parliament do it.^[15]
Thubten Gyatso issued a Declaration of Independence for his kingdom in Central Tibet from China during the summer of 1912 and standardised a Tibetan flag, though no other sovereign state recognized the independence.^[16] He expelled the Ambans and all Chinese civilians in the country, and instituted many measures to modernise Tibet. These included provisions to curb excessive demands on peasants for provisions by the monasteries and tax evasion by the nobles, setting up an independent police force, the abolition of the death penalty, extension of secular education, and the provision of electricity throughout the city of Lhasa in the 1920s.^[17] Thubten Gyatso died in 1933.

The 14th Dalai Lama was not formally enthroned until 17 November 1950, during the People's Republic of China invasion of the kingdom. In 1951, he and the Tibetan government formally accepted the Seventeen Point Agreement by which Tibet was formally incorporated into the People's Republic of China. Fearing for his life in the wake of a revolt in Tibet in 1959, the 14th Dalai Lama fled to India, from where he led a government in exile.^[18][19] With the aim of launching guerrilla operations against the Chinese, the CIA funded the Dalai Lama with US$1.7 million a year in the 1960s.^[20] In 2001 the 14th Dalai Lama ceded his absolute power over the government to an elected parliament of selected Tibetan exiles. His original goal was full independence for Tibet, but by the late 1980s he was seeking high-level autonomy instead.^[21] He continued to seek greater autonomy from China, but Dolma Gyari, deputy speaker of the parliament-in-exile said "If the middle path fails in the short term, we will be forced to opt for complete independence or self-determination as per the UN charter".^[22]

Residence

Starting with the 5th Dalai Lama and until the 14th Dalai Lama's flight into exile during 1959, the Dalai Lamas spent winters at the Potala Palace and summers at the Norbulingka palace and park. Both are in Lhasa and approximately 3 km apart.

Following the failed 1959 Tibetan uprising, the 14th Dalai Lama sought refuge in India. The then Indian Prime Minister, Jawaharlal Nehru, allowed in the Dalai Lama and the Tibetan government officials. The Dalai Lama has since lived in exile in Dharamshala, in the state of Himachal Pradesh in northern India, where the Central Tibetan Administration is also established. Tibetan refugees have constructed and opened many schools and Buddhist temples in Dharamshala.^[23]

• 

  Potala Palace
• 

  Norbulingka

Searching for the reincarnation

The search for the 14th Dalai Lama took the High Lamas to Taktser in Amdo

Palden Lhamo, the female guardian spirit of the sacred lake, Lhamo La-tso, who promised Gendun Drup the 1st Dalai Lama in one of his visions that "she would protect the reincarnation lineage of the Dalai Lamas"

By the Himalayan tradition, phowa is the discipline that transfers the mindstream to the intended body. Upon the death of the Dalai Lama and consultation with the Nechung Oracle, a search for the Lama's yangsi, or reincarnation, is conducted. Traditionally, it has been the responsibility of the High Lamas of the Gelugpa tradition and the Tibetan government to find his reincarnation. The process can take around two or three years to identify the Dalai Lama, and for the 14th, Tenzin Gyatso, it was four years before he was found. Historically, the search for the Dalai Lama has usually been limited to Tibet, though the third tulku was born in Mongolia. Tenzin Gyatso, however, has stated that he will not be reborn in the People's Republic of China, though he has also suggested he may not be reborn at all, suggesting the function of the Dalai Lama may be outdated.^[24] The government of the People's Republic of China has stated its intention to be the ultimate authority on the selection of the next Dalai Lama.^{[citation needed]}

The High Lamas used several ways in which they can increase the chances of finding the reincarnation. High Lamas often visit Lhamo La-tso, a lake in central Tibet, and watch for a sign from the lake itself. This may be either a vision or some indication of the direction in which to search, and this was how Tenzin Gyatso was found. It is said that Palden Lhamo, the female guardian spirit of the sacred lake Lhamo La-tso promised Gendun Drup, the 1st Dalai Lama, in one of his visions "that she would protect the reincarnation lineage of the Dalai Lamas."^{[citation needed]} Ever since the time of Gendun Gyatso, the 2nd Dalai Lama, who formalised the system, the Regents and other monks have gone to the lake to seek guidance on choosing the next reincarnation through visions while meditating there.^[25]

The particular form of Palden Lhamo at Lhamo La-tso is Gyelmo Maksorma, "The Victorious One who Turns Back Enemies". The lake is sometimes referred to as "Pelden Lhamo Kalideva", which indicates that Palden Lhamo is an emanation of the goddess Kali, the shakti of the Hindu God Shiva.^[26]

Lhamo Latso ... [is] a brilliant azure jewel set in a ring of grey mountains. The elevation and the surrounding peaks combine to give it a highly changeable climate, and the continuous passage of cloud and wind creates a constantly moving pattern on the surface of the waters. On that surface visions appear to those who seek them in the right frame of mind.^[27]

It was here that in 1935, the Regent Reting Rinpoche received a clear vision of three Tibetan letters and of a monastery with a jade-green and gold roof, and a house with turquoise roof tiles, which led to the discovery of Tenzin Gyatso, the 14th Dalai Lama.^[28][29][30]

High Lamas may also have a vision by a dream or if the Dalai Lama was cremated, they will often monitor the direction of the smoke as an indication of the direction of the rebirth.^[24]

Once the High Lamas have found the home and the boy they believe to be the reincarnation, the boy undergoes a battery of tests to affirm the rebirth. They present a number of artifacts, only some of which belonged to the previous Dalai Lama, and if the boy chooses the items which belonged to the previous Dalai Lama, this is seen as a sign, in conjunction with all of the other indications, that the boy is the reincarnation.^[31]

If there is only one boy found, the High Lamas will invite Living Buddhas of the three great monasteries, together with secular clergy and monk officials, to confirm their findings and then report to the Central Government through the Minister of Tibet. Later, a group consisting of the three major servants of Dalai Lama, eminent officials,^[who?] and troops^[which?] will collect the boy and his family and travel to Lhasa, where the boy would be taken, usually to Drepung Monastery, to study the Buddhist sutra in preparation for assuming the role of spiritual leader of Tibet.^[24]

If there are several possible reincarnations, however, regents, eminent officials, monks at the Jokhang in Lhasa, and the Minister to Tibet have historically decided on the individual by putting the boys' names inside an urn and drawing one lot in public if it was too difficult to judge the reincarnation initially.^[32]

List of Dalai Lamas

There have been 14 recognised incarnations of the Dalai Lama:

	Name	Picture	Lifespan	Recognised	Enthronement	Tibetan/Wylie	Tibetan pinyin/Chinese	Alternative spellings
1	Gendun Drup		1391–1474	–	N/A[33]	དགེ་འདུན་འགྲུབ་ dge 'dun 'grub	Gêdün Chub 根敦朱巴	Gedun Drub Gedün Drup
2	Gendun Gyatso		1475–1542	–	N/A[33]	དགེ་འདུན་རྒྱ་མཚོ་ dge 'dun rgya mtsho	Gêdün Gyaco 根敦嘉措	Gedün Gyatso Gendün Gyatso
3	Sonam Gyatso		1543–1588	?	1578	བསོད་ནམས་རྒྱ་མཚོ་ bsod nams rgya mtsho	Soinam Gyaco 索南嘉措	Sönam Gyatso
4	Yonten Gyatso		1589–1617	?	1603	ཡོན་ཏན་རྒྱ་མཚོ་ yon tan rgya mtsho	Yoindain Gyaco 雲丹嘉措	Yontan Gyatso, Yönden Gyatso
5	Ngawang Lobsang Gyatso		1617–1682	1618	1622	བློ་བཟང་རྒྱ་མཚོ་ blo bzang rgya mtsho	Lobsang Gyaco 羅桑嘉措	Lobzang Gyatso Lopsang Gyatso
6	Tsangyang Gyatso		1683–1706	1688	1697	ཚངས་དབྱངས་རྒྱ་མཚོ་ tshang dbyangs rgya mtsho	Cangyang Gyaco 倉央嘉措	Tsañyang Gyatso
7	Kelzang Gyatso		1707–1757	?	1720	བསྐལ་བཟང་རྒྱ་མཚོ་ bskal bzang rgya mtsho	Gaisang Gyaco 格桑嘉措	Kelsang Gyatso Kalsang Gyatso
8	Jamphel Gyatso		1758–1804	1760	1762	བྱམས་སྤེལ་རྒྱ་མཚོ་ byams spel rgya mtsho	Qambê Gyaco 強白嘉措	Jampel Gyatso Jampal Gyatso
9	Lungtok Gyatso		1805–1815	1807	1808	ལུང་རྟོགས་རྒྱ་མཚོ་ lung rtogs rgya mtsho	Lungdog Gyaco 隆朵嘉措	Lungtog Gyatso
10	Tsultrim Gyatso		1816–1837	1822	1822	ཚུལ་ཁྲིམས་རྒྱ་མཚོ་ tshul khrim rgya mtsho	Cüchim Gyaco 楚臣嘉措	Tshültrim Gyatso
11	Khendrup Gyatso		1838–1856	1841	1842	མཁས་གྲུབ་རྒྱ་མཚོ་ mkhas grub rgya mtsho	Kaichub Gyaco 凱珠嘉措	Kedrub Gyatso
12	Trinley Gyatso		1857–1875	1858	1860	འཕྲིན་ལས་རྒྱ་མཚོ་ 'phrin las rgya mtsho	Chinlai Gyaco 成烈嘉措	Trinle Gyatso
13	Thubten Gyatso		1876–1933	1878	1879	ཐུབ་བསྟན་རྒྱ་མཚོ་ thub bstan rgya mtsho	Tubdain Gyaco 土登嘉措	Thubtan Gyatso Thupten Gyatso
14	Tenzin Gyatso		born 1935	1937	1950 (currently in exile)	བསྟན་འཛིན་རྒྱ་མཚོ་ bstan 'dzin rgya mtsho	Dainzin Gyaco 丹增嘉措	Tenzing Gyatso

There has also been one nonrecognised Dalai Lama, Ngawang Yeshey Gyatso, declared 28 June 1707, when he was 25 years old, by Lha-bzang Khan as the "true" 6th Dalai Lama – however, he was never accepted as such by the majority of the population.^[11][34][35]

Future of the position

 

The main teaching room of the Dalai Lama in Dharamshala, India

15th Dalai Lama

In the mid-1970s, Tenzin Gyatso, the Fourteenth Dalai Lama, told a Polish newspaper that he thought he would be the last Dalai Lama. In a later interview published in the English language press he stated, "The Dalai Lama office was an institution created to benefit others. It is possible that it will soon have outlived its usefulness."^[36] These statements caused a furor amongst Tibetans in India. Many could not believe that such an option could even be considered. It was further felt that it was not the Dalai Lama's decision to reincarnate. Rather, they felt that since the Dalai Lama is a national institution it was up to the people of Tibet to decide whether the Dalai Lama should reincarnate.^[37]

The government of the People's Republic of China (PRC) has claimed the power to approve the naming of "high" reincarnations in Tibet, based on a precedent set by the Qianlong Emperor of the Qing Dynasty.^{[citation needed]} The Qianlong Emperor instituted a system of selecting the Dalai Lama and the Panchen Lama by a lottery that used a golden urn with names wrapped in clumps of barley. This method was used a few times for both positions during the 19th century, but eventually fell into disuse.^{[citation needed]} In 1995, the Dalai Lama chose to proceed with the selection of the 11th reincarnation of the Panchen Lama without the use of the Golden Urn, while the Chinese government insisted that it must be used.^{[citation needed]} This has led to two rival Panchen Lamas: Gyaincain Norbu as chosen by the Chinese government's process, and Gedhun Choekyi Nyima as chosen by the Dalai Lama.

During September 2007 the Chinese government said all high monks must be approved by the government, which would include the selection of the 15th Dalai Lama after the death of Tenzin Gyatso.^{[citation needed]} Since by tradition, the Panchen Lama must approve the reincarnation of the Dalai Lama, that is another possible method of control.^{[citation needed]}

In response to this scenario, Tashi Wangdi, the representative of the 14th Dalai Lama, replied that the Chinese government's selection would be meaningless. "You can't impose an Imam, an Archbishop, saints, any religion...you can't politically impose these things on people," said Wangdi. "It has to be a decision of the followers of that tradition. The Chinese can use their political power: force. Again, it's meaningless. Like their Panchen Lama. And they can't keep their Panchen Lama in Tibet. They tried to bring him to his monastery many times but people would not see him. How can you have a religious leader like that?"^[38]

The 14th Dalai Lama said as early as 1969 that it was for the Tibetans to decide whether the institution of the Dalai Lama "should continue or not".^[39] He has given reference to a possible vote occurring in the future for all Tibetan Buddhists to decide whether they wish to recognize his rebirth.^[40] In response to the possibility that the PRC might attempt to choose his successor, the Dalai Lama said he would not be reborn in a country controlled by the People's Republic of China or any other country which is not free.^[24][41] According to Robert D. Kaplan, this could mean that "the next Dalai Lama might come from the Tibetan cultural belt that stretches across northern India, Nepal, and Bhutan, presumably making him even more pro-Indian and anti-Chinese".^[42]
The 14th Dalai Lama supported the possibility that his next incarnation could be a woman.^[43] "Despite the complex historical, religious and political factors surrounding the selection of incarnate masters in the exiled Tibetan tradition, the Dalai Lama is open to change," author Michaela Haas writes.^[44] "Why not? What's the big deal?"^[45]