Spectral hole burning is the frequency-selective bleaching of the

absorption spectrum 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 fi ...

of a material, which leads to an increased transmission (a "spectral hole") at the selected frequency. Two basic requirements must be met for the phenomenon to be observed: # The spectrum is inhomogeneously broadened # The material undergoes, subsequent to light absorption, a modification which changes its absorption spectrum. Typical materials include

dye A dye is a colored substance that chemically bonds to the substrate to which it is being applied. This distinguishes dyes from pigments which do not chemically bind to the material they color. Dye is generally applied in an aqueous solution and ...

molecules dissolved in suitable host matrices; the frequency-selective irradiation is usually realized by a narrow-band

laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The firs ...

Particular case

Most

molecule A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bio ...

s and

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas ...

s always return from the

excited state In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation refers t ...

to the initial ground state. In some situations, however, this may not happen. For example, some organic dye molecules can undergo a

photochemical reaction Organic photochemistry encompasses organic reactions that are induced by the action of light. The absorption of ultraviolet light by organic molecules often leads to reactions. In the earliest days, sunlight was employed, while in more modern times ...

, which alters the whole

chemical structure A chemical structure determination includes a chemist's specifying the molecular geometry and, when feasible and necessary, the electronic structure of the target molecule or other solid. Molecular geometry refers to the spatial arrangement of a ...

of the molecule. If such a photochemically active molecule absorbs light, then with a probability of a few percent it will not return to the initial,

educt Eduction or variants may refer to: * Eduction (geology), a process in which the Earth's crust spreads sideways, exposing deep-seated rocks * Eductor-jet pump, a form of injector pump * A conclusion educed (induced or deduced) through a process o ...

state, but will rather switch over to a new product ground state. Often the homogeneous

of the new product is much different from that of the educt, and the corresponding inhomogeneous bands do not overlap. Spectral hole width can be expressed as follows: :

\nu_ = \frac \sqrt

where

\nu_

is spectral hole width,

\nu_

is homogeneous linewidth,

\nu_

is the centre frequency and

I_

is the saturation intensity.

References

Sources

* http://www.iupac.org/publications/pac/pdf/1995/pdf/6701x0191.pdf * http://www.physics.montana.edu/arebane/research/tutorials/hole_burning/index.html {{Authority control Spectroscopy