Spectral hole burning
Encyclopedia
Spectral hole burning is the frequency selective bleaching of the absorption spectrum of a material, which leads to an increased transmission (a "spectral hole") at the selected frequency.
Two basic requirements, that must be met for the observation of this phenomenon, are: 1) The spectrum is inhomogeneously broadened and 2) the material undergoes, subsequent to light absorption, a modification which changes its absorption spectrum. Typical materials include dye molecules dissolved in suitable host matrices and the frequency selective irradiation is usually realized by a narrow band laser
.
In most cases, molecules and atoms always return from the excited state
back to the initial ground state
. There are situations, however, when this is not always the case. For example, some organic dye molecules can undergo a photochemical reaction, which alters the whole chemical structure
of the molecule. If such photochemically active molecule absorbs light, then with a probability of a few % it will not return to the initial state called educt, but rather switches over to a new ground state called product. Often the homogeneous absorption spectrum of the product is much different from the educt, so that the corresponding inhomogeneous bands do not even overlap.
http://www.physics.montana.edu/faculty/rebane/Research/Tutorials/Hole_burning/HoleBurning_00.htm
Two basic requirements, that must be met for the observation of this phenomenon, are: 1) The spectrum is inhomogeneously broadened and 2) the material undergoes, subsequent to light absorption, a modification which changes its absorption spectrum. Typical materials include dye molecules dissolved in suitable host matrices and the frequency selective irradiation is usually realized by a narrow band laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
.
In most cases, molecules and atoms always return from the excited state
Excited state
Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being excited to an excited state....
back to the initial ground state
Ground state
The ground state of a quantum mechanical system is its lowest-energy state; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state...
. There are situations, however, when this is not always the case. For example, some organic dye molecules can undergo a photochemical reaction, which alters the whole chemical structure
Chemical structure
A chemical structure includes molecular geometry, electronic structure and crystal structure of molecules. Molecular geometry refers to the spatial arrangement of atoms in a molecule and the chemical bonds that hold the atoms together. Molecular geometry can range from the very simple, such as...
of the molecule. If such photochemically active molecule absorbs light, then with a probability of a few % it will not return to the initial state called educt, but rather switches over to a new ground state called product. Often the homogeneous absorption spectrum of the product is much different from the educt, so that the corresponding inhomogeneous bands do not even overlap.
Sources
http://www.iupac.org/publications/pac/pdf/1995/pdf/6701x0191.pdfhttp://www.physics.montana.edu/faculty/rebane/Research/Tutorials/Hole_burning/HoleBurning_00.htm