Untitled - IRS

260 GLOSSAR
Emittanz, spektrale Brilliance, spectral. Measure of power/area (intensity) per unit wavelength (or
frequency) of light. Defined ambiguosly in literature. Often also power per (unit area x unit
wavelength x unit solid emission angle). (Eq. (1.0)) [p. 11]
Entartung Degeneration. Number of substates with equal energie. One example are the magnetic
substates in absence of an external magnetic field and without (hyper)fineinteraction.
(Eq. (2.31)) [p. 21]
Entartungsparameter Degeneration parameter. Population number of one Eigenmode.
(Eq. (2.33)) [p. 22]
Exzimer Excimer. Molecule that is stable only in its excited states. The groundstate does not exist.
Exploited for Excimer-Lasers by generating the excimers by electron impact. Population
inversion is achieved intrinsicly, since the molecule is unstable after photon-emission. Excimerlasers
are two level lasers. (Eq. (1.0)) [p. 7]
Franck-Condon Prinzip The Frank-Condon principle states that electronic transitions take place in
times that are very short compared to the time required for the nuclei to move significantly.
Hence, the geometry does not change immediately upon an electric transition between two
electronic states. If, in the case of absorption, the excited stae needs a larger atomic distance
of the nuclei inside a molecule than the ground state, the transition is strongly hindered due
to low F.C. factors. In order for fluorescence to occur, the photoemission probability must be
quite large, so only transitions of the same spin are allowed. For example, if the ground state
is S0, then the fluorescing state would be S1. (Eq. (4.18)) [p. 96]
Gruppengeschwindigkeits Dispersion group velocity dispersion (GVD). A fs-laser pulse contains
light of a broad spectral range. In a normal dispersive medium the refractive index of blue
light exceeds the one of red light and hence the red fraction of the pulse travels faster than
the blue. This leads to a temporal broadening of the light pulse. (Eq. (4.58)) [p. 134]
GVD siehe Gruppengeschwindigkeits Dispersion (Eq. (4.58)) [p. 134]
Güteschaltung Q-switch A ’shutter’ placed between the amplifying rod and the end mirrors of a
laser can prevent laser action as long as it is closed. If conditions are otherwise correct for
laser action and the shutter is suddenly opened, the stored energy is released as a giant pulse
of light lasting only a few nanoseconds and having a peak power capacity that may be as
high as several hundred megawatts. This is known as Q-switching. The Q-switch may be a
mechanical shutter or, more usually, a liquid or solid optical shutter that is normally opaque
but can be made transparent by the application of an electrical pulse. The shutter may also
be an opaque dye which becomes transparent when exposed to laser light. (Eq. (1.0)) [p. 7]
Huygenschen Elementarwellen Huygens’ theorem. Huygens used for the description of light within
the framework of wave propagation, the picture that a wavefront can be described as an infinite
number of secondary spherical wavelets which evenate from every point of the wavefront.
The position of the wavefront at any later time is the envelope of all such wavelets. If some
parts of the wavefront are blocked, e.g. by a slit, the passing waves interfere and the typical
refraction patterns caused by an optical slit experiment are described by integration of all
spherical waves. (Eq. (2.67)) [p. 36]