OEM spectro Catalogue - Horiba

40
Magnification in the dispersion direction is:
o Slit height magnification
Slit height magnification is directly proportional to the ratio of the entrance and exit arm lengths.
h' = (LB/LA)h
In the case of a flat field spectrometer, the height magnification is changing with wavelength because
LB is changing.
Note: Geometric magnification is not an aberration!
Definitions
Etendue (G): a measure of the size of the beam that an optical system is able to accept, also called
the area - solid angle product.
The term étendue comes from the French (literally meaning extent). The french expression for this
property is “étendue géométrique”, meaning geometrical extent.
An optical system with an etendue G cannot accept a beam with an etendue larger than G.
The etendue of a beam is constant when the beam shape is changed by an optical element.
The etendue is related to the Lagrange invariant and the optical invariant, which share the property of
never increasing in any real optical system.
Geometric etendue (geometric extent), G, characterizes the ability of an optical system to accept light.
It is a function of the area, S, of the emitting source and the solid angle, Q, into which it propagates.
Etendue therefore, is a limiting function of system throughput.
For an elementary beam
d²G = dS dQ
and for a finite beam
dQ
dS
dS
dQ