Temperature-compensated spectrometer
The invention relates to a spectrometer comprising a hollow main optical body having at least one light channel, a light source, a diffraction grating having a grating central point, a light inlet opening, and a detector unit, which are arranged in such a way that the focal curve of the spectrometer satisfies the back focus equation. In order to create a spectrometer having sufficient spectral resolution from a low-price, light, and easy-to-process material, which spectrometer is able to operate in a large temperature interval even without thermostatic control, according to the invention the light inlet opening is arranged on a compensation body, the compensation body is arranged in the light channel and fastened to the main optical body between the light source and the diffraction grating, and the compensation body is dimensioned in such a way that the compensation body changes the distance between the light inlet opening and the grating central point when the main optical body thermally expands.
1. A spectrometer, comprising:
a hollow main optical body having at least one light channel;
a light source;
a diffraction grating having a grating central point;
a light inlet opening; and
a detector unit, which are arranged so that a focal curve of the spectrometer satisfies a back focus equation:
cos
2
α
L
A
-
cos
α
R
+
cos
2
β
L
B
-
cos
β
R
-
n
λ
K
=
0
where
α is an angle of incidence,
β is a diffraction angle,
L A is an inlet back focal length,
L B is an outlet back focal length,
R is a grating radius indicative of a radius of curvature of a spherical grating surface,
n is a diffraction order,
λ is a wavelength at the diffraction angle β and
K is a spherical grating constant, and further comprising:
a compensation body, the light inlet opening disposed on the compensation body, the compensation body disposed in the light channel and fixed on the main optical body between the light source and the diffraction grating, the compensation body configured so that during thermal expansion of the main optical body the compensation body changes the distance between the light inlet opening and the grating central point such that a shift of the focal curve is corrected by overcompensating the thermal expansion of the main optical body by expansion of the compensation body.
2. The spectrometer according to claim 1 , wherein the light inlet opening is located at a first end of the compensation body and a second end of the compensation body is fixed on the main optical body between the light inlet opening and the light source.
3. The spectrometer according to claim 1 , wherein the compensation body is substantially tubular.
4. The spectrometer according to claim 1 , wherein the compensation body is made of polyoxymethylene plastic (POM).
5. The spectrometer according to claim 1 , wherein the compensation body is a concentrically drilled bimetal disk.
6. The spectrometer according to claim 1 , wherein light transmission to the light inlet opening takes place via a light guide.
7. The spectrometer according to claim 1 , wherein the main optical body is one piece.
8. The spectrometer according to claim 1 , wherein the spectrometer has a plurality of light channels.
9. The spectrometer according to claim 1 , wherein the light inlet opening is made of a material having a negligible coefficient of thermal expansion.
10. The spectrometer according to claim 1 , wherein the light inlet opening is disposed on a connecting piece, and the connecting piece is disposed on the compensation body.