IR Laser Optics - Grating End Reflectors for Dye Lasers
TF AND UTF SERIES GRATING END REFLECTORS FOR DYE LASERS Optometrics has developed a line of ultra high damage threshold replica diffraction gratings. These are made by a proprietary process and have withstood incident energies far in excess of those of normal replica gratings. Gratings are supplied on a Pyrex® substrate.
The output wavelength of the dye laser can be tuned by turning the Littrow mounted diffraction grating end reflector about an axis parallel to the grooves. The equation relating wavelength to angle of incidence on the grating is n
l = 2d sin i. Using this relationship, one can calibrate the mirror mount micrometer to i and, using a grating as one of the reflectors in a dye laser, cause the spectral line width of the output to be reduced to a narrow region around the Littrow wavelength. Maximum reduction is attained by increasing dispersion to the practical limit. As can be seen from the equation for angular dispersion,
this limit is approached for the high blaze angle characteristic of echelles and finely spaced echellettes. Even greater selectivity can be attained by adding a Fabry-Perot etalon to the grating-mirror cavity. The efficiency of the spectral condensation in organic dye lasers is quite high, with figures of 70% being typical.
Gratings are normally used in one of two configurations: Littrow or grazing incidence (see figure below).
GROOVES PER MM
BLAZE λ (nm)
BLAZE ANGLE
DISPERSION (nm/mr) {Echelles @ 500 NM}
RULED
1200
300
10 22
0.82
1200
500
17 26
0.79
1200
750
26 45
0.74
1200
1000
36 52
0.67
1800
500
26 45
0.50
ECHELLES
31.6
Echelle
63
14.37
316
Echelle
63
1.44
79
Echelle
75
3.28
79
Echelle
63
5.75
HIGH RESOLUTION ECHELLES Special low period gratings designed for use in the high orders. Generally used with a second grating or prism to separate overlapping diffracted orders. Sup- plied on precision glass substrates, Echelles have a resolution of 80-90% of theoretical.
TF And UTF Series Gratings All dimensions in millimeters.
