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Infrared and Laser Products - Grating End Reflectors for Dye Lasers

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 nl = 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).

GRAZING INCIDENCE GRATINGS
Grazing incidence is a simple and inexpensive optical configuration that can tune and increase the resolution of a dye laser. A holographic grating, functioning as an end reflector in a dye laser cavity, is positioned so that laser radiation strikes the grating almost perpendicular to the grating normal. As the angle of incidence approaches 89 degrees, a relatively large area of the grating is illuminated by the laser beam, increasing angular dispersion and resolving power significantly. The sizes of the grazing and mirror (12.7 x 50.8 mm) are optimized for grazing incidence. The grating is fixed and tuning is achieved by rotation of the mirror. The laser beam is diffracted twice in grating incidence, resulting in a two fold increase in resolution. Low grating efficiency is characteristic of the grazing incidence configuration but is compensated for by the high gain of the dyes used. 

LITTROW SERIES GRATINGS
SPECIFICATIONS
Dimensional Tolerances - ±0.5mm
Thickness Tolerances - ±0.5mm
EFFICIENCIES
   Roled - 60 - 80% at blaze
       Holographic - 45 - 65% at peak
Clear Apertore - 90%
Groove parallelism to edge - ±0.5°

GROOVES
PER MM

BLAZE λ
(nm)

BLAZE
ANGLE

DISPERSION
(nm/mr)
{@ 500 nm}

12.5 x 25 x 6 CAT. NO 25 x 25 x 9.5 CAT. NO. 30 x 30 x 9.5 CAT. NO. 50 x 50 x 9.5 CAT. NO.
RULED
1200

300

10° 2' 0.82 3-4131 3-2131 3-3131 3-5131
1200

500

17°  26 0.79 3-4151 3-2151 3-3151 3-5151
1200

750

26°  45 0.74 3-4171 3-2171 3-3171 3-5171
1200 1000 36°  52 0.67 3-4111 3-2111 3-3111 3-5111
1800

500

26°  45 0.50 3-4851 3-2851 3-3851 3-5851

   Price($)*

75.00 99.00 105.00 159.00
         
            * Prices are in USD and are list prices only.
GROOVES PER MM BLAZE ANGLE BLAZE λ (nm) DISPERSION (nm/mr) @ 500 nm
ECHELLES
31.6

Echelle

63 14.37
316 Echelle 63 1.44
79 Echelle 75 3.28
79 Echelle 63 5.75

 
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USA
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