CdSe

CdSe  Laser systems with CdSe crystal have obvious advantage – much broader tuning range . In the difference-mixing of the output of parametric oscillator in CdSe to obtain the phase matched 9.4-24.3 µm tuning range . CdSe crystal has its band edge in the near infrared and shows transmission far into the infrared. The long wavelength limit determined by the onset of lattice absorption 1.5 cm-1 @ 24.3µm.

There is also a narrow impurity absorption centered at 18.5um which varies from one crystal to another. As a nonlinear optical material, CdSe crystal was explored for OPG, OPO and DFG in 1970’s .First of all, picoseconds pulses tunable from 10 to 20 µm were produced .Furthermore, CdSe was also used to achieve megawatt peak power in the range of 8-13 and 7-12  µm, based on OPG and OPO respectively.

Basic properties:

Structure
Wurtzite (Hexagonal)
Density
5.81 g/ cm3
Young’s Modulus
5×1011 dyne/cm2
Coef. of Thermal Expansion (500 K)
α 1=6.26×10-6/K;  α 3=4.28×10-6/K
Specific Heat
0.49 J/gK
Thermal conductivity (at 25 °C)
0.04 W/cmK
Max. Transmittance (λ =2.5-15 μm)
≥ 71 %
Absorption Coef. (λ =10.6 μm)
≤ 0.0015 cm-1 (including 2 surfaces)
Refractive index (λ =10.6 μm)
no= 2.4258, ne=2.4437 
Max. single crystal diameter/length
Ø50.8×40 mm
Max. IR optic blank diameter/length
Ø50×50 mm or plate 60×60×6 mm
Surface quality
As-cut, 60/40 scratch*dig per MIL-0-13830