GaSe (gallium selenide) is a nonlinear crystal that is used for frequency conversion in laser technology. GaSe is a semiconductor with a wide bandgap and a high nonlinear coefficient, making it suitable for second harmonic generation (SHG), difference frequency generation (DFG), and optical parametric oscillation (OPO).
In SHG, the frequency of a laser beam is doubled by passing it through a GaSe crystal. This process is used to generate light in the ultraviolet range, which is useful in applications such as fluorescence microscopy and laser spectroscopy.
DFG produces a new frequency that is equal to the difference between two input frequencies. GaSe can be used in DFG to generate tunable infrared radiation, which has applications in spectroscopy, sensing, and imaging.
OPO is a process that involves the generation of two coherent light beams with different frequencies. GaSe can be used as the nonlinear crystal in an OPO to generate tunable mid-infrared radiation, which has applications in remote sensing, environmental monitoring, and medical diagnostics.
GaSe has a relatively high damage threshold, which makes it suitable for high-power laser applications. It also has a wide transparency range, which makes it useful for a range of wavelengths. However, GaSe is a relatively soft material, which can make it difficult to polish and maintain its optical quality. Additionally, GaSe is a hygroscopic material, which means it can absorb moisture from the air and require careful handling and storage to maintain its performance.
|Transparency range, µm||0.62 20|
|Lattice parameters||a = 3.74, c = 15.89 Å|
|at 5.3 µm||no= 2.7233, ne= 2.3966|
|at 10.6 µm||no= 2.6975, ne= 2.3745|
|Non-linear coefficient, pm/V||d22 = 54|
|Walk off||4.1° at 5.3 µm|
|Optical damage threshold, MW/cm2||28 (9.3 µm, 150 ns); 0.5 (10.6 µm, in CW mode); 30 (1.064 µm, 10 ns)|