|Wavelength||800/400nm||Delay Range||250-600fs between 800nm (o-ray) and 400nm (e-ray)|
|Flatness||λ/4@633nm||Transmission Wavefront Distortion||λ/4@633nm|
|Surface Quality||20/10 S/D||Parallelism||<30 arc sec|
The group velocity is different for different wavelength, it is called group velocity mismatch (GVM), and then a time delay is introduced between fundamental and second harmonic generated (SHG) wavelength, in order to compensate this time delay, an time delay compensator with orthogonal polarizations are often used. Calcite crystals and alpha-BBO crystals are most popular materials to make the time delay compensators. By rotation of compensators, the time delay could be adjusted, the listed delay range are based on a rotation range of +/-12°.