In many laser applications a modulation of the laser beam is required. One of the prime methods of modulation is the utilization of the electro-optical effect in crystal materials. The special linear case is called the Pockels-effect, the eponym of the Pockels cells named EOM’s.
Electro-optic modulators are basing on the effect of the voltage induced birefringence. Pockels cells are a kind of EOM’s which enable via the supplied voltage a linear controllable birefringence. The cell contains an uniaxial crystal, transformed to a biaxial one, if an electric field is applied. If the new induced axis is arranged 45° to the polarization of a linear polarized incident beam, this beam will be split into two orthogonal each to other polarized part beams. These part beams pass the crystal with different velocity (because of the different valid refractive index)
The induced birefringence Δn is proportional to the applied electric field E. Via the crystal length l a controlled phase shift between the part beams is the result. By application of this effect it is possible to control the laser parameter polarization-degree, amplitude and phase.
DoroTEK delivers Pockels cells on basis of KD*P and LiNbO3 crystals. On demand it’s possible to produce complete modulation units, consisting of the Pockels cells, a polarizer and the retarder plate.
Selected technical parameter of Pockels Cells
|Spektral range||0,35 – 1,5 µm||0,4 – 4,5 µm|
|Contrast ratio||1000 : 1||300 : 1|
|Damage threshold (LIDT)||800 MW / cm2||300 MW / cm2|
|Transmission||> 98 %||> 98 %|
|Quarter-wave voltage for 1064 nm||3,2 kV||0,8 kV|
Datasheets of Pockels-Cells are available as downloads
KD*P-Pockels-Cell with polarizer
KD*P-Pockels-Cell with Brewster-Window
Pockels-Cells (Laser Modulators)