Unlike transverse mode Pockels cells where the half wave voltage is dependent upon the ratio of length to width (between electrodes), the half wave voltage for a longitudinal field cell is fixed for a given wavelength and varies only weakly with cell geometry. This results in very high voltage operation for most applications (e.g. > 6kV for 1064nm).
One solution obviously is to use transverse mode devices and for some applications this is appropriate. However, for many situations, only a longitudinal field device will provide the right optical performance (especially where higher extinction ratios are desired). The solution then is to combine two Pockels cells, each providing half the total rotation when driven from a common voltage source.
The logical conclusion of this approach is to combine both crystals in one package. This reduces losses, overall size, component count and alignment and set-up time (which then becomes the job of the manufacturer!). The result is a composite device which halves the required drive voltage at the expense of approximately twice the load capacitance.
As with all Leysop's longitudinal Pockels cells, the two crystal devices can be supplied in one, two or four terminal configurations (as seen in the above picture) and may be supplied either with index matching fluid filling the space between the crystals and the windows (preferred) or dry, with or without anti-reflection coatings on the crystals. Tilted off windows and/or wedged crystals may be specified if required to control interference effects caused by multiple reflections.
Two crystal Pockels cells can be produced in any aperture size, although to date only 8mm cells have been requested. Leysop also manufactures two crystal devices in the compact Pockels cell range (see here) and the ultra fast Pockels cell (UPC) in both single and double crystal versions (see here.)
Example Specifications: (Please email us if you have special requirements.)
|Half-wave Voltage @ 1.06μm||3.0kV|
|Optical Rise Time||< 0.25ns|
|Contrast Ratio @ 1.06μm||> 600:1|
|Damage Threshold Q-switched||600MW/cm2|
|Physical Dimensions||50mm dia.