PCD-3000 100kHz Q-switch driver for RTP / BBO Pockels cell

Pulse driver for Q-switching with RTP and small BBO Pockels cells.

High repetition rate RTP Q-switch driver

One of the most difficult aspects in dealing with electro-optic devices is the problem of working with high voltages. The majority of electro-optic devices present a capacitive load to the driver which further compounds the problem of finding a suitable driver. However, the relatively low voltage requirements of the transverse field RTP Pockels cell allow us to switch the high voltage at high repetition rates with acceptable power consumption at the driver.

We have developed the driver with the application of continuously pumped sources in mind (rather than flash-lamp pumped for example). For this reason we have not incorporated any facility for varying the delay from the input trigger pulse and the Q-switch output pulse. We have however provided full protection facilities based on internal current limiting to ensure that the demands on the internal HT power supply do not exceed its capability. There is also an internal rate generator for those applications where synchronization to external events is not required and free running use is acceptable.

Safety is of course also paramount and the high voltage output is provided by a safe high voltage (SHV) form of the BNC connector and a matching lead is supplied to connect to the Pockels cell terminals. The HT votage may be set precisely from the front panel to enable the unit to be set for optimum performance at the user's operating wavelength and to allow for the different voltage requirement of the three aperture options available.


Parameter Value
Repetition Rate 0 to 100kHz in five decade steps by internal or external generator
Output Voltage +200 to +3,000V adjustable with visual display
Output Pulse The standard system generates a positive going step function above zero. The generator can also be supplied giving a negative going step from the set HT level down to zero for quarter wave switching
External Trigger In +3.0 to 10.0V min. 10ns f.w.h.m. into 50Ω
Synchronization Output TTL approx. 30ns after trigger
Overload Protection (1) Repetition rates above 100kHz
(2) HT Current above 25mA
(3) Output stage fault overload

Protection occurs by automatic removal of the HT supply which can be re-instated by the reset switch
Power Input Universal 90 - 265V a.c. 47 - 440Hz via fused IEC inlet
Dimensions 150(h) x 250(w) x 330(d) (mm) Mass: 6kg
Step Voltage at End of an Open Circuit 50Ω Line
50W co-axial cable length Rise-Time Flat Top Fall Time Maximum Frequency at 2kV Maximum Voltage at 100kHz
125mm 5ns 175ns 400ns 80kHz 1,700V
250mm 5ns 160ns 500ns 66kHz 1,500V
500mm <7ns 150ns 700ns 50kHz 1,300V
1,000mm <8ns 120ns 1,000ns 40kHz 800V


The obvious application for this Q-switch driver is with RTP Pockels cells, but it is also possible to make BBO Q-switches of small aperture with two crystals and for quarter wave applications the voltage requirements are low enough for operation to ~50kHz.