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Experimental setup question.

If anyone aware of a technique to create pulses of several nanoseconds at a around 10Hz repetition rate from a CW laser source?

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  • $\begingroup$ a rotating slotted disk? $\endgroup$
    – Jim
    Commented Aug 27, 2015 at 15:45
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    $\begingroup$ One, or more likely two, Pockels cells might do it. It would be hard to find a 5kV supply to switch on and off in several nanoseconds, but switching one one (to transmit) and the second on (to re-block) with a several nanosecond time delay is doable (it is much easier to get a fast rise-time kilovolt signal than a fast rise and fall). Other electro-optical modulators might work as well. $\endgroup$
    – Jon Custer
    Commented Aug 27, 2015 at 15:51
  • $\begingroup$ Thanks @Jon, I'll look into that. I had been looking at trying to achieve it with a single Pockels cell and hitting a brick wall. $\endgroup$ Commented Aug 27, 2015 at 17:12
  • $\begingroup$ @Jim , a chopper wheel is not practical for nanosecond pulses, the width of the slot the would have to be around 10^{-5} degrees. $\endgroup$ Commented Aug 27, 2015 at 17:16
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    $\begingroup$ The easiest way is to open up the laser and insert a Q-switch into the laser cavity. You might run into thermal issues if the average power is too high though. $\endgroup$ Commented Aug 27, 2015 at 17:55

2 Answers 2

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You could use an electro-optic modulator. These don't need kV supplies, can have very fast rise/fall times, and can be fully programmable by using a digital delay generator (these can also be triggered optically for extremely good accuracy, preventing timing drift between the delay generator and whatever source you're using). You usually need the following:

1) Electro-optic modulator.

2) DC power supply (20 V or so).

3) RF amplifier.

4) Delay generator.

Using a delay generator (such as the Stanford Research Systems DG645) you can create modulated RF signals with a very wide range of waveforms which can then be used to open and close the electro-optic modulator to transfer the RF waveform to an amplitude modulation on the CW laser output.

This will not be cheap, though.

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I once worked with a laser technician who was a specialist with the high voltage supplies and circuitry for pockels cells, he told me klystrons were used to produce the very short high voltage pulses to drive the cells. Might not be easy to get. Maybe a rotating mirror to sweep a beam quickly past a thin slot?

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