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Pulse picker

The output of the pulse picker consists of 2 dots. The upper one is the picked pulse, the lower one is the 90 MHz train.

Normally, the picked pulse is transmitted into the frequency doubler, and the 76 MHz train is blocked inside the pulse picker. It is possible to adjust the height of the thing at the exit of the pulse picker which blocks the 76 MHz train.

To ‘pseudo’ bypass the pulse picker, adjust the vertical position of mirror 2 (the one after the light passed the crystal ), so the 76 MHz beam moves up (over the blocker) and enters the frequency doubler. The pulse picker can be switched off completely somewhere at the back of the control box

  • Optimize with power meter on the double or so result
  • height of the beam through crystal : the lower and closer to the transducer the more efficient pulse picking. Too low, the beam gets clipped. Use an IR viewer to watch the area just before the crystal.

NB : changing the height of the crystal also changes the timing : it takes longer before the acoustic wave hits the laser beam

  • Timing on the control box : coarse : don’t use, fine : use.
  • Power to the transducer.
  • Side knob : height of the crystal. You see if you move it on, it will go through several maxima. The best one should be the lowest (in position), without clipping. This height knob is an alternative to the timing on the controller.
  • 2 top knobs : angle of crystal : both are needed !!
  • Other side knob : focus (not so important).
  • Pulse picker bragg angle is wavelength dependend !

Cleaning of the crystal

Very carefully. Use methanol (never acetone, dissolves the glue).
Use just a lens paper with a drop of methanol. Don’t use hemostat.

Opening the pulse picker

Push the little buttons at the sides inwards (have little levers on the inside), but make sure not to push the side plates themselves inwards.

Pulse picking frequency

Works with a divider on the control box. Max frequency is 2 MHz.
So divider on 20 → 1.9 MHz.

Menu alignment

Pulse picker runs in auto-run mode : easier for aligning

Numbers on display

1 65 106
100 80
20
[don't know if originally the 1 was really 1]

Verdi 5W @812 nm : Mira about 450 mW output. Measured with power meter and attenuator.
Pulse picker output about 7 mW. Efficiency = 60%. (According to Maxim, should be 90 %)