This is looking down onto my work bench in the lab. The board is empty vero-board, which is a blank circuit board with a grid of holes for component legs and copper tracks on the underside that you break to form tracks.
The first few components are in.
Most of the components in. This board is the third go at getting this circuit to work. The last two had massive problems with noise that were ultimately unsolved. This go is important to me 'cause I heavily re-designed parts of the circuit. The input stage is completely my design and I have modified the three output stages. Ever since I was a kid I have wanted to design my own circuit. I never realised just how hard it is. Fingers crossed!
The completed device. Sorry about the focus and flash. Tom, feel free to download this and work your magic. The board is now sitting in it's perspex container, which I also built. :) The silver object in the left side wall of the box is a connector for the high-voltage power supply. The red and black wires leading out of the left of the photo connect to the low-voltage power. The grey wire leaving the right of the image is the link to the control circuity and the green/white/pink/yellow cable is the high-voltage output (the left end has screw terminals for connection to the optics). This device takes a 1300V DC input and, when triggered by the control circuitry, discharges a 3500V, 5 microsecond long pulse. Hence the amount of heatshrink on the output cable. The voltage pulse is applied to a special optical crystal which is used with some other optical elements to form an optical switch, which enables me to turn the laser on and off very, very rapidly. No, you can't just turn
My lab space. The experimental apparatus is all of the stuff between the computer (actually including the computer, it does data collection and analysis, or will when I finish writing the programs) and the black soldering iron behind the table leg at the very left of the picture. The two circuits that have been giving me so much grief are in the centre. The smaller control circuit is mounted vertically on the black optical bench. The laser (small) is just to the right with the the yellow stripe on the top and about 2/3 of the optics are to the left of the board. They're glowing green with laser light.
Arty photo looking down the optical switch. The laser is at the bottom of the photo, timing control circuit to the left. The glass rectangle is a beam splitter which directs 4% of the laser light into a photo-detector mounted on the timing board. The laser looks like it's always on but it's actually pulsing 7000 times a second, producing 0.5ns (i.e. less than a billionth of a second) long, 6kW (yes, it will blind you) pulses. I need to select one pulse out of the train, on demand. Because of the way lasers work there is no way to make the laser do this and no mechanical shutter can move fast enough to open and close for just one pulse. Thus the optical switch. The operator (me) arms the timing circuit, which then waits for the next laser pulse to be detected. Once that pulse is detected the circuit then waits until a microsecond or so before the next pulse is due and then fires the trigger signal down the grey wire to the high-voltage circuit... Next photo!
Arty side view, timing board to the right. Trigger pulse fires to high-voltage board which does some fairly tricky things with transistors and many capacitors (original design by Marx, ~1940) in order to drop 3.5kV across the white cylinder (Pockels cell) in the centre of the photo. The black tubes either side of the Pockels cell are polarising prisms (same as polarising sunglasses but more expensive) which are crossed and so don't let light through normally. When the HV pulse hits the Pockels cell it causes the crystal to rotate the plane of polarisation of the light by 90 deg, allowing (assuming spot-on timing) on pulse of laser light through the crossed polarisers. Voltage disappears, rest of pulses blocked. One pulse travels out of the switch and is absorbed by a solar cell, which is then probed and prodded by the white electronics boxes and computer (see 5th pic) to obtain high-quality data on the characteristics of the cell and, with a large dollop of physics, the materials
