School of Physics - Optics Group

Laser shutter using a camera shutter

For a very simple shutter, try the Sunex SHT934 camera shutter, about $30 each (thanks to the Strathclyde group for the tip).

datasheet

Laser shutter using an iPod drive

We often make shutters with hard drives from broken iPods. We'd like to thank the very helpful people at fixpod for supplying us with some broken drives at very low cost, and recommend them if you need to repair your broken iPod.

Laser shutter using a hard disk drive voice-coil actuator

We have developed a high-speed laser shutter based on voice-coil actuators found in generic hard disk drives: Maguire LP, Szilagyi S and Scholten RE, High performance laser shutter using a hard disk drive voice-coil actuator, Rev. Sci. Instrum. 75 (9) 30773079 (2004).

Update: sub-microsecond shutter

We have enhanced the shutter with a new driver circuit described below and a notched flag, achieving 500ns rise time and sub-microsecond pulse durations. See Scholten RE, Enhanced laser shutter using a hard disk drive voice-coil actuator, Rev. Sci. Instrum. 78 (2) 026101 (2007).


Shutter mechanicals


The shutter is readily constructed from a disassembled hard drive (as shown in an early prototype in the photo above), with the addition of a simple drive circuit. A high-current opamp (e.g. L165V or OPA548) can be used, but requires a bipolar power supply, and generally some sort of pulse shaping. The circuit in our paper, designed by Sandor Szilagyi, provides very fast switching, a small holding current, and bidirectional drive from a unipolar supply.

Erratum in 2004 circuit

Unfortunately, an error was made in transcribing the circuit into journal format, such that in the paper, Q2 and Q4 are shown inverted, i.e. with drain and source reversed. Thanks to Juergen Eurisch (Freiburg) for pointing this out. The correct circuit, and PCB layouts, are included separately at old shutter circuit. However, we suggest that you might like to try our new much simpler circuit, also designed by Sandor Szilagyi, with ideas from Ekapop Pairam (Georgia Tech).

An erratum has been published as Rev. Sci. Instrum. 78 019903 (2007).

New circuit

There are many single-chip H-bridge packages, which include TTL conversion and protection that prevents shoot-through (i.e. the wrong FETs switching on and short-circuiting). Infineon have a big range, e.g. the TLE5205-2, but can be hard to find. The Freescale/Motorola MC33886 is cheap and compact, but needs two separate TTL inputs, one for forward, one for reverse. We have instead used the National LMD18200.

Here are some pulse shapes:

New schematics and PCB layouts

The board is shown below; the size is 2.00" x 1.60" (50.8mm x 40.64mm).

If you would like a milled PCB as in the photo, without parts, just let me know and I'll see what I can do. Our workshop will be happy to assemble and test one for you, but the cost is $90 per hour.


How does it work?

The core is a MOSFET H-bridge in the LMD18200, which drives the unipolar supply through the coil, one way when the TTL input is low, and the other way when it is high. In the steady-state, the coil current is set by the supply voltage and the 220 ohm resistor, R1, and capacitor C4 charges to the voltage across R1. When the TTL signal switches, the potential across the coil and R1+C4 reverses. C4 discharges through the coil very rapidly (time constant set by C4 and the coil impedance), thus producing a sharp spike. You may need to change R1 and C4 to suit your coil. Please note that C4 must be a bipolar capacitor.

Future improvements

Walther Goethals (now at Diamond Tools Group BV, The Netherlands) patented much the same idea in 1999, when working at Lumonics. The patent is described here: Method and apparatus for actuating a shutter.

Walther's version reverses the current halfway through a sweep, to allow larger current and faster actuation, and reduced impact at the end. The patent includes electromagnetic damping (which is easily implemented with the LMD18200) at the end of the sweep.

Other implementations

Students at UBC have developed an 8-channel version using iPod hard drives. They have written a full report.

Peter Bechtold (Bayerisches Laserzentrum gGmbH) has built a compact version, with the new circuit mounted on the back of the unit:

 

Peter added a 10k pullup resistor on the input, and a switch to ground, to define the input and enable manual control. He used two smaller bipolar capacitors to allow selection of just one capacitor for a slower sweep when full speed is not required.

Ian Spielman (NIST) built a small board with four drivers. The shutters are used for imaging of BECs. The imaging beams are switched rapidly with AOMs. The probe beams are incident on the AOMS most of the time, to keep the AOMs warm, but prevented from actually reaching the BEC by hard-drive shutters after the AOM. Ian also uses an iPod hard drive shutter for the rubidium source in his BEC machine.

Simon Higgins (Monash) has put two hard-drive shutters in series to block x-rays at the Taiwan synchrotron. Here you see two of the electronic circuits, and what looks like one HDD but is in fact two clamped back-to-back. The whole think looks prettier with the cover on. Note the fan to keep the voice-coils cool.

Links

A solenoid-based laser safety shutter.
Created: 10 March, 1999
Last modified: 11 September 2006
Authorised and maintained by: A/Prof. R. Scholten, School of Physics