Laser shutters are very neat devices that allow an experimenter to turn on or off a laser beam with the flick of a switch. Anyone that has worked with lasers will know that turning your laser on and off a lot is not ideal for the laser. It's much better for the laser to block the beam somehow. In the lab, one can "turn off" the beam from down stream optics by using acousto-optic modulators (AOMs), electro-optic modulators (EOMs) or a physical shutter. I particularly like using AOMs because they are great devices. And, you can end up getting some odd effects when using them. AOMs and EOMs are pricey and unless you need one, they can be overkill in an experiment. So, if simplicity is your goal, I'd just block the beam with a shutter.

Our lab uses optical tweezers to unzip DNA and in the process of unzipping, you must turn off the laser beam in order to position it over a bead that you intend to pull on. Yes, you can manipulate the position of things with lasers. And yes, it's like a tractor beam albeit a tractor beam that's only useful in the microscopic scale. To turn "off" the laser beam, you need to block the beam such that it does not reach the sample plane in the microscope.

In this Instructable, I will discuss my version of a laser shutter. This design came about because a fellow lab mate was trying to make a laser shutter with a speaker. I was intrigued by this idea (which is very clever) and decided to make my own shutter using a hard drive as the actuator and not a speaker.

After making the shutter, I researched to see if other people had tried this before. Much to my elation, others had. They even made the circuits from scratch and if you can get the paper, it's a nice short read.

Maguire, L. P., S. Szilagyi, and R. E. Scholten. 2004. High performance laser shutter using a hard disk drive voice-coil actuator . Review of Scientific Instruments 75, no. 9: 3077. doi:10.1063/1.1786331.

I had the power of the Arduino platform when I designed this shutter so, I didn't have to build a circuit from scratch. With this design, anyone can make one with very little electronics know how and very cheaply.

Step 1: Teardown an old hard drive

Depending on the hard drive you have, you will need either regular screwdrivers or Torx screwdrivers in order to open it up. The below images are from a hard drive in which I did not use the read head and magnets from. I didn't take images of the tear down of the hard drive I used in the shutter so I'm including the below images as a reference. Just realize that the final shutter pieces look different than the parts from this hard drive.

Images 1 & 2
I removed all the screws from the hard drive ensuring that I got the hidden ones from under the sticker. This particular hard drive only had one but there are sometimes more. I saved these screws because they are useful in other projects.

Image 3
I also removed the circuitry on the back side of the hard drive. I recycled all the parts I couldn't use and you should too. If you are able to take off the SMD components for other projects from this circuit, then by all means do so.

Image 4
I opened up the hard drive by taking off the top cover. Inside is the hard drive platter, the read head and the magnets that position the read head. Sometimes there is a small magnet that holds the read head in a "locked" position that is located in the bottom right of the picture. This hard drive didn't have one but in others I've taken apart, there are. The small magnets are useful in this build so make sure to keep it in a safe place if you found one. Preferably not on you cell phone.

Image 5
I took out the read head and the magnets from the hard drive. This is not entirely necessary as is indicated in the paper but, I had to get at the bottom of the read head in order to solder some wires to it. Plus, I didn't feel like manipulating the hard drive enclosure to conform to an optics table. So, I went ahead and removed the magnets and read head from the enclosure entirely.

When you take out the magnets, be careful not to damage them. If you have an older style hard drive the magnets will be quite powerful and will require some leverage in order to be removed. These magnets are very strong so be careful around them. If you have an old CRT, you can use them to mess with the electron gun in it before moving on.
Did you measure the speed of the shutter driving it with the ardiuno? I'm looking to make a shutter to select pulses from a 1kHz pulsed laser so the minimum opening time is very important.
The video is private.
I assume one cant control the position of the head (like in the HD) due to lack of feedback (closed loop system) .<br>Pls let me know if you think otherwise.<br>
Not in its present form. I'm think you could use a PID current controller to precisely control the position of the head but, then you would have to calibrate it.
What an excellent proof of concept, I'm quite curious to see it in the final application.
Thanks! I'll definitely update the Instructable with a more in depth review of its performance.

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