User:Pranav Rathi/Notebook/OT/2011/03/01/Laser Shutter .2
The full detail is coming soon.
Motivation behind designing the shutter is speed, accuracy and variability (time). In our optical tweezers we need to center the trap over the tethered bead, to get the geometry right(because this affects the force measurement)and make our feed-back program run. To center the tether we need to turn the laser intensity on/off quickly for variable time intervals. To do this we used to use AOM, because it’s extremely quick (nsec) and variable. So I needed some-thing which can replace this AOM function. This shutter does it exact. It is fast with opening time of 4 and closing time 2 μsec. Since the shutter runs on/with the active voltage (controlled by the toggle foot switch), it remains active with the applied voltage, with the freedom to chose any active time. The speed of the shutter can also be controlled. In design the laser passes through an aperture, and the only moving part is the cylinder. No gears, and no electronics in the actual shutter, makes this design very stable and accurate, even under the heat produced by the laser beam. This shutter needs no special power supply, it can be run through a cell phone charge with an output of roughly 300mA/5V. Cost and construction time is also important. With this design, a shutter can be prepared under $40 with 10 hours of construction time (10 x 25 (hourly wage of a technician)=$250+40=$290). Still better than many commercially available shutter systems with same performance.
Design & Construction
There are three major parts of the system.
- Control box.
- Power supply.
The components used:
- 12V DC motor
- Wood rotation stage
- Spring with torque of 2e-6 N m
- Rubber padding
- Pillar Post Extension, Length=1" from Thorlabs (shutter cylinder)
- 30mm Cage Plate Optic Mount from Thorlabs
- Post-holder, base-plate ext...
- 1 power jack M&F
- 1 1/4" mono Panel-Mount Audio Jack M&F
- 1 Foot Paddle
- 1 100Ω pot with, 1 220Ω resistor
- 1 on/off toggle switch
- 1 LED
- 1 box enclosure
- some connection wires, solder gun and solder wire
Any power-supply which can provide 300mA at 5V and above. The motor torque is power dependent and the shutter speed is resorting spring's stiffness (torque) dependent. So choose the spring carefully before decide on the power supply. I would recommend a variable power-supply which can be bought easily from any where.