Category:Construction of Optical Tweezers and devices

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Revision as of 08:52, 23 January 2013 by Pranav Rathi (talk | contribs) (Fast laser shutter)

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This page contains all the devices I invented for optical tweezers (OT) and other optical-experimental setups. All the devices were made in very low budget and in short amount of time. Most of the devices are available commercially in one form or other, but these devices are specifically created to full-fill the requirements of optical tweezers which is designed but not limited to DNA-overstretching and unzipping.

Easy way to align two laser beams

In OT I use 1064nm IR laser for trapping, since it is invisible I align it with 633nm HeNe which helps me in number of ways: It let me align IR in farfield especially when i need to align the microscope and with HeNe it is easier to find the sample plane in eyepiece and camera. This post discusses the procedure-steps of alignment[1]

Slow laser shutter

During experiments I need to peep through the eyepiece many times to adjust the sample on the tweezers. It is not safe if the IR laser is on and it is also not safe for the laser to turn on/off many times. So I need to cutoff the beam for safety without turning the laser off. AOM can also do that but I had to be careful with it for two reasons: The beam would still scatter at the back plane of the AOM and I still receive a week IR emission coming out of AOM even at 0 Volts. So for the safety I invented an air-freshener based laser shutter. Air-freshener dispensers mechanics is very durable because it is made to work every 30 minutes or so for months and years makes it right candidate for this purpose. To enhance the safety I put two sensors on the two ends of shutter which updates the real position of shutter through green and red LEDs. The post discusses the details of make[2]

Fast laser shutter

During DNA experiments I need to center the trap over the tethered bead very precisely, to get the geometry right (this affects the force measurement) and make our feedback program run. To center the tether I need to turn the laser intensity (trap) on/off quickly for various time intervals. To do this I used to use AOM , because it’s extremely quick (nano second on/off time). But AOM has some inherent oscillation problem which makes its use as a switch unsuccessful. So I needed something else (a shutter) which can replace this AOM function. So I invented the fast shutter, which does it exactly with an opening time of 4 and closing time of 2 μsec. The shutter runs on a +5 volts and there is hardly any electronics involved. It is controlled through a foot-switch. The post discusses the make [3]

CNC filter system

During DNA experiments data acquisition I need to modulate the laser intensity many times. I usually do it with AOM, but for some tasks AOM is not that useful due to oscillation and x&y signal drift problem. So I invented the computer control filter system out of a disk drive. The system can be controlled directly through LabVIEW using NI-DAQ or Adriano micro-controller. The system uses 1" lens tubes to mount the filters.The post discusses the make[4]

X-Y stage control with joystick

For DNA experiments the sample-chamber mage are roughly 15X5mm in size. The field of view of camera is 200X180μm and there are only very very few good DNA tethers in any field of view at any time so I have to move around the sample a lot to find the right tethers. I uses to do it by hand by adjusting the linear micrometers but that is just awful, so i designed this linear x-y stage system control by joystick to do my job.The post discusses the make[5]

Acoustic and mechanical noise reader

Optical trap is really sensitive to airborne and mechanical vibrations in setup. I was receiving both in my data. So I needed something to study the noise and identify its sources. One way to do it to use piezo-sensor which is not easy to use. I needed some thing easier and quicker. So i invented AMNR out of class-2 stethoscope and a sensitive condenser mic. Condenser mic let me listen to airborne noise and stethoscope let me listen to mechanical vibrations. I use computer sound-card to acquire data and use LabVIEW to process it. The post discusses the make.[6]

Opto-mechanical controls with Lego

Optical trap is really sensitive to airborne noise and air-currents.