Monthly Archives: July 2011

Stepper Motor

Some of the links I read while hooking up the motor:

Motor Shield – Frequently Asked Questions

Motor Shield – How to rev up

Stepper Motor – Connect and use a stepper motor with the Make Controller Kit


It is hooked up to M1 and the wire color order from the top is:







Next up, using pwm to achieve continuos motion.

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Drawing Plots

Octave and GNUplot are installed on my computer. I used MacPorts.

I made this picture using Octave & GNUplot.

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Week 7 – Midweek Update

This past week at the LTC has been quite productive. On Wednesday, Marty helped Gaby set up the AOM, and I was able to experiment with it. Before setting up the AOM I hooked up the oscillator to the oscilloscope, and verified that it was actually capable of producing 80MHZ waves. It was able to do this, and that is what we are using to drive the AOM. The oscillator has quite precise controls, and we can adjust it to things like 81Mhz etc… without trouble. I want to make measurements of the 1st order angle vs frequency, and also, I want to make the first order frequency, then rotate the AOM to measure intensity of the first order vs the angle of rotation of the AOM.

The second very exciting event was setting up laser Sam’s scanning Fabry Perot Laser Sam helped set it up quite a lot. The general arrangement is shown in this schematic:

For the rest of the week and the beginning of next, I’ll be using the two set ups to make measurements of the laser. Learning about the FP, and how to scan for resonant frequencies is one of my goals, but to do that I need to figure how how to prevent the beam from displacing with shifted frequency. Professor Metcalf had some suggestions about this, when he suggested I look up hetrodyne.

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Inner workings of an AOM

The crystal is subject to a compression waves, which are the acoustic wavelength. The incident light beam, when striking at the correct angle, forms a diffraction pattern corresponding to the acoustic wavelength.

The transmitted light is Doppler shifted based on:

Sources: The Acousto-Optic Modulator and Optical Heterodyning

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Week 6

Today was spent setting up my laser, AOM and photodetectors. I read a lab manual on how to use an AOM, and I wanted to perform the demos it suggested. Unfortunately I could not find information on how to hook up the AOM. I need to ask Marty for help in hooking up the driver to it. The photodetectors are mounted to sliding tracks, so I can adjust them. The AOM has z axis freedom and can rotate in the x/y plane. One of the frequencies should emerge off center of the original transmission angle.

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Week 6 Day 1 & 2

Recently I decided to stop writing daily updates. Writing daily reminded me that at times it is better to have a long term view. Holding a thought for about a week before moving forward and acting on it suits my pace of idea generation. This gives me time to thoroughly examine the idea and look for flaws in it. The past weeks thoughts have focused around whispering gallery mode resonators.

One of the publications has a chart showing pump transmission power vs frequency. I wanted to make an arrangement so I could take similar measurements. After speaking with Professor Metcalf he suggested using an AOM to change the frequency of light, and to use a quarter wave plate to rotate the polarization, so I could separate the two frequencies (the light travels through it twice, in the schematic). After the AOM the light should pass through a resonator, and it should peak when the frequency is one of the modes of the resonator. Ideally I would like the resonator to be a whispering gallery mode resonator, but at the time I do not have one. Alternatively I could use a Fabry-Perot resonator, which I think I will do for initial testing. 

I was reading about the fabrication of WGMR, and I think it would be possible for me to construct some out of silica glass, using my lampwork glass shop. If I can learn how to measure the modes of the FP, then I could make several WGMR out of glass, at different sizes and slightly different shapes. Then I could use the WGMR instead of the FP.

A thought just occurred to me, I want to measure the frequency of the light and simply knowing the intensity is not enough. Could I calculate the frequency of the output light from the AOM? Should I interfere the two beams at some point to see what the frequency difference is? I can look up the process ‘hetrodyne’ for additional information.

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