Two-week Update

Haven't really been keeping up with the posts over the past few weeks.

For the most part, I spent a large portion of time working on a laser locking circuit which would combine peak-locking and DAVLL schemes.

In short, peak-locking is a very accurate (can lock laser to a specific hyperfine transition), but has a very narrow capture range and can be easily disturbed so that it unlocks. DAVLL is more robust, having a larger capture range and is able to maintain the laser's frequency with a range. The drawback is that the DAVLL scheme is not the most accurate, having a tendency to drift over time.

The purpose of attempting to combine these techniques is to have the accuracy of the peak-locking scheme and the robustness of the DAVLL scheme. So far, our attempt at combining these two methods is through direct addition (with adjustable gain) by feeding the signals through a summing amplifier. I completed the circuit earlier this week but only had limited testing opportunities since John wanted me to work on the PCB layout for AOM controllers.

Front view of the locking circuit, showing the various inputs.

 Top view of the locking circuit, showing the rats-nest that is the wiring.

The results of our limited testing showed that the circuit is somewhat quirky, not quite locking the laser as well as we had hoped. Possible issues may be the selection of the components used in the circuit, especially with integrator values. As an example, if the integrator provided too much feedback to the peak-locking scheme, it could possibly produce increasingly strong oscillations due to it over-correcting and losing lock that way. Another issue may be different locking points for the peak-locking and DAVLL schemes. One signal would tell the laser to correct to one particular frequency while the other signal may push the laser towards another frequency.


See Diode Laser Frequency Stabalization for a better explanation.

We also presented our mid-term talks this past Friday. Didn't quite go as well (for me) as I had expected. The "prompt" was to convey what we've been doing (not necessarily the overall objective), so I skimmed over a lot of details to focus on what I was doing with the laser locking circuit. Perhaps, I skimmed over too much when I compare mine to what others have done. I posted my slides below.

As a side note, I am using KiCad to layout the PCBs. It's a pretty neat open-source software package which allows you to design and layout circuits. I've messed a bit with the TinyCad-FreePCB combination, but I decided to work with KiCad instead because I feel that it more smoothly incorporates schematic designs (well, at least makes it easier) with one complete package compared to crossing over different programs.

KiCad Wiki
KiCad Step-by-Step Tutorial
KiCad Libraries