3.9.10

Downsampling the sub-aperture array worked pretty well in reducing the computation time for constructing the slope vector. The image itself is still pretty large, around 900x900 px, but this saves me from having to screw with the beam diameter further. An image of that size allows for roughly a 36x44 lenslet array. Sampling every other sub-aperture essentially doubles the speed; enough such that capturing an image and computing a down sampled, 18x22 dimension slope vector can happen at around 30 Hz, near the 40 fps frame rate of the camera at that resolution/shutter speed. I can get even closer by going to a 9x11 array, but the savings aren't great, and the resulting phase profiles start to look pretty crappy at higher spatial frequencies.

I think this is about as fast as I can expect to go without any (drastic?) changes to the beam size or any additional info on the DM dynamics. The DM presents an interesting problem. I can really only see the dynamics with a very high WFS frame rate (100 fps+), which means a small image with just a few sub-apertures. The trouble is that getting meaningful modal information is hard with so few sub-apertures, so computing an actual frequency response using the modes as control channels would be tough.

I want to move on to some controls applications. One thing I want to try first is to generate random disturbance commands, pass them through a low order FIR filter and apply them to DM61, first with a single modal channel, and the more. Eventually, I'd like to read the resulting open loop WFS data and try to identify the FIR coefficients in some way, either adaptively or using a subspace ID algorithm. This is basically the first step in designing a time-invariant LQG controller, the topic of the first paper I can probably get out. One interesting question in an adaptive situation would be to investigate how the convergence rate is affected by the density of the sub-aperture array. How badly does down sampling screw up the ID? I suspect its significant at higher resolutions.