This morning Lauren gave Henry and me a lecture on Gaussian beam propagation. I realized that the laser beams spread all the time when they go through space. Then Lauren told Zhila and me what to do next on the pump-probe project. We could not place the CCD camera on and collect data now for two reasons: first, we didn't know what intensity we needed to use for this experiment in order to ablate the Silicon surface; secondly, we could not gather image manually. Since laser pulse travels very fast and frequency of CCD camera is relatively low, we would not be able to know when to take pictures after a laser pulse was emitted.
Then we came up with solutions for each of the problem. We had known the minimum fluence we needed to ablate the silicon surface. In order to get the minimum energy, we only needed to know the spot size on the sample. Zhila and I measured the total length of the pump beam, then we used Gaussian beam's propagation formula and focusing equation to solve the spot size. Finally, we found the theoretically correct answer.
The rest of the afternoon, I was playing around with a CCD camera. Tomorrow, I will work more on writing Matlab code to connect the CCD camera with computer.
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