I spent the better part of the day (Wednesday) learning how to use MATLAB. The main source that I used to do this was “MATLAB Guide”, by Desmond J. Higham and Nicholas J. Higham. I made it through the first chapter or so and did some interesting examples including Mandelbrot set, Fibonacci numbers, and simple 2D plots.
I was then able to use MATLAB to input my data from yesterday and plot the two curves on the same set of axes (though it would have been nice to tell MATLAB to put them on orthogonal axes).
Note: I corrected for the x- and y- positions by setting the point of maximum intensity at (0,0).
That data is shown in the image below:
The red shows the data from the x-scan, while the blue corresponds to the y-scan. Notice the final data point at the origin for the y-scan. This is simply because I put the data from the two scans into the same matrix and there were more points for the x-scan than the y, and so the these points were all plotted at (0,0).
Also, below is a plot that Antoine constructed with the same data by using an iterative procedure in MATLAB:
[I apologize for the poor picture quality, but I had to use Paint since I saved these as PDF at lab and Blogger couldn't insert a PDF].
Regardless of the quality, it should be clear that the beam is Gaussian in shape (at least via this method).
I would like to make some more scans to better build up images such as those above, which would probably include scans along y = x and y = -x.
Aside from learning to use MATLAB today, we took a series of scans at specific positions of the excitation beam. We took a scan at maximum (0,0), at maximum x and the lower portion of the HM of y, and then at maximum y with both the upper and lower portions of the HM of x. These were full spectral scans, and each took about 1.5 hours to complete.
Note: There was a major shift in maximum signal change from yesterday to today. The maximum went from about 4.5 mV yesterday to about 7.5 mV today. This may be due to a few things: more power out of the laser OR the excitation beam is locally destroying the Si OR some other thing yet to be determined.Antoine was going to take one final scan today with the Si wafer slightly shifted so that if the effective change in amplitude was due to a local defect then we should be able to see it right away. For tomorrow, I intend to work some more on learning MATLAB and possibly changing the incident excitation beam on the Si to try and understand the skewness of the x-position (though I think it may have to do with a slight tilt in the wafer (i.e. not perfectly orthogonal to the incident THz beam)). Also, if I have time then I may try to take some more data, as I had mentioned, with the scans being along y = x and y = -x.