Simulating Thin-Film Samples Reflectivity on Mat Lab and Origin
Lauren Delgado, Vassar College ’19 and Prof. Brian DalyDuring this summer in URSI, our experiment focused on the thermal conductivities and sound velocities of various thin film samples using ultrafast laser spectroscopic methods. In these measurements, the samples are thin films of various novel thin film materials grown on wafers of silicon capped by an aluminum film. We then shoot laser pulses at these specimens to extract the quantities of how much optical absorption occurred. After collecting data on different materials, we would cross check our results with the computer programs MatLab and Origin. In MatLab, we could simulate various measurements of sound velocity, density, and thickness to reproduce what changes affect reflectivity over time. We also make plots of reflectivity versus frequency in by a method known as Fast Fourier Transforms (FFT). This was helpful because we could determine whether experimental results would match up with the computational results the program offered us. First, to model this data, we would simply change input parameters for each thin film material and run the MatLab program and save each “r_t” (reflectivity versus time) under new file names (according to what their specific thickness changes were). Following this, we would drag the data into Origin to be graphed as a plot and a FFT. After completing this step, using a selection tool on Origin, we could calculate the accuracy of each graph in by comparing the time in between each peak in the plot section versus peaks in the frequency section on theFFT.