2023 Abstract from Aiman and Jonathan

Testing the Reflector for BREAD (Broadband Experiment for Axion Detection)

Students: Aiman Imran, Jonathan Schiff

Mentors: Dr. Andrew Sonnenschein, Dr. Stefan Knirck

Little is known about dark matter. One candidate for the elementary unit of dark matter is the axion. In BREAD, a strong magnetic field is placed around a metal cylinder, creating detectable photons from an axion field. These photons are focused into a detector by a parabolic reflector. We first tested a prototype reflector by compressing images of reflected laser light into 1D arrays using Python. Using FWHM, the vertical spread was found as a function of height and angle of rotation, with an average of about 0.086 radians. We then tested two mirrors in preparation for future measurements. Total Integrated Scatter (TIS), a ratio of diffuse light to specular light, was measured by taking pictures of diffuse and specular reflected light and comparing intensities. The TIS of the prototype part was effectively 100% due to the large spread. Reflectivity, a percentage of how much light is reflected by a given surface, was measured by taking a ratio of the reflected light voltage to the direct light voltage at a photodiode. Similar testing was done on the final, diamond-turned reflector. Although the reflected light was wider than the photodiode’s sensor, an approximate reflectivity was achieved by multiplying the captured voltage by the reciprocal of the percentage captured. Focal distance was measured by finding the minimum vertical spread as a function of reflector distance from a screen. We again calculated TIS, which was about 1%, and used that to calculate the rms roughness of the surface as 11nm. Using a grating equation, we obtained an approximate value of the length between peaks in roughness on the surface as about 770nm. We found that the diamond-turned part was, overall, sufficiently accurate in its reflection of light.