Department of Physics
Dr. Anna Petrova-Mayor has been leading two undergraduate students in a laser project that has applicability in fields ranging from meteorology to biodefense. The research involves extending the capabilities of a powerful technique for measuring aerosols in the atmosphere: LIDAR – (Light Detection and Ranging). Lidars are capable of creating 3-D ‘movies’ of the motion of small aerosol particles, and hence of the motion of the air itself. These 3-d scans can cover regions on the order of a cubic mile.
The laser that is used in a LIDAR system emits linearly polarized light, i.e. if you put your sunglasses in the front of the LIDAR laser beam, you’d find that rotating your sunglasses either allows the beam to pass or blocks it. When linearly polarized light from the laser strikes an aerosol particle, the scattered light is no longer linearly polarized. A so-called depolarization occurs due (mostly) to the shape of the aerosol particle, so that the light becomes elliptically polarized after aerosol scattering. This is good news since it means that LIDARs can be used to distinguish types of particles by their depolarization ‘fingerprint’.
The bad news is that the rather complex mirror system within a LIDAR naturally produces its own depolarization effects. This ‘artifact’ depolarization must be compensated for, otherwise the effects of atmospheric aerosols cannot be reliably detected. Under Dr. Petrova-Mayor guidance, undergraduates Qiaochu Li and Scott Gimbal designed a system to perform precisely this compensation function. Simply put, they depolarized the laser light coming into the LIDAR mirror system (before striking the aerosol particles) in just the right way, so that the additional depolarization of the mirrors resulted in linearly polarized light emerging.
They presented their results at the International Laser Radar Conference in Port Heli, Greece in June of 2012, which will be included in the published preceedings. Further work is continuing in both determining atmospheric aerosol shape as well as elucidating the dielectric properties in mirrors that lead to the observed depolarization.