Polarimetry of scattered light using heterodyne detection

Heterodyne detection has been used to measure the polarization state of lig ht back-scattered from various targets (including flame-sprayed aluminium, sandpaper and painted surfaces). The samples are illuminated with a linearl y polarized single-frequency continuous-wave CO2 laser operating at a wavel ength of 10.6 mu m. The back-scattered co-polarized and cross-polarized com ponents are both coherently detected by beating with an optical local oscil lator. This process allows the relative amplitudes and phases of the two co mponents to be measured and hence the light's polarization state can be eva luated. When the target undergoes movement, the scattered light demonstrate s the usual properties of dynamic speckle, and the technique allows observa tion of the time evolution of the polarization ellipse.