Photopolarimetric lidar duel-beam switching device and Mueller matrix standoff detection method

Abstract

We present an optomechanical switching device (OSD) for a photopolarimetric lidar system with differential-absorption Mueller matrix spectroscopy standoff detection method. An output train of alternate continuous-wave CO2 laser beams [...L1:L2...] is directed onto suspect chemical-biological (CB) aerosol plume or the land mass it contaminates (S) vis-à-vis the OSD, where L1 [L2] is tuned on [detuned off] a resonant molecular absorption moiety of CB analyte. Moreover, both incident beams and their backscattered radiances, from S, are polarization-modulated synchronously so as to produce gated temporal voltage waveforms called scattergrams recorded on focus at the receiver end of polarization lidar sensor system. All 16 elements of the Mueller matrix (Mij) of S are measured via digital or analog filtration of constituent frequency components in these running scattergram data streams (phase-sensitive detection). A collective set of normalized differential elements {Mi,j} (ratioed to element M11) that are susceptible to the analyte, probed on-then-off its molecular absorption band, form a unique detection domain that is scrutinized. Any mapping onto this domain in Mueller-space, from incoming sensor scattergram data sets preprocessed by algorithm and forwarded through a trained neural network pattern recognition system, cues a standoff detection event.