An analog Mueller matrix acquisition and preprocessing system (AMMS) was developed for a photopolarimetric-based sensor with $9.1–12.0\mathrm{\mu m}$ optical bandwidth, which is the middle infrared wavelength-tunable region of sensor transmitter and “fingerprint” spectral band for chemical–biological (analyte) standoff detection. AMMS facilitates delivery of two alternate polarization-modulated ${\mathrm{CO}}_2$ laser beams onto subject analyte that excite/relax molecular vibrational resonance in its analytic mass, primes the photoelastic-modulation engine of the sensor, establishes optimum throughput radiance per backscattering cross section, acquires Mueller elements modulo two laser beams in hexadecimal format, preprocesses (normalize, subtract, filter) these data, and formats the results into digitized identification metrics. Feed forwarding of formatted Mueller matrix metrics through an optimally trained and validated neural network provides pattern recognition and type classification of interrogated analyte.