RESUMEN
A spatially adaptive Mueller matrix imaging polarimeter is described, simulated, and demonstrated with preliminary experiments. The system uses a spatial light modulator (SLM) in the polarization state generator (PSG) to create spatial carriers that controlled by the pattern written to the SLM. The polarization state analyzer (PSA) is a commercial division of focal plane imaging polarimeter. The PSG/PSA pair form a 9-channeled partial Mueller matrix polarimeter that measures a 3 × 3 sub-matrix of the Mueller matrix. We demonstrate that adapting the PSG modulation to the spatial frequency structure of the scene can reduce channel crosstalk and improve reconstruction accuracy. Initial experiments are performed that demonstrate the SLM's ability to produce sufficient modulation diversity to create the desired channel structure. Though there are several experimental challenges to obtain accurate Mueller matrix imagery, we demonstrate a system that adapts to the particular scene spatial frequency structure.
RESUMEN
Analysis of data generated by Mueller matrix polarimeters using two photoelastic modulators has been evolving with the improvements in data acquisition and digital signal processing (DSP). Historical processing of the temporal data generated by these devices has involved isolating the frequencies via hardware signal processing (e.g., lock-in amplifiers) or the numerical computation of Fourier integrals of recorded temporal data. Both avenues have their advantages, but the DSP aspects of the latter provide greater flexibility in choice of harmonics for processing. While conventional processing uses one harmonic for each desired Mueller matrix element, recent work has demonstrated that theoretical improvements are possible by coherently combining the information in multiple harmonic channels for each element. We demonstrate some recent progress in DSP that enables these polarimeters' data to be more fully exploited by addressing two key issues in the Fourier domain: spectral leakage and phase recovery. Adequately addressing these issues enables numerical analysis of the temporal data in the complex Fourier domain and delivers Mueller matrix results in which spectral phase information is used to recover the matrix elements and determine their signs automatically. We explore the application of this complex analysis and how the precision and accuracy of the results are affected by common experimental and DSP limitations compared to the usual magnitude-only analysis in the Fourier domain. The multi-harmonic method can provide a theoretical factor of 1.3-1.7 improvement in instrumental precision, and our experimental results approach that theoretical range.
RESUMEN
The paper describes a modification of a high-resolution heterodyne NIR spectrometer described by Rodin, et al. in Opt. Express22, 13825 (2014), wherein the noise amplitude of the heterodyne signal squared was proportional to the power of the incoherent radiation source (the sun). The addition of a second receiver collecting radiation from the sun into a second single-mode fiber created up to a factor of two increase in detected source power spectrum. The ability to add uncorrelated heterodyne IF signals as Gaussian noise (variance) provides the means by which multiple heterodyne receivers of signal from an incoherent source can increase the detected source power by the same multiple, thus avoiding the limit imposed by the antenna theorem for a single receiver (A. E. Siegman, Appl. Opt.5, 1588 (1966)).