# Review on Complete Mueller Matrix Optical Scanning Microscopy Imaging
## 2 Mueller Matrix Optical Scanning Architecture
### Temporal Domain Encoding/Decoding
PSA: polarization states analyzer. Obj: microscope objective. Cond: Condenser. GS: galvanometric scanner. TL: tube lens. S: sample. PMT: Photomultiplier tube. t: temporal polarization states generation. \(I^{H}\), \(I^{V}\), \(I^{45}\), \(I^{RCP}\): intensities collected at the generated horizontal, vertical, \(45^{\circ}\) and Right Circular Polarization (RCP) polarized states. polarization resolved in 4 s with 20 um lateral resolution. It is worth noting that such a sample does not exhibit all the polarimetric changes in presence of a pathology, decreasing the number of acquisition needed for studying only few polarimetric parameters. More recently, a MM polarimeter has been implemented into a non-linear commercial transmission scanning microscope using simple motorized optical devices [50]. It allows the acquisition of only four images coded by four distinct polarization states (horizontal, vertical, 45\({}^{\circ}\) and right circular) sequentially also based on DoA method. The main application was the study of starch molecules under certain conditions (thermal and mechanical stress). Similarly, a similar approach has been extended for small animal embryonic development analysis in the reflection configuration [45]. The ability of such a technique paves the way of acquiring the full MM images of the sample simultaneously with non-linear confocal microscopy due to its compactness and versatility. This could be of interest for tracking the source of the label-free contrasts for thick objects where the polarimetric imaging modality gives only an average information of the scattering sample fingerprint through the PSF volume. A promising advance in this direction has been proposed in 2020 for characterizing scattering media in MM reflectance configuration in a confocal mode [51]. The instrument demonstrated is capabilities by measuring the increasing of depolarization through highly scattering medium such as milk solution. The polarimetric changes of layered-like structure has been validated through Monte Carlo simulations and showed that the depolarization and retardance caused by a birefringent fiber is influenced by its shape and location. This work has been completed by performing a depth-resolved imaging of cornea that combines here Mueller matrix in both transmission and reflection configuration with non-linear microscopy utilizing Two-Photon Excitation Fluorescence (TPEF) and Second Harmonic Generation (SHG) [52]. In this work, both the PSG and PSAs are composed of a pair of LCVRs and a linear polarizer and the voltages are synchronized with the GS. Then, the MM images are extracted pixel-by-pixel based on the measurements of four different PSA states for each of the six PSG states, so a set of 24 images is obtained. These promising results show the capability of extracting the polarimetric contrasts at a specific depth through the sample randomly organized. Indeed, they demonstrate that the random changes in the corneal model as a layered medium in the order of micrometer can strongly affect its polarization properties. However, it is worth noting that these preliminary results deal with pure deterministic samples (here only birefringent) where the measured scattering results mainly from the accumulation of random orientation across the illumination volume.