Calibration and data extraction in a Stokes polarimeter employing three wavelengths simultaneously.

We present a method for calibration and data extraction for a Stokes polarimeter working with three different wavelengths simultaneously. In the Stokes polarimeter considered in this work, we use two liquid crystal variable retarders (LCVRs) combined with a Glan-Thompson linear polarizer. A recently developed fitting calibration procedure is used. We use the same calibration samples and LCVR voltages for all three wavelengths, giving simultaneous measurement and calibration. We compare the performance of the polarimeter, after calibration, using four or six calibration samples in our experiment. To generate the four known calibration beams, we use a linear polarizer oriented at 130° and 30° with respect to the horizontal, a horizontal linear polarizer followed by a half-wave plate (at 632 nm) with its fast axis at 30°, and a horizontal linear polarizer followed by a quarter-wave plate (at 632 nm) with its fast axis at 30°. For calibration with six reference beams, we add two known calibration beams by setting the fast axis of the half- and quarter-wave plates at 130°. Experimental results show good agreement with the expected results, with the fitting calibration procedure giving an approximately 50% reduction in total RMS error with four calibration samples. There is a negligible reduction in the error when six calibration samples are used compared to the case with four samples.

Characterization of the fluorescence intensity and color tonality in the exoskeleton of scorpions.

Scorpions are a mesodiverse and nocturnal group of arachnids inhabiting most biomes worldwide. Different species of scorpions have divergent adaptations to the substrate they live in, but most of them share an intriguing characteristic: their exoskeleton contains fluorophores that emit blue-greenish fluorescence under ultraviolet radiation. Although there are some reports in the literature on the study of fluorescence in scorpions, the biological functionality of this light emission is currently unknown and is under debate. In this work, the properties of emission from the scorpion's exoskeleton are studied by means of digitally processed photographs taken of living specimens under ultraviolet illumination and complemented with standard spectroscopic measurements of emission and excitation spectra. With the aim of identifying possible correlations between the fluorescence, the characteristics color of the exoskeleton and the biology of the scorpions, 4 families, 9 genera and 24 species were studied. Our results suggest that the intensity of fluorescence is heterogeneous throughout the scorpion's exoskeleton studied here in such a way that pedipalps and metasomal segments fluoresce more intensely than the mesosomal segments. The spectrum of fluorescence across species is practically identical, suggesting that the same fluorophores are present in their exoskeletons. However, the fluorescence intensity emitted by each species varies according to their characteristic color (associated with the exoskeleton optical reflectance). Since the coloration of the exoskeleton is determined by the concentration of melanin and other pigments according to the substrate where scorpions live in, we conclude by suggesting that fluorescence may correlate directly to the ecomorphotype of the scorpions.

Modal interferometer based on a single mechanically induced long-period fiber grating and a nanoparticles-coated film section.

A modal interferometer by a single mechanically induced long-period fiber grating (MI-LPFG) using a half-length coating fiber is presented. The coating material used for this Letter is a film of silica nanoparticles doped with an organic chromophore. The silica nanoparticles, with diameters within the range of 40-50 nm, were deposited over 3.5 cm length of fiber by the dip-coating method, forming a film with a thickness between 500 and 1250 nm. Then the modal interferometer was implemented by inscribing the MI-LPFG over the coated fiber section and a similar fiber length of the uncoated fiber. The experimental results show high-contrast transmission bands, where the position and depth of the absorption envelope band are finely selected by the grating period, the pressure applied, and the film thickness. The novel modal interferometer architecture based on a single MI-LPFG, combined with a functionalized nanoparticles coating film, offers an attractive platform for the development of fiber sensors and other fiber-based devices.

Circularly polarized light with high degree of circularity and low azimuthal error sensitivity.

The generation of circularly polarized light with a high circularity degree and low azimuthal error sensitivity was analyzed using a system composed by two waveplates. It is shown how the high circularity degree is achieved using a combination of a half- (λ/2) and a quarter- (λ/4) waveplate λ/2+λ/4 configuration. However, the lowest azimuthal sensitivity under small variations in the azimuths of the waveplates is obtained by employing a λ/4+λ/2 configuration. Analytical calculus particularized for quartz and MgF2 waveplates is presented.

Polarimetric characterization of bismuth thin films deposited by laser ablation.

A Mueller-Stokes analysis is applied to pure bismuth thin film samples prepared by the laser ablation technique by using a polarimeter with a 632.8 nm continuum wavelength laser. The complex refractive index is determined in the range of 250-1100 nm. Results from the Mueller matrix show the high sensitivity of diattenuation and polarizance parameters as a function of the sample thickness and the incidence angle, except at the pseudo-Brewster angle, where they exhibit the same value. Results show that the knowledge of the polarimetric response, with appropriate incident polarization states, could be used to design photonic Bi-based devices for several applications. Polarization dependence is the result of changes on the surface morphology as a result of the small value of the skin depth.

Q(M) and the depolarization index scalar metrics.

A depolarization scalar metric for Mueller matrices, named Q(M), is derived from the degree of polarization. Q(M) has been recently reported, and it has been deduced from the nine bilinear constraints between the sixteen elements of the Mueller-Jones matrix. We discuss the relations between Q(M) and the depolarization index.

Degree of polarization as a criterion to obtain the nine bilinear constraints between the Mueller-Jones matrix elements.

The degree of polarization is employed as a criterion to find the nine independent relations among the elements of the Mueller-Jones matrix. This procedure is applied by considering a previously determined, physically realizable Mueller matrix. On the other hand, the nine bilinear constrains are obtained by directly measuring the degree of polarization from an outgoing beam of light from an optical system by considering nine incident states of light taken from the Poincaré sphere. For practical purposes, all the incident polarization states must be scanned from the Poincaré sphere in order to satisfy the over-polarization and the over-gain conditions, respectively, for the physical realizability of the Mueller matrix.

Scattering by rough surfaces in a conical configuration: experimental Mueller matrix.

A simple method for measuring the Mueller matrix associated with rough surfaces in a conical configuration is presented. I present result of experimental measurements of the Mueller matrix for the angular distribution of the light scattered by a one-dimensional gold-coated randomly rough surface in a conical configuration. Effects related to the phenomenon of enhanced backscattering are reported.