In this work we demonstrate a proof-of-concept depolarization emulator that generates customized spatial patterns of the polarization state (SoP) and degree of polarization (DoP). It is based on a pixelated LCOS-SLM addressed with a spatially time-varying retardance function. Three different cases featuring spatial control of the DoP are realized to show the potential of the method, including a spirally-shaped depolarization pattern. The polarization properties of the output light beam are verified by imaging the SLM screen onto a polarizing camera and performing Mueller matrix imaging polarimetry. We obtain the time-averaged Mueller matrix of the SLM and show that the output effective polarization state is governed by the averaged retardance, while the degree of polarization is governed by the retardance semidifference. An intuitive explanation of this performance is provided in the Poincaré sphere. The proposed technique could be useful in testing imaging polarimeters, in laser beam manipulation and in biomedical imaging, where emulating depolarization effects with controlled precision can help understand the physical mechanisms that cause depolarization.
A variety of methods have been developed in the last years to generate vector beams. In this work we will present some techniques that we have developed for the efficient and compact generation of arbitrary polarized vector beams. They are based on the use of geometric-phase elements combined with liquid-crystal on silicon (LCOS) spatial-light modulators (SLM) in a common-path architecture. LCOS-SLMs were used to encode a phase-only diffractive mask that encodes complex functions with high diffraction efficiency. We demonstrate the generation of arbitrary scalar modes and vector beam modes.
An important problem in imaging polarimetry occurs when the optical axis of the system and the center of the camera sensor get misaligned. This situation typically occurs after rotating the polarizing element mounts in order to change the input state of polarization. This work presents a liquid-crystal polarization state generator, devoid of moving parts, which can generate any arbitrary state of polarization (SOP) on the Poincaré sphere through the phase-shift manipulation of two voltage-controlled variable retarders. The proposed optical system consists of a linear polarizer, cascaded by two liquidcrystal retarders (LCR1 and LCR2) and a quarter-wave plate. We show that by varying the retardance of LCR1 but keeping the LCR2 retardance constant, the SOP moves along the corresponding meridian of the Poincaré sphere. When the reverse is done, the SOP follows a trajectory along the given parallel. Experimental results are compared to numerical simulations where we calculate the Stokes parameters and represent the trajectories of the SOP on the Poincaré sphere as we change the voltage addressed to the LCRs. Good agreement between theory and experiment is obtained if we take into account the Fabry-Perot interference effects on these variable retarders. This system can also be used as a polarization state analyzer. To verify the performance of this system as analyzer, the Mueller Matrix of a retarder plate is determined by imaging polarimetry.
An optical characterization of amber samples from México, the Baltic Sea and fake samples is presented, with the aim of discriminate between genuine and fake samples. We sought to identify the physical variables that could serve as the basis for the development of a device whose operation was able to discriminate between samples of genuine and fake amber. The optical refractive index was determined by Spectroscopic Ellipsometry, Abbe refractometry, and by the Brewster angle. The Raman spectra and the fluorescence optical responses were also determined. The results obtained indicate that the refractive index is not a robust variable that can differentiate between genuine amber and a fake sample. On the other hand, the Raman spectra and the fluorescence responses provide information that allows discriminating between both types of samples. For this reason, we used the results obtained by fluorescence as a basis for the design and construction of a prototype simple, reliable, portable, and affordable for authentication of the Mexican amber.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.