Polarization-based Measurements Research Articles

Optical Polarization-Based Measurement Methods for Characterization of Self-Assembled Peptides' and Amino Acids' Micro- and Nanostructures.

In recent years, self-assembled peptides’ and amino acids’ (SAPA) micro- and nanostructures have gained much research interest. Here, description of how SAPA architectures can be characterized using polarization-based optical measurement methods is provided. The measurement methods discussed include: polarized Raman spectroscopy, polarized imaging microscopy, birefringence imaging, and fluorescence polarization. An example of linear polarized waveguiding in an amino acid Histidine microstructure is discussed. The implementation of a polarization-based measurement method for monitoring peptide self-assembly processes and for deriving molecular orientation of peptides is also described.

Fluorescence Polarization-Based Measurement of Protein-Ligand Interaction in Fungal Cell Lysates.

Fungi infect over a billion people worldwide and contribute substantially to human morbidity and mortality despite all available therapies. New antifungal drugs are urgently needed. Decades of study have revealed numerous protein targets of potential therapeutic interest for which potent, fungal-selective ligands remain to be discovered and developed. To measure the binding of diverse small molecule ligands to their larger protein targets, fluorescence polarization (FP) can provide a robust, inexpensive approach. The protocols in this article provide detailed guidance for developing FP-based assays capable of measuring binding affinity in whole cell lysates without the need for purification of the target protein. Applications include screening of libraries to identify novel ligands and the definition of structure-activity relationships to aid development of compounds with improved target affinity and fungal selectivity. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Use of saturation binding curves to optimize tracer and lysate protein concentrations Basic Protocol 2: Establishment of competition binding experiments Support Protocol 1: Preparation of fungal cell lysates Support Protocol 2: Preparation of human HepG2 cell lysate.

Plate reader microrheology

In this work, we report the development of a simplified method to perform microrheology to rapidly assess soft materials. This approach uses fluorescence polarization and a plate reader format to measure the rotational diffusion of nanoparticles within a sample of interest. We have established that this technique can be used to characterize a range of soft materials based on the rotational diffusion of nanoparticles in materials with viscosities exceeding 100 cP. Using these fluorescence polarization-based measurements, we describe formalism that enables the estimation of viscosity in polymer solutions and gels composed of polyethylene glycol, hyaluronic acid, and Matrigel after accounting for the length-scale dependent effects of the polymer environment on the nanoparticle rotational diffusion. Using this analysis, we show that the plate reader microrheology measurements of viscosity are in reasonable agreement with traditional particle tracking microrheology. The use of a plate reader format allows this approach to be higher throughput, less technically challenging, and more widely accessible than standard macro- and micro-rheological methods, making it available to non-experts. This approach has potential applications in clinical settings where conventional rheological equipment may not be available to rapidly characterize patient-derived samples.

Method of measurement of thickness of uniaxial anisotropic crystals and thermal control of bessel beam transformation

We propose a method of polarization-based measurement of thickness and birefringence of uniaxial crystal X-cuts, which consists in measuring the spectral transmittance of a "polarizer-crystal-analyzer" structure. With use of X-cuts of a congruent lithium niobate with a nominal thickness of 1.052 mm, the validity of the method is experimentally confirmed and recommendations on its practical use are made. A possibility to control the Bessel beam conversion in CaCO3 crystal via changing its thickness is shown. The controlled conversion of a zero-order Bessel beam into a second-order vortex Bessel beam due to effect of the thermal linear expansion of a crystal by heating is experimentally investigated.

Rotational Raman scattering as a source of polarized radiation for the calibration of polarization-based Thomson scattering

We discuss the use of rotational Raman scattering as a possible technique for the calibration of polarization based plasma diagnostics such as the polarimetric Thomson scattering (TS) systems proposed for the measurement of electron density ne and temperature Te in very hot fusion plasmas. First by using the Stokes vector formalism, we calculate the Mueller matrix of rotational Raman scattering from a diatomic gas (such as H2, D2 and N2) for a generic scattering angle and then we use it to describe in detail the polarization characteristics of the Raman radiation available in the typical conditions of a TS system in a fusion plasma. Then we consider the various experimental set-ups proposed for polarimetric TS and show that rotational Raman scattering can generate radiation with known intensity and polarization states that, although not equal to those of the TS radiation, are suitable for the calibration of polarimetric TS diagnostics. Finally we point out that in fusion experiments Raman polarimetry may be of interest also for the calibration of other polarization-based measurement systems, such as the motional Stark effect (MSE) diagnostics.

Correction to article “Ellipsometry with randomly varying polarization states”

We show that, under the right conditions, one can make highly accurate polarization-based measurements without knowing the absolute polarization state of the probing light field. It is shown that light, passed through a randomly varying birefringent material has a well-defined orbit on the Poincare′ sphere, which we term a generalized polarization state, that is preserved. Changes to the generalized polarization state can then be used in place of the absolute polarization states that make up the generalized state, to measure the change in polarization due to a sample under investigation. We illustrate the usefulness of this analysis approach by demonstrating fiber-based ellipsometry, where the polarization state of the probe light is unknown, and, yet, the ellipsometric angles of the investigated sample (Ψ and Δ) are obtained with an accuracy comparable to that of conventional ellipsometry instruments by measuring changes to the generalized polarization state.

Ellipsometry with randomly varying polarization states

We show that, under the right conditions, one can make highly accurate polarization-based measurements without knowing the absolute polarization state of the probing light field. It is shown that light, passed through a randomly varying birefringent material has a well-defined orbit on the Poincar sphere, which we term a generalized polarization state, that is preserved. Changes to the generalized polarization state can then be used in place of the absolute polarization states that make up the generalized state, to measure the change in polarization due to a sample under investigation. We illustrate the usefulness of this analysis approach by demonstrating fiber-based ellipsometry, where the polarization state of the probe light is unknown, and, yet, the ellipsometric angles of the investigated sample (Ψ and Δ) are obtained with an accuracy comparable to that of conventional ellipsometry instruments by measuring changes to the generalized polarization state.

Fundamental limits in single-molecule orientation measurements

Directionality inherent in the polarization of light affords the means of performing robust dynamic orientational measurements of molecules and asymmetric scatterers. In this paper, the precision with which measurements of this kind can be made is quantified for a number of common polarization-based measurement architectures using a metric derived from Fisher information. Specifically, a fundamental limit of 0.5 radian per detected photon (on average) is found, thus highlighting the importance of maximizing photon numbers by correct fluorophore selection. Informational dips, whereby measurement precision is degraded, are shown to arise in many realistic measurement scenarios, particularly for inference from null readings. The severity of these precision losses is therefore considered, and it is shown to decrease with increased system redundancy. Contamination of measured data from coherently and incoherently radiating extraneous sources, furthermore, causes a loss of precision. Analytic and numerical results are hence also presented in this vein.

Polarization-degree imaging contrast in turbid media: a quantitative study

Scattering in biological tissue can degrade imaging contrast and reduce the probe depth. Polarization-based measurement has shown its advantages in overcoming such drawbacks. Here, linear and circular polarization degree imaging is applied to a comblike metal target submerged in Intralipid solutions. Contrasts of the metal bars are measured quantitatively as functions of the Intralipid concentration and the submersion depths. Different behaviors in contrast for linear and circular polarizations are compared. Contributions to the background of circular polarization degree images by backscattering, snake, and diffusive photons are examined carefully.

Absorption and photoluminescence of ultrathin pseudomorphic InAs/GaAs quantum wells.

We present absorption data for 2--4-monolayer InAs/GaAs single quantum wells obtained at 77 K using a polarization-based measurement technique. The spectral contribution of the optical loss features arising from bulk GaAs was minimized using the polarization selectivity of absorption in single quantum wells. Based on polarization properties and the results of an envelope-function calculation, the double structure observed in the spectra is attributed to transitions involving confined heavy holes and both confined and unconfined electron states. No evidence of transitions with the participation of confined light holes was found. Well-width fluctuations deduced from the absorption data are a fraction of one monolayer in our samples. The absorption lines were broadened, indicating interface roughness on a scale comparable to the exciton diameter. A single photoluminescence peak overlapping with the lower-energy portion of the fundamental absorption feature was observed in all the samples at 77 K. Although the absorption line of the undoped two-monolayer sample displayed the least broadening, the photoluminescence was red shifted by approximately 70 meV relative to the absorption feature. Presumably, this behavior indicates long-range diffusion of the excitations. Measurements of the temperature dependence and pump-power dependence of the red shift in this sample support this interpretation.