Chiral π-conjugated molecules provide new materials with outstanding features for current and perspective applications, especially in the field of optoelectronic devices. In thin films, processes s...

Chiroptical Properties in Thin Films of π-Conjugated Systems.

Nanostructures with chiral geometries exhibit strong polarization rotation. However, achieving reversible modulation of chirality and polarization rotation in device-friendly solid-state films is difficult for rigid materials. Here, we describe nanocomposites, made by conformally coating twisted elastic substrates with films assembled layer-by-layer from plasmonic nanocolloids, whose nanoscale geometry and rotatory optical activity can be reversibly reconfigured and cyclically modulated by macroscale stretching, with up to tenfold concomitant increases in ellipticity. We show that the chiroptical activity at 660 nm of gold nanoparticle composites is associated with circular extinction from linear effects. The polarization rotation at 550 nm originates from the chirality of nanoparticle chains with an S-like shape that exhibit a non-planar buckled geometry, with the handedness of the substrate's macroscale twist determining the handedness of the S-like chains. Chiroptical effects at the nexus of mechanics, excitonics and plasmonics open new operational principles for optical and optoelectronic devices from nanoparticles, carbon nanotubes and other nanoscale components.

Reconfigurable chiroptical nanocomposites with chirality transfer from the macro- to the nanoscale

Polarized light point measurements and wide-field imaging have been studied for many years in an effort to develop accurate and information-rich tissue diagnostic methods. However, the extensive depolarization of polarized light in thick biological tissues has limited the success of these investigations. Recently, advances in technology and conceptual understanding have led to a significant resurgence of research activity in the promising field of bulk tissue polarimetry. In particular, with the advent of improved measurement, analysis, and interpretation methods, including Mueller matrix decomposition, new diagnostic avenues, such as quantification of microstructural anisotropy in bulk tissues, have been enabled. Further, novel technologies have improved the speed and the accuracy of polarimetric instruments for ex vivo and in vivo diagnostics. In this paper, we review some of the recent progress in tissue polarimetry, provide illustrative application examples, and offer an outlook to the future of polarized light imaging in bulk biological tissues.

https://www.spiedigitallibrary.org/journals/journal-of-biomedical-optics/volume-20/issue-6/061104/Polarized-light-imaging-in-biomedicine--emerging-Mueller-matrix-methodologies/10.1117/1.JBO.20.6.061104.pdf

Polarized light imaging in biomedicine: emerging Mueller matrix methodologies for bulk tissue assessment

This paper reviews the current status of instruments for measuring the full 4×1 Stokes vector S, which describes the state of polarization (SOP) of totally or partially polarized light, and the 4×4 Mueller matrix M, which determines how the SOP is transformed as light interacts with a material sample or an optical element or system. The principle of operation of each instrument is briefly explained by using the Stokes-Mueller calculus. The development of fast, automated, imaging, and spectroscopic instruments over the last 50 years has greatly expanded the range of applications of optical polarimetry and ellipsometry in almost every branch of science and technology. Current challenges and future directions of this important branch of optics are also discussed.

Stokes-vector and Mueller-matrix polarimetry [Invited].

Development of a broadband Mueller matrix ellipsometer as a powerful tool for nanostructure metrology

A spectroscopic Mueller matrix polarimeter with four photoelastic modulators (PEMs) and no moving parts is introduced. In the 4-PEM polarimeter, all the elements of the Mueller matrix are simultaneously determined from the analysis of the frequencies of the time-dependent intensity of the light beam.

Mueller matrix polarimetry with four photoelastic modulators: theory and calibration

Purging of a light beam path in an effective manner that minimizes the affect of the purging requirement on system throughput. In one embodiment, the invention is incorporated into a birefringence measurement system that has several components for directing light through a sample optical element and thereafter detecting and analyzing the light. The segment of the beam path through the sample is isolated to reduce the volume that requires continual purging.

Purging light beam paths in optical equipment

In our laboratory we built a Stokes polarimeter using two photoelastic modulators (PEMs). We applied two different signal processing methods to this dual PEM Stokes polarimeter. In one method, we used lock-in amplifiers to measure the PEM modulated signals. In the other method, we used Fourier analysis of a digitized waveform that contains the modulated signals. The dual PEM Stokes polarimeter can measure all normalized Stokes parameters. In this paper we present and compare results obtained using both signal processing methods. We discuss how each method benefits selected applications of the dual PEM Stokes polarimeter.

Evaluation of a dual PEM Stokes polarimeter using different signal processing methods

This disclosure is generally directed to systems for imaging polarization properties of optical-material samples. As one example, there is provided a system for precise, simultaneous imaging of both the in-plane and out-of-plane birefringence properties of sample material over a wide range of incidence angles. An example spatially resolved imaging approach described herein is amenable to determination of a wide range of polarimetric properties, in addition to the in-plane and out-of-plane birefringence measure discussed as a preferred embodiment.

Polarization properties imaging systems

We have developed a polarimeter for accurately measuring both the circular and linear polarization components of a
light beam from 400 nm to 800 nm. This polarimeter is designed to work at low light levels that are typical in
astronomical applications. It is optimized to detect the circular polarization signal that is orders of magnitude weaker
than the linear polarization signal. Two photoelastic modulators (PEMs) are the key polarization components employed
in this polarimeter to afford the high sensitivity required for the application. Using this instrument, we have quantified
the circular polarization signal produced by astrobiologically relevant microorganisms and compared the results to
macroscopic vegetation (such as leaves) and abiotic minerals. Our aim is to understand whether circular polarization
offers a viable technique for remote detection of chiral signatures and hence will be useful as an element of telescopic
searches for life elsewhere in the Universe. We see unambiguous circular polarization from photosynthetic microbes.
The circular polarization of reflected light is related to the circular dichroism of photosynthetic molecules. Therefore,
circular polarization spectroscopy offers the prospect of remotely sensing life's unique chiral signature.

Baoliang Wang

Papers

Mueller matrix polarimetry with four photoelastic modulators: theory and calibration

Purging light beam paths in optical equipment

Evaluation of a dual PEM Stokes polarimeter using different signal processing methods

Polarization properties imaging systems

A spectroscopic polarimeter for detecting chiral signatures in astrobiological samples