Full control of polarization state with a pair of electro-optic modulators for polarization-resolved optical microscopy

Birefringence compensation method of test-mass substrates for gravitational wave detectors with arbitrary polarization states

GW detectors are ultimately limited by thermal noise in their most sensitive region. Cryogenic operation combined with crystalline substrates and coatings is a promising approach to reduce this noise, thereby increasing their sensitivity and detection rate. However, crystalline materials can exhibit birefringent behaviors which will degrade the detector's sensitivity. Here, we demonstrate the use of a pair of identical electropolarization retarders to generate arbitrary polarization states and compensate birefringence of a KAGRA test-mass substrate.

Estimation of crossbridge-state during cardiomyocyte beating using second harmonic generation

Estimation of dynamic change of crossbridge formation in living cardiomyocytes is expected to provide crucial information for elucidating cardiomyopathy mechanisms, efficacy of an intervention, and others. Here, we established an assay system to dynamically measure second harmonic generation (SHG) anisotropy derived from myosin filaments depended on their crossbridge status in pulsating cardiomyocytes. Experiments utilizing an inheritable mutation that induces excessive myosin-actin interactions revealed that the correlation between sarcomere length and SHG anisotropy represents crossbridge formation ratio during pulsation. Furthermore, the present method found that ultraviolet irradiation induced an increased population of attached crossbridges that lost the force-generating ability upon myocardial differentiation. Taking an advantage of infrared two-photon excitation in SHG microscopy, myocardial dysfunction could be intravitally evaluated in a Drosophila disease model. Thus, we successfully demonstrated the applicability and effectiveness of the present method to evaluate the actomyosin activity of a drug or genetic defect on cardiomyocytes. Because genomic inspection alone may not catch the risk of cardiomyopathy in some cases, our study demonstrated herein would be of help in the risk assessment of future heart failure.

Second harmonic generation polarization microscopy as a tool for protein structure analysis

Cryo-electron microscopy and X-ray crystallography have been the major tools of protein structure analysis for decades and will certainly continue to be essential in the future. Moreover, nuclear magnetic resonance or Förster resonance energy transfer can measure structural dynamics. Here, we propose to add optical second-harmonic generation (SHG), which is a nonlinear optical scattering process sensitive to molecular structures in illuminated materials, to the tool-kit of structural analysis methodologies. SHG can be expected to probe the structural changes of proteins in the physiological condition, and thus link protein structure and biological function. We demonstrate that a conformational change as well as its dynamics in protein macromolecular assemblies can be detected by means of SHG polarization measurement. To prove the capability of SHG polarization measurement with regard to protein structure analysis, we developed an SHG polarization microscope to analyze microtubules in solution. The difference in conformation between microtubules with different binding molecules was successfully observed as polarization dependence of SHG intensity. We also succeeded in capturing the temporal variation of structure in a photo-switchable protein crystal in both activation and inactivation processes. These results illustrate the potential of this method for protein structure analysis in physiological solutions at room temperature without any labeling.

System for control of polarization state of light and generation of light with continuously rotating linear polarization

We present a technique for generating light in an arbitrary polarization state. The technique is based on interference of two orthogonally polarized light beams, whose amplitudes and phases are controlled with a Mach-Zehnder inteferometer with acousto-optic modulators (AOMs) placed in each arm. We demonstrate that via control over amplitudes, phases, and frequencies of acoustic waves driving the AOMs, any polarization state can be synthesized. In particular, we demonstrate generation of linearly polarized light, whose polarization plane continuously rotates at a rate from 1 kHz to 1 MHz. Such light finds applications in science (e.g., investigations of Bloch-Siegert effect) and technology (optically pumped magnetometers).

Polarization modulation by means of tunable polarization gratings in an azobenzene side-chain liquid-crystalline polymer film

Polarization modulation was achieved by means of a new type of grating recorded with two 532 nm beams at varying polarization angles in an azobenzene side-chain liquid-crystalline polymer film through light regulation instead of voltage control. In contrast to conventional polarization holographic gratings, the polarization state of the ± first-order diffracted beams of the recorded gratings depended strongly on angles between polarization directions of two recording beams, while the polarization state of the second-order diffraction remained unchanged. With the polarization angle changing from 0 to 90 deg, the ± first-order diffraction efficiency increased from 5.15% to 10.53%. Diffraction properties of the recorded gratings were attributed to the combination of polarization holographic gratings and amplitude gratings based on the calculation of Jones matrices and polarization holographic theory.

Stokes-vector and Mueller-matrix polarimetry [Invited]

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.

Full control of polarization state with a pair of electro-optic modulators for polarization-resolved optical microscopy: erratum

In our previous paper [Appl. Opt.55, 1082 (2016)APOPAI0003-693510.1364/AO.55.001082], we presented a methodology for full control of a polarization state using a pair of electro-optic modulators. In this erratum, we correct errors in Eqs. (9b) and (9c) in the original paper.