Measurement of birefringence using polarization phase-shifting Mach–Zehnder interferometer

Relationship between DNA damage and sperm head birefringence

Abstract: Sao Paulo State Univ UNESP, Botucatu Med Sch, Ctr Human Reprod Prof Franco Jr,Res Unit, Paulista Ctr Diag Res & Training,Dept Gynecol & O, Ribeirao Preto, Brazil

Variable-inclination Mach-Zehnder interferometer for testing laser robs

Abstract: In order to measure the transmission wavefront of laser rods and to improve the edge diffraction effect of small-aperture laser rods measured by Tayman or Fizeau interferometer, a variable-inclination Mach-Zehnder interferometer was proposed. The incident angle was changed by adjusting the tilting attitude of the phase shifting reflector, then the optical path difference was changed that the phase shift was introduced to the coherent light and the phase shifting interferometry was realized. The transmission wavefront of a laser rod (Nd:YAG) with the diameter of 6 mm and the length of 60 mm was measured by this interferometer, the peak-valley (PV) and root mean square (RMS) of the wavefront were 0.391λ and 0.056λ. The same laser rod was measured by ZYGO GPI XP interferometer, the peak-valley (PV) and root mean square (RMS) were 0.370λ and 0.064λ. The comparison results show that the interferometer can achieve high-precision detection of transmission wavefront of laser robs. The variable-inclination Mach-Zehnder interferometer has high phase-shifting precision and wide phase-shifting range, and the beam in the system can pass through the laser rod only once, which can suppress the multi-beam interference and improve the edge diffraction effect of the small-aperture laser rods.

Characterization of cellophane birefringence due to uniaxial strain by focused surface plasmon microscopy

Abstract: In this paper, we study the relationship of local birefringence and stress oriented inhomogeneous elasticity of a sample from the spatial frequency response of focused surface plasmon (FSP). The birefringence of the sample varies the propagation constant of surface plasmon with regard to its direction and produces an elliptic absorption pattern in the reflected spatial frequency distribution. Birefringence is calculated from the ratio of the propagation constant along the fast to slow axis of the sample. The change in eccentricity was proportional to the applied stress on cellophane film. A strong correlation (0.94∼0.97) exists between FSP and phase shifting interferometry results.

Temporal Polarization Phase-shifting for Digital Speckle Pattern Interferometry

Abstract: A temporal 4-step polarization phase-shifting technique for digital speckle pattern interferometry (DSPI) with one fixed and two rotatable polarizers is proposed. The fixed polarizer is used to filter out the reflected object beam in one polarization direction, and the two rotatable polarizers are used to perform the 4 times phase shifts. The Jones derivation illustrates the object surface phase distribution can be derived from the 4 speckle pattern interferograms, which are bright, gloomy, bright, and gloomy successively. The experiment shows that the proposed temporal polarization phase-shifting technique is able to extract the phase change caused by a tiny out-of-plane displacement. Unlike the PZT-driven phase-shifting, the polarization phase-shifting in this method is stable and accurate in the long term.

Dynamic Mach-Zehnder interferometer based on the lateral displacement of a point source array.

Abstract: A dynamic Mach-Zehnder interferometer based on lateral displacement of a point source array is proposed. The point source array is generated by a point source and a phase grating, where four point sources are of identical intensity. The lateral displacement of each point source can be adjusted to introduce π/2 phase steps in the interferograms. With a specially designed lens array in the spatial split imaging system, four separated and clear imaging interferograms can be captured in a single shot. Using a four-bucket algorithm, the phase distribution can be retrieved exactly, thereby realizing dynamic measurement. The experimental results show the feasibility and high precision of this dynamic Mach-Zehnder interferometer.

Two-dimensional birefringence imaging in biological tissue by polarization-sensitive optical coherence tomography.

Abstract: Using a low-coherence Michelson interferometer, we measure two-dimensional images of optical birefringence in bovine tendon as a function of depth. Polarization-sensitive detection of the signal formed by interference of backscattered light from the sample and a mirror in the reference arm give the optical phase delay between light that is propagating along the fast and slow axes of the birefringent tendon. Images showing the change in birefringence in response to laser irradiation are presented. The technique permits rapid noncontact investigation of tissue structural properties through two-dimensional imaging of birefringence.

Scanning Laser Polarimetry to Measure the Nerve Fiber Layer of Normal and Glaucomatous Eyes

Abstract: Purpose To determine whether retardation (change in polarization) measurements of healthy subjects and glaucoma patients obtained by using a confocal scanning laser polarimeter correspond to known properties of the nerve fiber layer. Methods A polarimeter, an optical device used to measure the change in linear polarization of light (retardation), was interfaced with a scanning laser ophthalmoscope to obtain retardation data at 65,536 locations (256 × 256 pixels) in a study of normal subjects and patients with primary open-angle glaucoma. To validate the instrument, we compared our measurements with known properties of the human retinal nerve fiber layer in 105 normal subjects. Additionally, we compared retardation measurements in eyes of 64 normal subjects and 64 age-matched glaucoma patients treated in a referral practice. Results In normal eyes, mean (± S.D.) peripapillary retardation was highest in the superior and inferior arcuate regions and lowest in the temporal and nasal regions, 12.0 ± 1.9, 13.1 ± 2.0, 7.0 ± 1.8, and 7.0 ± 1.6 degrees, respectively. Retardation decreased toward the periphery and was lower over blood vessels. In normal eyes, retardation decreased with increasing age in the superior and inferior regions. Mean retardation was statistically significantly higher among normal eyes than glaucoma eyes in the inferior and superior regions but not in the temporal or nasal areas. Conclusions Scanning laser polarimetry provides quantitative measurements that correspond to known properties of the retinal nerve fiber layer in normal and glaucomatous eyes.

Histopathologic Validation of Fourier-Ellipsometry Measurements of Retinal Nerve Fiber Layer Thickness

Abstract: • We describe a new technique for the measurement of retinal nerve fiber layer thickness and compare its results with histopathologic measurements in the same eyes. For these studies, two fixed monkey eyes were incised and placed on a pedestal in a plastic viewing dish. The eyes were perfused to maintain a pressure between 10 and 20 mm Hg. An ellipsometer, an optical device used to measure the change in polarization of light (retardation), was implemented in a laser tomographic scanner to obtain polarization data from the two monkey retinas. For the 15 measured locations, retardation ranged between a mean (± SD) of 0.9° ± 1.8° and 23.7° ± 0.3°. Subsequently, retinal nerve fiber layer thickness was measured at the imaged points in epoxy resin-embedded sections by an observer masked to the ellipsometry data. These values ranged between 20.4 μm and 213.9 μm. There was an excellent correlation (R =.83) between retardation and the histopathologic measurement of retinal nerve fiber layer thickness. Quantitating retinal nerve fiber layer thickness may enhance discrimination between glaucomatous and normal eyes earlier than is currently available by anatomic and functional approaches.

Measurement of the Stokes parameters of light

Abstract: We describe a measuring system for determining the state of polarization of a beam of light in terms of its Stokes parameters. The technique which can be fully automated incorporates a monochromator and single photon counting detection and can thus be applied over a large wavelength range for very weak optical signals. Fourier transformation of the data by an on-line minicomputer allows immediate calculation of the Stokes parameters. We discuss special applications to light emitted from excited atomic systems with and without cylindrical symmetry.

Birefringence measurements in human skin using polarization-sensitive optical coherence tomography.

Abstract: Optical coherence tomography enables cross-sectional imaging of tissue structure to depths of around 1.5 mm, at high-resolution and in real time. Incorporation of polarization sensitivity (PS) provides an additional contrast mechanism which is complementary to images mapping backscattered intensity only. We present here polarization-sensitive optical coherence tomography (OCT) images of human skin in vivo, demonstrating the ability of the technique to visualize and quantify the birefringent properties of skin. Variation in normal skin birefringence according to anatomical location is demonstrated, and discussed in relation to collagen distribution at each location. From measurements on a sample of five human volunteers, mean double-pass phase retardation rates of 0.340+/-0.143, 0.250+/-0.076, and 0.592+/-0.142 deg/microm were obtained for the dorsal hand, temple, and lower back regions, respectively. We demonstrate how averaging the Stokes parameters of backscattered light over a range of axial and lateral dimensions results in a reduction of speckle-induced noise. Examples of PS-OCT images from skin sites following wound healing and repair are also presented and discussed.