Interferometric Measurement of Angle

We present a simple technique for simultaneous determination of refractive index and thickness of moderately thick plane-parallel transparent glass plates (GPs) using a cyclic path optical configuration (CPOC) setup and a wedge shear plate as lateral shearing interferometer. The CPOC setup is used to simultaneously focus the counterpropagating converging beams at a common point at its hypotenuse arm. The apparent thickness and real thickness of the test GP are determined by observing three retrocollimation positions of the GP surfaces with respect to the common focus point. The RI is obtained by dividing the real thickness with apparent thickness of the GP. Presented in this paper are the results obtained for a test GP with a thickness of 14.983 mm and a RI of 1.515.

The beam splitting and polarizing principle of modified Wollaston prism are presented. This paper analyses the propagation track of light wave in modified Wollaston prism by wave-normal-tracing method at random incidence angle and the formula of the path difference between e and o light waves are deduced. Computer simulations are carried out to give the curve of the optical path difference varying with incidence angle, incident azimuth angle, structural angle and wave length. The results will provide a theoretical basis for the study of polarization prisms and the development of polarization splitting apparatus.

The digital micromirror device (DMD) which is one kind of Micro-Electro-Mechanical System has been widely adapted for use in lighting projection systems, and some new imaging systems such as high-dynamic range imaging, aperture-coded spectral imaging, or medical imaging. The micromirrors on the DMD surface are non-continuous distribution and capable of tilt relative to individual rotation axis, which is different from the plane mirror. Therefore, when the DMD is applied in a convergence imaging path, there is an optical path difference (OPD) between the off-axis chief ray and the on-axis chief ray, and moreover severe non-symmetric imaging on the focal plane. Based on the geometrical optics and aberration theory, this paper proposes a calculation formula that gives the OPD as a function of the image height, the incident angle, the DMD pixel size and the DMD tilt angle in the convergent imaging path. This formula can give the OPD of the system when the optical axis is vertical to the surface of the DMD in an ideal state, which has great significance to the design and adjustment of optical path using DMD devices.

Measurement of depth-dose distribution of protons by an imaging plate

This paper shows how simple, non-invasive measurement method is important for conserving large animals living underwater. We have studied free-ranging wild Indo-Pacific bottlenose dolphins (Tursiops aduncus) around Mikura Island, Japan for about 15 years. We usually observe dolphin behavior and record acoustics underwater including photo-identification of every dolphins. Despite lots of video data, more basic information such as body size have lacked. In order to measure body size of the animals non-invasively, we used commercial measurement software which can measure the distance between two points on 3D photos by commercial 3D camera. Accuracy evaluation tests using a tape measure between 15 and 250 cm were conducted at the field site (Mikura Island) and the errors were within 5 % of the actual sizes. We successfully measured body size of 33 free-ranging wild dolphins. Mean absolute percentage error of the same individuals in different photos was within 4 % for dolphins. The average size of the adult dolphins was 249.6cm, which was the similar to the average actual size of 4 by-caught dolphins of the population (251.7 cm). We also opportunistically measured green turtles (Chelonia mydas) during our dolphin survey. Mean absolute percentage error of the same individuals in different photos was within 2 % for turtles. The average straight carapace length (SCL) of the 14 turtles was 48.3 cm (37.9 – 67.7 cm), which is much smaller than the adult green turtle length (80 – 111 cm). A simple measurement method is thus important to know the size of the large animals underwater, which indicates animal age and health condition, and are important for conserving these large animals.

Jamin-Lebedeff (JL) polarization interference microscopy is a classical method for determining the change in the optical path of transparent tissues. Whilst a differential interference contrast (DIC) microscopy interferes an image with itself shifted by half a point spread function, the shear between the object and reference image in a JL-microscope is about half the field of view. The optical path difference (OPD) between the sample and reference region (assumed to be empty) is encoded into a color by white-light interference. From a color-table, the Michel-Levy chart, the OPD can be deduced. In cytology JL-imaging can be used as a way to determine the OPD which closely corresponds to the dry mass per area of cells in a single image. Like in other interference microscopy methods (e.g. holography), we present a phase retrieval method relying on single-shot measurements only, thus allowing real-time quantitative phase measurements. This is achieved by adding several customized 3D-printed parts (e.g. rotational polarization-filter holders) and a modern cellphone with an RGB-camera to the Jamin-Lebedeff setup, thus bringing an old microscope back to life. The algorithm is calibrated using a reference image of a known phase object (e.g. optical fiber). A gradient-descent based inverse problem generates an inverse look-up-table (LUT) which is used to convert the measured RGB signal of a phase-sample into an OPD. To account for possible ambiguities in the phase-map or phase-unwrapping artifacts we introduce a total-variation based regularization. We present results from fixed and living biological samples as well as reference samples for comparison.

In seismic engineering problems, artificial boundaries are often introduced in finite-volume models within an infinitely large earth. The reflection and refraction of seismic waves at these boundaries can distort waveforms within the model, making it an important issue to mitigate their effects. Absorbing Boundary Condition (ABC) has been widely used for this purpose since Berenger introduced it in 1994. However, the Lysmer-Kuhlemeyer (LK) viscous boundary, which employs dimensionless parameters a and b, is often recommended with values of 1.0 for both parameters, which is not always optimal for absorbing energy at different incident angles. This study aims to find the optimal a and b values for different incident angles. First, the discontinuous deformation analysis (DDA) method is used to simulate the usual artificial boundaries, such as free and fixed boundaries, demonstrating the waveform disturbance phenomenon caused by reflections inside the model. Next, it is shown that the LK boundary with a = 1.0 and b = 1.0 can effectively absorb reflection interference when the incident wave is perpendicular to the artificial boundary. However, for cases with incident angles, the LK boundary with a = 1.0 and b = 1.0 fails to provide effective absorption. Consequently, the Monte Carlo simulation method is employed to randomly select a and b values, using DDA to simulate seismic wave propagation within the model. The optimal a and b values corresponding to the incident angle are found based on the maximum absorption rate. A large number of calculations are performed for different incident angles, and the empirical formulas for a and b are derived.

The variations of the intensity of the reflected light near null as a function of the angle of incidence are compared for three ellipsometric techniques. For films of either SiO(2) or Si(3)N(4) on silicon, the highest accuracy of the film thickness measurement is always obtained when the angle of incidence is either equal or nearly equal to the principal angle for all thicknesses of the film layer. Based on these results, it is shown that a variable angle of incidence spectroscopic ellipsometer operated at the principal angle of incidence and using a rotating analyzer combines the advantage of versatility with near maximum accuracy and sensitivity.

A novel, to our knowledge, method for the measurement of angular displacement for arbitrarily shaped objects is presented in which the angular displacement is perpendicular to the optical axis. The method is based on Fourier-transforming the scattered field from a single laser beam that illuminates the target. The angular distribution of the light field at the target is linearly mapped on a linear image sensor placed in the Fourier plane. Measuring this displacement facilitates the determination of the angular displacement of the target. It is demonstrated both theoretically and experimentally that the angular-displacement sensor is insensitive to object shape and target distance if the linear image sensor is placed in the Fourier plane. A straightforward procedure for positioning the image sensor in the Fourier plane is presented. Any transverse or longitudinal movement of the target will give rise to partial speckle decorrelation, but it will not affect the angular measurement. Furthermore, any change in the illuminating wavelength will not affect the angular measurements. Theoretically and experimentally it is shown that the method has a resolution of 0.3 mdeg ( approximately 5 murad) for small angular displacements, and methods for further improvement in resolution is discussed. No special surface treatment is required for surfaces giving rise to fully developed speckle. The effect of partially developed speckle is considered both theoretically and experimentally.

We theoretically study the angular rotation displacement based on the hybrid interferometers, which contain a beam splitter (BS) and an optical parameter amplication (OPA) for beam splitting and recombination. Two schemes with different orders of an OPA and a BS are discussed and both of them can realize the super resolving and sensitive angular rotation displacement. The sensitivity of angular rotation displacement can surpass the shot noise limit 12l N with the orbital angular momentum input beams. The squeezing strength of an OPA and the reflectivity of the BS play a decisive role on the resolutions and sensitivities while the losses play a negative effect on the sensitivity.

A technique for estimation of wrist angular displacement in radial/ulnar deviation and flexion/extension

A metamaterial perfect absorber (MPA) using elliptical silver nanoparticles is proposed and investigated to provide 100% absorption for both transverse electric and transverse magnetic polarizations with a wide range of incident angles and polarization independence. Metamaterial absorbers with narrow absorption performance over a wide frequency range are significantly desired in sensing applications. Incident angle insensitivity and polarization angle independence are key features of MPAs. The output characteristics are examined using the three-dimensional finite difference time domain method. The effective medium theory and transmission line theory are applied to investigate the simulation results. Here, the 100% absorption occurs at resonance wavelength of λres = 2290 nm, and maximum sensitivity and figure of merit become 200 nm/RIU and 720 RIU-1, respectively. The results show that an absorption spectrum is insensitive to the incident angle of 0°-60°. The proposed device can be used as a high-performance biosensor and photodetector.

High-precision micro-displacement measurement in a modified reversal shearing interferometer using vortex beams

A novel method for measurement of angular displacement in one or two dimensions for arbitrarily shaped objects is presented. The method is based on Fourier transforming the scattered field form a single beam that illuminates the target. The angular distribution of the light field at the target is linearly mapped onto an array image sensor placed in the Fourier plane. Measuring this displacement facilitates the determination of the angular displacement. It is demonstrated both theoretically and experimentally that angular displacement sensor is insensitive to object shape target distance and any longitudinal or transverse movement of the target, if the image sensor is placed in the Fourier plane. A straightforward procedure to place the image sensor in the Fourier plane is presented here. Theoretically and experimentally, it is shown that the method has a resolution of 0,3 mdeg for small angular displacement and methods for further improvements in resolution are discussed. No special surface treatment for surfaces having irregularities of the order of or larger than the wavelength of the incident light. It is shown that this is the case for most surfaces of practical interest. Furthermore it is shown that robust, non contact optical systems for industrial applications can be produced.

A systematic method for the optical design and analysis of a multipass cell (MPC) with two spherical mirrors is presented. By varying the parameters, including the distance between the mirrors, the position of the incident point, and the incident angles, a variety of dense patterns can be formed on the mirrors. Three MPCs with exemplary patterns of seven circles, rotating triangles, and petals are designed and built. We compare and analyze the parameters of each MPC with respect to the volume, the optical path length (OPL), the number of reflections, and the stability of the final spot position. This new type of MPC exhibits the superior characteristics of compactness, a long effective OPL, and affordable cost, which make it very suitable for applications to trace gas sensing.