Pinhole Plate Research Articles

Design and Analysis of Orthogonal Polarization Point Diffraction Pinhole Plate

The pinhole plate is a key component of the point diffraction interferometer (PDI). The reasonable improvement and simulation of this device would enhance the application of point diffraction interferometry technology during the measurement of wavefronts. The traditional point diffraction interferometry measurement method is easily disturbed by environmental noise, making it difficult to obtain high-precision dynamic measurements. This paper introduces a four-step phase-shift PDI that can be employed in a common optical path. By using the principle of the finite-difference time-domain method (FDTD), a simulation model of the orthogonal polarization point diffraction pinhole plate (OP-PDPP) structure is established. The results show that when Cr is used as the film material in the pinhole plate, the parameters include a film thickness of 150 nm, a pinhole diameter of 2 μm, a wire grid period of 150 nm, and a wire grid width of 100 nm; in addition, the comprehensive extinction ratio of the pinhole plate is the greatest and the diffraction wavefront error is the smallest. Finally, the constructed experimental system is used to test the wavefront of a flat sample with a 25.4 mm aperture, and the test results are compared with those of the ZYGO interferometer. The difference in the peak-to-valley (PV) value between the OP-PDI and the ZYGO interferometer measurement is 0.0028λ, with an RMS value difference of 0.0011λ; this verifies the feasibility of the scheme proposed in this paper. The experimental results show that the proposed OP-PDPP is an effective tool for high-precision dynamic measurement.

A method to measure the uniformity of the virtual image distance in an augmented reality or virtual reality device

AbstractThe virtual image distance in an augmented reality (AR) or virtual reality (VR) device is an important factor in determining its performance. In this paper, a method for measuring the virtual image distance and its uniformity is proposed. The setup for measurement consists of a two‐dimensional spatial sensor array on the translational stage and a pinhole array plate placed in front of the AR or VR device. As the distance between the pinhole plate and the two‐dimensional spatial sensor array were changed, the positions of the rays through each pinhole were measured by a two‐dimensional spatial sensor array. The ray trajectories through each pinhole were obtained by fitting these positions to straight lines. The relative distances between these ray trajectories were calculated with respect to the distance from the pinhole plate. This method is effective for measuring the uniformity, such as the azimuthal dependence of the virtual image distance or the dependence of the virtual image distance on the distance from the optical axis of the VR lens.

Complex optical elements for scanning helium microscopy through 3D printing

Developing the next generation of scanning helium microscopes requires the fabrication of optical elements with complex internal geometries. We show that resin stereolithography (SLA) 3D printing produces low-cost components with the requisite convoluted structures whilst achieving the required vacuum properties, even without in situ baking. As a case study, a redesigned pinhole plate optical element of an existing scanning helium microscope was fabricated using SLA 3D printing. In comparison to the original machined component, the new optical element minimised the key sources of background signal, in particular multiple scattering and the secondary effusive beam.

Improving the demultiplexing performances of the multiple Bessel Gaussian beams (mBGBs)

As approximate non-diffracted beams, Bessel Gaussian (BG) beams are more suitable to be used in free-space optical (FSO) communication system than Laguerre Gaussian (LG) vortex beams because of its self-recovering property. However, due to the limitation of its detection method, the multiplexing communication based on multiple Bessel Gaussian beams (mBGBs) has not been investigated deeply. In this paper, we propose a method for simultaneous demodulation of 36-mBGBs using 6 × 6 multiplexing phase hologram (MPH). To solve the problem that the energy of some BG beams are too low at the demodulation end, a method is proposed to optimize the pinhole size of the pinhole plate at the demodulation end. Compared with the traditional decomposition method, the proposed method not only improves the decoding efficiency greatly, but also has better robustness. In addition, the communication performance of 32-mBGBs encoded with four ASCII codes has been constructed and investigated numerically. The results show that the transmitted information can be clearly decoded by setting a reasonable threshold value, which is beneficial to the practical application of mBGBs in FSO communications.

Manipulation of Orbital-Angular-Momentum Spectrum Using Pinhole Plates

The orbital angular momentum (OAM) spectrum of light, produced by superposition of vortex beams, is important for applications in optical metrology and classical and quantum communication. Nonetheless, manipulation of the OAM spectrum remains challenging. The authors propose a technique for control of the OAM spectrum using structured pinhole plates, which can generate both wide and narrow OAM spectra. In particular, a rather simple pinhole plate can produce an interesting series of discrete, equally spaced OAM modes: an OAM comb, akin to a frequency comb. This approach could be extended beyond photonics to work with rf, acoustic, electron, or neutron composite vortices.

Geometric Sensitivity of Variable Pinhole SPECT with a Keel-edge Pinhole Model

A variable pinhole (VP) collimator is formed by stacking several tungsten plates with different apertures. The configuration of the VP can be optimized for target region-of-interests at different rotation angles. Hence, both the resolution and sensitivity of the system can be improved. However, it is difficult to analytically implement the exact system model that simulates the step shapes between adjacent layers. In this study, we compared the conventional keel-edge and knife-edge pinhole models with the VP model using simulations. The keel-edge and knife-edge models were evaluated based on various specifications to identify the optimum system model. The simulation results showed that the keel-edge model with 80% channel length (keel-edge 80%) elicits the best performance with a fixed acceptance angle and pinhole plate thickness. The results in this study are expected to be applied to full-scale SPECT with a VP collimator which is currently under development.

Effects of multi-context information recorded at different regions in holographic polymer-dispersed liquid crystal on optical reconfiguration

A holographic polymer-dispersed liquid crystal (HPDLC) memory to record multi-context information for an optically reconfigurable gate array is formed by constructing a laser illumination system to implement successive laser exposures at different small regions in a glass cell filled with LC composites. The context pattern arrangements for circuit information are designed in a 3 × 3 in.2 photomask by electron beam lithography, and they are recorded as laser interference patterns at nine regions separated in an HPDLC sample by a laser interferometer composed of movable pinhole and photomask plates placed on motorized stages. The multi-context information reconstructed from the different regions in the HPDLC is written to a photodiode array in a gate-array VLSI by switching only the position of laser irradiation using the displacement of the pinhole plate under the control of a personal computer (PC). The effects of multi-context information recorded at different regions in the HPDLC on optical reconfiguration are discussed in terms of the optical system composed of ORGA VLSI and HPDLC memory. The internal structures in the HPDLC memory formed by multi-context recording are investigated by scanning electron microscopy (SEM) observation, and the configurations composed of LC and polymer phases are revealed at various regions in the HPDLC memory.

Generation of high-order optical vortices with asymmetrical pinhole plates under plane wave illumination

We propose a novel and simple method for generating optical vortex with high topological charge (TC), merely using an asymmetrical pinhole plate illuminated by plane wave. N pinholes are arranged along a particular spiral line around the plate origin, with constant azimuth angle increment and varied radial distances. The radial differences introduce a constant variation of m/N wavelength to the optical paths from the N pinholes to the observation plane origin, and this increases the phases of the transmitting waves by progressively 2mπ/Nand totally 2mπ. We numerically calculate the transmitted light field according to the Fresnel diffraction theory, and find the vortex with TC m around the observation plane origin. The experimental verifications are performed using some self-made asymmetrical pinhole plates fabricated by a femtosecond laser, with the high TC vortices both generated and detected in a Mach-Zehnder type interferometer. The experimental results coincide with the theoretical simulations well.

Effect of Overlapping Projections on Reconstruction Image Quality in Multipinhole SPECT

Multipinhole single photon emission computed tomography (SPECT) imaging has several advantages over single pinhole SPECT imaging, including an increased sensitivity and an improved sampling. However, the quest for a good design is challenging, due to the large number of design parameters. The effect of one of these, the amount of overlap in the projection images, on the reconstruction image quality, is examined in this paper. The evaluation of the quality is based on efficient approximations for the linearized local impulse response and the covariance in a voxel, and on the bias of the reconstruction of the noiseless projection data. Two methods are proposed that remove the overlap in the projection image by blocking certain projection rays with the use of extra shielding between the pinhole plate and the detector. Also two measures to quantify the amount of overlap are suggested. First, the approximate method, predicting the contrast-to-noise ratio (CNR), is validated using postsmoothed maximum likelihood expectation maximization (MLEM) reconstructions with an imposed target resolution. Second, designs with different amounts of overlap are evaluated to study the effect of multiplexing. In addition, the CNR of each pinhole design is also compared with that of the same design where overlap is removed. Third, the results are interpreted with the overlap quantification measures. Fourth, the two proposed overlap removal methods are compared. From the results we can conclude that, once the complete detector area has been used, the extra sensitivity due to multiplexing is only able to compensate for the loss of information, not to improve the CNR. Removing the overlap, however, improves the CNR. The gain is most prominent in the central field of view, though often at the cost of the CNR of some voxels at the edges, since after overlap removal very little information is left for their reconstruction. The reconstruction images provide insight in the multiplexing and truncation artifacts.

The multi‐module, multi‐resolution system : A novel small‐animal SPECT system

We have designed and built an inexpensive, high-resolution, tomographic imaging system, dubbed the multi-module, multi-resolution system, or M3R. Slots machined into the system shielding allow for the interchange of pinhole plates, enabling the system to operate over a wide range of magnifications and with virtually any desired pinhole configuration. The flexibility of the system allows system optimization for specific imaging tasks and also allows for modifications necessary due to improved detectors, electronics, and knowledge of system construction (e.g., system sensitivity optimization). We provide an overview of M3R, focusing primarily on system design and construction, aperture construction, and calibration methods. Reconstruction algorithms will be described and reconstructed images presented.

Polarization phase-shifting point-diffraction interferometer

A new instrument, the polarization phase-shifting point-diffraction interferometer, has been developed by use of a birefringent pinhole plate. The interferometer uses polarization to separate the test and reference beams, interfering what begin as orthogonal polarization states. The instrument is compact, simple to align, and vibration insensitive and can phase shift without moving parts or separate reference optics. The theory of the interferometer is presented, along with properties and fabrication techniques for the birefringent pinhole plate and a new model used to determine the quality of the reference wavefront from the pinhole as a function of pinhole size and test optic aberrations. The performance of the interferometer is also presented, along with a detailed error analysis and experimental results.

Investigation of thermophoretic protection with speed-controlled particles at 100, 50, and 25mTorr

Thermophoresis is considered as a candidate for protection of extreme ultraviolet lithography masks from particle contamination during vacuum exposures. A thermophoretic force is exerted on a particle by surrounding gas molecules within a temperature gradient. Gas molecules on the “warm side” of the particle provide more momentum than on the “cool side,” so particles move from the warm to the cool region. In this study, thermophoretic protection of a critical surface from particles injected with known initial speeds into a quiescent gas has been investigated at 100, 50, and 25mTorr. Initial particle speed was varied from 10to31m∕s depending on the gap distances (1, 2, and 3cm), particle sizes (125 and 220nm), and system pressures. A pinhole plate is used to supply speed-controlled particles with almost no accompanying gas flow. The results demonstrate that the window of protection offered by thermophoresis is very narrow for inertial particles, and that thermophoresis offers the greatest protection for low-velocity particles subject to diffusional motion in the vacuum system. Furthermore, the experimental results verify the results of an analytical model, developed by Asbach et al. [Appl. Phys. Lett. 87, 234111 (2005)]. The analytical model can be used to predict the particle stopping distance under any thermophoretic gradient.

Experimental task-based optimization of a four-camera variable-pinhole small-animal SPECT system.

We have previously utilized lumpy object models and simulated imaging systems in conjunction with the ideal observer to compute figures of merit for hardware optimization. In this paper, we describe the development of methods and phantoms necessary to validate or experimentally carry out these optimizations. Our study was conducted on a four-camera small-animal SPECT system that employs interchangeable pinhole plates to operate under a variety of pinhole configurations and magnifications (representing optimizable system parameters). We developed a small-animal phantom capable of producing random backgrounds for each image sequence. The task chosen for the study was the detection of a 2mm diameter sphere within the phantom-generated random background. A total of 138 projection images were used, half of which included the signal. As our observer, we employed the channelized Hotelling observer (CHO) with Laguerre-Gauss channels. The signal-to-noise (SNR) of this observer was used to compare different system configurations. Results indicate agreement between experimental and simulated data with higher detectability rates found for multiple-camera, multiple-pinhole, and high-magnification systems, although it was found that mixtures of magnifications often outperform systems employing a single magnification. This work will serve as a basis for future studies pertaining to system hardware optimization.

ミニチュア円筒鏡型分析器（ＣＭＡ）を用いた脱離イオンの運動エネルギー分布測定―凝縮Ｈ２Ｏの内殻励起誘起Ｈ｀＋´脱離研究への応用―

We have developed a miniature cylindrical mirror analyzer (CMA) for ion kinetic energy measurements. The CMA consists of a shield for electric field, inner and outer cylinders, a pinhole, and microchannel plates. We have applied it for the measurements of kinetic energy distribution of H+ desorbed by O 1s transitions of condensed H2O.

Design of nondestructive emittance measurement device for H− beams

For the diagnostics of high-brightness particle beams as necessary for the European Spallation Source, spallation neutron source IFMIF (D1+), and HIDIF (Bi1+) nondestructive methods have to be developed. Conventional beam diagnostics are established, but are mostly destructive methods and suffer from the power density deposited on surfaces like slits or pinhole plates and beam loss. For negative ions a nondestructive method based on photoneutralization can be used to determine the transverse phase space distribution with high time resolution and a large number of phase space points. The interaction of laser light and H− ions produces a small number of neutral atoms as well as detached electrons. The beam of charged particles is separated magnetically from the neutral beam and the distribution of neutral hydrogen is measured. Under the assumption that the influence of the dipole is small enough, the laser induced emittance measurement can be used, e.g., near the entrance of radio-frequency quadrupole. The basic concept for the laser driven emittance measurement device will be presented together with design considerations and preliminary simulations on ion beam transport.

Three-Dimensional Crystallographic Orientation Measurement of Polycrystalline Alumina by Raman-Microprobe Polarization.

Crystallographic orientation of individual grains on the surface of the thick specimen was successfully determined by polarized Raman spectroscopy.(1) Depth resolution of a few μm in Raman-microprobe polarization was achieved using a high-magnification objective lens and a pinhole plate. This enables determination of the crystallographic orientation of single grains in ceramics.(2) Raman tensor elements of sapphire, c and d, belonging to the Eg mode were analyzed. The analysis leads to c>>d for 378cm-1 line. As a result, the intensity of Raman scattering was expressed as S378cm-1//∝{1-sin2θcos2(φ-φExp)}sin2θ×cos2(φ-φExp).(3) Three-dimensional c-axis orientations of translucent alumina grains were successfully determined by polarized Raman lines at 645 and 378cm-1.

A transverse phase-space measurement technique for high-brightness, H − beams

A common method of measuring transverse phase-space distributions in charged-particle beams is to intercept the beam with slits, pinhole plates, or wire grids, and to measure the beam distribution after a drift with a parallel-channel collector or a fluorescent screen. Many of the next generation of accelerator applications (e.g., in heavy-ion fusion and transmutation of nuclear waste) will utilize high-beam currents with small phase-space distributions. The power densities of beams will be too large to permit the interception of entire beams. This paper describes a measurement technique that is applicable to H − beams: a small portion of the beam is separated from the full beam by means of photoneutralization with a laser that is upstream from a sweep magnet. Phase-space measurements are made on only the neutralized beam.

The Low-Q Diffractometer at the Los Alamos Neutron Scattering Center

Instrument criteria are presented for the Low-Q Diffractometer (LQD) at the Los Alamos Neutron Scattering Center (LANSCE), and a design is shown to meet these criteria. The collimator consists of multiple-aperture pinhole plates, and incorporates ''dynamic gravity focusing'' to center all wavelengths on the detector. Preliminary test results, making use of the Proton Storage Ring, a liquid hydrogen moderator, and two different position-sensitive detectors are shown.

Pinhole plate diagnostic for neutral particle beam accelerator

An unusual method of forming a foil with highly accurate hole placements and overlayed stripper/neutralizer foil allows accurate beam divergence and density diagnostics when used in conjunction with a downstream fluorescent screen and high resolution photography.

Influence of the vibrating system of a multipinhole-plate ultrasonic nebulizer on its performance

A multipinhole-plate ultrasonic atomizer was experimentally optimized, employing a bender bimorph vibrator structure made up of a thin pinhole plate and a circular ring piezoelectric element. Effects of the vibration mode upon the performance were studied in terms of the sound pressure generation and the behavior of bubbles caused by cavitation. The performance was also examined with regard to the number of pinholes and the shape of the pinhole plate. As a result, the atomizer was proved to be able to jet and nebulize ordinary liquid most efficiently by the second harmonic vibration mode if the vibrating system is supported along the circumference of the ring piezoelectric element. It was also proved that the maximum atomizing rate is approximately proportional to the number of pinholes and that the spray pattern can easily be controlled by changing the shape of the pinhole plate.