A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

The fact that light carries both linear and angular momentum is well-known to physicists. One application of the linear momentum of light is for optical tweezers, in which the refraction of a laser beam through a particle provides a reaction force that draws the particle towards the centre of the beam. The angular momentum of light can also be transfered to particles, causing them to spin. In fact, the angular momentum of light has two components that act through different mechanisms on various types of particle. This Review covers the creation of such beams and how their unusual intensity, polarization and phase structure has been put to use in the field of optical manipulation.

Tweezers with a twist

A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Fringe projection techniques: Whither we are?

Thirty years ago, Coullet et al. proposed that a special optical field exists in laser cavities bearing some analogy with the superfluid vortex. Since then, optical vortices have been widely studied, inspired by the hydrodynamics sharing similar mathematics. Akin to a fluid vortex with a central flow singularity, an optical vortex beam has a phase singularity with a certain topological charge, giving rise to a hollow intensity distribution. Such a beam with helical phase fronts and orbital angular momentum reveals a subtle connection between macroscopic physical optics and microscopic quantum optics. These amazing properties provide a new understanding of a wide range of optical and physical phenomena, including twisting photons, spin-orbital interactions, Bose-Einstein condensates, etc., while the associated technologies for manipulating optical vortices have become increasingly tunable and flexible. Hitherto, owing to these salient properties and optical manipulation technologies, tunable vortex beams have engendered tremendous advanced applications such as optical tweezers, high-order quantum entanglement, and nonlinear optics. This article reviews the recent progress in tunable vortex technologies along with their advanced applications.

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Optical vortices 30 years on: OAM manipulation from topological charge to multiple singularities

We developed a novel addressable scanless multifocal multiphoton microscope. This microscope works in a fast scanless
mode. Subjectively selected sample (or multiple samples located in separated areas) in a large field of view can be
imaged by illuminating only the area (or areas) where the target sample (or samples) locate(s). In this way, by precisely
designing the multiple foci according to the size and position of the area of interest, we can concentrate all the laser
energy and dwell time on that area of the sample, making full use of the available laser power and avoiding photodamage
in other areas. Since no scanning is involved, the acquisition time of a multiphoton image is decided only by the
sensitivity and readout time of the CCD camera. Moreover, the interfocal distance of the multiple foci matches the lateral
resolution of the imaging system, so that the two-photon image was recorded with high lateral resolution. However,
crosstalk (spatial interference) on out-of-focus planes occurs between adjacent points when they are too close, degrading
the resolution, especially the axial resolution of the imaging system.

Multifocus nonlinear optical microscopy based on SLM

FINCHSCOPE is a new technology of fluorescence holographic microscopy. It has been successfully applied to recording high-resolution three-dimensional fluorescence images of biological specimens without the need for scanning. In this study, we revealed and analyzed an intrinsic phenomenon, called ghost lens effect, on spatial light modulator which is the core element enabling the incoherent correlation in the FINCHSCOPE. The ghost lens effect can degrade the imaging quality by introducing multiple spherical waves with different focal lengths into the correlation and thus increasing the noise in the recorded holograms.

Fast fluorescence holographic microscopy

A series of 400-nm-thick sandwich structured Pb(1+x)ZrO3/(Pb,Eu)ZrO3/Pb(1+x)ZrO3(PZO/PEZO/PZO) antiferroelectric thin films with different Pb excess content (x) (x=0%, 10%, 20%, and 30%) in the PZO precursors have been successfully deposited on Pt(111)/Ti/SiO2/Si substrates by a solâ€“gel method. The effects of Pb excess content on the dielectric properties, and energy storage performance of the PZO/PEZO/PZO thin films have been investigated in detail. It is found that all the films show a unique perovskite phase structure. With increasing Pb excess content in the PZO precursors, P-E hysteresis loop changes from slanted to square shape. Meanwhile, a larger antiferroelectric to ferroelectric switching field (EAF) and ferroelectric to antiferroelectric switching field (EFA) are observed in the films with higher Pb excess content. When increasing Pb excess content from 0% to 30%, the energy storage density of the sandwich structured films is remarkably improved from 11.4 to 14.8 J/cm3 at 1000 kV/cm.

PbZrO3-Based Antiferroelectric Thin Film Capacitors with High Energy Storage Density

Circular targets are widely used in machine vision. The localization of circle center plays a crucial role in machine vision applications. In the process of camera imaging, the circles change to the ellipses in the image plane of camera because of perspective transformation. The center of ellipse usually does not coincide with the projected center of the circle, leading to a deviation of circle center. Based on perspective transformation and analytic geometry we present a new approach, in which the concentric circular targets are adopted and the true projective position of the circular target can be determined accurately. Both simulation and experiment results show that the proposed method is valid and robust. The true positions of the circular centers can be localized by proposed method without the center deviations.

Correction of circular center deviation in perspective projection

In this paper, we analyze the security of the classical double random phase encoding (DRPE) technique in Fourier
domain, as well as its extended schemes in Fresnel and fractional Fourier domains. These schemes are resistant to bruteforce
attacks, for their large key spaces. However, due to the linearity property of their encryption transformations, they
are vulnerable to other attacks, such as chosen-plaintext attack and known-plaintext attack. We successfully break each
of the three encryption schemes with the help of a certain quantity of plaintext-ciphertext pairs. Each attack is validated
by computer simulations. The cryptanalysis indicates that, to minimize the risks, it is recommendable to introduce
nonlinear operations to optical encryption systems.

Xiang Peng

Papers

Multifocus nonlinear optical microscopy based on SLM

Fast fluorescence holographic microscopy

PbZrO3-Based Antiferroelectric Thin Film Capacitors with High Energy Storage Density

Correction of circular center deviation in perspective projection

Optical cryptanalysis of DRPE-based encryption systems