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 demonstrate that the optical encryption scheme with a reference wave in joint transform correlator (JTC) is vulnerable to the known-plaintext attack (KPA) from the point of view of cryptanalysis. By implementing this attack, an opponent can access the encryption key with the help of several skillful steps and a pre-knowledge of a plaintext–ciphertext pair. The theoretical analysis and a set of numerical simulations are carried out to demonstrate how the secret key of the encryption system can be derived out with our proposed strategy.

Cryptanalysis of optical encryption with a reference wave in a joint transform correlator architecture

An improved spatiotemporal correlation method for high-accuracy random speckle 3D reconstruction

We developed a hybrid SHG-TPEF polarization imaging system that allowed the excitation beam from an fs Ti:Sappire
laser being bi-directionally raster scanned across the focal plane using a pair of orthogonal galvanometers. To implement
high-speed scanning, the turning regions of the triangular waves were smoothed by a custom-designed waveform. The
SHG and TPEF signals from samples were recorded by two PMTs in the forward and backward direction. Using this
imaging system, we obtained 3D images of the sarcomere structure via SHG and DiO-stained lipid membrane via TPEF
in live cardiomyocytes isolated from neonatal and adult rats. The results demonstrated the potential applications of SHG
and TPEF in the research of myofibrillogensis.

3D myofibril imaging in live cardiomyocytes via hybrid SHG-TPEF microscopy

The invention relates to the technical field of three-dimensional measuring, and especially relates to a three-dimensional imaging system based on a two-axis rotation platform, and a calibration method thereof. The technical scheme provided by the invention mainly comprises three important parts: 1, calibrating a binocular three-dimensional sensor; 2, calibrating the two-axis rotation platform; and 3, according to calibration results of the binocular three-dimensional sensor and the two-axis rotation platform, automatically matching the depth images of a detected object from different visual angles. Through the three-dimensional imaging system based on the two-axis rotation platform, and the calibration method thereof, the binocular three-dimensional sensor and the two-axis rotation platform can be simultaneously calibrated, and three-dimensional images of the detected object can be automatically matched by use of the calibration results.

Three-dimensional data acquisition system and acquisition method based on two-axis rotation platform

We report a new method of sensing a three-dimensional (3D) object surface with an arbitrary geometric shape. In this approach, the first-order beams diffracted from two acousto-optic deflectors (AODs) interfere with each other to form a spatial carrier that is used to encode the depth information from the 3D object surface. A direct digital synthesizer is utilized to control two AODs to generate sequentially spatial carriers with different spatial frequencies so that a modified temporal phase-unwrapping technique can be applied for decoding the shape information of the test surface. Preliminary experimental results are presented to demonstrate the effectiveness of this method.

Xiang Peng

Papers

Cryptanalysis of optical encryption with a reference wave in a joint transform correlator architecture

An improved spatiotemporal correlation method for high-accuracy random speckle 3D reconstruction

3D myofibril imaging in live cardiomyocytes via hybrid SHG-TPEF microscopy

Three-dimensional data acquisition system and acquisition method based on two-axis rotation platform

Three-dimensional vision with dual acousto-optic deflection encoding.