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 multiregional multiphoton microscope that employs a fast one-dimensional discrete-line scanning approach based on a spatial light modulator (SLM). The phase-only SLM shapes an incoming mode-locked, near-infrared Ti:sapphire laser beam into multiple specific discrete-lines, which are designed according to the sizes and locations of the target samples. Only the target-sample areas of are scanned 
one-dimensionally, resulting in an efficient use of the laser’s power. Compared with conventional multiphoton microscopies, this technique shortens scanning time and minimizes photodamage by concentrating scanning energy and dwell time on the areas of interest. Additionally, our discrete-line-focus design eliminates the cross-talk that occurs in conventional one-dimensional line-scanning multiphoton microscopes, thus enhancing the lateral and axial resolutions of the line-scanning imaging system.

1D-scanning addressable multiregional multifocal multiphoton microscopy

Automatic registration is a key researcher issue in 3D measurement field. In this work, we developed the
automatic registration system, which is composed of a stereo system with structured light and two axis
turntables. To realize the fully automatically 3D point registration, the novel method is proposed for
calibration the stereo system and the two turntable direction vector simultaneously. The plane calibration
rig with marked points was placed on the turntable and was captured by the left and right cameras of the
stereo system with different rotation angles of the two axis turntable. By the shot images, a stereo system
(intrinsically and extrinsically) was calibrated with classics camera model, and reconstruction 3D
coordinates of the marked points with different angle of the two turntable. The marked point in different
angle posted the specific circle, and the normal line of the circle around the turntable axis direction vector.
For the each turntable, different points have different circle and normal line, and the turntable axis
direction vector is calculated by averaging the different normal line. And the result show that, the
proposed registration system can precisely register point cloud under the different scanning angles. In
addition, there are no the ICP iterative procedures, and that make it can be used in registration of the
point cloud without the obvious features like sphere, cylinder comes and the other rotator.

An automatic registration system of multi-view 3D measurement data using two-axis turntables

It is usually difficult to calibrate the 3-D vision inspection system that may be employed to measure the large-scale
engineering objects. One of the challenges is how to in-situ build-up a large and precise calibration target. In this paper,
we present a calibration target reconstruction strategy to solve such a problem. First, we choose one of the engineering
objects to be inspected as a calibration target, on which we paste coded marks on the object surface. Next, we locate and
decode marks to get homologous points. From multiple camera images, the fundamental matrix between adjacent images
can be estimated, and then the essential matrix can be derived with priori known camera intrinsic parameters and
decomposed to obtain camera extrinsic parameters. Finally, we are able to obtain the initial 3D coordinates with
binocular stereo vision reconstruction, and then optimize them with the bundle adjustment by considering the lens
distortions, leading to a high-precision calibration target. This reconstruction strategy has been applied to the inspection
of an industrial project, from which the proposed method is successfully validated.

Calibration target reconstruction for 3-D vision inspection system of large-scale engineering objects

The research is based on the design computer technique and optical 3D scanning technology, which integrated with cloud data, human engineering and surface simulation and reconstruction technology. In addition, a web based design education prototype with 3D scanning and printing technique will be created by researcher as well, in order to verify the results of the research in the actual application environment. It will allows us to refine our system and propose more subjects under with similar technologies to help to develop creative skills of students who are often got stuck with 3D modeling which are not helpful for those who wish to study design without sketching and modeling skill.

An Interactive Model of Creative Design Behavior with 3D Optical Technology

Based on the optical memory effect of scattered light, we developed a new single-pixel camera concept. The retrieved images contain both 3D and spectral information about the sample. A spatial light modulator (SLM) generates a random intensity modulation. The signal recorded by the single-pixel detector is cross correlated by the calculated point spread function (PSF) signals of the SLM to retrieve the image. In this publication, both simulations and experimental results are presented.

Xiang Peng

Papers

1D-scanning addressable multiregional multifocal multiphoton microscopy

An automatic registration system of multi-view 3D measurement data using two-axis turntables

Calibration target reconstruction for 3-D vision inspection system of large-scale engineering objects

An Interactive Model of Creative Design Behavior with 3D Optical Technology

Single-pixel scatter-plate microscopy.