“Unpaired Image-to-Image Translation using Cycle-Consistent Adversarial Networks”の学習報告

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

Materials with relatively small refractive indices (n<2), such as glass, quartz, polymers, some ceramics, etc., are the basic materials in most optical components (lenses, optical fibres, etc.). In this review, we present some of the phenomena and possible applications arising from the interaction of light with particles with a refractive index less than 2. The vast majority of the physics involved can be described with the help of the exact, analytical solution of Maxwell’s equations for spherical particles (so called Mie theory). We also discuss some other particle geometries (spheroidal, cubic, etc.) and different particle configurations (isolated or interacting) and draw an overview of the possible applications of such materials, in connection with field enhancement and super resolution nanoscopy.

Refractive index less than two: photonic nanojets yesterday, today and tomorrow [Invited]

For quantitative phase imaging (QPI) based on transport-of-intensity equation (TIE), partially coherent illumination provides speckle-free imaging, compatibility with brightfield microscopy, and transverse resolution beyond coherent diffraction limit. Unfortunately, in a conventional microscope with circular illumination aperture, partial coherence tends to diminish the phase contrast, exacerbating the inherent noise-to-resolution tradeoff in TIE imaging, resulting in strong low-frequency artifacts and compromised imaging resolution. Here, we demonstrate how these issues can be effectively addressed by replacing the conventional circular illumination aperture with an annular one. The matched annular illumination not only strongly boosts the phase contrast for low spatial frequencies, but significantly improves the practical imaging resolution to near the incoherent diffraction limit. By incorporating high-numerical aperture (NA) illumination as well as high-NA objective, it is shown, for the first time, that TIE phase imaging can achieve a transverse resolution up to 208 nm, corresponding to an effective NA of 2.66. Time-lapse imaging of in vitro Hela cells revealing cellular morphology and subcellular dynamics during cells mitosis and apoptosis is exemplified. Given its capability for high-resolution QPI as well as the compatibility with widely available brightfield microscopy hardware, the proposed approach is expected to be adopted by the wider biology and medicine community.

High-resolution transport-of-intensity quantitative phase microscopy with annular illumination

Transport of intensity equation: a tutorial

Angular and polarization multiplexing techniques are utilized in both object and reference arms in the digital holographic microscopy system to improve its resolution. The angular multiplexing provides on-axis and off-axis illumination and reference beams with different carrier frequencies. Polarization multiplexing prohibits the occurrence of interference between low and high object spatial frequencies and reference beams. The proposed system does not require special light sources or filtering masks. Experimental results show that the resolution of the synthesized image exceeds the resolution determined by the numerical aperture of the imaging microscope objective.

Resolution improvement in digital holography by angular and polarization multiplexing.

We demonstrated a scheme to spectrally combine two high power, broad-linewidth single beams using a steep edge filter as the combining element. 10.12 kW combined output power is achieved with a beam quality of M2
x = 11.4 and M2
y = 10.4. To the best of our knowledge, this is the highest output power ever reported for the filter based SBC system. Despite the broad emission spectrum of the single channel, the combining efficiency is measured to be 98.9%, which proves the high efficiency of the filter for both the reflection and transmission cases. A detail analysis of the thermal behavior is carried out to aid in the optimization of the beam quality. This SBC system permits the efficient combining of the beams with broad linewidth and provides another approach to achieve a combined output beam beyond 10 kW level.

10 kW-level spectral beam combination of two high power broad-linewidth fiber lasers by means of edge filters

Microscale lenses are mostly used as near-sighted lenses. The far-field imaging properties of a microscale spherical lens, where the lens is spatially separated from the object, are experimentally studied. Our experimental results show that, for a blu-ray disc (an object) whose spacing is 300 nm, the lens can magnify the stripe patterns of the disc when the lens is spatially separated from the object. In the experimentally tested range (0-14 μm), all the magnified images are virtual images. When the distance is increased from 0 to 14 μm the magnification decreases from 1.47× to 1.20× and the field of view increases from 3.8 to 12.2 μm. The image magnification cannot be described by standard geometrical optics.

Experimental far-field imaging properties of a ~5-μm diameter spherical lens

The isotropic and anisotropic image edge enhancements by employing Airy spiral phase filters are proposed and demonstrated. The coherent spread functions of the image systems are derived from transmittance functions of their corresponding filters. In the isotropic method, the distributions of the coherent spread function with the radius of the main ring ρ0 and the scaled parameter w0 are numerically analyzed. It is found that the width of the main lobe determining the resolution decreases with the increased ρ0, and the amplitudes of the side lobes connecting with the contrast fluctuate with w0. Compared with the existing spiral phase filters, higher contrast and resolution can be achieved by adjusting the two parameters in the Airy spiral phase filter. Moreover, an off-axis Airy spiral phase filter by controlling the center position (ρ0,ϕ1) is designed and employed to implement anisotropic edge enhancement. In the experiments, two methods of image edge enhancement have been verified by using the amplitude-contrast and phase-contrast objects.

Jun Ma

Papers

Resolution improvement in digital holography by angular and polarization multiplexing.

10 kW-level spectral beam combination of two high power broad-linewidth fiber lasers by means of edge filters

Experimental far-field imaging properties of a ~5-μm diameter spherical lens

Image edge enhancement using Airy spiral phase filter.

Iterative autofocusing strategy for axial distance error correction in ptychography