Aperture-scanning Fourier ptychography [Opt. Express22, 13586 (2014)] is a promising non-interferometric wavefront measurement technique. It eliminates the thin-sample requirement in typical Fourier ptychography employing angle-varying illumination. However, as aperture-scanning Fourier ptychography is based on step-by-step scanning, it requires long data acquisition time and a high-stability optical system. In this paper, we propose a single-shot aperture-scanning Fourier ptychography method. In our method, multiple low-resolution images are collected in a single shot by inserting a Dammann grating at a certain distance before the aperture, and the images are subsequently converted to a high-resolution complex wavefront. Compared with scanning-based aperture-scanning Fourier ptychography, the total acquisition time of the proposed method is dramatically reduced. The feasibility of our proposed method is demonstrated by proof-of-concept experiments.

Single-shot aperture-scanning Fourier ptychography.

It is beneficial to improve the resolution by a diffuser in imaging systems, because higher frequency information could be involved into the captured patterns via scattering effect. In this paper, a lensless imaging method is designed by 1-D scanning. A diffuser is placed upstream of the object, which is translated in a one-dimensional path and corresponding positions are corrected by cross-correlation. Our method requires a diffraction pattern of the object without a diffuser to speed up convergence and improve resolution. In field reconstruction, the amplitude constraint is added into the iterative phase retrieval algorithm. The high-quality complex-valued images can be obtained with ∼15 patterns. As a ptychography, the proposed method only needs a 1-D device, which could simplify the experimental equipment for reducing costs and measurement time.

Ptychography imaging by 1-D scanning with a diffuser.

Phase retrieval with extended field of view based on continuous phase modulation.

A coherent-modulation-imaging-based (CMI) algorithm has been employed for on-shot laser beam diagnostics in high-power laser facilities, where high-intensity short-pulsed lasers from terawatt to petawatt are designed to realize inertial confinement fusion (ICF). A single-shot intensity measurement is sufficient for wave-front reconstruction, both for the near-field and far-field at the same time. The iterative reconstruction process is computationally very efficient and was completed in dozens of seconds by the additional use of a GPU device to speed it up. The compact measurement unit—including a CCD and a piece of pre-characterized phase plate—makes it convenient for focal-spot intensity prediction in the target chamber. It can be placed almost anywhere in high-power laser facilities to achieve near-field wave-front diagnostics. The feasibility of the method has been demonstrated by conducting a series of experiments with diagnostic beams and seed pulses with deactivated amplifiers in our high-power laser system.

https://iopscience.iop.org/article/10.1088/1612-2011/13/5/055001/pdf

On-shot laser beam diagnostics for high-power laser facility with phase modulation imaging

We proposed an iterative method for phase retrieval and diffractive imaging based on Babinet's principle and complementary random sampling (CRS). We demonstrated that the whole complex amplitude (not sieved) of an object wave can be accurately retrieved from the diffraction intensities of the object wave sampled by a group of binary CRS masks and the diffractive imaging for the object can be realized through a single digital inverse diffraction. Some experimental results are given for the demonstration. Our experimental results reveal that, using CRS, the influence of a binary random sampling mask on the retrieved field can be well eliminated, and the accuracy and efficiency of the phase retrieval can be greatly improved.

Phase retrieval and diffractive imaging based on Babinet's principle and complementary random sampling.

Wavefront control is a significant parameter in inertial confinement fusion (ICF). The complex transmittance of large optical elements which are often used in ICF is obtained by computing the phase difference of the illuminating and transmitting fields using Ptychographical Iterative Engine (PIE). This can accurately and effectively measure the transmittance of large optical elements with irregular surface profiles, which are otherwise not measurable using commonly used interferometric techniques due to a lack of standard reference plate. Experiments are done with a Continue Phase Plate (CPP) to illustrate the feasibility of this method.

Measurement of the complex transmittance of large optical elements with Ptychographical Iterative Engine

Accurate measurements of the transmittance of large optical elements are essential to improve the energy density in inertial confinement fusion (ICF). The required complex transmittance of such optical elements used in ICF is obtained by computing the phase difference between the illuminating and transmitting fields using modulation coherent imaging (MCI). A phase plate designed as a modulator has a known transmission function in this technique. It presents a simple and quick method to measure the transmittance of large optical elements with irregular surface profiles by retrieving it from only two diffraction patterns recorded by a CCD camera. The complex transmittance of a continuous phase plate (CPP) with a large aperture used in ICF is measured experimentally, and the results are found to agree with the designed value.

Measurement of the complex transmittance of large optical elements with modulation coherent imaging

A modified extended-ptychographical-iterative-engine (ePIE) algorithm is proposed to overcome the
disadvantages of ePIE technique and reduce the influence of stage hysteresis or backlash error. The exit wave
of a rotatable "screen" illuminated by plane wave is used as the illumination on the specimen, and the complex
transmission functions of the rotatable object and specimen can be simultaneously reconstructed. Compared with
the standard x-y scanning PIE algorithm, the proposed algorithm can completely avoid the influence of stage
hysteresis (or backlash error). The proposed algorithm also has higher convergence speed and better accuracy
than the standard PIE algorithm.

Phase imaging with rotating illumination

The invention discloses a light beam phase on-line measuring device and method. The device comprises a beam contracting device, a phase plate array and a light spot detector which are sequentially arranged along the spread direction of light beams to be tested. The phase plate array is formed by sequentially arraying N phase plates, wherein the phase distribution of the phase plates has been known, and N is a positive integer larger than one. The phase plate array and the light spot detector are fixed through fixing supporting rods. The output end of the light spot detector is connected with the input end of the computer. Only one light spot detector, one or more random phase plates with known distribution and a corresponding fixing device are needed by the measuring device, so that cost is far lower than that of a common interferometer. Only one diffraction light spot needs recording, so that requirements for environment stability are low, the resolution ratio is greatly improved, the convergence rate of the CDI algorithmic can be remarkably improved, and robustness can be increased. The measuring device and method can be used for high-precision detection and wavefront phase measurement of optical elements, the wavefront detection of pulse laser, and especially the wavefront on-line measurement in a high power laser driver.

Light beam phase on-line measuring device and method

The invention discloses a device and method for transmission type optical element layering phase position imaging. The device is composed of a coherent light source, a beam expander, a convergent lens, a to-be-tested optical element, a two-dimensional electric transversely-moving table, a detector and a computer. A convergent spherical wave formed in the mode that quasi-parallel light emitted by the coherent light source passes through the convergent lens serves as illumination light of the to-be-tested optical element, the two-dimensional electric transversely-moving table is driven under control of the computer to move the to-be-tested optical element, diffraction spots generated when the to-be-tested optical element is at different positions are recorded through the detector at the position a certain distance behind the to-be-tested optical element, and complex-amplitude transmission rate functions of layers of the to-be-tested optical element and phase positions of the layers of the to-be-tested optical element are obtained through processing of the computer. The structure of the optical element can not be damaged in the measurement process.

Device and method for transmission type optical element layering phase position imaging

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