Qing-Yang Yue

Laplacian differential reconstruction of in-line holograms recorded at two different distances

We analyze the diffraction of the picture obtained by the subtraction of two in-line holograms recorded in two planes at distances of z and z+Deltaz apart from the object plane. Our theoretical analysis reveals that the reconstructed field at the object plane is approximately equal to the Laplacian second-order differentiation of the object wave in transverse direction when Deltaz is much smaller than the distance z, that is, the reconstructed image presents a high quality of edge enhancement. We further investigate the dependence of the edge-enhancement quality on the longitudinal differential distance Deltaz and find that the reconstructed images have the sharpest edge-enhancement and high signal-to-noise ratio at the same time only when the value of Deltaz/z lies between 0.7% and 0.9% under our experimental condition. We also construct a criteria function, named the entropy of the image, to automatically focus the edge-enhanced image and demonstrate its adaptability in experiments.

Simple method for generation of vector beams using a small-angle birefringent beam splitter.

A simple and practical system for generation of vector beams with arbitrary polarization and complex-amplitude distributions is proposed. The system mainly consists of a scalar computer-generated hologram (CGH), a small-angle birefringent beam splitter (BBS), and a Fourier lens with a filtering aperture (FA). The CGH is placed in front of the Fourier lens. The BBS is inserted between the CGH and the Fourier lens. When the CGH specially designed according to the method described in this Letter is illuminated by a plane beam or a Gaussian beam, a desired vector beam can be obtained through the FA placed at the back focal plane of the Fourier lens. Because no coupling element and half-wave plate are to be placed between the CGH and the BBS, the extinction ratios of both the two orthogonal polarization components for the vector beam can be better than 10(-5) and so high-quality vector beams can be generated.

Double-channel angular-multiplexing polarization holography with common-path and off-axis configuration

We propose a double-channel angular-multiplexing polarization holographic imaging system with common-path and off-axis configurations. In the system, its input plane is spatially divided into three windows: an object window and two reference windows, and two orthogonal linear polarizers are attached, respectively, on the two reference windows; a two-dimensional cross grating is inserted between the input and output planes of the system. Thus the object beam passing through the object window and the two orthogonal polarized reference beams passing through the two reference windows can overlap each other at the output plane of the system and form a double-channel angular-multiplexing polarization hologram (DC-AM-PH). Using this system, the complex amplitude distributions of two orthogonal polarized components from an object can be recorded and reconstructed by one single-shot DC-AM-PH at the same time. Theoretical analysis and experimental results demonstrated that the system can be used to measure the Jones matrix parameters of polarization-sensitive or birefringent materials.

One-shot time-resolved holographic polarization microscopy for imaging laser-induced ultrafast phenomena.

A time-resolved holographic polarization microscopy, based on angular multiplexing holographic technique, is proposed for imaging ultrafast phenomena in polarization-sensitive transparent materials. This method can retrieve and image the complex amplitude distributions of two orthogonal polarization components of two sequential vector wavefronts with ultrashort time interval by a single short recording. Some experimental results for imaging the pulse laser induced ultrafast events based on the method are given. It is demonstrated that this technique may provide a potential tool for characterizing ultrafast processes in polarization-sensitive materials, especially in the non-reproducible experiment conditions.

Measurement of vector transmission matrix and control of beam focusing through a multiple-scattering medium based on a vector spatial light modulator and two-channel polarization holography

An experimental system for measuring the complex vector transmission matrix (VTM) of an anisotropic multiple-scattering medium (AMSM) is proposed. In this system, a simple vector spatial light modulator unit composed of a conventional transmittance spatial light modulator and a small-angle birefringent beam splitter is introduced to realize programmable and quantitative control of both the amplitudes and phases of two orthogonal polarization components of the input vector beam point by point. At the same time, a two-channel angular-multiplexing holographic polarization recording geometry is applied to realize the synchronous holographic measurement of the two orthogonal polarization components of the scattered light field. Using this system, we measured the VTM of an AMSM composed of the ZnO scattering layer. At the same time, we also demonstrated that the system can be directly applied to realize focusing a vector beam through the AMSM based on the measured VTM.

Quantitative phase imaging system with slightly-off-axis configuration and suitable for objects both larger and smaller than the size of the image sensor

We propose a quantitative phase imaging system with exact slightly-off-axis configuration and suitable for objects both smaller and larger than the size of the effective recording region of the image sensors. In this system, the object is illuminated by a convergent spherical beam and a specially designed aperture filter is placed on the spatial frequency plane of the object wave; at the same time, a point source emitting from the edge of the aperture is taken as the reference beam, so that the optimal frequency condition for reconstruction of slightly-off-axis digital holograms can be always guaranteed for both large and small objects as well as different magnification (or the field of view) configurations. At the same time, a 1x2 single-mode optical fiber splitter is used for generating the reference and the illumination beams. Benefited from such fiber-based slightly-off-axis design, the proposed system provides a low-cost way to convert a regular microscope into a slightly-off-axis holographic one for microbiological specimens with a high spatial resolution.

Wavefront sensing based on a spatial light modulator and incremental binary random sampling

A wavefront sensing method based on a spatial light modulator (SLM) and an incremental binary random sampling (IBRS) algorithm is proposed. In this method, the recording setup is built just by a transmittance SLM and an image sensor. The tested wavefront incident to the SLM plane can be quantitatively retrieved from the diffraction intensities of the wavefront passed through the SLM displaying a IBRS pattern. Because only two modulation states (opaque and transparent) of the SLM are used, the method does not need to know the concrete modulation function of the SLM in advance. In addition by introducing the concept of the incremental random sampling into wavefront sensing, the adaptability of phase retrieving based on the diffraction intensities is significantly improved. To the best of our knowledge, no previous study has used this concept for the same purpose. Some experimental results are given for demonstrating the feasibility of our method.

Determining the vortex densities of random nondiffracting beams

The evolutionary and statistical properties of the optical vortices that exist in random nondiffracting beams (RNDBs) are analyzed. It is found that the phase singularities (PSs) in the RNDBs originate from the zero rings of Bessel beams with the same ring-shaped spatial spectrum structure (but with zero phase fluctuations) as those of the RNDBs provided. It is also found that the average PS density or vortex density is determined by the average duration of the zero rings of the corresponding Bessel function. According to this model, we successfully derived, for the first time to our knowledge, an analytical formula for quantitatively predicting the PS density of the RNDBs. This formula could be helpful for understanding and designing RNDBs in their applications.

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

We proposed an iterative method for phase retrieval and diffractive imaging based on Babinets 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.