Takashi Kakue

High-speed phase imaging by parallel phase-shifting digital holography.

Parallel phase-shifting digital holography can obtain three-dimensional information of a dynamically moving object with high accuracy by using space-division multiplexing of multiple holograms required for phase-shifting interferometry. We demonstrated high-speed parallel phase-shifting digital holography and obtained images of the phase variation of air caused by a compressed gas flow sprayed from a nozzle. In particular, we found the interesting phenomenon of periodic phase distributions. Reconstructed images were obtained at frame rates of 20,000 and 180,000 frames per second.

Experimental demonstration of parallel two-step phase-shifting digital holography

Parallel two-step phase-shifting digital holography is a technique for single-shot implementation of phase-shifting interferometry and requires only the intensity distribution of the reference wave and spatial two phase-shifted holograms. We constructed a system of parallel two-step phase-shifting digital holography and experimentally demonstrated the technique, for the first time. The system uses an originally fabricated image sensor having an array of 2 × 1 micro polarizers. Each micro polarizer was attached on pixel by pixel. In the experiment, the unwanted images, the zero-order diffraction wave and the conjugate image, are removed from the reconstructed image of objects by the system, while the images superimpose on the image of objects reconstructed by Fresnel transform alone. Also the capability of single-shot and three-dimensional imaging is demonstrated by the system.

Parallel phase-shifting digital holographic microscopy

We propose parallel phase-shifting digital holographic microscopy (PPSDHM) which has the ability of three-dimensional (3-D) motion measurement using space-division multiplexing technique. By the PPSDHM, instantaneous information of both the 3-D structure and the phase distributions of specimens can be simultaneously acquired with a single-shot exposure. We constructed a parallel phase-shifting digital holographic microscope consisting of an optical interferometer and an image sensor on which micro polarizers are attached pixel by pixel. The validity of the PPSDHM was experimentally verified by demonstrating the single-shot 3-D imaging and phase-imaging ability of the constructed microscope.

Lensless zoomable holographic projection using scaled Fresnel diffraction.

Projectors require a zoom function. This function is generally realized using a zoom lens module composed of many lenses and mechanical parts; however, using a zoom lens module increases the system size and cost, and requires manual operation of the module. Holographic projection is an attractive technique because it inherently requires no lenses, reconstructs images with high contrast and reconstructs color images with one spatial light modulator. In this paper, we demonstrate a lensless zoomable holographic projection. Without using a zoom lens module, this holographic projection realizes the zoom function using a numerical method, called scaled Fresnel diffraction which can calculate diffraction at different sampling rates on a projected image and hologram.

Improvement of color reproduction in color digital holography by using spectral estimation technique

We propose a color digital holography by using spectral estimation technique to improve the color reproduction of objects. In conventional color digital holography, there is insufficient spectral information in holograms, and the color of the reconstructed images depend on only reflectances at three discrete wavelengths used in the recording of holograms. Therefore the color-composite image of the three reconstructed images is not accurate in color reproduction. However, in our proposed method, the spectral estimation technique was applied, which has been reported in multispectral imaging. According to the spectral estimation technique, the continuous spectrum of object can be estimated and the color reproduction is improved. The effectiveness of the proposed method was confirmed by a numerical simulation and an experiment, and, in the results, the average color differences are decreased from 35.81 to 7.88 and from 43.60 to 25.28, respectively.

Parallel phase-shifting color digital holography using two phase shifts

We propose parallel phase-shifting color digital holography using two phase shifts. This technique enables the instantaneous acquisition of three-dimensional information of a moving color object. The interference fringe image that contains six holograms with two phase shifts for three wavelengths is recorded by a single shot exposure. Decreasing the degree of space-division multiplexing of these holograms makes it possible to suppress the degradation of the image quality owing to the aliasing caused by the multiplexing. Numerical simulation and preliminary experiments demonstrate the validity of the proposed technique; the reconstructed images of the proposed technique are clearer than those of the previously reported single-shot phase-shifting color digital holography that uses four phase steps.

Single-shot femtosecond-pulsed phase-shifting digital holography

Parallel phase-shifting digital holography is capable of three-dimensional measurement of a dynamically moving object with a single-shot recording. In this letter, we demonstrated a parallel phase-shifting digital holography using a single femtosecond light pulse whose central wavelength and temporal duration were 800 nm and 96 fs, respectively. As an object, we set spark discharge in atmospheric pressure air induced by applying a high voltage to between two electrodes. The instantaneous change in phase caused by the spark discharge was clearly reconstructed. The reconstructed phase image shows the change of refractive index of air was -3.7 × 10(-4).

High-Speed Three-Dimensional Microscope for Dynamically Moving Biological Objects Based on Parallel Phase-Shifting Digital Holographic Microscopy

We succeeded in 3-D motion-picture imaging for dynamic motion of biological objects swimming at different depths by parallel phase-shifting digital holographic microscopy (PPSDHM). PPSDHM is a technique for high-quality instantaneous 3-D imaging of specimens in the microscopic field of view by single-shot recording of multiple phase-shifted holograms. We constructed a PPSDHM for recording high-speed dynamic phenomena and then motions of biological objects in water were recorded at 20 000 and 150 000 frames/s, respectively, which is the fastest among the previous reports on 3-D imaging of biological objects.

Band-limited double-step Fresnel diffraction and its application to computer-generated holograms

Double-step Fresnel diffraction (DSF) is an efficient diffraction calculation in terms of the amount of usage memory and calculation time. This paper describes band-limited DSF, which will be useful for large computer-generated holograms (CGHs) and gigapixel digital holography, mitigating the aliasing noise of the DSF. As the application, we demonstrate a CGH generation with nearly 8K × 4K pixels from texture and depth maps of a three-dimensional scene captured by a depth camera.

Aliasing-reduced Fresnel diffraction with scale and shift operations

Numerical simulation of Fresnel diffraction with fast Fourier transform (FFT) is widely used in optics, especially computer holography. Fresnel diffraction with FFT cannot set different sampling rates between source and destination planes, while shifted-Fresnel diffraction can set different rates. However, an aliasing error may be incurred in shifted-Fresnel diffraction in a short propagation distance, and the aliasing conditions have not been investigated. In this paper, we investigate the aliasing conditions of shifted-Fresnel diffraction and improve its properties based on the conditions.