Daisuke Barada

Doppler phase-shifting digital holography and its application to surface shape measurement

Digital holography utilizing the optical Doppler effect is proposed in which the time variation of interference fringes is recorded using a high-speed CMOS camera. The complex amplitude diffracted from the object wave is extracted by time-domain Fourier transforming the recorded interference fringes. The method was used to measure the surface shape of a concave mirror under a disturbed environment.

Simultaneous two-wavelength Doppler phase-shifting digital holography.

This paper presents a method based on the use of an image sensor for obtaining the complex amplitudes of beams diffracted from an object at two different wavelengths. The complex amplitude for each wavelength is extracted by the Doppler phase-shifting method. The principle underlying the proposed method is experimentally verified by using the method with two lasers having different wavelengths to measure the surface shape of a concave mirror.

Angular multiplex recording of data pages by dual-channel polarization holography

Simultaneous recording of two data pages by dual-channel polarization holography is experimentally demonstrated. Two data pages are transferred as two orthogonal scalar wave components of a vector wave. The signal vector wave and reference beam are superposed on a polarization-sensitive medium. The two recorded data pages are simultaneously and independently reconstructed. Furthermore, holographic angular multiplex recording is performed.

Color digital holography using a single monochromatic imaging sensor

Color digital holography utilizing the Doppler effect is proposed. The time variation of holograms produced by superposing images at three wavelengths is recorded using a high-speed monochromatic imaging sensor. The complex amplitude at each wavelength can be extracted from frequency information contained in the Fourier transforms of the recorded holograms. An image of the object is reconstructed by the angular spectrum method. Reconstructed monochromatic images at the three wavelengths are combined to produce a color image for display.

Holographic 3D display observable for multiple simultaneous viewers from all horizontal directions by using a time division method

A holographic three-dimensional display system with a viewing angle of 360°, by using a high-speed digital micromirror device (DMD), has been proposed. The wavefront modulated by the DMD enters a rotating mirror tilted vertically downward. The synchronization of the rotating mirror and holograms displayed on the DMD allows for the reconstruction of a wavefront propagating in all horizontal directions. An optical experiment has been demonstrated in order to verify our proposed system. Binocular vision is realized from anywhere within the horizontal plane. Our display system enables simultaneous observation by multiple viewers at an extremely close range.

Computer simulation of photoinduced mass transport on azobenzene polymer films by particle method

The formation and erasure of photoinduced surface relief gratings (SRGs) on azobenzene-containing polymers are simulated using a calculation model based on the moving-particle semi-implicit method. For the convection calculation, an anisotropic diffusion model is proposed. The gradient force of the optical electric field and the influence of surface tension are considered as driving forces for photoinduced mass transport. The viscosity of polymer films changes with the light intensity in our model. Particle motions in SRG formation and erasure are calculated and the SRG pitch and polarization dependences of the SRG growing and erasing rates are investigated. These theoretical results coincide qualitatively with our experimental results.

Dual-channel polarization holography: a technique for recording two complex amplitude components of a vector wave

In this Letter, the principle of polarization holography for recording an arbitrary vector wave on a thin polarization-sensitive recording medium is proposed. It is analytically shown that the complex amplitudes of p- and s-polarization components are simultaneously recorded and independently reconstructed by using an s-polarized reference beam. The characteristics are experimentally verified.

Constructive spin-orbital angular momentum coupling can twist materials to create spiral structures in optical vortex illumination

It was discovered that optical vortices twist isotropic and homogenous materials, e.g., azo-polymer films to form spiral structures on a nano- or micro-scale. However, the formation mechanism has not yet been established theoretically. To understand the mechanism of the spiral surface relief formation in the azo-polymer film, we theoretically investigate the optical radiation force induced in an isotropic and homogeneous material under irradiation using a continuous-wave optical vortex with arbitrary topological charge and polarization. It is revealed that the spiral surface relief formation in azo-polymer films requires the irradiation of optical vortices with a positive (negative) spin angular momentum and a positive (negative) orbital angular momentum (constructive spin-orbital angular momentum coupling), i.e., the degeneracy among the optical vortices with the same total angular momentum is resolved.

Fast calculation of computer-generated holograms based on 3-D Fourier spectrum for omnidirectional diffraction from a 3-D voxel-based object

We have derived the basic spectral relation between a 3-D object and its 2-D diffracted wavefront by interpreting the diffraction calculation in the 3-D Fourier domain. Information on the 3-D object, which is inherent in the diffracted wavefront, becomes clear by using this relation. After the derivation, a method for obtaining the Fourier spectrum that is required to synthesize a hologram with a realistic sampling number for visible light is described. Finally, to verify the validity and the practicality of the above-mentioned spectral relation, fast calculation of a series of wavefronts radially diffracted from a 3-D voxel-based object is demonstrated.

Retardagraphy: a technique for optical recording of the retardance pattern of an optical anisotropic object on a polarization-sensitive film using a single beam

A technique that employs a single laser beam is proposed for recording the retardance of an optical anisotropic object. The retardance pattern is converted into a polarization pattern using a quarter-wave plate and recorded on a polarization-sensitive medium. The recording medium is illuminated by homogeneous polarized light, and the light transmitted by the recording medium is analyzed to reconstruct the recorded retardance pattern.