Yoshiyuki Ohtake

Generation of high-quality higher-order Laguerre-Gaussian beams using liquid-crystal-on-silicon spatial light modulators

We report on the high-quality holographic generation of higher-order Laguerre-Gaussian (LG) beams using a liquid-crystal-on-silicon spatial light modulator. The effects of the input beam pattern on the output LG beam quality are investigated in detail through theoretical discussions and experiments. Correlation analyses between observed beam patterns and theoretical mode profiles reveal that higher beam quality is achieved for output LG beams generated from a top-hat input beam than from a Gaussian input beam.

Mode purities of Laguerre-Gaussian beams generated via complex-amplitude modulation using phase-only spatial light modulators.

We investigate output mode purities of Laguerre-Gaussian (LG) beams generated from four typical simultaneous amplitude and phase modulation methods with phase-only spatial light modulators (SLMs). Numerical simulations supposing the practical SLM, i.e., stepwise phase modulation with a pixelated device, predict an output mode purity of beyond 0.969 for the LG beams of less than radially and azimuthally fifth order. Experimental results of generating LG beams are also shown to demonstrate the effects of the simultaneous phase and amplitude modulation.

Universal generation of higher-order multiringed Laguerre-Gaussian beams by using a spatial light modulator.

Laguerre-Gaussian (LG) beams of various higher-order radial modes are generated by using a reflective phase-only liquid crystal on silicon (LCOS) spatial light modulator (SLM). Because of the LCOS SLMs phase-modulation characteristic of a wide spatial bandwidth, a phase modulation scheme effectively generates higher-order LG beams of up to the fifth-order radial mode. We also perform correlation analyses between the observed and the theoretical two-dimensional mode profiles to universally obtain correlation coefficients of more than 0.946, which suggest mode generations of high quality.

An experiment to throw more light on light

Abstract We performed an experiment which was proposed by Ghose, Home and Agarwal showing both classical wave-like and particle-like behaviors of single photon states of light in a single experiment, in conformity with quantum optics.

High-quality generation of a multispot pattern using a spatial light modulator with adaptive feedback

We propose and demonstrate high-quality generation of a uniform multispot pattern (MSP) by using a spatial light modulator with adaptive feedback. The method iteratively updates a computer generated hologram (CGH) using correction coefficients to improve the intensity distribution of the generated MSP in the optical system. Thanks to a simple method of determining the correction coefficients, the computational cost for optimizing the CGH is low, while maintaining high uniformity of the generated MSP. We demonstrate the generation of a 28×28 square-aligned MSP with high uniformity. Additionally, the proposed method could generate an MSP with a gradually varying intensity profile, as well as a uniform MSP consisting of more than 1000 spots arranged in an arbitrary pattern.

Effects of dielectric planar interface on tight focusing coherent beam: direct comparison between observations and vectorial calculation of lateral focal patterns

We report direct observation of lateral focal patterns through an acrylic material to investigate the effects of aberrations caused by a planar dielectric interface. Numerical analyses based on vectorial Huygens-Fresnel diffraction theory were also performed to examine the behavior of three-dimensional point spread functions. Experimental and numerical results showed agreement of the behavior of the peak position in the focal patterns with changes in the interface position. Our approach has the potential to predict the effects of aberrations in confocal laser scanning microscopes and super-resolution applications.

Sidelobe reduction of tightly focused radially higher-order Laguerre-Gaussian beams using annular masks

We report the reduction of sidelobes in tight focusing patterns of radially higher-order Laguerre-Gaussian (LG) beams with nonhelical phase structures. Numerical calculations based on the vectorial Debye theory reveal that a class of annular masks reduces sidelobes in the tight focusing patterns only for radially even-order LG beams. The present scheme produces small focal spots beyond the diffraction limit suitable for application to scanning microscopy, laser fine processing, etc.

Shaping tight-focusing patterns of linearly polarized beams through elliptic apertures

We propose elliptic deformation of apertures for shaping focusing patterns of tightly focused linearly polarized beams. Numerical integration of the vectorial Rayleigh-Sommerfeld diffraction formula predicts the formation of symmetric focusing patterns by shrinking the aperture shape in the direction perpendicular to the polarization of the beams. The elliptic deformation is also applied to a focused linearly polarized beam through an annular aperture to demonstrate the formation of smaller symmetric focal spot than that through a simple oval aperture.

High-quality generation of higher-order Laguerre-Gaussian beams using liquid crystal on silicon spatial light modulator

We report holographic generation of higher-order Laguerre-Gaussian (LG) beams using a liquid crystal on silicon spatial light modulator (LCOS-SLM) device. In our experimental set-up, a flat-top light beam was projected on the LCOS-SLM to generate LG beams of various mode indices without changes of the optical system. Additionally, the size of the holographic phase pattern was optimized for each beam to maximize the mode purity of the obtained beam. Holographic generation of LG beams is easily influenced by a distortion of the optical system and deviation of the phase setting from an ideal one. Nevertheless, we obtained high-quality LG beams with an additional phase pattern on the LCOS-SLM for canceling the distortion of the optical system and with calibration of the phase control voltage for precise expression of the phase patterns. Numerical analyses are also performed for two-dimensional beam profiles to verify the quality of the obtained beams. Through fitting the obtained profiles to theoretical ones, we calculate the correlation coefficients R between the observed and fitted profiles to find that R > 0.95 for all beams and that the correlation coefficients behave similarly to the theoretically estimated mode purities, facts indicating that the quality of the obtained LG beams is close to the theoretical limit in our experiments.

A Test of the Complementarity Principle in Single-Photon States of Light

The complementarity principle, the way usually accepted was originally proposed by Niels Bohr. First, he postulated that one could perceive the quantum world only through classical measurements. But the classical measurements of a pair of physical quantities (or “observables”) such as position and momentum could only be made in a mutually exclusive manner. Such a pair he called complementary. Thus he made the complementarity principle. He even extended this principle to a pair of concepts like the wave and particle pictures of light, which were confronted with each other in classical physics. Namely, if one is to detect light as a wave, he must abandon the possibility of detecting its particle nature, or vice versa. This sounds similar to the uncertainty principle of Werner Heisenberg, which says that two mutually conjugate observables cannot possibly be detected simultaneously beyond a certain level of inaccuracy. The product of uncertainties of the conjugate observables cannot be smaller than a certain universal constant called Planck’s constant ħ. However, Bohr’s principle is a wider and more vague concept. The wave and particle pictures of light are not such a conjugate pair, yet Bohr tried to establish that they were not possibly detected in a single experiment because of the complementarity principle. Was he right?