Spectral-broadness simulation of a Littman/Metcalf external cavity diode laser with a dynamic-curvature end mirror.

We propose a dynamic-spectral-broadness Littman/Metcalf external cavity diode laser, which replaces the flat end mirror of the external cavity with a curved one with a tunable radius of curvature (RoC). The concept was verified via simulation; first, the frequency selectivity of the cavity was calculated for each RoC using Gaussian-beam optics combined with ray tracing, and second, laser oscillation and amplified spontaneous-emission (ASE) spectra were obtained using the transmission-line laser model. The simulation revealed a tuning range with spectral broadness: 250 kHz for single-mode operation, 1.2-47 GHz for multi-mode operation, and 50 GHz-3.9 THz for ASE.

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.

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.

Structure of optical singularities in coaxial superpositions of Laguerre-Gaussian modes.

We investigate optical singularities in coaxial superpositions of two Laguerre-Gaussian (LG) modes with a common beam waist from the viewpoints of a general formulation of phase structure, experimental generation of various superposition beams, and evaluation of the generated beams' fidelity. By applying a holographic phase-amplitude modulation scheme using a phase-modulation-type spatial light modulator, output fidelity beyond 0.960 was observed under several typical conditions. Additionally, an elliptic-type folded singularity, which provides a different class of phase structures from familiar helical singularities, was predicted and observed in a superposition involving two LG modes of both radially and azimuthally higher orders.

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.

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.

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.

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 SLM's 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.

Numerical method for coherent electron dynamics with position-dependent effective-mass distributions in semiconductor heterostructures.

We develop a numerical scheme for solving the time-dependent Kohn-Sham equation in semiconductor heterostructures. Based on the efficient and accurate method recently proposed by Watanabe and Tsukada [Phys. Rev. E 65, 036705 (2002)], an extension is made for treating effective-mass mismatch between different semiconductor materials. A demonstrative calculation shows that the energy of the quantum-well state is accurately conserved during the time-evolution calculation with the present method. Examples under the existence of Hartree and exchange-correlation interactions are also shown as demonstrations of nonlinear electron dynamics in quantum wells. The present method is particularly useful for analyzing nonlinear coherent charge oscillations in semiconductor quantum wells, taking into account many-body effects.