Laguerre-Gaussian beams are solutions of the paraxial wave equation and carry orbital angular momentum, which can be transferred to trapped particles. Orbital angular momentum of light beams can be better understood by considering angular momentum flux. Phase singularity and orbital angular momentum are different concepts and should be distinguished.

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The historical and present research work of our group in laser beam on optical beam quality is reviewed in this paper. An invented intracavity CO₂ laser with M_e² < 1 is presented, and the optical beam quality of beam from subwavelength aperture is investigated. Equivalent optical beam quality of quantum well laser beam is demonstrated. The progress will promote scientific development in correlative fields, also bring potential applications for optical industry.

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This paper reviews a method of the irradiance profile smoothing on the high-power laser system. In the multi-beam laser irradiation geometry, the coherence control of laser beam is necessary to reduce the irradiation nonuniformity in the wide spatial frequency region. The laser beam with spatio-temporal phase modulation (STPM) provides a unique feature that it is nearly coherent in propagating amplifiers through a frequency converter, while it becomes partially coherent in a focal spot. Such a unique beam can be generated by a multi-stage optical system consisting of series of phase modulators and diffraction gratings.

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The recent progresses in the generation and transformation of partially coherent beams are reviewed. The analytical propagation formulae for the cross-spectral density of the partially coherent anisotropic Gaussian-Schell model (GSM) beams through ABCD optical systems are provided. These formulae provide a powerful tool for analyzing and calculating the transformation of partially coherent GSM beams, such as focusing, spectral shift, and fractional Fourier transform etc. A new kind of resonator with spatial-temporal phase modulation is proposed and analyzed. This kind of resonator can produce partially coherent flattop-alike beams under properly chosen parameters. The changes of the coherence of light in optical resonator are investigated. The generation of partially coherent laser beam directly from spatial-temporal phase modulated optical resonator is investigated experimentally. The results show that intra-cavity phase modulation is an effective way to generate partially coherent beams. The two-slit interference experiment confirms that the output beam is partially coherent.

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A computer generated hologram (CGH) is a useful tool for various optical applications, such as beam multiplexing, patterning, beam homogenizer, etc. The precise technologies are important issue for the fabrication of CGH, and the algorithm is more essential for designing it. I discuss the detailed consideration on the CGH design which is required to reconstruct a complex image. I also introduce efficient methods to design a hologram which creates a desired pattern at the Fresnel region and on a spherical surface.

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Based on the optical rotatory effect of liquid crystal, we have fabricated a compact and efficient optical device for control of space-variant polarization. Using this device we generated vector beams that have axially-symmetric polarization from a linearly-polarized beam. In this paper, we describe the measured characteristics of polarization distributions and beam patterns in the near- and far-field regions, comparing these with theoretical predictions.

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An important technique required in the application of laser systems to fusion is the ability to generate high energy to satisfy the conditions for self-ignition and to improve the uniformity of laser irradiation. To achieve this result, it is necessary to introduce a kinoform phase plate (KPP) that is able to produce an optimum envelope profile. However, a KPP is sensitive to beam aberrations caused by the nonlinear refractive index in optical components. To overcome this problem we have developed a multi-segmented KPP and demonstrated its usefulness and strength against phase distortions by numerical simulations.

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A high-repetition-rate electron-beam-pumped KrF laser amplifier under development at AIST is described. The outline of the laser system developed for long-time operations under repetitive pumping conditions is introduced and test results measured at a repetition rate of 1 Hz are presented. The laser system and experimental results are evaluated in view of future laser drivers of inertial fusion energy.

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This work presents a theoretical explanation and experimental evidence of pulses- intensity displacement and pulse- broadening profiles of a Q-switched and mode-locked Nd:YAG laser- pumped distributed feedback dye laser (DFDL). Experimental results followed by a theoretical simulation indicate that DFDL pulses peaked noticeably later than their corresponding Nd:YAG laser pulses. The DFDL pulse corresponding to the peak- power pump laser pulse occurs few pulses later than the expected location. The observed and simulated delays were found to depend upon the inter-pulse periods of the pumping Q-switched and mode-locked laser. We report the theoretical basis for the influence of temperature grating relaxation times on the dye laser's pulse characteristics, and apply the transient grating technique to measure the refractive index of a lasing dye solution. Results indicate that the thermal effects of preceding pulses integrate the gain for receding pulses. These results provide a good understanding of temperature grating relaxation times and their impact on the lasing characteristics of DFDL.

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