Far-field intensity distribution of a beam generated by a resonator with a phase-unifying mirror

The far-field intensity distribution (FFID) of a beam generated by a phase-unifying mirror resonator was investigated based on scalar diffraction theory. Attention was paid to the parameters, such as obscuration ratio and reflectivity of the phase-unifying mirror, that determine the FFID. All analyses were limited to the TEM00 fundamental mode.     

Wave-optical evaluation of interference fringes and wavefront phase in a hard-x-ray beam totally reflected by mirror optics

The intensity flatness and wavefront shape in a coherent hard-x-ray beam totally reflected by flat mirrors that have surface bumps modeled by Gaussian functions were investigated by use of a wave-optical simulation code. Simulated results revealed the necessity for peak-to-valley height accuracy of better than 1 nm at a lateral resolution near 0.1 mm to remove high-contrast interference fringes and appreciable wavefront phase errors. Three mirrors that had different surface qualities were tested at the 1 km-long beam line at the SPring-8/Japan Synchrotron Radiation Research Institute. Interference fringes faded when the surface figure was corrected below the subnanometer level to a spatial resolution close to 0.1 mm, as indicated by the simulated results.     

Polarization distribution in a Gaussian beam reflected from a resonant medium

It is shown that the distribution of parameters of light polarization in the cross section of a Gaussian beam reflected from a resonant medium is substantially inhomogeneous. This inhomogeneity is especially pronounced in the wavelength range of light absorption by metals.     

A new integral characteristic of the degree of difference of the spatial distribution of a laser beam from a Gaussian distribution

A new integral characteristic that makes it possible to rapidly estimate the degree of difference of a measured distribution of a laser beam in a cross-section from a Gaussian distribution is proposed. A high degree of sensitivity of the method to different types of distributions is demonstrated.     

Optimum control of the laser beam intensity profile with a deformable mirror

A new deformable mirror control system is developed. This system consists of a deformable mirror, a CCD camera, an image processor, a computer, and actuator drive power supplies. A genetic algorithm is adopted as a control algorithm to obtain an optimum surface profile of the deformable mirror. A circular cross-sectional Gaussian beam was transformed into a beam with a rectangular contour using this system. Although the transfer function of this system is complicated and unknown, this system can be used to obtain the optimum beam profile within the achievable limits of a deformable mirror.     

The effect of reflected beam electrons on the distribution of energy deposited in a target

When a solid target is irradiated by an electron beam generated in a direct-action diode and transported to the target in a magnetic guide field, an important role belongs to electrons returned to the target as a result of multiple reflections from the target and the accelerating field region. The energy spectrum of electrons incident on the target and the deposited energy depth profile the target were studied by the Monte-Carlo method. An algorithm for calculating these characteristics was developed, based upon the method of separating the total electron flux into components with respect to the multiplicity of crossing of the target-vacuum interface.     

Wavefront distortion of the reflected and diffracted beams produced by the thermoelastic deformation of a diffraction grating heated by a Gaussian laser beam

It may be advantageous in advanced gravitational-wave detectors to replace conventional beam splitters and Fabry-Perot input mirrors with diffractive elements. In each of these applications, the wavefront distortions produced by the absorption and subsequent heating of the grating can limit the maximum useful optical power. We present data on the wavefront distortions induced in a laser probe beam for both the reflected and diffracted beams from a grating that is heated by a Gaussian laser beam and compare these results to a simple theory of the wavefront distortions induced by thermoelastic deformations.     

Multifractality of laser beam spatial intensity in a turbulent medium

We present the results of a laser beam passing through a turbulent medium. First we measure the geometric parameters and the spatial coherence of the beam as a function of wind velocities. A multifractal detrended fluctuation analysis algorithm is applied to determine the multifractal scaling behavior of the intensity patterns. The measurements are fitted with models used in the analysis of river runoff records. We show the surprising result that the multifractality decreases when the spatial coherence of the laser is decreased. Universal scaling properties could be applied to the spatial characterization of a laser propagating in a turbulent medium or random medium.     

Distortion in a 2-D scan pattern generated by combining a plane mirror and a regular polygon scanner

The distortion in a 2-D scan pattern generated by a system of a plane mirror and a regular polygon scanner was investigated using the matrix formulation of reflection by plane mirrors. A particular configuration involving the two scan elements was identified which does not introduce any distortion in its 2-D scan pattern.     

Scanning multichannel analyzer of the spatial distribution of the radiation power of a technological CO2 laser

Translated from Izmeritel'naya Tekhnika, No. 2, pp. 14–15, February, 1989.     

离子束增强沉积VO2多晶薄膜的相变模拟

用多晶薄膜晶粒—晶界两相结构模型,考虑晶格畸变和载流子对晶界势垒区的隧穿机制,在10～100℃范围内,模拟了离子束增强沉积(IBED)VO2多晶薄膜的相变。模拟结果显示,由于晶粒中间隙位置氩的存在,使VO2晶格畸变,导致了薄膜中部分晶粒的相交温度降低,使IBED VO2薄膜在48℃开始由半导体相向金属相转变。     

Gaussian-reflectivity mirror resonator for a high-power transverse-flow CO2 laser

A Gaussian-reflectivity mirror resonator is proposed to achieve high-quality laser beams. To analyze the laser fields in a Gaussian-reflectivity mirror resonator, the diffraction integral equations of a Gaussian-reflectivity mirror resonator are converted to the finite-sum matrix equations. Consequently, according to the Fox-Li laser self-reproducing principle, we describe the mode fields and their losses in the proposed resonator as eigenvectors and eigenvalues of a transfer matrix. The conclusion can be drawn from the numerical results that, if a Gaussian-reflectivity mirror is adopted for a plano-concave resonator, a fundamental mode can easily be obtained from a transverse-flow CO2 laser and high-quality laser beams can be expected.     

Spatial shifts of the conjugate beam generated by a nondegenerate photorefractive phase-conjugate mirror

We demonstrate that the phase conjugation of a beam during nondegenerate four-wave mixing is accompanied by a spatial shift relative to the degenerate conjugate-beam location. Experiments with a photorefractive phase-conjugate mirror reveal that the phase-conjugate beam shifts have a nonmonotonic dependence on the probe's detuning frequency and comprise both lateral displacements of up to 218 mum and angular tilts of up to 34 arc sec. An approximate theory based on spatial dispersion coefficients is in partial agreement with the experimental results.     

Generation of flattened Gaussian beam profiles in a Nd:YAG laser with a Gaussian mirror resonator

We report the experimental generation of a family of flattened Gaussian beams with bell-shaped, flattened, and annular intensity profiles in an electro-optically Q-switched Nd:YAG laser with a variable reflectivity mirror of a Gaussian reflectivity profile as an output coupler. The laser beams of different profiles were generated by modifying the resonator magnification. The propagation characteristics of the experimentally generated flat Gaussian beams were found to be in agreement with theory. To the best of our knowledge this is the first time such a family of flattened Gaussian beams is experimentally generated intracavity using a single variable reflectivity mirror.     

Propagation properties of a hard-edged diffracted beam generated by a Gaussian mirror resonator

Based on the scalar diffraction theory, the propagation and focusing properties of a hard-edged diffracted beam generated by a Gaussian mirror resonator were investigated. Explicit expressions for the field distribution of the truncated beam that propagates through a paraxial optical ABCD system were derived in detail. Numerical examples are given to illustrate our analytical results.     

Real-time measurements of spatial velocity distribution with a laser Doppler imaging system

A new laser Doppler imaging system with a TV camera has been constructed, which brightly displays 1-D velocity distribution on a monitor. Some characteristics of this system have been experimentally investigated from measurements of simple velocity distribution on a constantly rotating ground glass disk. From an adaptation to fluid flow, it has been shown that the measurements of spatial velocity distribution can be achieved in real time.