Influence of spatiotemporal coupling induced by an ultrashort laser pulse shaper on a focused beam profile

4f pulse shapers have been widely used to temporally manipulate femtosecond optical pulses by spectral filtering. When the temporal waveform is manipulated with a spatial light modulator consisting of segmented pixels, the spatial profile of the output beam also varies because of diffraction at the pixel array, which is known as a spatiotemporal coupling effect. This effect produces a complicated spatio-temporal profile near the focus of the ultrashort pulses, which may affect the interpretation of experimental results obtained with shaped ultrashort pulses. We investigate the spatial intensity distribution at the focus of temporally shaped pulses through ablation experiments. The three-dimensional space-time beam profile is also numerically calculated.     

椭圆柱透镜组准直半导体激光束的优化设计

采用光线矢量法设计了两个相互垂直的椭圆截面柱透镜组来准直半导体激光束。利用多目标优化中的加权和法进行优化计算,并提出自适应加权系数优化法。此方法能根据计算结果自动调整加权系数,从而达到最佳的优化结果。计算结果表明,该准直系统可达到45μrad左右的发散角,远远优于其它截面柱透镜组（毫弧度数量级）的准直效果。同时两柱透镜间距取适当值,还可在远场形成圆形光宽。     

Small-signal-equivalent circuits for a semiconductor laser

Passive electrical circuits whose voltage and current equations are exactly equivalent to the small-signal rate equations of a semiconductor laser are derived to model an electrically modulated laser (verified to be the same as that given in the literature), an optically modulated laser (i.e., a laser used as an optical amplifier), and a multimode laser. These circuits offer a fast and efficient simulation tool with little computational complexity in which the small-signal assumption (i.e., small modulation range) is neither violated nor insufficient for the simulation.     

Optical investigations of short-lived processes using an electron beam pumped semiconductor laser

Translated from Izmeritel'naya Tekhnika, No. 6, pp. 22–23, June, 1994.     

Mode hopping in a side-mode-injected semiconductor laser

Abstract

We report what appear to be the first experimental observations of mode hopping in a semiconductor laser under intermodal (side-mode) injection. The mode hopping is dependent on the frequency detuning and the launched probe power.     

Rational design of a diffractive homogenizer for a laser beam

The problem of designing a diffractive optical element (DOE) that produces a uniform-intensity beam from a spatially variable source is considered. Under the thin-lens approximation, the DOE is fully characterized by a phase function. Fresnel approximation is used to simplify the relationship between the input amplitude, the phase function, and the image intensity. The case where the light source has partial coherence is considered. A simple design procedure based on a lenslet array is proposed. It is shown that under certain physical assumptions, this `engineering' solution leads to an effective design capable of producing a uniform intensity from a time-varying, non-uniform source.     

Full characterization of a high-power semiconductor disk laser beam with simultaneous capture of optimally sized focus and farfield

We report on a beam characterization method that is based on the simultaneous measurement of the focus field and the farfield, thus avoiding problems with beam fluctuations during the measurement. By using reflections from both sides of a planoconvex lens, the method implements two branches of an optical system working simultaneously. Also, by letting the planoconvex lens be antireflection treated, and by allowing for both of the reflected fields to fill large and approximately equal areas on a camera detector array, the method significantly lowers the intensity onto the detector array, thus minimizing the need for additional disturbing attenuation filters to avoid camera saturation. In the numerical retrieval of the phase distribution, based on the measured intensity distributions of the focus and farfield, iterative propagation between the two branches is performed. The phase retrieval uses the two-step algorithm for the numerical field propagation conveniently providing an arbitrary choice of sampling distance in each plane.     

Bottle beam from a bare laser for single-beam trapping

We demonstrate that a laser beam converging from a specific transverse mode is a bottle beam, as described in J. Opt. Soc. Am. B 20, 1220 (2003). To our knowledge, this is the first time that a bottle beam has been generated directly from a laser. By calculating the radiation forces on a dielectric Rayleigh sphere in the bottle beam, we show that the single beam can trap high-refractive-index particles at the multiple axial sites of intensity maxima, and it can confine low-index particles on a transverse plane within the bottle regions. Such a novel laser beam may have other applications.     

Polarization switching time for semiconductor laser radiation

Expressions are derived for the polarization switching time for semiconductor laser radiation. These expressions can be used to assess the influence of the laser diode parameters on the polarization switching time of the output radiation. The results of an analysis of these expressions show that the main parameters influencing the polarization switching of the output radiation from a semiconductor laser are the nonlinear gains. Pis’ma Zh. Tekh. Fiz. 23, 87–95 (May 12, 1997)     

Resonator fiber optic gyro employing a semiconductor laser

Resonator fiber optic gyro (RFOG) based on the Sagnac effect has the potential to achieve the inertial navigation system requirement with a short sensing coil. Semiconductor laser is one of the key elements for integration and miniaturization of the RFOG. In this paper, an RFOG employing a semiconductor laser is demonstrated. The model of the laser frequency noise induced error in the RFOG is described. To attenuate the laser frequency noise induced error, active frequency stabilization is applied. An online laser frequency noise observation is built, as a powerful optimum criterion for the loop parameters. Moreover, the laser frequency noise observation method is developed as a new measurement tool. With a fast digital proportional integrator based on a single field programmable gate array applied in the active stabilization loop, the laser frequency noise is reduced to 0.021 Hz (1σ). It is equivalent to a rotation rate of 0.07°/h, and close to the shot noise limit for the RFOG. As a result, a bias stability of open-loop gyro output is 9.5°/h (1σ) for the integration time 10 s in an hour observed in the RFOG. To the best of our knowledge, this result is the best long-term stability using the miniature semiconductor laser.     

Low-loss deflection prism for a laser beam with Brewster angle

A low-loss deflection prism for a laser beam is proposed, and its various characteristics such as beam quality, transmittance, deflection angle, and polarization state are presented. The prism having a trapezoidal form is made from BK7 glass and is designed for a He-Ne laser beam. When a p-polarized beam is incident on the slant surface of the prism at the Brewster angle, the totally reflected and transmitted beam is deflected by 90 degrees, and the measured transmittance is nearly 98%. The theoretical transmittances of the proposed prism are compared with those of a Pellin-Broca prism.     

Unipolar semiconductor laser for the terahertz frequency range

In this paper a new design is proposed for a unipolar semiconductor laser with longitudinal transport of electrons and a stepped variation in the thickness of quantum wells, in which population inversion is obtained, and as a result the electrons of the first subband in the narrow part of the well, with injection into the wide part, preferentially populate its second subband. Deceased Pis’ma Zh. Tekh. Fiz. 23, 90–94 (February 26, 1997)     

Geometric bowing effect of a laser beam

We describe and analyze an effect that is observed when a laser beam is projected toward the sky at a shallow angle. An observer standing below the beam sees that the beam is bending and propagating toward the ground instead of propagating upward.     

Near-threshold spectral modes and coherence of a semiconductor laser and a diode-pumped neodymium laser

The spectral, coherence, and polarization characteristics of a semiconductor injection laser and a diode-pumped Nd laser operating on second harmonic have been thoroughly traced for the first time during the transition via the generation threshold and on the passage from one mode to another with increasing pump current. It is shown that the behavior of the intensity, coherence, and noise near the threshold is indicative of the possible analogy between laser generation and phase transitions of the first or second order.