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We present a beam combination technique to improve the brightness of diode lasers based on both spectral beam combination and polarization beam combination. We use eight diode laser arrays (DLAs) and two diffraction gratings to construct two independent external cavities by using spectral beam combination, and then combine the outputs of these two cavities by using polarization beam combination. The experiment shows that the total output power can be as high as 310.2 W by using this technique with eight DLAs, which are commercial standard cm-bars, each producing ∼60 W of output power. The beam qualities of the combined beam are M2 = 13.55 and 10.27 in the slow and fast axis, respectively. The brightness of the combined output is as high as 252 MW·cm−2·sr−1.

This work aims to characterize the retardation of birefringent samples such as wave-plates and birefringent wedges where the principal axis is uniform over the sample zone. The in-line procedure described and implemented for the purpose uses four frames of intensity data that are digitally recorded and combined to characterize the sample in terms of its retardance from 0 to 2π as also to uniquely identify the direction of its fast axis. Simulated and experimental results presented are in good agreement with the proposed theory.

A blind-angle calibration method is introduced for self-spectral calibration of a compound zero-order waveplate. By rotating the waveplate at blind detection angles, the wavelength-dependent retardance and the orientation of the effective fast axis can be determined through iterative least-squares calculations of the spectra measured by a multi-channel spectrometer. Excellent agreement between the experimental values and the theoretical values is achieved, indicating that the new method can be used as a reliable way to calibrate compound zero-order wave plates. Using the new method, there is no need to rotate the waveplate at specific detection angles. A high-precision waveplate holder or complex adjustment procedure is not required.

Teleseismic earthquakes data recorded by 8 broadband digital seismic stations deployed in the Kumaun-Garhwal and adjoining area of NW Himalaya are analyzed to investigate the seismic anisotropy in the upper mantle. Shear-wave splitting parameters (ɸ and ∂t) derived from the analysis of core-refracted SKS/SKKS phases provide first hand information about seismic anisotropy and deformation in the upper mantle beneath the region. A total, 209 good measurements of seismic anisotropy have been obtained from the two years of collected high-quality teleseismic data in the study region. The analysis shows considerable strength of anisotropy (delay time(∂t) 0.6–2.8 s) with average ENE–WSW-oriented fast polarization orientation at most of the stations while other one either along with the absolute plate motion (APM) of the Indian plate or parallel to strike of the Himalayan mountain belt. The Fast axis direction observed at stations close to between the MBT and MCT aligns parallel to the strike of local geological faults and orthogonal to absolute plate motion (APM) direction of the Indian plate. The large variation in the splitting strength and fast polarization trends around the Kumaun-Gharwal and adjacent in NW Himalaya have invoked both lithospheric and asthenospheric anisotropy.

It is vitally important to numerically simulate the output power spatial distribution of diode laser stacks when they are used in beam shaping and pumping for other lasers. Here, we propose a numerical simulation technique by considering the discreteness of the propagation angles of individual emitters in diode laser stacks in the fast axis. Using this proposed simulation technique, we calculated the spatial distribution of the outputs of the four diode laser stacks and the total output power of the 3000 W fiber-coupled diode laser. The calculated results agree well with the experimentally measured values. Therefore, when designing a laser, this is a useful way to select diode laser stacks based on specifications.

The smile effect is inevitable during the packaging process of diode laser stacks. Position errors and direction errors are used to describe the smile effect. A theoretical smile model has been built, and a beam propagation model of the external cavity has been further proposed based on the smile model. Beam properties such as spectrum, intensity distribution, and beam quality of combined beams have been simulated and discussed. The results show that position errors have little impact on intensity distribution of combined beams but make spectrum slightly broadened. Direction errors make intensity generate side lobes and degrade beam quality significantly. Compared with position errors, direction errors in both slow axis and fast axis have more detrimental effect on output beams. Thus, it is more important to control angle deflection of beams than positions of emitters during the manufacturing process of DLSs.

This study presents an innovative dual-screen projection system (DSPS) based on a balance-type dual micromirror structure. This design solves the problem of existing micro-projectors only being able to display a single small picture. The proposed balance-type dual micromirror structure was fabricated using a signal-mask LIGA-like technology with piezoelectric actuation to form a DSPS. The DSPS consists of dual micromirrors as a fast axis, an eccentric structure as a slow axis, and slender piezoelectric actuators. A Y-shaped beam connects two micromirrors to achieve a balance-type dual micromirror structure in which the synchronous scanning of both micromirrors form motion behaviors that approximate to a balance. Experimental results show that the driving frequencies of the slow axis and the fast axis are 3.75 kHz and 11.7 kHz, respectively. The mechanical deflection angles of the slow axis and the fast axis are capable of achieving 2° and 9.6°, respectively, with an applied voltage of 30 V pp . The device can simultaneously display DSPS scanning pictures in a Lissajous scanning manner as dual square patterns, dual heart patterns, a pair of rectangular patterns, and a pair of elliptical patterns. The proposed device achieves the simultaneous display of two patterns with a projection resolution of 320 × 240. Therefore, this DSPS is applicable in scenarios that require dual identical projection screens, such as head-up and head-mounted displays, and when two identical images are needed for both the left and right eyes.

Intra-cavity phase anisotropy causes each laser longitudinal mode to split into two orthogonally polarized frequencies. When the frequency difference generated by small anisotropy is about 40 MHz or less, only one frequency of the splitting mode oscillates while the other is always in lock-in state due to strong mode competition. In that case the longitudinal mode spacing deviates from its original value. And the spacing of two adjacent longitudinal modes shows differential variations depending on direction of cavity length tuning and mode polarization. In this paper, the relationship between spacing variation and small intra-cavity anisotropy is demonstrated experimentally and theoretically. The equivalent fast axis of anisotropy is determined additionally by its correlation with laser intensity tuning of the two orthogonally polarized components. The novel measurement method is successfully tested in several applications.

Shear-wave splitting results are presented for the broad-band stations of the Romanian seismic network. For stations BUC1 and CRAR (located in Moesian Platform), IAS (in East-European Platform), TIRR and CVD (in Central Dobrudja–Black Sea microplate), TIM and DRGR (in Dacia-Tisza plate, including Apuseni Mts.), BURAR, BZS and GZR (in, or very close to the Carpathian Arc), the fast directions (φ) are around 135°. The mean delay values (δt) of the slow wave are slightly greater for the stations placed in platform areas (δt ~ 1.5 s) than for the stations situated in the (proximity) of Carpathians (δt ~ 1.2 s). For the MLR station located in the South-Western part of Vrancea area, at the Carpathian Bend, the fast direction is 48°, similar to VOIR station (located in Southern Carpathians, 70 km West of MLR). At VRI and PLOR, located in the North-Eastern part of Vrancea, the fast axis is oriented approximately on North–South direction, with a possible dependence of the splitting parameters with back azimuth. At least for some stations, the splitting results are not consistent with vertical coherent lithospheric anisotropy.

Direct drives and ball screw drives are the most promising feed drive systems for high speed machining. For optimum performance the drives and the feedback control system must be exploited to their physical limits. Thus, input saturation of the feed drives becomes a very important design parameter. A new design method based on a nonlinear stability analysis has been developed to take this into account. The improvements regarding machine tool design and the selection of suitable drive systems made possible by this method are shown and discussed.