Estimation of the far-field centre is carried out in beam auto-alignment. In this paper, the features of the far-field of a square beam are presented. Based on these features, a phase-only matched filter is designed, and the algorithm of centre estimation is developed. Using the simulated images with di?erent kinds of noise and the 40 test images that are taken in sequence, the accuracy of this algorithm is estimated. Results show that the error is no more than one pixel for simulated noise images with a 99% probability, and the stability is restricted within one pixel for test images. Using the improved algorithm, the consumed time is reduced to 0.049 s.

Inverse symmetric Dammann grating is a special grating, whose transition points are reflection symmetric about the midpoint with inverse phase offset in one period. It can produce even-numbered or oddnumbered array illumination when the phase modulations are p or a specific value. Numerical solutions optimized by the steepest-descent algorithm for binary phase and multilevel phases with splitting ratio from 1 × 4 to 1 × 14 are given. Fabrication of 1 × 6 array without the zero-order intensity and 1 × 7 array with the zero-order intensity are made from the same amplitude mask. A 6 × 6 output without the crossed zero-orders was achieved by crossing two one-dimensional 1 × 6 inverse symmetric Dammann gratings. This grating may have potential value for practical applications.

A novel method for obtaining a single shot multi-point high dynamic range pulse contrast measurement is presented. We use Dammann gratings to generate multiple beamlets by division of amplitude on ultra- short laser pulses. The analysis results show that this method can achieve high dynamic range in pulse contrast measurement on a single shot by using photomultiplier tube (PMT) detectors and the long work- ing distances to minimize cross talk between channels. Some distortion of pulse shape is also analyzed detailedly with the Dammann grating and its compensation grating, which may degrade the pulse contrast measurement in some degree by pulse stretching and spectrum clipping.

A general model for different apertures and flat-topped laser beams based on the multi-Gaussian function is developed. The general analytical expression for the propagation of a flat-topped beam through a general double-lens system with apertures is derived using the above model. Then, the propagation characteristics of the flat-topped beam through a spatial filter are investigated by using a simplified analytical expression. Based on the Fluence beam contrast and the Fill factor, the influences of a pinhole size on the propagation of the flat-topped multi-Gaussian beam (FMGB) through the spatial filter are illustrated. An analytical expression for the propagation of the FMGB through the spatial filter with a misaligned pinhole is presented, and the influences of the pinhole offset are evaluated.

Beam alignment is used to control the pointing, rotation, and position of a beam automatically. We give an overview of the beam alignment system for a four-pass amplifier system. The coupling relationships between dependent quantities and deviations thereof for parameters of key optical elements are analyzed using matrix optics techniques. The rotation characteristics of a near field are discussed. The characteristics of the four-pass adjustment in the cavity spatial filter are shown and the output characteristics are provided. Finally, we develop an adjustment procedure.参考文献原文>R. A. Zacharias, N. R. Beer, E. S. Bliss, S. C. Burkhart, S. J. Cohen, S. B. Sutton, R. L. Van Atta, S. E. Winters, J. T. Salmon, M. R. Latta, C. J. Stolz, D. C. Pigg, and T. J. Arnold, “Alignment and wavefront control systems of the national ignition facility,” Opt. Eng. 43, 2873–2884 (2004).

The generalized analytical expression for the propagation of flat-topped multi-Gaussian beams through a misaligned apertured ABCD optical system is derived. Using this analytical expression, the propagation characteristics of flat-topped multi-Gaussian beams through a spatial filter are investigated. The analytical formula of the electric field distribution in the focal plane is also derived for revealing the effects of the misalignment parameters clearly. It is found that different misalignment parameters have different influences on the electric field distributions of the beam focus spot and the output beam characteristics. The intensity distribution of the beam is mainly determined by the misalignment matrix element E, and the phase distribution is affected by the misalignment matrix elements G and E.