Array element tiling is one of the key technologies for the coherent beam combination in a high-power laser facility. In this paper, we proposed a method of the array element auto-tiling based on capacitive displacement sensor. The method was verified on a double-pass tiled-grating compressor in XG-III laser facility. The research showed that the method is an effective way to control the misalignment errors automatically, with high precision and long-term stability.
In a high-energy chirped-pulse-amplified laser system, grating tiling technology provides an effective means to increase the aperture of the gratings and to scale the energy and irradiance of short-pulse lasers. The difficulties lie in controlling tiling errors accurately between the sub-gratings and keeping long time stability. In this paper, a two-pass full-tiled grating-compressor (TGC) with real- time control unit is developed for the first time. The far-field distributions of the 0<sup>th </sup>order and -1 <sup>st</sup> order diffracted beams of the two pairs of tiled gratings are monitored by the same CCD system, with the main laser chain being not disturbed. In this way, we realize online real-time control of tiling errors. Through a method of locking the far-field image to compensating the temporal drift, we can realize the automation of the assembly. The TGC has successfully applied in the multi-function XGIII laser facility, and focusing focal spot and output pulse width are obtained.
Development of a phased-array-grating compressor is a crucial issue for high-energy ultrashort pulse petawatt lasers. To achieve tiled array gratings and increase stability of tiled-grating frames, a new tiled grating frame is designed. In the tiled-grating frame, an integrated support structure is adopted to increase the natural frequency of the tiled-grating and the flexible hinges are used rather than the spring to increase the joint stiffness between the grating and the support frame. The experiment indicates that stability of the tiled-grating can be maintained for more than 1 h and the standard deviation of the tiling error is 35.7 nm, which satisfies the design requirement.
The stability of phased-array optics is a crucial issue for far-field focal-spot quality. The tiled approach of phasing optical elements is a widely used technique. Here it is adopted to maintain the long-time stability of a tiled system by a proportional-integral-differential (PID) algorithm. Experimental data is taken with 2×1 tiled-flat square mirrors driven by 3-axis piezoelectric actuators. The feedback frequency is over 80 Hz and the displacement error is below 4 nm. The optical measurement results show that the state-locked operation is continuously maintained for hour-long periods in PID control mode.
To meet the needs of some physical experiments for high energy short pulse laser, TGC (tiled gratings compressor)
technology and beams-combination technology are required. Progress of TGC and beams-combination at CAEP is
introduced. On TGC technology, interference pattern and far field distribution is used to initially eliminate the tiling
error, and displacement sensor is used as feedback to maintain the posture of the sub-gratings. As for beams-combination
a preliminary method of feedback control in subsections is proposed and will be expected to be used in an integrated test-bed.