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Tham khảo tài liệu 'advances in solid-state lasers: development and applicationsduration and in the end limits part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 232 Advances in Solid-State Lasers Development and Applications duration and in the end limits the possibility to obtain rectangular-shaped amplified envelopes for macro-pulses longer than few ps or even few hundreds of ns depending on the amplifiers saturation level. In order to overcome amplification distortions it is necessary to inject in the amplifier chain a conveniently shaped macro-pulse with a temporal envelope designed to compensate saturation effects Butterworth et al. 1996 . This can be done by modulating the radio-frequency driving signal of the AOM pulse picker. An example of rectangular-shaped and custom-shaped macro-pulses is shown in Fig. 15. Fig. 15. Examples of two different deflected waveforms. a Rectangular-shaped macro-pulse envelope b Macro-pulse envelope reshaped for amplification distortions compensation. Note that the energy of the modulated envelope is reduced to 1 3. In the example reported here the master oscillator for pulse train amplification experiments is an high-frequency passively mode-locked Nd YVO4 oscillator Agnesi et al. 2005 . The 3-cm long V-folded resonator is pumped by a 1-W cw laser diode emitting at 808 nm yielding 20-mW average power 5-GHz repetition rate 6-ps long mode-locking pulses. The AOM pulse-picker yields typically 500-ns long macro-pulses containing approximately 2500 picosecond micro-pulses from the continuous train any macro-pulse length 50 ns can be chosen . The macro-pulses are amplified employing three Nd YVO4 slabs as shown in Fig. 16. Each 14 x 4 x 2 mm3 ữ-cut 1 doped vanadate slab is side-pumped by a pulsed 150-W peak power laser diode array. A couple of optical isolators are employed to prevent self-lasing and dangerous high-intensity back-injections in the direction of the master oscillator. The deflected laser beam emerging from the acousto-optic modulator needs to be carefully collimated to a vertical dimension optimally matched to the pumped layer while the path between the three amplification .
