KEYWORDS: Signal to noise ratio, Picosecond phenomena, Laser applications, Beam path, Signal detection, Signal attenuation, Plasma, Electrons, Physics, Mirrors
With the development of ultrafast laser technology, the peak energy of ultrashort pulses continues to increase. In addition to the demand for energy enhancement, many frontier physical experiments also put forward more stringent requirements for signal-to-noise ratio (SNR) of lasers. When the petawatt-level laser interacts with the target for physical experiments, the pre-pulses interact with the target in advance, affecting the density scale length of the pre-plasma and changing the spectral distribution of the generated electrons. In order to meet the requirements of pre-pulse control schem, we developed a SNR active control module based on isolated pre-pulses, which generates an isolated pre-pulse with adjustable time delay and relative intensity. The time delay of the isolated pre-pulse can be continuously adjusted in the range of -1300 ps to 0 ps. At the same time, by controlling the number of attenuators in the pre-pulse optical path, the relative intensity of the pre-pulse can be adjusted in the range of 10-8 to 10-3. We placed the module in front of the main amplification chain of the ShenguangⅡ ninth picosecond petawatt laser, adjusted the time delay and relative intensity of the pre-pulse, and measured the SNR at the terminal. The results verified the feasibility of the SNR active control scheme based on isolated pre-pulse.
Ultrashort pulse is important to exploring laser acceleration in many areas, such as fast ignition, advanced radiography capability. Petawatt laser should not only improve output energy on a single beam, but also combine multi-beams coherently. Diagnostics of temporal and phase synchronization is developed for coherent beam combination on a 10ps laser pulse. When two pulses are guided into the diagnostics, one goes through a temporal delay unit and a lens with a focal length 500mm, then arrives at detector unit, the other goes through a phase delay unit and the same lens, and then arrives at detector unit, too. First, temporal synchronization is adjusted by temporal delay unit and monitored by a cross-correlation generator in the detector unit. Second, phase synchronization is adjusted by phase delay unit and monitored by a far field interferogram in the detector unit. In our design, temporal resolution is 6.7fs in temporal synchronization, and phase resolution is 0.007π in phase synchronization. Experiment has proved that this diagnostics is useful to realize synchronization between two ultrashort pulses both in temporal and in spatial.
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