Femtosecond Ultra-Intensity PW Laser Facility
About Femtosecond Ultra-Intensity LaserBased on chirped pulse amplification(CPA) technology, femtosecond ultra-intense laser can reach ultra-high peak power and ultra-intense focused intensity. As a research focus with high innovation potential, it has been widely applied in frontier of physics researches, such as particle acceleration, laboratory astrophysics and photonuclear reaction. Figure 1 is schematic of CPA technology. It contains four parts: mode-locking oscillator that produces femtosecond seed pulses, stretcher that stretches the seed pulses, amplifier that amplifies energy of the seed and compressor that offers dispersion with opposite sign as the stretcher does. Figure 2 illustrates development of peak power that lasers can reach and researches people can do since CPA technology was adopted (from a report of G. Mourou). ELI is an under-construction femtosecond laser facility with the highest peak power in the world. 
Fig.1. Schematic of CPA technology, Fig.2. Development history of peak power that lasers can reach Development of "Xtreme Light (XL)" series of intense femtosecond lasersBecause of the important applications of femtosecond ultra-intense lasers, we started researches of femtosecond ultra-intense laser technology in 1997. Based on our experience in this area, we designed femtosecond Ti:sapphire oscillators, adopted innovative technology such as spectrum shaping, self-focusing amplification and parasitic oscillation suppression and realized laser pulse with peak power of 1TW (1TW=1012W), 20TW and 350TW successively (“XL” series facility). It benefited researches such as laser plasma tunneling and generation of hot electrons. 
Fig.3. 1.16 PW XL-III femtosecond ultra-intense Ti:sapphire laser facility Recently, pulse amplification with high contrast ratio has been a challenge in such researches. We proposed a combination of femtosecond parametric amplification and double chirped pulse amplification. Adopting this method, we enhanced pulse contrast ratio of pre-amplifier and realized generation of 1.16PW (1PW=1015W) femtosecond pulses with contrast ratio of 10-10. We solved the problem of improving pulse contrast ratio and created the highest peak power record then. Figure 4 is layout of the facility. This facility has been applied in research of large size cluster electrons acceleration and femtosecond laser driven proton acceleration and is available to researchers at home and abroad. 
Fig.4. Scheme of high-contrast parametric and double chirped pulse amplification |
Sub-10fs Ti: sapphire oscillatorAdopting all-chirped-mirror dispersion compensation design, we produced mode-locking Ti:sapphire which can directly output pulses below 10fs and transferred it into products. It can offer seed for pulse amplification. By pre-compensating gain narrowing effect of pulse amplification, it can support ultra short pulse output. The oscillator can also be applied to optical frequency comb.  Contrast lifting and stretcher unitsBy adopting femtosecond pulse parametric amplification, after two amplification stages based on BBO, we improved the main pulse contrast ratio to 10-11.  
Left: Amplification setup; Right: Stretcher setup(top) and measurement of stretched pulse(bottom). Energy AmplifierBy suppressing parasitic oscillation, after final amplification stage with pump pulse energy of 105 J, we realized laser pulse output with energy of 48.6 J, 20 minute per shot.  CPA Compressor Specifications: Energy:32.3J (105J pump)   |
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