High-energy large-aperture titanium:sapphire chirp-pulsed amplification laser system

The chirp-pulsed amplification (CPA) technique involves stretching and compressing a laser pulse in the temporal domain before and after amplification.1 Since this technique was first proposed in 1985, it has been used to successfully solve the problem of how to achieve ultrashort laser pulse amplification.2 In addition, the development of mode-locking lasers—particularly the advent of the self-mode-lock titanium-sapphire (Ti:S) laser— has allowed the duration of ultrashort laser pulses to reach the femtosecond (fs) domain.3 Since the 1990s, the Ti:S/CPA technique has thus been used to rapidly develop ultra-intense and ultrashort lasers. Theoretically, the amplified output energy of such lasers can be greatly improved with the use of large-aperture Ti:S crystals. When larger-aperture Ti:S crystals are pumped at higher pump fluence and energy, however, the transverse amplified spontaneous emission (TASE) and parasitic lasing (PL) within the booster-amplifier volume are easier to suppress than the amplified pulse energy.4 This is the main barrier to realizing high-energy Ti:S/CPA amplifiers, even as Ti:S crystals with increasing diameters are produced. At present, there are two main approaches to suppress transverse PL in these laser systems. First, the matched-index cladding (passive) technique can be used to increase the loss of spontaneous emission. In the second (active) technique, optimization of the time delay and lightly doped Ti:S crystals are used to control the transverse gain. To date, several countries have built petawatt-level ultra-intense and ultrashort laser systems (of which the focused intensity can be used to achieve 1021W/cm2) that are based on the Ti:S/CPA approach.5–7 Many Figure 1. Schematic diagram of the chirp-pulse amplification (CPA) experimental setup. Ti:S: Titanium sapphire. CW-SLM: Continuouswave single-longitudinal-mode. R.A: Regenerative amplifier.  : Change in wavelength. amp: Amplifier.