中央研究院 原子與分子科學研究所

A Ti:sapphire laser system has been constructed with two synchronized main beams of 110 TW and 13 TW, and a 5-TW wavelength-tunable synchronized auxiliary beam for versatile control of laser-plasma interaction. The first main beam provides 3.3-J, 30-fs, 810-nm pulses, and the second 450-mJ, 34-fs, 805-nm pulses. The auxiliary beam comes from amplified spectral windows selected from a supercontinuum of high spatial coherence and provides 38-fs pulses with tunable wavelengths (870–920 nm). The two main beams can be focused down to M² = 1.2 and 1.1, with 77 and 81% energy enclosed in the focal spots, respectively. The energy fluctuations are 1.1 and 1.8 %, and the pointing fluctuations are 4.5 and 4.8 μrad, respectively. By using a preamplifier and saturable absorber before the pulse stretcher to suppress amplified spontaneous emission, the temporal contrast of the 110-TW main beam reaches 4 ⨯10¹⁰ at the -100-ps timescale. Even though the auxiliary beam is generated from a highly nonlinear process, by confining the supercontinuum generation in a single self-trapping filament, a spatial coherence close to the main beams can be achieved. It can be focused down to M² = 1.3, with 72 % energy enclosed in the focal spot. The energy fluctuation is 2.6 %, and the pointing fluctuation is 4.7 μrad. The versatility of synchronized multiple-beams with tunable wavelengths, good energy and pointing stability, and the spatiotemporal quality of the laser system has been essential to our experiments in high-harmonic generation, extreme-UV lasers, and laser-wakefield accelerators in which precision control of laser-plasma interaction is facilitated by a concerted sequence of driving pulses.