Colorado State University has developed one of the most powerful lasers in the world, ALEPH. ALEPH is a Petawatt-Class Laser ultra-short pulse Ti:sapphire laser system that produces 0,85 PW pulses of 30 femtosecond duration at an unusually high repetition rate of 3.3 pulses per second. It can also ultrahigh-contrast λ =400 nm femtosecond pulses of up to 10 J, obtained by frequency doubling 800 nm pulses of fs duration. An intensity of 6.5×10^(21) Wcm^(-2) is obtained focusing the beam with an f/2 parabola.
It consists of a conventional Ti:Sa front end that delivers λ=800 nm pulses into a chain of three high power Ti:Sa amplification stages pumped by Nd:YAG slab amplifiers. The 250 mJ output of this laser front end is further amplified in three multi-pass Ti:Sa amplifiers pumped by the frequency doubled output of eight compact flash lamp-pumped high energy Nd:glass slab amplifiers, developed at CSU. The slab geometry has long been recognized as a way to significantly reduce the limitations in repetition rate inherent to the more commonly used rod geometry. These pump laser allows Ti:sappire system operation at a repetition rate of up to 3.3 Hz in burst mode. The beam propagates in a zig-zag path in the gain medium aided by total internal reflection in the polished wall of the slabs eliminating first-order thermal and stress-induced focusing, and also reducing stress-induced birefringence.
Each slab amplifier generates pulses with ~18 J energy and 15 ns duration at 1053 nm. The rms pulse energy fluctuation for 1053nm slab pump laser is ~1%. The amplified beams are frequency doubled by LBO crystals to generate 11 J pulses at 527 nm. The eight slab amplifiers arms produce a total 527 nm pump energy of 88 J, with a uniform nearly flat-top beam profile this is used to pump the three main Ti:Sa amplifiers. The amplifier chain generates 800 nm pulses of up to 37 J energy before compression. A gold grating compressor compresses these pulses into pulses of up to 26 J energy with duration as shot as 30 fs. These pulses are frequency doubled to generate the ultrahigh contrast 400 nm pulses that constitute the normal mode of operation.
Y. Wang, S.J. Wang, A. Rockwood, B.M. Luther, R. Hollinger, A. Curtis, C. Calvi, C.S. Menoni, and J. J. Rocca, “0.85 PW laser operation at 3.3 Hz and high-contrast ultrahigh-intensity lambda=400 nm second-harmonic beamline”. Optics Letters. 42(2017).10.1364/ol.42.003828.
US Department of Energy, LASERNET US