High-intensity laser produces 13 terawatts
A new Nd:glass laser being developed at the Laboratoire pour l`utilisation des lasers intenses, (LULI, Ecole Polytechnique, Palaiseau, France) delivers a peak power of 13 TW (6 J in 450 fs) at 1.06 µm.1 The system is an improvement over an earlier one that used multiple amplifiers and six beams, with each beam delivering 100 J in 0.6 ns, to produce a total peak power of 1 TW.
The new laser represents the first phase of a system being developed to produce several hundred terawatts using disk amplifiers with pulse compression. Eventually, the LULI researchers expect to reach peak powers in the petawatt (1015 W) region. These high pulse energies are produced using chirped-pulse amplification (CPA). This technique prevents breakdown of the solid-state laser material--bubble formation in the Nd:glass amplifiers--that would otherwise occur at such high peak-pulse powers because of the intense electric fields generated.
Developed about ten years ago, CPA stretches the laser pulses before they are amplified, thereby reducing the peak power in the amplifier material. After amplification the pulses are recompressed. This technique has enabled production of intense laser pulses at much higher peak powers than was previously possible.
Implementation of CPA in the LULI system starts with a Ti:sapphire oscillator pumped by a 12-W argon-ion laser. The ~80-fs, 1-nJ output pulses of the Ti:sapphire laser are first stretched to ~1 ns, then injected into a Ti:sapphire regenerative amplifier, which is pumped by a frequency-doubled Nd:YAG laser. The regenerative amplifier provides gain close to 106, which results in ~500-ps output pulses with energies of ~5 mJ. These "preamplified" pulses then propagate themselves through a Nd:glass laser chain (silicate and phosphate glasses are used to maximize the amplification bandwidth) that delivers pulses of several joules to the last compression stage of the system. After compression the system delivers ~300-fs pulses with energies of ~4 J (see figure on p. 16).
Pulse energies of such magnitude are opening up new research fields in physics, including relativistic laser-matter interaction studies, dense-matter production for astrophysics research, particle acceleration by beatwaves and wake field effects. This new laser is likely to enable research that has only been possible using computer simulation.
1. Sophie Baton, "Des impulsions laser ultra-intense," Centre National de la Recherche Scientifique Info, 305 (May 1995).
In May 1996 the existing silicate and phosphate glass amplifier rods of the LULI laser system will be replaced by disks, which should increase the output pulse energies from ~4 to ~20 J in 300 fs.