Exawatt Lasers

Todd Ditmire of the University of Texas will talk about the present and future of the university’s Texas Petawatt Laser program at the Optical Society’s (OSA’s) Annual Meeting, Frontiers in Optics (FiO; Oct. 11 to 15, 2009, San Jose, CA). At present the Texas Petawatt Laser producing pulses at the petawatt (10^15 W) power level, the laser could reach the exawatt (10^18 W) power level with modifications.

The Texas Petawatt Laser currently produces petawatt power through a process of chirping, in which a short light pulse (150 fs in duration) is stretched out in time. This resulting longer pulse is amplified to higher energy and then recompressed to its shorter duration, thus providing a modest amount of energy, 190 J, in a very brief interval.

The Texas device is capable of producing power densities exceeding 10^21 W/cm2.

To get to exawatt powers, Ditmire hopes to combine largely existing laser technology and his already tested 100 fs pulses with new laser-glass materials that would allow amplification up to energies of 100 kJ. The laser’s 190 J current energy level is typical of laser labs at or near the petawatt level, such as those in Oxford, England; Osaka, Japan; and Rochester, NY. With support from the government and the research community, building an exawatt laser might take the years to achieve, Ditmire estimates.

Europe’s big lasers: the exawatt roadmap

Over the next decade, a trio of planned pan-European research facilities will give scientists access to unprecedented laser powers and intensities, opening the door to exotic science that will shed light on the origins of the universe and, it is hoped, provide the foundations for a sustainable energy future.

The overall construction cost for this new generation of “super lasers” is in excess of €2 bn, with operational budgets running to several hundred million euros per year.

A major European laser facility in the works is the Extreme Light Infrastructure (ELI), a project that’s being led by scientists at the Laboratoire d’Optique Appliquée (LOA) at the Ecole Polytechnique, Palaiseau, France. Scheduled to fire up in 2015, ELI will enable fundamental science to be carried out at the very highest laser powers (in the exawatt regime, 10^18 W) and intensities (10^24 W/cm2).

According to Collier, though, the jury is still out on the best approach to realize a high-repetition-rate 200 PW laser. “For a certain class of experiments, you want this power to be focused as if it were a single beam in order to get maximum intensity. Obviously we can’t deliver that amount of energy in a single beamline.”

One possible contender is a titanium:sapphire single-laser beamline called ILE, a work-in-progress at LOA. Even when fully optimized, however, the peak output power from ILE falls way short, at around 20 PW. The solution could be to coherently lock multiple beams into a single output, though this is a daunting challenge in its own right.

This site previously looked at zettawatt and exawatt laser plans.

A zettawatt system could be built using Yb:glass, with the advantages of being relatively compact due to the high Fsat of this material and being diode pumpable, much development work needs to be accomplished to reach this intensity level with this material. The proposed systems described below have been stimulated by the construction , both in France and in the U.S, of lasers delivering a few megajoules of energy as well as the availability of large telescope technology (10m diameter) and deformable mirrors

An exawatt system on the other hand,which would produce 10 kJ in 10 fs, i.e., 10^25 W/cm2, could be readily constructed. Only one percent or 30 kJ of the NIF/LMJ energy would be necessary. The beam size will be of the order of one meter in diameter. The amplifying method will be composed of a matrix of 25 Ti:sapphire 20×20 cm^2 crystals and two gratings of meter-size.

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