Monday, August 20, 2012

Petawatts proliferate

Borrowing a phrase from a 2006 Laser Focus World petawatt article, it is even more true today that "petawatts proliferate." All petawatt lasers aim to deliver petawatt-power-level pulses. But to understand just why so many petawatt-class (or sub-petawatt-class) laser systems are either in operation or being developed, it's necessary to understand the petawatt pulse itself and the groundbreaking applications that are causing these laser powerhouses to proliferate. What is the petawatt pulse width, the pulse duration, the peak power level, and the frequency at which these petawatt pulses are delivered? And just what type of light-matter interaction studies and other applications make petawatt-level pulses so appealing?

In mid July, Laser Focus World reported that the National Ignition Facility (Livermore, CA) delivered 500 terawatts (0.5 petawatts or PW) to its target in a step towards laser-initiated fusion. The 1.85 MJ energy is generated by NIF's 192 laser beams in a football-field-sized structure. And just a month prior, we reported on Ohio State University's Science Center for Advanced Research on Lasers and Engineered Targets (SCARLET), which aims to deliver the same 0.5 PW power-level pulses from a much smaller facility with a one-shot-per-minute repetition rate (see image below). However, compared to NIF, the 30 fs pulsewidth SCARLET creates sub-millijoule pulses that have a lot of power, but cannot compare to NIF's 1.85 MJ peak.

At the extreme of the petawatt-class-laser craze is definitely the Extreme Light Infrastructure (ELI)--Europe's project that will increase the peak power of ultrashort-pulse lasers to a whopping 200 PW and peak intensities of 10exp25 Watts per square centimeter. Not yet built, the ELI will begin with a more modest 10 PW laser and advance to 200 PW by 2017. In his Photonics Frontiers article in Laser Focus World in January 2011, Jeff Hecht described some of the applications that make ELI and all petawatt-class lasers so exciting; for example, proton acceleration to the 70-250 MeV range is needed for cancer therapy and ultrahigh-energy ultrashort pulses enable photonuclear physics studies that could lead to nuclear waste disposal.

This year's OSA CLEO conference included a special Petawatt Lasers Technologies (CMD4) series of sessions, which detailed the following petawatt-class laser systems (a reference paper is linked for each):

CAEP China:


LLE University of Rochester, USA:

In addition to these CLEO presenters, petawatt laser systems are proliferating worldwide; here are a few more examples of systems in operation or systems planned to be built:

Texas Petawatt Laser, The University of Texas at Austin, USA:

Hercules Petawatt Laser, University of Michigan, USA:

Z-Petawatt, Sandia National Laboratories, USA:

Vulcan laser, Rutherford Appleton Laboratory, England:

XCELS, Russia:

PHELIX laser, Germany:

One of the best YouTube videos available on the how petawatt lasers work and their many applications is from Todd Ditmire on the Texas Petawatt laser team. check it out, and I'm sure you'll see why petawatts proliferate and will continue to do so (at least until exawatt lasers arrive!).

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