27 Feb 2008
The most intense laser in the world could improve radiation treatment of cancer and shed new light on ultra fast light-matter interactions.
A 300 TW laser with an intensity of 2x1022 W/cm2 has been developed by researchers in the US. They claim that the laser, which is a modification of an existing 50 TW laser, sets new records for both output power and beam intensity. What's more, the laser can produce the intense beam once every ten seconds, while existing petawatt-scale lasers can take up to an hour to recharge (Optics Express 16 2109).
"We have demonstrated the highest power and highest intensity repetitive short-pulse laser," Victor Yanovsky, a researcher at the University of Michigan, told optics.org. "Several groups are working on these types of laser, but we made it first by upgrading our existing 50 TW Hercules laser system."
The Ti:sapphire laser emits at a wavelength of 800 nm with a repetition rate of 0.1 Hz and a pulse duration of 30 fs. The researchers believe that such intense lasers may be helpful in developing better proton and electron beams for radiation treatment of cancer, among other applications.
"The aim of our research was to investigate the basic science of light-matter interactions at ultrahigh intensity and particle acceleration," commented Yanovsky. "New physics such as radiation reactions, quantum effects and relativistic ion plasma is predicted at high intensities. Practical applications of particle acceleration include ion cancer therapy."
The team increased the intensity of its 50 TW Hercules laser system by focusing the beam to a wavelength-limited spot measuring 1.3 µm. The Hercules design is based on chirped-pulse amplification, which uses diffraction gratings to stretch a very short duration laser pulse so that it lasts 50,000 times longer.
"Nanojoule-energy short pulses with a duration of 10 fs are expanded by 50,000 times to a pulsewidth of 0.5 ns using a grating-based stretcher," explained Yanovsky. "This stretched pulse can then be amplified to much higher energies without damaging the optics in its path. We passed the beam through a series of Ti:sapphire crystals, which boosts the pulse energy to around 20 J."
After the beam is amplified, an optical compressor reverses the stretching and squeezing of the laser pulse until it's close to its original duration. The beam is then focused to a tiny spot using adaptive optics, resulting in an ultra high intensity beam.
"The beam is compressed to 30 fs using a grating-based vacuum compressor," explained Yanovsky. "We then use a f/1 parabolic mirror to focus the beam to a 1.3 um spot - this increases intensity by 8 orders of magnitude."
The next steps for the team are to shorten the pulse duration to 10 fs and stabilize the carrier-envelope phase.