Coherent Wins Laser Contract

SANTA CLARA, Calif., June 15 -- Coherent has been selected to supply a custom ultrafast amplified laser system for a multimillion dollar experimental proton beam cancer treatment system to be constructed at Fox Chase Cancer Center in Philadelphia, Pa.

The final output beam of this laser system will produce 5-10 J pulses with a duration of <50 femtoseconds. This corresponds to a peak power of around 100 terawatts. The beam will be focused to a near diffraction limited spot size in the proton beam generator, to achieve power densities as high as 1021 W/cm2. Such exceedingly high power densities are required to generate the proton beam to be used for tumor therapy research at the center.

Coherent will supply a Mira laser pumped by a continuous wave Verdi laser. The Mira output will be amplified in two stages, using a Coherent Legend regenerative amplifier followed by a Coherent multipass amplifier. The 25-TW output of the laser system will be amplified to the 100-TW level in a custom amplifier built jointly by Coherent and Fox Chase. This amplifier will be pumped by a custom-designed 50 Joule Nd:glass laser, also supplied by Coherent.

Charlie Ma, senior physicist at Fox Chase, said, "Proton beams are in the early stages of investigation as an alternative to conventional x-rays for destructive treatment of tumors."

One of the main drawbacks of radiation therapy is ancillary damage -- the radiation is absorbed along its entire path as it transits the body. Compared with conventional x-rays, high-energy protons lose less energy as they pass through tissue until their energy drops below a threshold level, at which point they are absorbed in a very short distance. This means that energy is selectively deposited at the end of their path, allowing high damage to the tumor with greatly reduced intervening tissue damage.

Ma said, "The depth of penetration is a function of the proton energy. The new Fox Chase system is aimed at delivering proton energies up to 250 MeV, which is sufficient to treat tumors at any depths in the body."

These high-energy protons are formed by ablating a thin target with the focused laser beam. Ma said this is an economically and practically attractive alternative to using a synchrotron or cyclotron to generate high-energy protons.

For more information, visit: www.coherent.com