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Enhancement of reflected photons from a flying mirror moving at the speed of light
-accelerating applications such as observing and controlling electrons in atoms and realizing ultra-high intense fields-
Nov. 30 , 2009
A research team of the Laser Accelerator Group, Quantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA, President Toshio Okazaki) succeeded in increasing the reflected photon signal by producing flying mirrors moving nearly at the speed of light (formed as a plasma wave, hereafter mirror) irradiated by an intense laser pulse and reflecting another laser pulse with the mirror in a head-on setup.
At JAEA, researchers invented the flying mirror method, which involves a bunch of electrons produced by irradiating laser pulses into helium gas and demonstrated the proof-of-principle experiment in 2007. Because the mirror moves nearly at the speed of light, the wavelength of the light reflected by the mirror is shortened and the pulse duration is compressed due to the relativistic effect. However, the signal obtained in the 1st experiment was smaller than the theoretical expectation.
The JAEA research team conducted the flying mirror experiment by developing a new method � they produced stable mirrors by using a more intense laser and irradiating another laser pulse onto the mirror head-on. As a result, the incident 820-nm laser photons were converted to extreme ultraviolet photons ranging from 12.8 nm to 22.0 nm. The obtained photon number at this time is 4000 times higher than that obtained in 2007, where the laser pulse was focused onto the mirror at an oblique incidence angle. The obtained photon number is close to the theoretical expectation, thus this result proved that the flying mirror method works well.
The flying mirror method can generate attosecond pulse-duration and tunable wavelength X-ray photons by controlling the speed of the mirror. Thus, this technique is expected to be a novel method that might enable us to observe and control the motions of electrons in atoms or molecules. If we make a concave-surface mirror, this can enhance the focused light intensity dramatically. This opens a new field of physics such as ultraintense field science, where the vacuum is broken by the extreme laser field. The present result is a milestone toward the realization of these dreams.
The research results have been published in "Physical Review Letters" (a scientific journal issued by the American Physical Society) on December 4, 2009.
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