Harmonizing High Harmonics

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Science  31 Aug 2007:
Vol. 317, Issue 5842, pp. 1149
DOI: 10.1126/science.317.5842.1149d

Intense infrared laser pulses can ionize the atoms of an inert gas and give rise to x-ray emission at high multiples (or harmonics) of the driving field frequency when the liberated electrons recombine with their parent ions. Selecting the output wavelength and boosting its intensity, however, have been experimentally challenging and have in large part been approached by trial-and-error. One severe problem is that the phase of emitted x-rays is out of kilter with the driving infrared laser field. Cohen et al. propose to address this issue by using a weak counter-propagating, quasi-continuous laser field to modulate the phase of the emitted harmonics. They show by simulation that tuning the wavelength of the counter-propagating laser field, and thus modulating the refractive index experienced by the driving field, could efficiently correct the phase mismatch. — ISO

Phys. Rev. Lett. 99, 53902 (2007).

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