Intensity clamping and controlled efficiency of X-ray generation under femtosecond laser interaction with nanostructured target in air and helium

Abstract

We have performed theoretical calculations aimed at modeling the propagation dynamics of a focused femtosecond laser beam in a nonlinear gas medium. It was obtained that when helium is blown into the focal area, the intensity clamping level is about 2,5 times higher than when air is present. The conditions for optimal placement of the target relative to the position of the vacuum focus and, accordingly, allowing to achieve maximum intensity are found. It was found that under interaction in air femtosecond Cr:forsterite laser ( λ=1,24 μm, E<1 mJ, 100 fs) with nanostructured iron containing tape the intensity clamping effect is observed. Replacing the air medium with helium leads to essentially increase in line (6.4keV) X-ray yield. Increasing the pulse duration to 300fs led to an increase in the X-ray output twice and reached 3*105 photons/pulse in solid angle.