No abstract

We revealed that interaction of femtosecond laser induced filament with the metal target placed in air is accompanied by x-ray bursts. The average energy of x-ray photons is increased by up to 4 times as compared to the transform-limited pulses (60 fs) when the positively chirped laser pulses (500 fs) are produced by the monofilament. Increase of x-ray response is also accompanied by the enhancement of the average ablation rate. The temperature of the hot electrons from filament induced plasma obtained from x-ray spectra made it possible to estimate the peak intensity inside the femtosecond laser filament, which turned out to be about 200 TW cm−2.

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.