Fast spectral measurement of soft x-ray emission from ultrafast laser processing

Abstract

Avoiding Pile-Up during spectral X-ray measurements during ultrafast laser processing with a single detector requires long measurement times at large distances from the processing area due to the short pulse duration and high photon fluxes. To enable fast measurements, an algorithm is presented which calculates the underlying Pile-Up free spectrum of any measured spectrum. Therefore, a statistical approach was used to describe the mean number of photons ⟨𝑛⟩ and their corresponding photon energies Eph hitting the detector at each pulse. This number of photons hitting the detector each pulse was assumed to be geometrically distributed, whereas the photon energies follows a modified Maxwell-Boltzmann distribution, mainly defined by the temperature Thot of the hot electrons in the laser plasma. An initial guess of ⟨𝑛⟩ and Thot was used to calculate an expected Pile-Up spectrum at the detectors position. Comparing the calculated Pile-Up spectrum with the measured one and iteratively adjusting ⟨𝑛⟩ and Thot results in the underlying Pile-Up free spectrum.