DOI: 10.1088/0953-4075/48/22/224004

Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities of {10}^{15}-{10}^{16}\; W cm^{-2}. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about 25 and 40\;\mathrm{eV} for simulated delay times up to +70\;\mathrm{fs} after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 818 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and 30\;eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. We resolved the time-scale for laser-heating of hydrogen, and PIC results for lasermatter interaction were successfully tested against the experiment data. Show Partial Abstract