Absolute gas density profiling in high-order harmonic generation.

We propose and implement a method to determine the absolute density profile of a gas jet producing high-order harmonics. By measuring the transverse profile of the fluorescence emitted by the plasma, we retrieve the local density in the gas jet. We use this technique during the optimization of the high-harmonics of 515 nm, 10 µJ, 130 fs pulses at 500 kHz and find that we can generate in absorption-limited conditions.