Photon Statistics from Non-Hermitian Floquet Theory: High Harmonic Generation and Above-Threshold Ionization Spectra Detected via IR Detectors

Although it seems that obtaining quantum properties of light from classical calculations is a self-contradictory claim, it is shown here that a unified mechanism governs the three distinct measurements of high harmonic generation spectra (HGS), above-threshold ionization (ATI), and IR photon number distribution, none of which require the quantization of the electromagnetic field. Here, the conditions that enable the calculations of HGS and ATI spectra for atoms interacting with high-intensity laser fields from photon statistics are first derived. Through the non-Hermitian theoretical simulation, the regimes where there is correspondence between the HHG and ATI spectra and annihilated pump photons (with post-selection) are identified. Consequently, the HGS and ATI spectra, as detected by XUV detectors, can be obtained by monitoring the fluctuations of the infrared absorbed photons.