Higher harmonic and supercontinuum generation arising from electronic self-phase modulation under ultrafast laser pulses for various states of matter

Abstract

An electromagnetic model is presented to explain the higher harmonic generation. The electronic cloud distortion model is used based on the carrier-envelope phase at the optical cycle response for gases and solids to explain the experimental Higher Harmonic Generation (HHG) and Supercontinuum Generation from the interaction of high-intensity ultrafast pulses. The theory reveals the salient experimental features observed from the HHG in the form of the three characteristic regimes for different states of matter. The electronic self-phase modulation model from nonlinear Kerr index n2 reveals three salient features of the HHG: decreasing Harmonics generation followed by a plateau to descending HHG signals to the cutoff frequency using the method of the stationary phase on ESPM. This ESPM model is a fundamental and an alternative model to the quantum mechanical interpretation of HHG. In addition, the ESPM model gives additional features of spectral broadening about the N odd harmonics supporting the theoretical ansatz presented in this paper. Here we used 50 fs laser pulse at intensities of 1012 to 1015 W/cm2 to simulate and experimentally compare the salient features of HHG and supercontinuum about each harmonic from various materials such as gases and solids supporting the ESPM model. The outcome from the ESPM model is a supercontinuum background superimposed with the sharp HHG which was experimentally observed before in various forms of matter.