A theoretical study of the high-order harmonics of a 200 nm laser from H 2 and HeH +

Abstract

Using a time-dependent quantum mechanical method, based on the evolution of the electron density in real time, a theoretical study is made of the high harmonic generation in H 2 and HeH +, corresponding to a 200 nm laser. For H 2, four laser intensities in the range 10 13–10 16 W cm −2 are employed while only one intensity (≈ 10 16 W cm −2) is employed for HeH +. Up to the 45th order (4.44 nm) harmonic for H 2 and the 53rd order (3.77 nm) harmonic in HeH + are predicted. For H 2, increase in laser intensity I does not change the structure of the high harmonic spectrum but increases the yield of each harmonic according to a fractional law of I 1.5. Polar molecules/molecular ions might serve as excellent sources for higher harmonics, the yield and order of the harmonic increasing with increasing mass, ionization potential and polarizability.