A theoretical study of the high-order harmonics of a 200 nm laser from H2 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 H2 and HeH+, corresponding to a 200 nm laser. For H2, four laser intensities in the range 1013–1016 W cm−2 are employed while only one intensity (≈ 1016 W cm−2) is employed for HeH+. Up to the 45th order (4.44 nm) harmonic for H2 and the 53rd order (3.77 nm) harmonic in HeH+ are predicted. For H2, 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 I1.5. 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.