Complicated high-order harmonic generation due to the falling edge of a trapezoidal laser pulse

High-order harmonic generation (HHG) is investigated for and its isotopologues under seven and ten-cycle trapezoidal laser pulses at an 800 nm wavelength and I = 4 × 1014 W cm−2 intensity. We numerically solved the full-dimensional electronic time-dependent Schrodinger equation (TDSE) with and without the Born–Oppenheimer approximation (BO). We show that contribution to the HHG spectrum from the trailing edge of a trapezoidal laser pulse can result in a redshift and complexity in the total HHG spectrum. This effect can be removed by considering different laser pulse durations and nuclear motion that is not possible for sin2 and Gaussian laser pulses. We have resolved the contributions to the redshift and other patterns in the HHG spectra into the different electronic and vibrational channels and the interference thereof.