Generation of enhanced even harmonics of fundamental radiation in temporally separated two-color laser fields

Sayrac M., Kolomenskii A. A. , Dong J., Schuessler H. A.

JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA, vol.233, pp.22-27, 2019 (SCI-Expanded) identifier identifier


High harmonic generation (HHG) produces coherent light in the extreme ultraviolet (XUV) spectral region. We present results on generation of high harmonics (HHs) with a temporally separated two laser pulses of fundamental (omega(0)) and its second harmonic (2 omega(0)) in argon (Ar), molecular nitrogen (N-2) and carbon dioxide (CO2) gases having close ionization potentials. The special feature of this study is that the omega(0) and 2 omega(0) fields are temporary separated, so that the fundamental radiation comes first and the second harmonic radiation arrives to the interaction region with a delay. High harmonic spectra were measured for parallel and perpendicular relative polarizations of the fundamental and the second harmonic fields. With the combined (omega(0) + 2 omega(0)) field more than an order of magnitude enhancement of the HHs signal was observed compared to the coo or the 2 omega(0) field alone. An increased conversion efficiency into HHs, notably of the even orders of 2(2m + 1) (m = 1 - 3) was found for the latter case. We also discuss similarities and differences of the HH generation in the three gas media with single and two-color fields.