Selective generation of an intense single harmonic from a long gas cell with loosely focusing optics based on a three-color laser field

摘要

The selective generation of an intense single harmonic has been experimentally achieved in argon from a long gas cell with loosely focusing optics using a three-color laser field. When compared with the single harmonic emission from a continuous gas jet, both the intensity and the purity of the selected single harmonic emission from the long gas cell show dramatic improvements; the peak intensity is more intense by as much as 1–2 orders of magnitude, while the contrast ratio (i.e., the spectral purity) is simultaneously increased by several times. The underlying physics of this enhancement can be explained using the strong field approximation model with the propagation effect.