Experimental and theoretical studies of two-color-pump resonance-induced enhancement of odd and even harmonics from a tin plasma

Abstract

We study high-order harmonic generation from a laser-produced tin plasma using 780 and 390 nm, 40 fs, 1 kHz pulses. Varying the chirp of the laser radiation, we observe variation of the harmonic frequency and intensity. The enhanced 16th and 17th harmonics are attributed to the influence of the strong ionic transitions of tin. Theoretical calculations of the photoabsorption spectra reveal the decisive role of Sn II and Sn III transitions in the enhancement of single harmonics. Varying the fundamental frequency we study numerically the spectral width where the harmonic is enhanced. We find, both theoretically and experimentally, that this width is wider than the one of the corresponding resonance in the photoabsorption spectrum. The resonance line modification can be explained by the Stark shift of the autoionizing state in the laser field, as well as the photoionization of this state.

Beyond CarbonK-Edge Harmonic Emission Using a Spatial and Temporal Synthesized Laser Field

“…So far a large number of strategies involving the tailoring of the input laser pulse for HHG have been implemented. Using a combination of fields of two or more colors to temporally synthesize the desired strong laser field [10][11][12][13][14][15][16][17][18][19][20], or using chirping techniques [21], seems like a promising route. The new approach we propose involves combining the two techniques to controllably shape the final laser field both in time and in space.…”

Laser harmonic enhancement using the quasi-phase-matching in laser plasma

“…The enhancement factor in the case of weak (~10%) second field was varied in the range of 3-8, while the theoretical calculations predicted a 100-fold enhancement [16,40]. The two-color pump at low ratio of second and fundamental waves has also been applied in the case of plasma HHG [41,42] and approximately same amendments, as for gas harmonics, were demonstrated. The use of the multi-jet configuration of laser plasma allows further modification and amendment of HHG through the propagation processes.…”

Why plasma harmonics?

“…7b, [82]), comparative research of plasma and gas media for efficient HHG [83], temporal characterisation of plasma harmonics [84,85], generation of continuum plasma harmonics [86], stabilisation of harmonic yield over one million laser shots on the rotating targets (Fig. 8a, [87]), generation of high-order harmonics using picosecond driving pulses [88], various applications of 1 kHz lasers for plasma HHG to increase the average power of converted radiation [89,90], analysis of coherence properties of plasma harmonics [91], use of double-pulse technique for plasma HHG [92], demonstration of the quantum path interference of the long and short trajectories of electrons in plasma HHG experiments (Fig. 8b, [93]), etc.…”