Selective Enhancement of a Single Harmonic Emission in a Driving Laser Field with Subcycle Waveform Control

Abstract

We experimentally demonstrate a robust scheme to select a single high-order harmonic among the harmonic comb by using a driving laser field with subcycle waveform control, which is synthesized by the fundamental 800 nm laser pulse and two controlling laser pulses at 400 and 267 nm with perpendicular polarizations. By controlling the relative phase among the pulses of different colors, a single high-order harmonic is selectively enhanced while the adjacent harmonics are greatly suppressed with the intensity contrast increased by more than 1 order of magnitude and the peak intensity enhanced simultaneously by more than 2 orders of magnitude compared to the case by using only the fundamental 800 nm laser pulse. Such phenomena can be mainly attributed to the intra-atomic phase matching realized with the sub-cycle waveform controlled field.

Waveforms for optimal sub-keV high-order harmonics with synthesized two- or three-colour laser fields

“…Similarly, enhancement of HHG has been predicted in many theoretical simulations (Supplementary Discussion). More recently, advancement in optical parametric amplification (OPA) and optical parametric chirped-pulse amplification (OPCPA) technology has made it possible to perform coherent wavelength multiplexing of ultra-broadband (over two or more octaves) pulses with full phase and amplitude control, thus allowing the generation of any optical waveform [8][9][10][11][12][13][14][15][16][17][18] . With so many 'knobs' accessible, it is of critical importance to develop a general algorithm for optimal waveform control for the efficient enhancement of high-harmonic generation and for other strong field phenomena.…”

Coherent control of high-harmonic generation using waveform-synthesized chirped laser fields

“…By coherently synthesizing the field amplitudes, the subcycle field shape (or waveform) can be changed, therefore both the ionization and the subsequent electron motion can be steered. Commonly used additional colors include the second harmonic and the third harmonic of the fundamental due to experimental convenience [14][15][16][17][18][19][20][21][22], although other colors have also been widely explored [23][24][25][26][27][28][29]. This multicolor amplitude synthesis has led to substantial progress on coherent harmonic control towards various purposes, such as extending the harmonic cutoff, enhancing the HHG yield, generating an isolated attosecond pulse, etc.…”

“…The other harmonic control technique makes use of one or more colors in addition to the fundamental [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. By coherently synthesizing the field amplitudes, the subcycle field shape (or waveform) can be changed, therefore both the ionization and the subsequent electron motion can be steered.…”

Macroscopic scaling of high-order harmonics generated by two-color optimized waveforms in a hollow waveguide

“…To overcome low up-conversion efficiency of HHG, it has been proposed to modify the subcycle laser waveform by optimally synthesizing multicolor laser pulses [31][32][33][34][35][36][37] (see review in Ref. [38]).…”