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

Abstract

We show that waveform-synthesized chirped laser fields are efficient tools for coherent harmonic control. A single harmonic order, or two harmonic orders, can be selectively enhanced by using a two-color field allowing a moderate linear chirp for each color. Different harmonic orders within a wide spectral range can be selectively enhanced by adjusting the laser parameters. Our theory bridges two current harmonic control techniques, namely, singlecolor phase shaping and multicolor amplitude synthesis, and opens the door to new harmonic control possibilities.

Enhancing high-order harmonic generation by sculpting waveforms with chirp

“…One way is to simply add a term in the chirp-free phase function that is quadratic in the time t so that the laser field has a time-dependent frequency that is linear in time, as done in Refs. [4,8,18]. In order to determine the role of the chirp, typically the pulse durations and peak amplitudes are fixed (i.e., independent of chirp).…”

“…Specifically, HHG spectra can be very sensitive to the carrier-envelope phase (CEP) [2] and the chirp [3,4] of a single few-cycle pulse, or to the time delay between two-color synthesized few-cycle laser pulses [5]. An optimized few-cycle or many-cycle waveform of the laser field can, e.g., selectively enhance a single harmonic while suppressing neighboring harmonics [6][7][8], or, alternatively, greatly enhance HHG yields across a large range of harmonic photon energies [5,[9][10][11][12][13][14][15][16].…”

“…The values of the parameters are often obtained by optimization techniques using iterative algorithms with feedback loops [6,8,9,[11][12][13][14][15][16], but can also be determined on the basis of physical arguments, e.g., for the purpose of increasing ionization rates and/or recollision energies of the active electron in HHG processes [5,9,10]. Chirp is an additional parameter for controlling the driving laser waveform and, hence, HHG spectra.…”

“…The value of the chirp parameter in a linearly chirped many-cycle driving laser pulse has been shown to greatly affect the shape of the HHG spectrum because it can compensate the chirp of the emitted harmonics [18][19][20][21]. More recently, the use of waveforms composed of two or more color, linearly chirped many-cycle driving laser pulses has been shown to enable one to selectively enhance particular harmonics [7,8].…”

Extremely Nonlinear Optics Using Shaped Pulses Spectrally Broadened in an Argon- or Sulfur Hexafluoride-Filled Hollow-Core Fiber

“…Additionally, the spectral, spatial and temporal properties of the HHG radiation make it a versatile tool in atomic and molecular spectroscopy [2]. To realize a matched source for the envisaged spectroscopic applications, much work has been done in controlling the shape of the HHG spectrum by either modifying the driving laser field [3,4] or using multicolor fields [5]. Using shaped driving laser fields is also a promising way to increase the HHG conversion efficiency.…”