Role of Intrapulse Coherence in Carrier-Envelope Phase Stabilization

Abstract

The concept of coherence is of fundamental importance for describing the physical characteristics of light and for evaluating the suitability for experimental application. In the case of pulsed laser sources, the pulse-to-pulse coherence is usually considered for a judgment of the compressibility of the pulse train. This type of coherence is often lost during propagation through a highly nonlinear medium, and pulses prove incompressible despite multioctave spectral coverage. Notwithstanding the apparent loss of interpulse coherence, however, supercontinua enable applications in precision frequency metrology that rely on coherence between different spectral components within a laser pulse. To judge the suitability of a light source for the latter application, we define an alternative criterion, which we term intrapulse coherence. This definition plays a limiting role in the carrier-envelope phase measurement and stabilization of ultrashort pulses. It is shown by numerical simulation and further corroborated by experimental data that filamentation-based supercontinuum generation may lead to a loss of intrapulse coherence despite near-perfect compressibility of the pulse train. This loss of coherence may severely limit active and passive carrier-envelope phase stabilization schemes and applications in optical high-field physics.

Optical parametric amplification of sub-cycle shortwave infrared pulses

“…The highest pulse energy of the input pulse to the CaF 2 plate comes at the cost of the need to compensate for the lowest nonlinear refractive index, and thus, it leads degradation of the plate in a long term use. We observed the instability of the spectrum of the idler pulse after~20-min WLG and damage appeared in the plate 33,35 . To solve this problem, the CaF 2 plate was continuously moved perpendicular to the beam path.…”

“…We had expected that a sapphire or YAG plate might efficiently generate the white light owing to a high nonlinear refractive index and low critical power, while the low dispersion of a CaF 2 plate might be beneficial for broadening the white-light spectra 33 .…”

In-line Spectral Interferometry in Shortwave-Infrared Laser Filaments in Air

“…We observe CEP-dependent interference in the spectrum of the generated visible white light. The effect is robust against large pulse-energy fluctuations, indicating that SWIR filamentation preserves the intrapulse coherence [19]. Numerical simulations reveal rigid carrier-level clamping of both the peak optical field and the CEP of the entire propagating waveform.…”

Carrier-envelope-phase-stable soliton-based pulse compression to 44 fs and ultraviolet generation at the 800 kHz repetition rate

“…It was shown in [24] that asymmetric broadening in supercontinuum generation should be avoided to preserve intrapulse coherence and to minimize CEP stability degradation. Although for the case of soliton self-compression strong selfsteepening mostly extends the blue end of the spectrum, the evaluated CEP variation is similar to that of symmetric SPM supercontinuum in the sapphire plate.…”