Field-resolved THz-pump laser-probe measurements with CEP-unstable THz light sources.

Area of Science:

• Physics
• Optics
• Spectroscopy

Background:

• Stable carrier-envelope phase (CEP) light sources are crucial for field-resolved light-matter interaction studies.
• Many powerful light sources, including infrared free-electron lasers (IR-FELs), lack CEP stability, limiting their use in phase-resolved research.
• IR-FELs, despite their unique characteristics, have not achieved CEP-stable operation.

Purpose of the Study:

• To present a novel method for conducting linear and non-linear phase-resolved terahertz (THz) pump-probe experiments with CEP-unstable THz sources.
• To enable field-resolved measurements using previously unsuitable coherent light sources.
• To demonstrate a technique that overcomes the limitations of CEP-unstable radiation in THz spectroscopy.

Main Methods:

• Extraction of THz carrier-envelope phase (CEP) information for each pulse using a specialized electro-optical detection scheme.
• Correlation of extracted CEP values with THz-induced responses in parallel pump-probe experiments.
• Sorting and averaging of data to reconstruct an absolute phase-resolved response.

Main Results:

• Successful demonstration of field-resolved THz time-domain spectroscopy with sub-cycle temporal resolution.
• Utilized CEP-unstable infrared free-electron laser (IR-FEL) radiation at a 13 MHz repetition rate.
• Achieved phase resolution with a previously phase-incoherent THz source.

Conclusions:

• The presented method robustly enables phase-resolved THz experiments with CEP-unstable sources.
• The technique is suitable for high-repetition-rate, short-pulse THz radiation and common time-domain experiments.
• Implementation at IR-FEL facilities will open new avenues for studying coherent light-driven phenomena with enhanced signal-to-noise ratios.