Phase characterization in broadband THz wave detection through field-induced second harmonic generation

Area of Science:

• Optics and Photonics
• Terahertz (THz) Science and Technology
• Nonlinear Optics

Background:

• Broadband heterodyne detection is crucial for precise THz pulse characterization.
• Field-induced second-harmonic generation (FIS H G) in ambient air offers a non-contact method for THz detection.
• Understanding phase shifts in THz measurements is essential for accurate signal retrieval.

Purpose of the Study:

• To theoretically and experimentally investigate the THz pulse phase measured by FIS H G.
• To analyze the influence of electrode positioning on THz phase spectra.
• To identify the cause of an observed anomalous phase shift near the beam focus.

Main Methods:

• Utilized broadband heterodyne detection with FIS H G in ambient air.
• Scanned wire-shaped electrodes along the detection plasma to study THz phase dependence.
• Performed theoretical analysis to explain observed phase phenomena.

Main Results:

• Demonstrated THz pulse phase measurement using FIS H G heterodyne detection.
• Observed a dependence of THz phase spectra on electrode position.
• Identified an additional phase shift around the beam focus.

Conclusions:

• The anomalous phase shift near the beam focus is attributed to the Gouy shift of both the optical probe and THz beams.
• This study clarifies phase behavior in FIS H G-based THz detection.
• Provides insights for optimizing THz measurement techniques.