Terahertz-field-induced optical birefringence in common window and substrate materials

Area of Science:

• Optics and Photonics
• Materials Science
• Terahertz Spectroscopy

Background:

• Terahertz (THz) spectroscopy is a powerful technique for material characterization.
• Understanding material response to intense THz fields is critical for developing advanced THz spectroscopy systems.

Purpose of the Study:

• To investigate the nonlinear optical response of common window and substrate materials under intense terahertz (THz) electromagnetic pulses.
• To quantify the induced optical birefringence and extract relevant material parameters.

Main Methods:

• Application of intense THz electromagnetic pulses (field strengths > 2 MV cm⁻¹) at ~1 THz to various materials.
• Measurement of induced transient optical birefringence using pump-optical probe spectroscopy.
• Analysis of the nonlinear optical response, including Kerr effect and linear electro-optic effect.

Main Results:

• Transient birefringence was observed in diamond, sapphire, MgO, TPX, LDPE, and SiN, consistent with a Kerr-effect-type response.
• Crystalline quartz exhibited a linear electro-optic signal, while silicon showed a response beyond the perturbative regime.
• Nonlinear refractive indices were extracted for most materials, and the electro-optic coefficient for quartz.

Conclusions:

• The nonlinear optical properties of common THz materials have been characterized under intense THz fields.
• Results provide essential data for selecting appropriate materials for THz spectroscopy windows and substrates, especially in high-field THz pump-optical probe spectroscopy.
• Understanding these nonlinear effects is crucial for mitigating potential distortions and optimizing the performance of THz spectroscopic systems.