Tunable terahertz waves generated by mixing two copropagating infrared beams in GaP

Area of Science:

• Optics and Photonics
• Condensed Matter Physics
• Terahertz Science

Background:

• Efficient generation of coherent terahertz (THz) waves is crucial for various scientific and technological applications.
• Phase matching in isotropic crystals for nonlinear frequency conversion typically requires complex setups.
• Gallium phosphide (GaP) exhibits a reststrahlen band in the THz region, offering potential for novel phase-matching schemes.

Purpose of the Study:

• To demonstrate efficient generation of coherent THz waves using nonlinear frequency mixing in a zinc blende GaP crystal.
• To achieve broadband tunability of the generated THz radiation.
• To leverage the reststrahlen band of GaP for achieving phase matching in an isotropic medium.

Main Methods:

• Mixing two copropagating coherent infrared beams with wavelengths near 1 micrometer within a GaP crystal.
• Utilizing the reststrahlen band of GaP to achieve quasi-phase matching for efficient nonlinear conversion.
• Continuously tuning the wavelength of one infrared beam over a bandwidth of approximately 15.3 nm to achieve THz wave tuning.

Main Results:

• Efficient generation of coherent terahertz (THz) waves was achieved.
• A wide tuning range of 71.1–2830 microm (0.106–4.22 THz) was successfully demonstrated.
• The highest output peak power reached 15.6 W at a wavelength of 173 microm.

Conclusions:

• The use of GaP's reststrahlen band enables efficient phase matching for THz wave generation in an isotropic crystal.
• This technique provides a broadband and tunable source of coherent THz radiation.
• The demonstrated method offers a promising route for practical THz applications requiring high power and tunability.