Terahertz parametric oscillator based on KTiOPO₄ crystal

Area of Science:

• Nonlinear optics
• Terahertz (THz) spectroscopy
• Solid-state physics

Background:

• Terahertz (THz) wave generation is crucial for various scientific and technological applications.
• Potassium titanyl phosphate (KTP) is a well-established nonlinear optical crystal, but its use in THz-wave parametric oscillators was unexplored.
• Surface-emitted parametric oscillators offer a compact and efficient platform for THz generation.

Purpose of the Study:

• To investigate the feasibility of using KTP crystals as the nonlinear medium in a surface-emitted terahertz-wave parametric oscillator.
• To demonstrate tunable THz-wave generation using KTP.
• To characterize the output properties of the KTP-based THz-wave parametric oscillator.

Main Methods:

• A surface-emitted terahertz-wave parametric oscillator was designed and constructed using a KTP crystal.
• The Stokes beam propagated along the x-axis, and the pumping beam was incident at a small angle θ(ext) to the x-axis.
• Polarizations of the pumping beam, Stokes beam, and THz wave were aligned along the z-axis.
• The external angle θ(ext) was varied to tune the generated THz frequency.

Main Results:

• The KTP crystal was successfully employed as the nonlinear medium in a surface-emitted THz-wave parametric oscillator.
• Tunable THz-wave generation was achieved, with distinct tuning ranges observed from 3.17 to 3.44 THz, 4.19 to 5.19 THz, and 5.55 to 6.13 THz.
• A maximum THz output energy of 336 nJ was recorded at 5.72 THz with 80 mJ of pumping energy.
• Frequency gaps were observed, coinciding with infrared-absorbing A₁ modes of the KTP crystal.

Conclusions:

• KTP crystals are suitable nonlinear media for surface-emitted terahertz-wave parametric oscillators.
• The demonstrated KTP-based THz-wave parametric oscillator provides a tunable source of THz radiation.
• The observed frequency gaps highlight the influence of material absorption on THz generation efficiency.