Phlystron -- A photonic terahertz amplifier

TL;DR

The paper introduces the Phlystron, an all-optical THz amplifier operating at 0.35 THz, demonstrating a 3.3-fold energy increase and offering a scalable solution for high-power multicycle THz sources.

Contribution

It presents the first power-scalable all-optical THz amplifier based on phase modulation in PPLN, inspired by electronic klystrons, with potential for higher gain and scalability.

Findings

Achieved 3.3-fold increase in THz energy with commercial crystals.

Demonstrated amplification at 0.35 THz using phase modulation and group delay dispersion.

Scaling analysis suggests potential for higher gain with larger devices and multi-stage setups.

Abstract

High-energy (mJ) and high-peak-power (MW) multicycle terahertz (THz) pulses are essential for nonlinear THz spectroscopy and compact accelerator technologies, yet their generation by nonlinear optical frequency conversion remains inefficient and imposes severe demands on femtosecond driving lasers. Amplifying existing THz pulses offers an appealing alternative, but no power-scalable amplifier has been realized in the sub-THz regime. Here, we demonstrate an all-optical THz amplifier operating at 0.35 THz based on the modulation of nanosecond laser pulses by a weak THz field in periodically poled lithium niobate (PPLN). The THz-induced phase modulation is converted into an amplitude modulation using controlled group delay dispersion, forming a tailored pulse train that can efficiently drive high-energy THz generation in a second crystal, thereby amplifying the THz seed. By analogy to electronic klystrons, we term this device the Phlystron, in which the electron beam carrying the power is replaced by a photon beam. In this proof-of-concept experiment, a 3.3-fold increase in THz energy is achieved with commercial crystals. Scaling analysis indicates the potential for higher gain when using large-aperture PPLN devices and multi-stage amplification. The Phlystron thus provides a scalable route to powerful multicycle THz sources driven by readily available narrowband lasers.