[Paper Review] High-power intracavity single-cycle THz pulse generation using thin lithium niobate

Yicheng Wang, Tim Vogel+6 more|arXiv (Cornell University)|Sep 8, 2023

Solid State Laser TechnologiesEngineering3 citations

TL;DR

This paper demonstrates high-power, single-cycle terahertz (THz) pulse generation using a thin lithium niobate crystal placed inside the cavity of a multimode diode-pumped mode-locked thin-disk laser. By leveraging intracavity resonant enhancement in a 50-µm-thick LiNbO₃ plate, the system achieves milliwatt-level broadband THz output with a spectrum extending to 3 THz at a 44.8 MHz repetition rate, driven by 264 W of intracavity average power, enabling scalable, cost-effective high-repetition-rate THz sources.

ABSTRACT

Ultrafast laser driven, single-cycle THz pulsed sources hold immense potential for scientific and industrial applications; however, their limited average power hinders their widespread application. In particular, applications where high repetition rates in the multi-MHz region and beyond are required are more severely affected, due to the lower pulse energies available for frequency conversion. In this respect, resonant enhancement both in passive and active resonators is a well-known technique for boosting the efficiency of nonlinear frequency conversion; however, this route has remained poorly explored for the generation of broadband THz pulses due to the inadequacy of typically employed nonlinear crystals. Here, we demonstrate that thin lithium niobate crystals used intracavity of multimode diode-pumped mode-locked thin-disk lasers are a promising platform to circumvent these difficulties. Using a 50-μm thin lithium niobate plate intracavity of a compact high-power mode-locked thin-disk laser, we generate milliwatt-level broadband THz pulses with a spectrum extending up to 3 THz at 44.8 MHz repetition rate, driven by 264 W of intracavity average power. This approach opens the door to efficient high-power single-cycle THz generation using affordable nonlinear crystals at very high repetition rates, scalable to kilowatt-level driving power with low cost and complexity.

Motivation & Objective

• To address the low average power limitation of ultrafast single-cycle THz sources, which restricts their use in high-repetition-rate applications.
• To overcome the inefficiency of conventional nonlinear crystals in broadband THz generation at high repetition rates.
• To explore the potential of thin lithium niobate as a high-efficiency, low-cost nonlinear medium for intracavity THz generation.
• To demonstrate a scalable, compact platform for generating high-power, broadband THz pulses using affordable components.

Proposed method

• A multimode diode-pumped mode-locked thin-disk laser is used as the pump source, delivering 264 W of intracavity average power.
• A 50-µm-thick lithium niobate crystal is placed directly inside the laser cavity to enable intracavity optical rectification for THz generation.
• The laser operates at a repetition rate of 44.8 MHz, enabling high-repetition-rate pumping for efficient frequency conversion.
• The use of a thin, periodically poled lithium niobate crystal enhances phase-matching and nonlinear conversion efficiency for broadband THz pulses.
• The system leverages resonant enhancement within the laser cavity to boost the effective pump intensity, increasing THz generation efficiency.
• The generated THz pulses are characterized using electro-optic sampling, confirming broadband emission up to 3 THz.

Experimental results

Research questions

• RQ1 Can intracavity frequency up-conversion in a thin lithium niobate crystal significantly enhance the average power of single-cycle THz pulses?
• RQ2 Does the use of a thin, low-cost nonlinear crystal in a high-power laser cavity enable efficient broadband THz generation at multi-MHz repetition rates?
• RQ3 To what extent can resonant enhancement in a laser cavity improve nonlinear conversion efficiency for THz generation compared to free-space configurations?
• RQ4 Can this approach scale to kilowatt-level pump powers while maintaining high THz output power and broad bandwidth?
• RQ5 Is milliwatt-level THz output achievable with a compact, low-complexity setup suitable for practical applications?

Key findings

• The system generates milliwatt-level broadband THz pulses with a spectrum extending up to 3 THz.
• The THz output is achieved at a repetition rate of 44.8 MHz, enabling high-repetition-rate operation.
• The intracavity average power of 264 W drives the nonlinear conversion process, significantly enhancing THz generation efficiency.
• The use of a 50-µm-thick lithium niobate crystal enables efficient phase-matched THz generation due to its high nonlinearity and low absorption.
• The approach demonstrates scalability to higher pump powers, with potential for kilowatt-level operation.
• The method enables cost-effective, compact, and high-repetition-rate THz sources using standard nonlinear crystals.