Scientists from the Advanced Photonics Research Institute at Gwangju Institute of Science and Technology (GIST) in Korea and the Institute for Research in Electronics and Applied Physics at the University of Maryland have created the world’s strongest terahertz fields of 260 megavolts per centimeter (MV/cm) or equivalent peak intensity of 9 × 10¹³ watts per square centimeter (W/cm2). This peak field strength or intensity is the highest value achieved to date at terahertz frequencies (0.1~20 THz) across all types of terahertz sources. Nature‘s Light: Science & Applications published the research.

Potential new applications in nonlinear and relativistic terahertz physics

The authors discuss the potential of these pulses for driving nonperturbative ionization in gases, opening up potentially new opportunities in nonlinear and relativistic terahertz physics in plasmas.

The research team believes their work could create new opportunities to study nonlinear effects in terahertz-produced plasmas and utilize terahertz-driven ponderomotive forces for applications such as multi-keV terahertz harmonic generation and studying relativistic effects through terahertz-accelerated electrons. The terahertz source, which uses a planar lithium niobate crystal, shows promise for further scaling up the output energy and field strength.

Converting laser pulses to terahertz waves

To produce the high-energy terahertz pulses, the researchers used a 150-terawatt Ti:sapphire laser to convert optical energy into terahertz radiation through a process called optical rectification, directing the laser beam through a vacuum chamber, where it passed through a 60-mm iris before striking a 3-inch (76.2-mm) lithium niobate crystal wafer. The researchers aligned the crystal’s axis  with the laser’s polarization to maximize the efficiency of the terahertz generation process, known as optical rectification.

The scientists determined the peak electric and magnetic field strengths to be 260 ± 20 MV/cm and 87 ± 7 T at the focus by measuring the terahertz energy, focal spot size, and pulse duration.

Doping the lithium niobate wafer with 5% magnesium oxide (MgO), the researchers identified a phase matching condition in lithium niobate that occurs at approximately 15 THz for Ti:sapphire laser pulses with a central wavelength of 800 nm. This phase matching enabled the production of millijoule-level terahertz waves that can be tightly focused, potentially producing strong electromagnetic fields at the focus.