In a remarkable breakthrough, a team of scientists from Korea and the United States has successfully created the world's most powerful terahertz pulses, opening up new possibilities in the field of terahertz physics. The research, led by Dr. Chul Kang from the Advanced Photonics Research Institute at the Gwangju Institute of Science and Technology in Korea and Professor Ki-Yong Kim from the University of Maryland, has demonstrated the ability to instantly ionize atoms and molecules, leading to plasma formation.
Terahertz waves, which lie between the microwave and infrared regions of the electromagnetic spectrum, have traditionally been considered non-ionizing. However, the research team has discovered that when a sufficient number of terahertz photons are focused, they can become ionizing radiation. This groundbreaking finding has the potential to revolutionize various applications, including spectroscopy, imaging, sensing, and communication.
To generate these high-energy terahertz pulses, the scientists employed a powerful 150-terawatt-class Tilaser. By converting optical energy into terahertz radiation using a lithium niobate crystal, known for its strong nonlinear properties and high damage resistance, the team achieved a peak terahertz field strength of 260 megavolts per centimeter. This intensity stands as the highest ever recorded for terahertz frequencies, ranging from 0.1 to 20 THz.
The key to this achievement lies in the use of a large-diameter (75 mm) lithium niobate wafer doped with 5% magnesium oxide. This innovative approach allowed for the production of scalable terahertz radiation. Additionally, the team discovered a new phase matching condition in lithium niobate that eliminates the need for the conventional tilted pulse front method. By ensuring that the optical laser pulse generating the terahertz radiation travels at the same speed as the terahertz waves within the lithium niobate, the researchers were able to generate high-frequency terahertz waves, peaking around 15 THz, using Tilaser pulses with an 800 nm central wavelength.
The innovative phase matching condition enabled the production of millijoule-level terahertz waves, which can be tightly focused to create strong electromagnetic fields. The team measured peak electric and magnetic field strengths of 260 ± 20 MV/cm and 87 ± 7 T, respectively. These intense terahertz pulses have the capability to tunnel ionize atoms and molecules in various materials, converting them into plasma. The researchers successfully demonstrated terahertz-driven ionization in metals, semiconductors, and polymers.
The study's findings have significant implications for the future of terahertz physics and its applications. The researchers believe that their work will open new avenues for studying nonlinear effects in terahertz-produced plasmas and utilizing terahertz-driven forces for various purposes. These include multi-keV terahertz harmonic generation and investigating relativistic effects by accelerating electrons with terahertz radiation.
Furthermore, the team emphasizes the potential for further scaling up the output energy and field strength of their terahertz source, which uses a planar lithium niobate crystal. They anticipate the possibility of generating super-strong (~GV/cm) terahertz fields in the future, further expanding the horizons of terahertz physics and its applications.
This groundbreaking research not only enhances our understanding of terahertz physics but also holds immense potential for numerous technological advancements in fields that require high-intensity terahertz sources. As the scientific community continues to explore the capabilities of these powerful terahertz pulses, it is evident that this breakthrough will have far-reaching implications across various domains, from fundamental research to practical applications.
