Palm-Sized Harnessing of Terahertz Band

Saturday - July 8 2023, 02:45 UTC - 1 year ago

At the RIKEN Center for Advanced Photonics, a team is exploring a strategy to produce terahertz waves by converting the output from an infrared laser, by using a nonlinear crystal known as lithium niobate. This method has traditionally required enormous lasers to generate terahertz waves powerful enough for most practical applications, but the team hopes to develop palm-sized, powerful terahertz wave sources. They have recently taken huge strides toward this goal and have multiple industrial collaborations underway.

Using new palm-sized devices, RIKEN researchers may have finally harnessed the terahertz band of the electromagnetic spectrum to effectively ‘X-ray’ things without using harmful ionizing radiation. Countless technologies—from smartphones and TVs to infrared instruments on the James Webb Space Telescope and high-speed wireless telecommunication devices using microwaves—exploit sections of the electromagnetic spectrum. But somewhere between commonly used microwaves and infrared light, lies a neglected region called the terahertz band. Terahertz waves have numerous exciting potential uses, not least because they can be used to see through or inside materials in a similar way to X-rays. Unlike X-rays, however, terahertz waves don’t deliver damaging ionizing radiation. But terahertz technologies have so far languished because it has been difficult to adapt microwave- or visible-light technologies to the terahertz range at useful sizes and power outputs.

For example, one approach to generate terahertz waves has been to develop electrical devices that produce higher frequency, ultrashort-wavelength microwaves. But this has been difficult in part because these devices need highly optimized parameters to produce greater electrical performance, which has proved challenging.

An alternative strategy is to produce terahertz waves by converting shorter, higher-frequency waves of infrared light, using materials known as nonlinear crystals. At the RIKEN Center for Advanced Photonics, the team is exploring this second strategy—producing terahertz waves by converting the output from an infrared laser. This method has traditionally required enormous lasers to generate terahertz waves powerful enough for most practical applications. But this has limited the take-up of terahertz technology for real-world applications—where portable devices for in situ analysis would be far more valuable.

In the Tera-Photonics Research Team, which leads by a researcher, is exploring to develop palm-sized, powerful terahertz wave sources for applications in industry and fundamental research. They have recently taken huge strides toward this goal and have multiple industrial collaborations underway.

They have focused on using lithium niobate, a nonlinear crystal that produces a beam of terahertz waves when irradiated with near-infrared laser light. When the researcher assumed leadership of the team in 2010, it was impossible to produce sufficiently powerful terahertz waves using this method, despite many years of work.

In 2011, they had to stop lab research for several months after a major earthquake struck Sendai, Japan, where their campus is. During that period, he remembered the result of a previous experiment that had caught his attention, and, he found an exciting hint of a possible path forward.

At that time, they used a near-infrared laser with pulse durations in the nanoseconds. The results indicated that when shorter, sub-nanosecond laser pulses were used, terahertz-wave generation as a function of the input laser pulse was altered. He then uncovered a 1993 paper that reported the effects of laser pulse duration in nonlinear crystals. The study analyzed visibile-light sources and mathematically predicting that sub-nanosecond pulse durations should give higher terahertz-wave outputs.

Hope of the team is to continue to develop palm-sized, powerful terahertz wave sources for applications in industry and fundamental research.