A method for generating powerful multicycle pulses of terahertz radiation proposed by Lobachevsky University researchers
Developing new scientific and technological tools based on terahertz radiation isone of the cutting–edge areas of modern photonics research.The potential for using electromagnetic waves in the terahertz spectrum is becoming increasingly promising in such fields as the acceleration of charged particles, the study of material properties through their interaction with electromagnetic radiation, and the development of innovative safety systems. In many cases, terahertz pulses with a large number of oscillation cycles are required to effectively interact with matter.
Researchers from the General Physics Department at the UNN Faculty of Radiophysics have developed a new method for generating multicycle terahertz waves, enabling a substantial boost in radiation power and the ability to control its characteristics depending on specific practical needs.
"Generating multi-period electromagnetic pulses in the terahertz frequency range is a highly challenging task. Techniques from laser technology and electronics are ineffective in this range. We have succeeded in developing a nonlinear optical method capable of producing several dozen oscillations of the terahertz field using a single short laser pulse. This method enables scaling up the radiation power by increasing the laser pumping energy," explained Mikhail Bakunov, one of the study's authors, Head of the General Physics Department at the UNN Faculty of Radiophysics.
Generally, multi-period terahertz radiation is generated by applying a laser pulse to a crystal made up of many layers with alternating nonlinear characteristics. Two adjacent layers generate one cycle of a terahertz wave, and the thickness of the layer determines its frequency. However, this expensive approach does not allow for obtaining a sufficiently powerful radiation beam at the output, and changing the radiation frequency requires manufacturing a structure with the desired period.
Researchers from Nizhny Novgorod suggested utilizing a lithium niobate monocrystal with a precisely chosen orientation of its crystallographic axes. This approach allows for tuning the generated frequency across a broad spectrum by merely changing the angle of incidence of the pump laser beam on the crystal. In this case, the output radiation power can be boosted by employing commercially available large-diameter crystal plates and high-intensity wide laser beams.
"Our calculations have been validated by experimental results.The method proves to be more efficient and cost-effective compared to existing solutions. The scientific community has already shown interest in the development. Colleagues from the University of Pécs in Hungary are exploring the method as a means for particle acceleration. We believe the technology can be further refined. We are currently searching for materials that could substitute the lithium niobate crystal used in the design, potentially enhancing the method’s effectiveness," Mikhail Bakunov said.
The project was supported by a grant from the Russian Science Foundation ("Generation and detection of terahertz radiation by ultrashort laser pulses under conditions of resonant and multiphoton absorption"). The research was carried out by scientists from the General Physics Department at the UNN Faculty of Radiophysics. The findings were published in the prestigious journal Optics Letters.
