scientists control thz radiation flying focus

Scientists Develop a New Method to Control THz Radiation in Air

Introduction to Terahertz Radiation (THz)

Terahertz (THz) radiation, spanning frequencies from 0.1 to 10 THz, is integral to technologies such as imaging, sensing and spectroscopy. Despite decades of research on THz wave manipulation, precise control of their direction in air remains a challenge.

A Breakthrough by the Research Team at Ecole Polytechnique (CNRS)

A research team at Ecole Polytechnique (CNRS), part of Institute Polytechnique de Paris, has recently demonstrated the ability to steer laser-generated terahertz (THz) radiation in air using a novel technique known as "flying focus." Their findings, published in Physical Review Letters, could unlock new avenues for THz wave manipulation, potentially driving the development of innovative technologies.

Aurélien Houard and His Team's Research on THz Radiation

20 Years of Research on THz Radiation

"My research group has spent almost 20 years studying the production of terahertz (THz) radiation via laser-induced filaments in air," said Aurélien Houard, senior author of the paper, in an interview "A key benefit of these filaments is that they can form far from the laser source in open air. However, the THz emission has remained constrained along the laser axis, limiting its effectiveness for remote sensing applications."

The Flying Focus Technique

Steering Laser-Produced THz Radiation

Houard and his research team sought to effectively steer laser-produced terahertz (THz) radiation in air using "flying focus" a recently introduced technique. This approach is specifically designed to regulate the group velocity of focused femtosecond laser pulses.

The Role of Group Velocity in THz Radiation

"The group velocity plays a crucial role in defining the angular distribution of THz radiation within the filaments," explained Houard. "We then opted to test this principle using plasma filaments in air to determine whether we could regulate ionization velocity and consequently, the THz radiation angle."

Manipulating the Ionization Front for THz Wave Control

Controlling the Ionization Front

In essence, the method used by the researchers involve manipulating the ionization front of the laser (the point where air molecules lose electrons). By controlling this point, the researchers can direct THz waves, steering them at predetermined angles or even reversing their direction.

Frequency Manipulation for Increased Control

"By manipulating the frequency components of the laser pulse, the flying focus technique enables remote control over both the direction and velocity of the plasma generated at the laser's focus," Houard explained. "This allows for an increase in the radiation intensity produced by the plasma and provides control over the direction in which it is emitted."

Promising Results and Future Directions

Initial Success in Experiments

The preliminary experiments conducted by Houard and his team showed highly promising results, demonstrating the potential of the flying focus technique for steering THz waves through air. In the future, their findings may inspire other research groups to adopt this novel method and explore its applicability in various fields, potentially leading to advancements in technologies such as remote THz spectroscopy for detailed material analysis.

Next Steps in THz Radiation Research

Reversing the Direction of THz Radiation

"The study demonstrates that the flying focus technique can reverse the direction of secondary radiation, resulting in backward THz emission," explained Houard. "We now plan to investigate different approaches to improve THz emission from the filament and explore the application of this technique to other forms of secondary radiation produced by laser filaments."

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