Check for THz radiation directly at the source

Photograph of a supercontinuum created by a short-pulsed laser. Creating a plasma produces light that spans the visible and invisible parts of the electromagnetic spectrum. Credit: Frontiers in Optoelectronics (2023). DOI: 10.1007/s12200-023-00095-y

Finding and developing efficient terahertz (THz) sources is one of the main scientific goals of the 21st century. The THz region of the electromagnetic spectrum is composed of light frequencies between the infrared and the microwave bands and accounts for one of the last almost unexplored regions of light without many stable and efficient sources and detectors currently available for the THz frequency range.

Recent efforts to create THz sources include the use of large laser facilities using ultra-short pulsed lasers capable of delivering roughly the amount of power used in a trillion 1 W bulbs for the duration of one quadrillionth of a second. The intensity of the focus of these lasers is strong enough to rip electrons from the materials (matter turned into plasma), which leads to the generation of light in the entire electromagnetic spectrum.

Unfortunately, to produce stronger THz frequencies in this method, current laser technology only allows a few “shots” to be fired over a few minutes or hours. This means that in order to measure and identify THz sources correctly, an identification method capable of fully identifying the radiation produced within a single shot must be developed.

The researchers led by Prof. X.-C. Zhang at The Institute of Optics, University of Rochester in New York, US, developed a method to detect the THz electric field by converting it to visible light known as “THz field-induced second harmonic” (TFISH) generation. This method uses nonlinear optics (the study of the interaction between matter and intense light) to double the frequency of the optical beam in the presence of THz waves.

While this measurement method has been used for almost two decades, researchers have developed a new strategy to measure the radiation directly at the plasma source as it is being produced. The work, titled “Local measurement of terahertz field-induced second harmonic generation in a plasma filament,” was published on December 13, 2023 in Frontiers in Optoelectronics.

Since the THz wave is trapped in the plasma when it is initiated, the nonlinear conversion from THz to visible light is extremely efficient and can even be detected by the unaided eye. In their system, the researchers generate plasma in dry air with intense radiation and use a second weak laser beam of optical radiation to probe the plasma at an angle that is out of line. By timing the arrival of the probing beam to create the plasma, the researchers can describe the dynamics of the plasma, providing a complete measurement suite for the THz source.

Additionally, using a grating to change the timing of the probing beam, the researchers demonstrated the first TFISH signal measurements made within a single laser shot. This method provides the largest bandwidth for THz single-shot detection to date.

More information:
Kareem J. Garriga Francis et al, Local measurement of terahertz field-induced second harmonic generation in plasma filaments, Frontiers in Optoelectronics (2023). DOI: 10.1007/s12200-023-00095-y

Presented by Frontiers Journals

Citation: Probing for THz radiation directly at the source (2023, December 21) retrieved 22 December 2023 from

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