Benjamin Clough

Recent Progresses in Terahertz Wave Air Photonics

Terahertz (THz) wave generation and detection using gaseous medium as both the THz wave emitter and sensor, also termed “THz wave air photonics”, has attracted much scientific attention. We report the most recent progresses in THz generation and detection in laser-induced gas plasma. The overall emphasis of this paper is on THz wave detection with gaseous medium, while in the generation part, emphasis will be on the case with two-color laser excitation.

Laser air photonics: beyond the terahertz gap

Through the ionization process, the very air that we breath is capable of generating terahertz (THz) electromagnetic field strengths greater than 1 MV/cm, useful bandwidths of over 100 THz, and highly directional emission patterns. Following the ionization of air, the emitted air-plasma fluorescence or acoustics can serve as an omnidirectional, broadband, THz wave sensor. Here we review significant advances in laser air photonics that help to close the “THz gap,” enabling ultra-broadband THz wave generation and detection, for applications including materials characterization and non-destructive evaluation. The feasibility for remote sensing, as well as the remaining challenges and future opportunities are also discussed.

THz air photonics for standoff detection

By “seeing” the fluorescence or “hearing” the sound emitted by plasma, coherent detection of broadband THz waves by laser-induced plasma at standoff distance is feasible. We will report these recent developments in THz wave sensing with air-plasma photonics.

Science, technology, and application of THz air photonics

The significant scientific and technological potential of terahertz (THz) wave sensing and imaging has been attracted considerable attention within many fields of research. However, the development of remote, broadband THz wave sensing technology is lagging behind the compelling needs that exist in the areas of astronomy, global environmental monitoring, and homeland security. This is due to the challenge posed by high absorption of ambient moisture in the THz range. Although various time-domain THz detection techniques have recently been demonstrated, the requirement for an on-site bias or forward collection of the optical signal inevitably prohibits their applications for remote sensing. The objective of this paper is to report updated THz air-plasma technology to meet this great challenge of remote sensing. A focused optical pulse (mJ pulse energy and femtosecond pulse duration) in gas creates a plasma, which can serve to generate intense, broadband, and directional THz waves in the far field.

Laser Air Photonics: Covering the ＂Terahertz Gap＂ and Beyond

Laser air photonics involves the interaction of high-peak-power femtosecond laser pulses with air. Through the ionization process, the very air that we breath is capable of generating terahertz (THz) electromagnetic field strengths greater than 1 MV/cm, useful bandwidths of over 100 THz, and highly directional emission patterns. Following the ionization of air, the emitted air-plasma uorescence or acoustics can serve as an omnidirectional, broadband, THz wave sensor. Frequencies lying within the THz band were historically termed the ”THz gap,” due to the relative difficulty for generating and detecting the radiation at these frequencies. Here we review significant advances in laser air photonics that help to close this ”gap,” enabling ultra-broadband THz wave generation and detection through nonlinear optical processes. Research opportunities and applications including non-destructive evaluation, material characterization, and feasibility for remote sensing, are discussed.