A Simpler Way To Amp Up High-Frequency Lasers

Researchers have used liquids to develop a high power tabletop radiation source in the terahertz region of the electromagnetic spectrum.

AsianScientist (Nov. 9, 2017) – Scientists at the Tata Institute of Fundamental Research (TIFR), Mumbai, have devised a high power radiation source in the terahertz (THz) region of the electromagnetic spectrum. They published their findings in Nature Communications.

The search for new and brighter radiation sources is an enduring quest in science and technology. While there are many sources that generate radiation across the entire electromagnetic spectrum, the THz region has been a challenge to produce and it is only in the last twenty years that sources have become available.

High power THz radiation has typically been produced by large, complex machines like free electron lasers. Compact sources, relying on semiconductor antennas and special crystals excited by visible or infrared femtosecond laser pulses, have very limited energy outputs, typically in the nanojoule level or lower. High power femtosecond lasers have been used to create THz emission that is a thousand times larger, in the microjoule range, from a plasma formed in air under special conditions.

In this study, scientists irradiated common laboratory liquids like methanol, acetone, dicholorethane, carbon disulphide and even water, with moderate energy femtosecond laser pulses, ionizing the liquid and forming long plasma channels called filaments. Contrary to the long-held belief that that liquids could not give out significant THz radiation because they would efficiently reabsorb whatever radiation was generated, the researchers measured energies as high as 50 microjoules. This energy level is thousands of times larger than that emitted by most existing sources, and ten to 20 times larger than that produced by irradiating air.

The researchers further demonstrated that the experimental conditions were simpler than those required to generate THz radiation in air. The mechanism that facilitates the large output (in spite of the deleterious absorption) is the induction of secondary emissions in the liquid by the femtosecond laser pulse, which would then combine with the incident laser pulse to produce the observed THz radiation.

The TIFR researchers are bullish about the applications of their liquid source, the brightest among compact, tabletop sources. They foresee many applications in THz imaging, material analysis, explosives detection and THz nonlinear optics.

The article can be found at: Dey et al. (2017) Highly Efficient Broadband Terahertz Generation from Ultrashort Laser Filamentation in Liquids.


Source: Tata Institute of Fundamental Research
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