In a significant breakthrough, scientists at the Tata Institute of Fundamental Research (TIFR), Mumbai have devised a high power radiation source in the much sought after terahertz (THz) region of the electromagnetic spectrum. This study, done in collaboration with laboratories in Greece and France, will be unveiled in the journal Nature Communications on Oct 30, 2017.
The search for new and brighter radiation sources is an enduring quest in science and technology [1,2]. While there are many sources across the entire electromagnetic spectrum, the terahertz region (wedged between the infrared/optical and the microwave regions) has been a challenge and it is only in the last twenty years that sources have started becoming available.
(a) A high power laser pulse ionizes and creates plasma in a common laboratory liquid like acetone or dichloroethane or even water. The plasma can be seen as a long line along the length of the tube containing the liquid (see inset). This line is called a filament and it radiates, among others, copious terahertz radiation. (b) Integrated terahertz energy obtained from various liquids and air. (c) Power spectrum of terahertz obtained from the filamentation of acetone, ethanol and air.
Credit: Indranuj Dey, G. Ravindra Kumar
High power terahertz radiation has typically been available from large, complex machines like Free Electron Lasers. Compact sources, relying on semiconductor antennas and special crystals excited by visible/infrared femtosecond laser pulses, have very limited energy outputs, typically in the nanojoule (billionth of a joule) level or lower.
They are not useful for many applications. High power femtosecond lasers have however, excited terahertz emission that are a thousand times larger (microjoules) from a plasma formed in air, under special conditions .
For a long time, researchers in this area have believed that liquids could not give out significant terahertz radiation, because they would efficiently reabsorb whatever was generated. Yet, this is where the TIFR researchers proved successful. In their experiments, they 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.
To their delight they measured energies as high as 50 microjoules, thousands of times larger than the energies emitted by most existing sources and 10-20 times larger than those produced from air. Their careful characterization and systematic study showed that the experimental conditions were simpler than those needed for air.
The mechanism that facilitates the large output (in spite of the deleterious absorption) has emerged from models used by their theoretical collaborators from the Institute of Electronic Structure and Laser, Foundation for Research and Technology Hellas, Greece and Ecole Polytechnique, Paris. The essence of this model is that the femtosecond laser pulse induces secondary emissions in the liquid which would then combine with the incident laser pulse to produce the observed terahertz radiation.
The TIFR researchers are bullish about the applications of their liquid source, the brightest among compact, tabletop sources. They foresee many applications in terahertz imaging, material analysis, explosives detection and terahertz nonlinear optics. This new source certainly increases the stock of terahertz radiation. Shall we say, terahertz liquidity boosted?
 Tonouchi, M. "Cutting-edge terahertz technology." Nat. Photonics 1, 97-105 (2007).
 Baierl, S. et al. "Nonlinear spin control by terahertz-driven anisotropy fields." Nat. Photonics 10, 715-718 (2016).
 Kim, K. Y., Taylor, A. J., Glownia, J. H. & Rodriguez, G. "Coherent control of terahertz supercontinuum generation in ultrafast laser-gas interactions." Nat. Photonics 2, 605-609 (2008).
G. Ravindra Kumar | EurekAlert!
Meteoritic stardust unlocks timing of supernova dust formation
19.01.2018 | Carnegie Institution for Science
Artificial agent designs quantum experiments
19.01.2018 | Universität Innsbruck
On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.
We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
19.01.2018 | Materials Sciences
19.01.2018 | Health and Medicine
19.01.2018 | Physics and Astronomy