Attosecond Light from Industrial Laser

A laser light shines in a gas cell where UCF researchers generate attosecond pulses. (Source: UCF)

University of Central Florida researchers are making the cutting-edge field of atto­second science more accessible to researchers from all disci­plines. The ability to make measurements with attosecond precision allows researchers to study the fast motion of electrons inside atoms and molecules at their natural time scale. Measuring this fast motion can help researchers under­stand funda­mental aspects of how light interacts with matter, which can inform efforts to harvest solar energy for power generation, detect chemical and biological weapons, perform medical diag­nostics and more.

“One of the main challenges of atto­second science is that it relies on world-class laser facilities,” says Michael Chini, an associate professor in UCF’s Department of Physics. “We are fortunate to have one here at UCF, and there are probably another dozen worldwide. But unfor­tunately, none of them are truly operated as user facilities, where scientists from other fields can come in and use them for research.” This lack of access creates a barrier for chemists, biologists, materials scientists and others who could benefit from applying atto­second science techniques to their fields, Chini says.

“Our work is a big step in the direction of making atto­second pulses more broadly accessible,” Chini says. “We show that indus­trial-grade lasers, which can be purchased commer­cially from dozens of vendors with a price tag of around $100,000, can now be used to generate atto­second pulses.” Chini says the setup is simple and can work with a wide variety of lasers with different parameters.

Attosecond science works somewhat like sonar or 3D laser mapping, but at a much smaller scale. When an attosecond light pulse passes through a material, the interaction with electrons in the material distorts the pulse. Measuring these dis­tortions allows researchers to construct images of the electrons and make movies of their motion. Typically, scientists have used complex laser systems, requiring large laboratory faci­lities and clean-room environ­ments, as the driving lasers for attosecond science.

Producing the extremely short light pulses needed for attosecond research – essentially consisting of only a single oscillation cycle of an electro­magnetic wave – has further required propagating the laser through tubes filled with noble gases, such as xenon or argon, to further compress the pulses in time. But Chini’s team has developed a way to get such few-cycle pulses out of more commonly available indus­trial-grade lasers, which previously could produce only much longer pulses.

They compress approxi­mately 100-cycle pulses from the industrial-grade lasers by using molecular gases, such as nitrous oxide, in the tubes instead of noble gases and varying the length of the pulses they send through the gas. They demons­trate com­pression to only 1.6 cycles, and single-cycle pulses are within reach of the technique, the researchers say. The choice of gas and duration of the pulses are key, says John Beetar, a doctoral student in UCF’s Depart­ment of Physics. “If the tube is filled with a molecular gas, and in particular a gas of linear molecules, there can be an enhanced effect due to the tendency of the molecules to align with the laser field,” Beetar says.

“However, this alignment-caused enhance­ment is only present if the pulses are long enough to both induce the rotational alignment and experience the effect caused by it,” he says. “The choice of gas is important since the rota­tional alignment time is dependent on the inertia of the molecule, and to maximize the enhancement we want this to coincide with the duration of our laser pulses. The reduction in complexity asso­ciated with using a commercial, industrial-grade laser could make attosecond science more approach­able and could enable inter­disciplinary appli­cations by scientists with little to no laser background,” Beetar says. (Source: UCF)

Reference: J. E. Beetar et al.: Multioctave supercontinuum generation and frequency conversion based on rotational nonlinearity, Sci. Adv. 6, eabb5375 (2020); DOI: 10.1126/sciadv.abb5375

Link: CREOL – College of Optics and Photonics, University of Central Florida, Orlando, USA

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