Extreme Raman Red Shift Nitrogen-Filled Hollow-Core Fiber
Science & Technology

Discovered: Innovative Way to Tune Lasers Toward Infrared Wavelengths

A laser optical pulse (blue) enters from the left into the hollow-core fiber stuffed with nitrogen gasoline (purple molecules) and, alongside propagation, experiences a spectral broadening in direction of longer wavelengths, depicted as an orange output beam (proper). This nonlinear phenomenon is attributable to the Raman impact related to the rotations of the gasoline molecules beneath the laser discipline, as schematically illustrated within the backside panel. Credit score: Riccardo Piccoli (INRS)

Researchers at Institut nationwide de la recherche scientifique (INRS) have found an economical means to tune the spectrum of a laser to the infrared, a band of nice curiosity for a lot of laser functions.

They collaborated with Austrian and Russian analysis groups to develop this innovation, which is now the topic of a patent software. The outcomes of their work had been just lately revealed in Optica, the flagship journal of the Optical Society (OSA). On this discipline of examine, many laser functions have a decisive benefit if the laser wavelength is situated and probably tunable within the infrared area. Nevertheless, that is nonetheless hardly the case with present ultrafast laser applied sciences, and scientists want to discover varied nonlinear processes to shift the emission wavelength. Particularly, the Optical Parametric Amplifier (OPA) has up to now been the one well-established device to attain this infrared window. Though OPA programs supply a broad vary of tunability, they’re advanced, usually product of multiples levels, and fairly costly.

INRS researcher Luca Razzari makes a speciality of nanophotonics and nonlinear optics. Credit score: Christian Fleury (INRS)

The staff of Professor Luca Razzari, in collaboration with Professor Roberto Morandotti, has demonstrated that giant wavelength tunability may also be achieved with a easy and far cheaper system: a hollow-core (capillary) fiber stuffed with nitrogen. As well as, this strategy readily delivers optical pulses shorter than these of the enter laser and with excessive spatial high quality. The researchers additionally had the good thing about INRS experience on this discipline, for the reason that particular system to stretch and maintain such fibers is marketed by the startup few-cycle.

Normally, hollow-core fibers are stuffed with a monatomic gasoline equivalent to argon so as to symmetrically broaden the spectrum of the laser after which recompress it right into a a lot shorter optical pulse. The analysis staff found that by utilizing a molecular gasoline equivalent to nitrogen, spectral broadening was nonetheless doable, however in an surprising method.

Moderately than spreading symmetrically, the spectrum was impressively shifted towards much less energetic infrared wavelengths. This frequency shift is the results of the nonlinear response related to the rotation of the gasoline molecules and, as such, it may be simply managed by various the gasoline stress (i.e., the variety of molecules) within the fiber.
Dr. Riccardo Piccoli, who led the experiments in Razzari’s staff.

As soon as the beam is broadened towards the infrared, the researchers filter the output spectrum to preserve solely the band of curiosity. With this strategy, power is transferred into the near-infrared spectral vary (with effectivity comparable to that of OPAs) in a pulse thrice shorter than the enter, with none advanced equipment or further pulse post-compression system.

To finish the analysis, the INRS scientists joined with Austrian and Russian colleagues.

We pooled our experience after discovering at a convention how related the phenomena our two teams had noticed had been.
Luca Razzari

The staff of researchers based mostly in Vienna headed by Professor Andrius Baltuska and Dr. Paolo A. Carpeggiani had a complementary technique to that of INRS. Additionally they used a nitrogen-filled hollow-core fiber, however reasonably than filtering the spectrum, they compressed it in time with mirrors able to adjusting the part of the broadened pulse. “On this case, the general shift within the infrared was much less excessive, however the remaining pulse was a lot shorter and extra intense, completely suited to attosecond and strong-field physics,” says Dr. Carpeggiani.

The Moscow-based staff, led by Professor Aleksei Zheltikov, targeted on creating a theoretical mannequin to clarify these optical phenomena. By combining these three approaches, the researchers had been ready to totally perceive the advanced underlying dynamics in addition to obtain not solely the acute purple shift utilizing nitrogen, but additionally environment friendly pulse compression within the infrared vary.

The worldwide staff believes the tactic may very properly meet the growing demand for long-wavelength ultrafast sources in laser and strong-field functions, beginning with cheaper industrial-grade tunable programs based mostly on the rising ytterbium laser expertise.

Reference: “Excessive Raman purple shift: ultrafast multimode nonlinear space-time dynamics, pulse compression, and broadly tunable frequency conversion” by P. A. Carpeggiani, G. Coccia, G. Fan, E. Kaksis, A. Pugžlys, A. Baltuška, R. Piccoli, Y.-G. Jeong, A. Rovere, R. Morandotti, L. Razzari, B. E. Schmidt, A. A. Voronin and A. M. Zheltikov, 8 October 2020, Optica.
DOI: 10.1364/OPTICA.397685

Researchers have obtained monetary help from the Pure Sciences and Engineering Analysis Council of Canada (NSERC), PROMPT, the Austrian Science Fund (FWF), the Russian Basis for Primary Analysis (RFBR), the Welch Basis, and the Russian Science Basis (RSF).

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