An innovative method to tune lasers toward infrared wavelengths

Date:
October 14, 2020
Source:
Institut national de la recherche scientifique - INRS
Summary:
Researchers have discovered a cost-effective way to tune the
spectrum of a laser to the infrared, a band of great interest for
many laser applications.



FULL STORY ========================================================================== Researchers at Institut national de la recherche scientifique (INRS)
have discovered a cost-effective way to tune the spectrum of a laser to
the infrared, a band of great interest for many laser applications. They collaborated with Austrian and Russian research teams to develop this innovation, which is now the subject of a patent application. The results
of their work were recently published in Optica, the flagship journal
of the Optical Society (OSA).


==========================================================================
In this field of study, many laser applications have a decisive advantage
if the laser wavelength is located and possibly tunable in the infrared
region.

However, this is still hardly the case with current ultrafast laser technologies, and scientists need to explore various nonlinear processes
to shift the emission wavelength. In particular, the Optical Parametric Amplifier (OPA) has so far been the only well-established tool to
reach this infrared window. Although OPA systems offer a broad range
of tunability, they are complex, often made of multiples stages, and
quite expensive.

The team of Professor Luca Razzari, in collaboration with Professor
Roberto Morandotti, has demonstrated that large wavelength tunability
can also be achieved with a simple and much less expensive system:
a hollow-core (capillary) fiber filled with nitrogen. In addition,
this approach readily delivers optical pulses shorter than those of the
input laser and with high spatial quality. The researchers also had the
benefit of INRS expertise in this field, since the special system to
stretch and hold such fibers is marketed by the startup few-cycle.

Asymmetrical spectral broadening Usually, hollow-core fibers are filled
with a monatomic gas such as argon in order to symmetrically broaden
the spectrum of the laser and then recompress it into a much shorter
optical pulse. The research team discovered that by using a molecular
gas such as nitrogen, spectral broadening was still possible, but in an unexpected manner.

"Rather than spreading symmetrically, the spectrum was impressively
shifted toward less energetic infrared wavelengths. This frequency shift
is the result of the nonlinear response associated with the rotation of
the gas molecules and, as such, it can be easily controlled by varying
the gas pressure (i.e., the number of molecules) in the fiber," explains
Dr. Riccardo Piccoli, who led the experiments in Razzari's team.

Once the beam is broadened toward the infrared, the researchers filter
the output spectrum to keep only the band of interest. With this
approach, energy is transferred into the near-infrared spectral range
(with efficiency comparable to that of OPAs) in a pulse three times
shorter than the input, without any complex apparatus or additional
pulse post-compression system.

An international collaboration To complete the research, the INRS
scientists joined with Austrian and Russian colleagues. "We pooled our expertise after discovering at a conference how similar the phenomena
our two groups had observed were," says Razzari.

The team of researchers based in Vienna headed by Professor Andrius
Baltuska and Dr. Paolo A. Carpeggiani had a complementary strategy
to that of INRS. They also used a nitrogen-filled hollow-core fiber,
but rather than filtering the spectrum, they compressed it in time with
mirrors capable of adjusting the phase of the broadened pulse. "In this
case, the overall shift in the infrared was less extreme, but the final
pulse was much shorter and more intense, perfectly suited to attosecond
and strong-field physics" says Dr. Carpeggiani.

The Moscow-based team, led by Professor Aleksei Zheltikov, focused on developing a theoretical model to explain these optical phenomena. By
combining these three approaches, the researchers were able to fully
understand the complex underlying dynamics as well as achieve not only
the extreme red shift using nitrogen, but also efficient pulse compression
in the infrared range.

The international team believes the method could very well meet the
increasing demand for long-wavelength ultrafast sources in laser and strong-field applications, starting with less expensive industrial-grade tunable systems based on the emerging ytterbium laser technology.


========================================================================== Story Source: Materials provided by Institut_national_de_la_recherche_scientifique_-_INRS.

Original written by Audrey-Maude Ve'zina. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. P. A. Carpeggiani, G. Coccia, G. Fan, E. Kaksis, A. Pugžlys, A.

Baltuska, R. Piccoli, Y.-G. Jeong, A. Rovere, R. Morandotti,
L. Razzari, B. E. Schmidt, A. A. Voronin, A. M. Zheltikov. Extreme
Raman red shift: ultrafast multimode nonlinear space-time dynamics,
pulse compression, and broadly tunable frequency conversion. Optica,
2020; 7 (10): 1349 DOI: 10.1364/OPTICA.397685 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201014082748.htm

--- up 7 weeks, 2 days, 6 hours, 50 minutes
* Origin: -=> Castle Rock BBS <=- Now Husky HPT Powered! (1337:3/111)