Precise molecular fingerprinting on the fly

December 22, 2015, Max Planck Institute of Quantum Optics
Time-domain interference signal of the beats between the two frequency-agile laser combs and part of the resulting spectrum of the CO2 molecule. Credit: MPQ, Laser Spectroscopy Division

Electro-optic modulators, which can switch light on and off within just picoseconds, are enabling ever faster telecommunication over optical glass fibres, so that large movies can be streamed more smoothly across oceans into our homes. The same tools have now been harnessed for high-speed and accurate molecular sensing, as reported by an international collaboration around Dr. Nathalie Picqué, Max Planck Institute of Quantum Optics and Ludwig-Maximilians-Universität Munich, in a letter published in Nature Photonics, 21 December 2015. The collaboration partners are with the Laboratoire Interdisciplinaire Carnot de Bourgogne (France) and the Institut des Sciences Moléculaires d'Orsay (France).

Molecules absorb light at well-defined particular colours or optical frequencies. Usually such characteristic frequencies are located in the infrared region of the electromagnetic spectrum. Precisely measuring a set of such absorption dips unambiguously identifies the molecules and quantifies their abundance in the probed environment. Because detection of molecules by optical absorption spectroscopy is sensitive and nonintrusive, it finds an increasing number of applications, from biomedical diagnostics to atmospheric sensing.

In the gas phase, the absorption lines are narrow so that high spectral resolution is needed to distinguish the different lines. Although many powerful spectroscopic techniques have been developed, rapid and precise high-resolution sensing is still a challenge.

A team of scientists at MPQ reports a promising new technique of near-infrared spectroscopy. They use modulators and a nonlinear optical fibre to produce two frequency combs, each with more than a thousand evenly spaced infrared spectral lines with a remarkably flat intensity distribution. Line spacing and spectral position can be selected quickly and freely by simply dialing a knob. Such frequency-agile optical combs offer unprecedented freedom when interrogating a molecular spectrum via a powerful technique called multiplexed dual-comb spectroscopy. Two mutually coherent combs are combined in an interferometer. Unprecedented refresh rates (80 kHz) and tuning speeds (10 nm s-1) at high signal-to-noise ratio are achieved.

Such unique combination holds much promise for trace gas sensing, a domain relevant to physics, biology, chemistry, industry or atmospheric sciences. "Furthermore, the frequency-agile frequency comb generator might also become an enabling tool for applications beyond spectroscopy, like for arbitrary waveform generation, radio-frequency photonics, or microscopy," concludes Dr. Ming Yan, a post-doc working at the experiment.

Explore further: Mid-IR frequency combs enable high resolution spectroscopy for sensitive gas sensing

Related Stories

Watching the heart beat of molecules

October 17, 2013

A team of scientists around Prof. Theodor W. Hänsch and Dr. Nathalie Picqué at the Laser Spectroscopy Division of the Max Planck Institute of Quantum Optics (Garching), in a collaboration with the Ludwig-Maximilians-Universität ...

Precision gas sensor could fit on a chip

February 27, 2015

Using their expertise in silicon optics, Cornell engineers have miniaturized a light source in the elusive mid-infrared (mid-IR) spectrum, effectively squeezing the capabilities of a large, tabletop laser onto a 1-millimeter ...

Recommended for you

Structure of fossil-fuel source rocks is finally decoded

November 13, 2018

The fossil fuels that provide much of the world's energy orginate in a type of rock known as kerogen, and the potential for recovering these fuels depends crucially on the size and connectedness of the rocks' internal pore ...

Atomic parity violation research reaches new milestone

November 12, 2018

A reflection always reproduces objects as a complete mirror image, rather than just its individual parts or individual parts in a completely different orientation. It's all or nothing, the mirror can't reflect just a little. ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.