Tiny crystalline resonators produce mid-infrared frequency combs for fingerprinting of molecules

Jan 11, 2013
Tiny crystalline resonators produce mid-infrared frequency combs for fingerprinting of molecules
Cover of the July 2012 issue of Nature Photonics, displaying crystalline microresonators used for mid-infrared frequency comb conversion. Credit: Nature Photonics

Most molecules, including those of importance in medical diagnostics or pollution monitoring, have characteristic "fingerprints" in the mid-infrared spectral region. However, state-of-the-art mid-infrared frequency comb techniques require systems that are often costly and limited in their applications. In an article just published in Nature Communications (January 8th, 2013), scientists of the Laser Spectroscopy Division of the Max-Plank-Institute of Quantum Optics, in a collaboration with the Ecole Polytechnique de Lausanne (Switzerland), the Ludwig-Maximilians-Universität Munich, the Menlo Systems GmbH and the Institut des Sciences Moléculaires d'Orsay (France), have demonstrated the generation of mid-infrared frequency combs with small crystalline micro-resonators. Such miniaturized instruments, which can detect and characterize such molecules quickly and with high sensitivity, could revolutionize many areas of science and technology.

Optical generators are coherent light sources, which produce a "comb" of many precisely evenly spaced spectral lines. During the last decade, such combs have revolutionized the art of measuring the frequency of light, as recognized in 2005 by the award of the Physics Nobel Prize to Prof. Theodor W. Hänsch. Today frequency combs are becoming enabling tools for new and unexpected applications. In particular, frequency combs are strongly impacting molecular spectroscopy by dramatically improving the recording speed, the resolution and the accuracy of Fourier spectrometers. The mid-infrared spectral range, also called molecular fingerprint region, is of primary importance to molecular physics. However, as reviewed in an article published in the July 2012 issue of Nature Photonics, emerging mid-infrared frequency comb techniques still need considerable improvements: the systems are often based on nonlinear frequency conversion of near-infrared laser sources, which makes them bulky, and their use is limited to specialists.

The new technique developed by a team of scientists at MPQ avoids these obstacles. Here, mid-infrared frequency comb radiation is generated by exciting whispering gallery modes in a small toroidal monolithic resonator. A crystalline micro-resonator with a quality-factor exceeding 109 is pumped by a continuous-wave laser. By a nonlinear process called four-wave mixing, it produces a broad comb spectrum consisting of discrete lines spaced by 100 GHz at mid-infrared wavelengths near 2.5 µm. "The remarkable characteristics of such comb generators are their small size, large line-spacing, high power per comb line, and efficient conversion," says Dr. Christine Wang, the post-doc who has performed the experiment. "An appropriate choice of the material – here magnesium fluoride – and proper engineering are crucial to realize broad spectral span and low-phase noise, as required for frequency comb operation." Such miniaturized sources hold much promise for on-chip frequency-comb spectrometers. The spectrum of the fundamental vibrations of liquid phase samples might be measured within a few nanoseconds with a similar refresh time!

Explore further: Researchers build reversible tractor beam that moves objects 100 times farther than other efforts

More information: Wang, C. et al. Mid-infrared optical frequency combs at 2.5 μm based on crystalline microresonators, Nature Communications 4, Article number: 1345, Issue of January 8th, 2013, DOI: 10.1038/ncomms2335

Related Stories

Cutting light with a comb

Dec 14, 2012

(Phys.org)—Quantum physicists from ETH Zurich have discovered special properties in a laser, thanks to which portable devices can be built to analyse gases and liquids accurately and reliably in the future.

An octave spanning chip-based optical ruler

Aug 08, 2011

More than a decade ago, the frequency comb technique was developed at the Max Planck In-stitute of Quantum Optics by Professor Theodor W. Hänsch. The new tool has stimulated fun-damental research as well ...

Recommended for you

Backpack physics: Smaller hikers carry heavier loads

4 hours ago

Hikers are generally advised that the weight of the packs they carry should correspond to their own size, with smaller individuals carrying lighter loads. Although petite backpackers might appreciate the ...

Extremely high-resolution magnetic resonance imaging

4 hours ago

For the first time, researchers have succeeded to detect a single hydrogen atom using magnetic resonance imaging, which signifies a huge increase in the technology's spatial resolution. In the future, single-atom ...

'Attosecond' science breakthrough

5 hours ago

Scientists from Queen's University Belfast have been involved in a groundbreaking discovery in the area of experimental physics that has implications for understanding how radiotherapy kills cancer cells, among other things.

Quantum holograms as atomic scale memory keepsake

5 hours ago

Russian scientists have developed a theoretical model of quantum memory for light, adapting the concept of a hologram to a quantum system. These findings from Anton Vetlugin and Ivan Sokolov from St. Petersburg ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (1) Jan 11, 2013
I can't tell the difference between surface acoustic wave frequency combs:
Änd what is described here.

Since I am not trained or paid to know the difference I am going to wallow in my ignorance and assert there is no difference.