04-Sep-2009 - Max-Planck-Gesellschaft zur Förderung der Wissenschaften e.V.

"On-the-fly" spectroscopy with a diode laser and a frequency comb

MPQ scientists achieve high precision optical broadband spectroscopy by applying frequency comb technique to tunable diode lasers

The research field of optical spectroscopy has already attracted attention of generations of scientists, starting with Fraunhofer's discovery of dark lines in the sun spectrum in 1814 followed by the work of Kirchhoff and Bunsen in 1859 explaining these lines as absorption of light in atoms and molecules. Within the last decade, the invention of optical frequency combs has revolutionized the field of spectroscopy and enabled measurements with previously unattainable precision. Now, MPQ scientists (from the "Laboratory of Photonics & Quantum Measurements" lead by EPFL tenure track professor T.J. Kippenberg) developed a novel measurement scheme for broadband and fast measurements of optical spectra utilizing the accuracy of an optical frequency comb and transferring it to an easy-to-use tunable diode laser.

These tunable diode lasers can be swept in frequency (i.e. the "color" of the laser can be changed) to measure the spectral response of anything of interest, for example light absorption in gases but also the response of photonic elements in the growing field of nano-photonics. However, sweeping the frequency of a tunable diode laser alone does not allow for precise spectroscopic measurements, unless the instantaneous frequency of the diode laser at a certain time is known precisely. Here, the new measurement scheme comes into play, enabling an "on-the-fly" calibration of the sweeping diode laser using an optical fiber laser based frequency comb. The achieved precision of the spectroscopic measurement is better than 1 MHz (note that the frequency of the laser light is around 200 THz, corresponding to a relative accuracy of 5x10 to the -9).

As a first application, the newly developed spectroscopy scheme has been used by MPQ scientists Pascal Del'Haye and Dr. Arcizet to obtain absorption spectra of on-chip monolithic optical microresonators made of fused silica (so called microtoroids). These measurements allowed for the first time to analyze dispersion properties of these devices (conventional spectroscopy methods had so far failed due to the extremely narrow (sub-MHz) absorption lines of the microresonators). Numerical simulations as well as the experimental results show that the mode structure of microtoroids is extremely uniform, i.e. the optical modes that are supported by the device are nearly spaced equidistant. This surprising result is a consequence of the spatial shape of the optical modes within the resonator (leading to "red" modes at low frequencies being more confined inside the resonator than "blue" modes at high frequencies) that is partly compensated by a different material dispersion for different light frequencies (here, the "red" modes are travelling slower, i.e. the resonator seems to be larger for the "red" modes). "The small total dispersion of microtoroids makes them a well suited device for applications in microphotonics as well as for frequency comb generation via nonlinear optical frequency conversion", states Prof. Tobias Kippenberg. A patent of the new technique has been filed together with Max Planck Innovation.

Original publication: P. Del'Haye, O. Arcizet, M. L. Gorodetsky, R. Holzwarth & T. J. Kippenberg; "Frequency comb assisted diode laser spectroscopy for measurement of microcavity dispersion"; Nature Photonics, Advance Online Publication, August 2009

Facts, background information, dossiers
  • lasers
  • nanophotonics
  • Max-Planck-Innovation
More about Max-Planck-Gesellschaft
  • News

    How to remove dirt easily

    Dirt is not always dirt. Some dirt, such as dust, adheres only slightly to surfaces. But there is also dirt, such as dried paint, which sticks strongly. How can the adhesive properties of a surface be adjusted so that different types of dirt do not stick to it? This knowledge is essential t ... more

    A chemical factory for all cases

    In the future, bottlenecks in the supply of medicines could be more easily eliminated. An automated machine for radial synthesis developed by chemists at the Max Planck Institute of Colloids and Interfaces will enable the flexible production of medical agents and other chemical products. Th ... more

    Shaking off the correlated-electron traffic jam

    An international team of researchers from Switzerland, Germany, the USA and Great Britain has uncovered an anomalous metallic behavior in an otherwise insulating ceramic material. The team used ultrashort light pulses with a wide range of colors to watch what happens when the insulating qua ... more

More about Ecole Polytechnique Fédérale de Lausanne
  • News

    Photoelectrochemical water-splitting efficiency hits 4.5%

    Photoelectrochemical (PEC) water splitting for hydrogen fuel generation has been considered the Holy Grail of electrochemistry. But to achieve it, many scientists believe the materials have to be abundant and low cost. The most promising oxide photocathodes are cuprous oxide (Cu2O) photoele ... more

    Visualizing chemical reactions

    Researchers at the joint EPFL-Empa lab in Sion have developed a reactor system and an analysis method that has allowed them to observe the real-time production of synthetic natural gas from CO2 and H2 for the first time. Infrared (IR) thermography is used to determine the temperature of hu ... more

    A cheaper way to scale up atomic layer deposition

    Atomic layer deposition (ALD) involves stacking layers of atoms on top of each other like pancakes. The atoms come from a vaporized material called a precursor. ALD is a well-established technique for manufacturing microelectronics like semiconductors and magnetic heads for sound recording, ... more

  • Videos

    Water generates electricity (with a pinch of salt!)

    EPFL researchers have developed a system that generates electricity from osmosis with unparalleled efficiency. Their work, featured in "Nature", uses seawater, fresh water, and a new type of membrane just three atoms thick. more

    Stretchable electronics that quadruple in length

    EPFL researchers have developed conductive tracks that can be bent and stretched up to four times their original length. They could be used in artificial skin, connected clothing and on-body sensors. more

More about MPI für Quantenoptik
  • News

    An ultrafast glimpse of the photochemistry of the atmosphere

    Researchers at Ludwig-Maximilians-Universitaet (LMU) in Munich have explored the initial consequences of the interaction of light with molecules on the surface of nanoscopic aerosols. The nanocosmos is constantly in motion. All natural processes are ultimately determined by the interplay be ... more

    Modelling the molecular architecture

    Searching for new substances and developing new techniques in the chemical industry: tasks that are often accelerated using computer simulations of molecules or reactions. But even supercomputers quickly reach their limits. Now researchers at the Max Planck Institute of Quantum Optics in Ga ... more

    Direct Observation of Giant Molecules

    The tiny size of conventional diatomic molecules in the sub-nanometer regime hinders direct optical resolution of their constituents. Physicists from the Quantum Many Body Division at MPQ led by Prof. Immanuel Bloch were able to bind pairs of highly excited atoms at a distance of one microm ... more