Application: High resolution spectroscopy
Product: IRis-F1
Kenichi N. Komagata, Valentin J. Wittwer, Thomas Südmeyer, Lukas Emmenegger, Michele Gianella
Arxiv; 2022
View abstract
| Access preprint publication
Quantum cascade laser (QCL) frequency combs have revolutionized mid-infrared (MIR) spectroscopy by their high brightness and fast temporal resolution, and are a promising technology for fully-integrated and cost-effective sensors. As for other integrated comb sources such as micro-combs and interband cascade laser, QCLs have a comb spacing of several GHz, which is adequate for measurements of wide absorbing structures, typically found in liquid or solid samples. However, high-resolution gas-phase spectra require spectral interleaving and frequency calibration. We developed a frequency calibration scheme for fast interleaved measurements with combs featuring multi-GHz spacing. We then demonstrate dual-comb spectroscopy with 600 kHz accuracy in single-shot 54-ms measurements over 40 cm−1 using two QCLs at 7.8 μm. This work is an important contribution towards fast fingerprinting of complex molecular mixtures in the MIR. Moreover, the calibration scheme could be used with micro-combs for spectroscopy and ranging, both in comb-swept and comb-calibrated setups.
Application: High resolution spectroscopy
Product: IRis-core
Michele Gianella, Simon Vogel, Valentin Wittwer, Thomas Südmeyer, Jérôme Faist, Lukas Emmenegger
Optics Letters; 2022
View abstract
| Access journal publication
In dual-comb spectroscopy, there is a one-to-one map between the frequencies of the measured beat notes and the frequencies of the optical comb lines. Its determination usually involves the use of one or more reference lasers with known frequencies. Quantum cascade laser frequency combs, however, are often operated in a free-running mode, and without a reference, the determination of the RF-to-optical frequency map is not trivial. Here, we propose a method by which the comb shift is measured with an unbalanced Mach–Zehnder interferometer, and the spectral point spacing is determined through the intermode beat measured on the laser electrodes. The frequency axis is accurate within ∼ 0.001 cm−1.
Application: Gas analysis, High resolution spectroscopy, Time resolved vibrational spectroscopy
Product: IRis-F1
Josef A. Agner, Sieghard Albert, Pitt Allmendinger, Urs Hollenstein, Andreas Hugi, Pierre Jouy, Karen Keppler, Markus Mangold, Frédéric Merkt & Martin Quack
Molecular Physics; 2022
View abstract
| Access journal publication
Optical frequency-comb spectroscopy has proven a very useful tool for high-resolution molecular spectroscopy. Frequency combs based on quantum-cascade lasers (QCL) offer the possibility to easily explore the mid-infrared spectral range (4 µm to 12 µm), but are characterised by large repetition frequencies (∼ 10 GHz) which make them seemingly unsuitable for high-resolution spectroscopy. Here, we present techniques to overcome this limitation. We have employed the combined advantages of high temporal and high spectral resolution to measure the infrared (IR) spectra of CF4 and CHCl2F in pulsed, skimmed supersonic beams. The low rotational temperature of the beams and the narrow expansion cone after the skimmer enabled the recording of spectra of cold samples with high resolution. The spectra cover the range from 1200 cm−1 to 1290 cm−1 and the narrowest lines have a full width at half maximum of 15 MHz, limited by the Doppler effect. The results demonstrate the potential of QCL dual-comb spectroscopy for broadband (> 60 cm−1) acquisition of spectra at high spectral (better than 5·10−4 cm−1, 15 MHz) and temporal (better than 4 µs) resolution and high sensitivity in the mid-infrared range. The power of the new technology is demonstrated by comparison with previous results for these molecules obtained by FTIR and diode laser spectroscopy.
Application: High resolution spectroscopy
Product: IRis-F1
Muriel Lepère, Olivier Browet, Jean Clément, Bastien Vispoel, Pitt Allmendinger, Jakob Hayden, Florian Eigenmann, Andreas Hugi, Markus Mangold
Journal of Quantitative Spectroscopy and Radiative Transfer; 2022
View abstract
| Access journal publication
| Access preprint publication
To meet the challenges of high-resolution molecular spectroscopy, increasingly sophisticated spectroscopic techniques were developed. For a long time FTIR and laser-based spectroscopies were used for these studies. The recent development of dual-comb spectroscopy at high-resolution makes this technique a powerful tool for gas phase studies. We report on the use and characterization of the IRis-F1, a tabletop mid-infrared dual-comb spectrometer, in the newly developed step-sweep mode. The resolution of the wavenumber axis is increased by step-wise tuning (interleaving) and accurate measurement of the laser center wavelength and repetition frequency. Doppler limited measurements of N2O and CH4 reveal a wavenumber accuracy of 10−4 cm−1 on the covered range of > 50 cm−1. Measured half-widths of absorption lines show no systematic broadening, indicating a negligible instrument response function. Finally, measurements of nitrogen pressure broadening coefficients in the ν4 band of methane show that quantum cascade laser dual-comb spectroscopy in step-sweep mode is well adapted for measurements of precision spectroscopic data, in particular line shape parameters.
Application: High resolution spectroscopy
Product: IRis-F1
K. Komagata, A. Shehzad, G. Terrasanta, P. Brochard, R. Matthey, M. Gianella, P. Jouy, F. Kapsalidis, M. Shahmohammadi, M. Beck, V. J. Wittwer, J. Faist, L. Emmenegger, T. Südmeyer, A. Hugi, and S. Schilt
Optics Express; 2021
View abstract
| Access journal publication
We demonstrate coherent averaging of the multi-heterodyne beat signal between two quantum cascade laser frequency combs in a master-follower configuration. The two combs are mutually locked by acting on the drive current to control their relative offset frequency and by radio-frequency extraction and injection locking of their intermode beat signal to stabilize their mode spacing difference. By implementing an analog common-noise subtraction scheme, a reduction of the linewidth of all heterodyne beat notes by five orders of magnitude is achieved compared to the free-running lasers. We compare stabilization and post-processing corrections in terms of amplitude noise. While they give similar performances in terms of signal-to-noise ratio, real-time processing of the stabilized signal is less demanding in terms of computational power. Lastly, a proof-of-principle spectroscopic measurement was performed, showing the possibility to reduce the amount of data to be processed by three orders of magnitude, compared to the free-running system.
Application: High resolution spectroscopy
Product: IRis-F1
Gustavo Villares, Andreas Hugi, Stéphane Blaser & Jérôme Faist
Nature Communications; 2014
View abstract
| Access journal publication
Dual-comb spectroscopy performed in the mid-infrared—where molecules have their strongest rotovibrational absorption lines—offers the promise of high spectral resolution broadband spectroscopy with very short acquisition times (μs) and no moving parts. Recently, we demonstrated frequency comb operation of a quantum-cascade-laser. We now use that device in a compact, dual-comb spectrometer. The noise properties of the heterodyne beat are close to the shot noise limit. Broadband (15 cm−1) high-resolution (80 MHz) absorption spectroscopy of both a GaAs etalon and water vapour is demonstrated, showing the potential of quantum-cascade-laser frequency combs as the basis for a compact, all solid-state, broadband chemical sensor.
Application: High resolution spectroscopy
Product: IRis-F1
Muriel Lepère, Olivier Browet, Sylvain Leonis, Jean Clément, Pitt Allmendinger, Kuno Knapp, Florian Eigenmann, Markus Mangold
SPIE Proceedings; 2021
View abstract
| Access journal publication
For a long time FTIR and laser-based spectroscopies have been used for high resolution molecular spectroscopy studies. The recent development of Dual-Comb Spectroscopy at high resolution (<0.001 cm-1) makes this technique a powerful tool for gas phase studies. The IRis-F1 is a dual-comb spectrometer building on quantum cascade laser frequency combs. We show that it is very well adapted for measurements of line shape parameters. Despite its weak abundance, methane effect on climate and atmospheric chemistry is important. We measured with IRis-F1 the half-widths of absorption lines of methane diluted in nitrogen, and compared with results obtained by other spectroscopies.
Application: High resolution spectroscopy
Product: IRis-F1
Gianella, Michele; Nataraj, Akshay; Tuzson, Béla; Jouy, Pierre; Kapsalidis, Filippos; Beck, Mattias; Mangold, Markus; Hugi, Andreas; Faist, Jérôme; Emmenegger, Lukas
Optics Express, Optical Society of America; 2020
View abstract
| Access journal publication
We present gapless, high-resolution absorption and dispersion spectra obtained with quantum cascade laser frequency combs covering 55 cm−1. Using phase-sensitive dual comb design, the comb lines are gradually swept over 10 GHz, corresponding to the free spectral range of the laser devices, by applying a current modulation. We show that with interleaving the spectral point spacing is reduced by more than four orders of magnitude over the full spectral span of the frequency comb. The potential of this technique for high-precision gas sensing is illustrated by measuring the low pressure (107 hPa) absorption and dispersion spectra of methane spanning the range of 1170 cm−1 - 1225 cm−1 with a resolution of 0.001 cm−1.
Application: High resolution spectroscopy
Product: IRis-F1
Shehzad, A.; Brochard, P.; Matthey, R.; Kapsalidis, F.; Shahmohammadi, M.; Beck, M.; Hugi, A.; Jouy, P.; Faist, J.; Südmeyer, T.; Schilt, S.
Optics Express, Optical Society of America; 2019
View abstract
| Access journal publication
The generation of frequency combs in the mid-infrared (MIR) spectral range by quantum cascade lasers (QCLs) has the potential for revolutionizing dual-comb multi-heterodyne spectroscopy in the molecular fingerprint region. However, in contrast to frequency combs based on passively mode-locked ultrafast lasers, their operation relies on a completely different mechanism resulting from a four-wave mixing process occurring in the semiconductor gain medium that locks the modes together. As a result, these lasers do not emit pulses and no direct self-referencing of a QCL comb spectrum has been achieved so far. Here, we present a detailed frequency noise characterization of a MIR QCL frequency comb operating at a wavelength of 8 µm with a mode spacing of ∼7.4 GHz. Using a beat measurement with a narrow-linewidth single-mode QCL in combination with a dedicated electrical scheme, we measured the frequency noise properties of an optical mode of the QCL comb, and indirectly of its offset frequency for the first time, without detecting it by the standard approach of nonlinear interferometry applied to ultrafast mode-locked lasers. In addition, we also separately measured the noise of the comb mode spacing extracted electrically from the QCL. We observed a strong anti-correlation between the frequency fluctuations of the offset frequency and mode spacing, leading to optical modes with a linewidth slightly below 1 MHz in the free-running QCL comb (at 1-s integration time), which is narrower than the individual contributions of the offset frequency and mode spacing that are at least 2 MHz each.