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We present a rack-mounted ultra-low-noise laser system for Sr lattice clocks, with spectral purity transfer stability of 4×10−18@1s and 2×10−19@100s. We realize a system stability of 5×10-16@1s, representing state-of-the-art performance for rack-mounted commercial systems.

Long-distance time and frequency transfer methods based on optical fibre links attractive both for very high-performance applications and also for many industrial and societal applications, and they complement and offer an alternative to radio- and satellite-based methods.

We present a compact, radiation tolerant, space frequency comb that is scheduled for an in-orbit-demonstration in low-earth-orbit with a launch in 2024.

Precision measurements represent a cornerstone in fundamental science. The capability of observing and quantifying subtle phenomena and events allows new discoveries and it confirms or confutes the theories describing our understanding of nature. The optical frequency comb, providing hundreds of thousands of phase-locked and evenly spaced laser lines, is one of the most fascinating enabling optical technologies and it is the result of a continuous pursuit for precision. Within the two decades from its inception, it has become a key instrument in many laboratories and has revolutionized numerous fields, spanning from time, frequency and length metrology to attosecond physics, gas-sensing and molecular fingerprinting. In this letter we summarize some steps of an exciting journey started 20 years ago, with a certain focus on the authors' contribution, finally leading to the demonstration of frequency measurements at the 20 th decimal digit, and we show some prospective developments.

Optical frequency measurements are among the most precise tools available to science. With the rapid advances in optical clocks now achieving a low 10−17 stability at 1 s and averaging down to the 10−19 level in a few hundred seconds, real-time sensing of subtle phenomena becomes essential. To render possible such measurements, we introduce real-time optical phase tracking with ultra-low-noise frequency combs as a fundamental means to constantly monitor frequency offsets. This enables the characterization of optical frequency synthesis with stability and accuracy at the 20th decimal place within a measurement time of

The single-sideband phase noise power spectral density and Allan deviation of a portable microwave oscillator system based on an optical frequency comb stabilized to an ultra-low expansion Fabry-Perot reference cavity is characterized at carrier frequencies of 4.0, 8.0, and 16.0 GHz. Compared to industry standard sapphire loaded cavity oscillators, the photonic microwave oscillator shows superior phase noise at offset frequencies $3.0 \times 10^{-14}$ obtains at an averaging time of 400 ms.

We demonstrate a compact mid-IR system using difference frequency generation based on a femtosecond Ytterbium fiber laser system with a repetition rate of 100 MHz. Based on the fundamental 1040 nm beam, we use frequency conversion in a nonlinear fiber to generate a tuneable signal beam for mid-IR generation based on difference frequency generation. We investigate different nonlinear fibers for signal generation between 1100 nm and 1600 nm for optimum mid-IR generation between 3 µm and 10 µm, for which power levels of more than 200 mW have been observed at an emission wavelength of 4 µm.

Quantum technologies are nowadays emerging as enabling tools for practical applications, such as quantum sensing, quantum computing and quantum metrology. Lasers play a central role in many of these technological platforms, e.g. for atomic clocks, ion-based or neutral atom-based quantum computers or atom interferometers. Here we present a complete laser system to cool, trap and control strontium atoms in an optical lattice or in tweezer arrays. A sub-Hz linewidth master laser, locked to a high-finesse optical cavity provides the frequency reference for an ultra-low noise comb. The rack-mounted laser system consists of all cooling, repumping, and clock lasers stabilized to the optical frequency comb. Each of the involved laser frequencies can therefore be tuned and mapped in the frequency domain with a high degree of stability. The system is controlled via a software interface, allowing to operate the cold-atom-based physics package autonomously. The system is tailored for the operation of 88Sr or 87Sr optical lattice clocks, or for quantum computing applications, but other sub-Hz lasers could be obtained by phase locking additional clock laser frequencies to the ultra-stable comb, enabling convenient and accurate optical frequency ratio measurements. The laser system architecture and the relevant characterization measurements will be presented, proposing some user-cases such as quantum computing and atom interferometry on strontium atoms. This represents a technological leap for quantum optics, allowing to explore further applications of quantum sensors outside a traditional lab.

Long-distance time and frequency transfer methods based on optical fibre links have evolved rapidly in recent years, demonstrating excellent performance for frequency transfer and considerable promise for accurate time transfer. Optical fibre links, besides provisioning extreme data transfer rates, are attractive both for very high-performance applications such as optical clock comparisons, basic research or relativistic geodesy, but also for many industrial and societal applications, and they complement and offer an alternative to radio- and satellite-based methods. CLONETS-DS is a European Union-funded research and innovation action intended to facilitate the vision of a sustainable, pan-European optical fibre network for precise time and frequency reference dissemination, by bringing together expertise from national metrology institutes (NMI), academic groups and research infrastructures (RI), research and education networks at the national and European level (NREN, GEANT) and innovative high-tech small and medium enterprises (SME). The proposed project aims to establish a pan-European time and frequency reference system as a European Research Infrastructure which serves the European science community. It is based on transmitting ultra precise time and frequency information via optical fiber. The proposed project builds on several projects of the European metrology research programmes such as NEAT-FT, OFTEN and TiFOON, the former GN3+ project ICOF, the novel work package 6, Optical Time and Frequency Network (OTFN), of the GN4-3 project of GEANT and its direct precursor project CLONETS [1]. We now go far beyond previous efforts by designing a sustainable, pan-European, ultra-precise time-and-frequency reference-system available to the European research community. This newly designed European Research Infrastructure will consider user needs, architecture requirements, engineering models and roadmaps, and will develop a sustainability model for the future service, thus strengthening the European research area and its innovative potential.

We present a transportable photonic microwave oscillator, porting optical stability to a 10 GHz microwave signal. The system is composed of two main sub-units: a compact 8 height-unit (HU) 194 THz ultra-stable laser with Hz linewidth showing a fractional frequency stability (modified Allan deviation) of 8.5 × 10-15 at 1 s and a 3 HU ultra-low noise optical frequency comb used to phase-coherently divide the optical frequency reference’s spectral purity down to a 10 GHz microwave signal. Characterizing the synthesized microwave by means of a commercial digital cross-correlator, a phase noise power spectral density of -70 dBc/Hz at 1 Hz and -160 dBc/Hz at 10 kHz Fourier frequency is measured, maintaining a white plateau at -165 dBc/Hz up to 10 MHz offset.

Long-distance precise time and ultra-stable frequency transfer methods based on optical fibre have evolved rapidly in recent years, demonstrating excellent performance. CLONETS-DS is a European Union-funded research and innovation action intended to facilitate the vision of a sustainable, pan-European fibre network for time and frequency dissemination.

We present a fully phase-locked comb-disciplined-laser system, conceived to operate the Matter-wave Atomic Gradiometer Interferometric Sensor (MAGIS-100). Via phase-locking to the comb, four ECDLs and a Ti:Sapphire laser inherit the stability of an ultra-stable laser.

Aims. We study the 2D spectral line profile of HARPS (High Accuracy Radial Velocity Planet Searcher), measuring its variation with position across the detector and with changing line intensity. The characterization of the line profile and its variations are important for achieving the precision of the wavelength scales of 10^{-10} or 3.0 cm/s necessary to detect Earth-twins in the habitable zone around solar-like stars. Methods. We used a laser frequency comb (LFC) with unresolved and unblended lines to probe the instrument line profile. We injected the LFC light (attenuated by various neutral density filters) into both the object and the reference fibres of HARPS, and we studied the variations of the line profiles with the line intensities. We applied moment analysis to measure the line positions, widths, and skewness as well as to characterize the line profile distortions induced by the spectrograph and detectors. Based on this, we established a model to correct for point spread function distortions by tracking the beam profiles in both fibres. Results. We demonstrate that the line profile varies with the position on the detector and as a function of line intensities. This is consistent with a charge transfer inefficiency (CTI) effect on the HARPS detector. The estimate of the line position depends critically on the line profile, and therefore a change in the line amplitude effectively changes the measured position of the lines, affecting the stability of the wavelength scale of the instrument. We deduce and apply the correcting functions to re-calibrate and mitigate this effect, reducing it to a level consistent with photon noise., Comment: 9 pages, 6 figures, 3 tables, accepted

The evolution of pump and probe technologies, especially terahertz time domain spectroscopy has led to a multitude of applications as well as an significant improvement in the available devices regarding dynamic range, bandwidth and measurement speed. Using a spectrometer based on electro-optical modulator ECOPS sampling, we present time domain spectroscopy pulses recorded at measurement rates of up to 60 kHz - faster than any result reported so far to our knowledge.

The General Theory of Relativity predicts the redshift of spectral lines in the solar photosphere, as a consequence of the gravitational potential of the Sun. This effect can be measured from a solar disk-integrated flux spectrum of the Sun's reflected light on solar system bodies. The laser frequency comb (LFC) calibration system attached to the HARPS spectrograph offers the possibility to perform an accurate measurement of the solar gravitational redshift (GRS) by observing the Moon or other solar system bodies. We have analysed the line shift observed in Fe absorption lines from five high-quality HARPS-LFC spectra of the Moon. We select an initial sample of 326 photospheric Fe lines in the spectral range 476-585 nm and measure their line positions and equivalent widths (EWs). Accurate line shifts are derived from the wavelength position of the core of the lines compared with the laboratory wavelengths. We fit the observed spectral Fe lines using CO$^5$BOLD 3D synthetic profiles. Convective motions in the solar photosphere do not affect the line cores of Fe lines stronger than about $\sim 150$ mA. In our sample, only 15 FeI lines have EWs in the range $150, Comment: Accepted for publication in Astronomy & Astrophysics

The demand for high speed Terahertz measurement devices for industrial and research applications is growing rapidly. From plant biology to nondestructive testing in the automotive industry, there is a long list of applications demanding rapid scanning of femtosecond pulses. We present a novel approach to speed up the repetition rate control by a factor of 10 compared to conventional approaches using electro-optical means . Hence, we have demonstrated repetition rate changes of 100 kHz in less than 1 ms. This increase in speed enables novel applications in Terahertz spectroscopy which will be presented.

Frequency comb synthesized microwaves have been so far realized with tabletop systems, operated in well-controlled environments. Here, we demonstrate state-of-the-art ultrastable microwave synthesis with a compact rack-mountable apparatus. We present absolute phase noise characterization of a 12 GHz signal using an ultrastable laser at ∼ 194 T H z and an Er:fiber comb divider, obtaining − 83 d B c / H z at 1 Hz and < − 166 d B c / H z for offsets greater than 5 kHz. Employing semiconductor coating mirrors for the same type of transportable optical frequency reference, we show that − 105 d B c / H z at 1 Hz is supported by demonstrating a residual noise limit of division and detection process of − 115 d B c / H z at 1 Hz. This level of fidelity paves the way for the deployment of ultrastable photonic microwave oscillators and for operating transportable optical clocks.

Laser frequency combs (LFCs) are well on their way to becoming the next-generation calibration sources for precision astronomical spectroscopy. This development is considered key in the hunt for low-mass rocky exoplanets around solar-type stars whose discovery with the radial-velocity method requires cm/s Doppler precision. In order to prove such precise calibration with an LFC, it must be compared to another calibrator of at least the same precision. Being the best available spectrograph calibrator, this means comparing it to a second - fully independent - LFC. This test had long been pending, but our installation of two LFCs at the ultra-stable spectrograph HARPS presented the so far unique opportunity for simultaneous calibrations with two separate LFCs. Although limited in time, the test results confirm the 1 cm/s stability that has long been anticipated by the astronomical community., 22 pages, 14 figures. View the Nature Astronomy publication under https://rdcu.be/b1tMB . Nature Astronomy article available under https://www.nature.com/articles/s41550-020-1010-x

International audience; The recent demonstration of a terahertz (THz) molecular gas laser pumped by a mid-infrared quantum cascade laser (QCL) has opened up new perspectives for this family of sources, traditionally relying on CO2-laser pumping. A so far open question concerning QCL-pumped THz molecular lasers (MLs) is related to their spectral purity. Indeed, assessing their frequency/phase noise is crucial for a number of applications potentially exploiting these sources as local oscillators. Here this question is addressed by reporting the measurement of the frequency noise power spectral density (PSD) of a THz ML pumped by a 10.3µm-wavelength QCL, and emitting 1mW at 1.1THz in continuous wave. This is achieved by beating the ML frequency with the 1080 th harmonic of the repetition rate of a 1560nm frequency comb. We find a frequency noise PSD < 10Hz 2 /Hz (-95dBc/Hz) at 100kHz from the carrier. To demonstrate the effect of the stability of the pump laser on the spectral purity of the THz emission we also measure the frequency noise PSD of a CO2-laser-pumped 2.5THz ML, reaching 0.1Hz 2 /Hz (-105dBc/Hz) at 40kHz from the carrier, limited by the frequency noise of the frequency comb harmonic. Finally, we show that it is possible to actively phase-lock the QCL-pumped molecular laser to the frequency comb repetition rate harmonic by controlling the QCL current, demonstrating a sub-Hz linewidth. 2

We report the development of a complete turn-key 5 × 10-16 ultra-stable laser system for operating neutral strontium atoms for optical lattice clocks or for quantum computing.

We report the development of a field-deployable frequency comb operated as clockwork for transportable Sr-clocks. While referencing it at ~194.4THz, we characterize spectral lines at ~214.6THz. Prospects on complete Sr-lattice laser systems will be outlined.

An optically stabilized dual-comb system at telecom wavelength is used to drive a mid-infrared spectroscopy for parallel gas-phase detection in the functional group region from 2800-3600 cm-1. A coherent broadband intensity-enhanced spectrum in the mid-infrared region is obtained through dispersion engineered silicon nitride dual-core waveguides.

We present DFG frequency comb systems operating between 3 and 5 pm based on femtosecond Er- and Yb-fiber laser-amplifier systems, providing an average power of up to 250 mW and 31 pW per comb mode with 1.5 Hz optical linewidths in the mid-IR.

We report on a transportable and easy-to-operate optical clock utilizing the 2S1/2 - 2D3/2 transition of a single trapped 171Yb+ ion at 436 nm. Developed within a pilot project for quantum technology in Germany lead by industry, the clock is set up in two 19″ racks. In this way, transportation can easily be realized, and the large degree of automatization allows for operation outside highly specialized laboratories for applications beyond basic research. Comparisons to existing high-accuracy optical clock systems enable a verification of the clock's stability and uncertainty budget at the low 10−17 level. During these tests, operation with 99.8% availability over more than 14 days has been achieved.

We present a fully operational ultra-stable-laser system for cooling, trapping and manipulating Rydberg states in optical tweezer arrays of neutral Sr-atoms. Some CW-lasers are phase-coherently disciplined by an ultra-low-noise comb referenced to a sub-Hz ultra-stable-laser.

A micro-integrated laser module has been developed for the deployment in a compact, transportable 171Yb+ optical clock. With this laser module, the clock laser system demonstrated a Modified Allan Deviation of less than 1.5×10-15 for 1 s ≤ 100 s when compared against a superior reference laser. © 2020 The Author(s)

International audience; Abstract:We report the measurement of the frequency noise power spectral density (PSD) of a THz molecular laser (ML) pumped by a mid-infrared (MIR) quantum cascade laser (QCL). This is obtained by beating the ML frequency with the harmonic of the repetition rate of a 1560nm frequency comb (FC). We find a frequency noise PSD

The far-infrared (FIR) is one of the few wavelength ranges where no astronomical data with sub-arcsec resolution exist yet. Neither of the medium-term satellite projects like SPICA, Millimetron or OST will resolve this malady. Information at high spatial and spectral resolution in the FIR, taken from atomic fine-structure lines, highly excited CO, and especially from water lines would, however, open the door for transformative science. This calls for interferometric concepts. We present first results of our feasibility study IRASSI (Infrared Astronomy Satellite Swarm Interferometry) for a FIR space interferometer. Extending on the principal concept of the ESPRIT study, it features heterodyne interferometry within a swarm of 5 satellite elements. The satellites can drift in and out within a range of several hundred meters, thereby achieving spatial resolutions of, 43 pages (preprint format), 10 figures, 6 tables; in press, to appear in Advances in Space Research, Special Issue on Space-VLBI (eds. Leonid Gurvits et al.)

Optical frequency combs give access to the fast oscillation of optical clocks' transitions, nowadays reaching 10−17/√τ level of stability [1] and 10−18 level of accuracy [2]–[4]. Besides allowing a phase-coherent down-conversion to the electronically accessible radio frequencies for generating a time scale, they represent a gear in the optical domain enabling comparisons between optical frequency standards based on different atomic species [5]. Due to the need of high signal-to-noise ratio of the optical beat notes between the clocks' local oscillators and the frequency comb teeth, dedicated non-linear amplifiers with subsequent frequency conversion to the spectral region of interest is desired. Such approach allows to speed up measurement time for performing clocks' inter-comparisons and increase the robustness of the experimental setup.

Chronometrie levelling [1–3] is a technique of deriving gravitational potential differences from clock frequency comparisons allowing the determination of height differences. Interferometric optical fibre links (IFL) [4] enable chronometric levelling between distant labs housing optical clocks [5]. An IFL is a phase stabilized telecom fibre link connection establishing a fixed optical phase relationship between two locations up to ∼1000 km apart [6]. To perform a chronometric levelling campaign between the stationary optical clocks of the Physikalisch-Technische Bundesanstalt (PTB) and PTB's transportable Strontium clock [7] placed at the Max Planck Institute of Quantum Optics (MPQ) we have established a new 940 km long IFL between the two locations. At both link ends the frequencies of the clock lasers are compared to the 1,5 pm link transfer laser via fs-combs. To enable chronometric levelling experiments at the level of 10 cm height resolution, we aim a fractional frequency uncertainty of the frequency transfer of 40 dB.

Waveform-stable, pulsed laser sources have enabled both time-domain and frequency-domain precision metrology, through real-time measurement of electric-field-driven light-matter interactions on their native femto- and attosecond time scales, and by harnessing the frequency-comb nature of high-repetition-rate pulse trains. Particular interest has been shown in these sources for use in infrared (IR) molecular fingerprinting [1,2], offering increased sensitivity and specificity compared to traditional, thermal-source-based Fourier-transform spectroscopy, for applications such as biomedical spectroscopy or trace-chemical sensing. Here, we present a compact, 50-MHz source of high-power, waveform-stable IR pulses. Driven by a 2μm based fiber chirped pulse amplifier (FCPA), three parallel nonlinear fiber channels are used to cover the spectral range of 1.4 to 20 μm.

Since its invention in the late 1990s, the frequency comb technology revolutionized the world of optical frequency metrology [1] and is now widely available as of-the-shelf product around the globe. While promising use cases for space-based applications exist, the space technology readiness, particularly regarding miniaturization and ruggedness, remains an obstacle for its deployment. In April 2015 and January 2016 the first frequency comb system FOKUS I was launched into space on a TEXUS sounding rocket, demonstrating the robustness and reliability of the technology [2].

Recently, a novel type of molecular THz laser with ∼mW-level output power was demonstrated [1,2]. This laser is optically pumped by a mid-IR Quantum Cascade Laser (QCL), therefore resulting in a much more compact, frequency agile and deployable source compared to standard, CO 2 -laser pumped, far-infrared gas lasers. This achievement has revived the interest for molecular THz lasers, in particular for their exploitation as low-phase noise THz local oscillators (LOs) operating at room temperature. Compared to CO 2 -laser pumping, a QCL pump offers an unrivalled frequency agility that allows accessing an unprecedented number of molecular transitions. On the other hand, its lower frequency stability can potentially impact the frequency noise of the THz laser source [3–5]. Here we report the first measurement of the frequency noise power spectral density (PSD) of a 1.073THz ammonia laser pumped by a 10.3μm QCL. This is achieved by using a commercial harmonic mixer to generate a beating between the ammonia laser frequency and the 1080th harmonic of the 1GHz repetition rate of a custom-made, 1560nm frequency comb (FC). We then exploit a voltage-controlled oscillator to track the beat-note signal and realize the frequency to amplitude conversion [6]. The measured frequency noise PSD is shown in Fig.1. In the range ∼30–100kHz we find a frequency noise 2 -pumped, 2.5THz methanol laser, reaching 0.1Hz2/Hz (−110dBc) at 40kHz from the carrier, limited by the frequency noise of the FC harmonic. Finally, we will show that it is possible to actively phase-lock the QCL-pumped ammonia laser to the FC repetition rate harmonic by controlling the QCL drive current, demonstrating a sub-Hz linewidth. These results pave the way to the development of QCL-pumped molecular lasers as compact, low-phase noise THz sources operating a room temperature.

Context. Convective motions in the solar atmosphere cause spectral lines to become asymmetric and shifted in wavelength. For photospheric lines, this differential Doppler shift varies from the solar disk center to the limb. Aims. Precise and comprehensive observations of the convective blueshift and its center-to-limb variation improve our understanding of the atmospheric hydrodynamics and ensuing line formation, and provide the basis to refine 3D models of the solar atmosphere. Methods. We performed systematical spectroscopic measurements of the convective blueshift of the quiet Sun with the Laser Absolute Reference Spectrograph (LARS) at the German Vacuum Tower Telescope. The spatial scanning of the solar disk covered 11 heliocentric positions each along four radial (meridional and equatorial) axes. The high-resolution spectra of 26 photospheric to chromospheric lines in the visible range were calibrated with a laser frequency comb to absolute wavelengths at the 1 m s−1 accuracy. Applying ephemeris and reference corrections, the bisector analysis provided line asymmetries and Doppler shifts with an uncertainty of only few m s−1. To allow for a comparison with other observations, we convolved the results to lower spectral resolutions. Results. All spectral line bisectors exhibit a systematic center-to-limb variation. Typically, a blueshifted “C”-shaped curve at disk center transforms into a less blueshifted “\”-shape toward the solar limb. The comparison of all lines reveals the systematic dependence of the convective blueshift on the line depth. The blueshift of the line minima describe a linear decrease with increasing line depths. The slope of the center-to-limb variation develops a reversal point at heliocentric positions between μ = 0.7 and 0.85, seen as the effect of horizontal granular flows in the mid photosphere. Line minima formed in the upper photosphere to chromosphere exhibit hardly any blueshift or even a slight redshift. Synthetic models yield considerable deviations from the observed center-to-limb variation. Conclusions. The obtained Doppler shifts of the quiet Sun can serve as an absolute reference for other observations, the relative calibration of Dopplergrams, and the necessary refinement of atmospheric models. Based on this, the development of high-precision models of stellar surface convection will advance the detection of (potentially habitable) exoplanets by radial velocity measurements.

We have extended the existing interferometric fibre link PTB-Strasbourg with a branch connecting the node at Karlsruhe Institute of Technology (KIT) to the Max Planck Institute of Quantum Optics (MPQ) in Garching/Munich. This fibre connection enables chronometric levelling experiments between PTB and MPQ, separated by a line-of-sight distance of about 460 km. Here, we study the performance of the PTB-MPQ fibre link which mainly employs stimulated Brillouin scattering as means of amplification. We consider two configurations: a single-span loop configuration and an antiparallel configuration with frequency transfer over the two concatenated, individually stabilized forward and backward links.

Within the OPUS collaboration, we develop optical frequency references based on spectroscopy of the $^1{S_0}\rightarrow ^3P_1$ intercombination line of 88Sr at 689 nm in thermal and laser-cooled strontium beams for operation on sounding rockets. One main objective is to identify suitable experimental setups and core components for a compact and robust strontium beam clock, providing a stepping stone for future spaceborne devices. Recent results demonstrate successful laser stabilization to the inter-combination line in a thermal beam breadboard setup.

Frequency combs are an enabling technology for metrology and spectroscopic applications in fundamental and life sciences. While frequency combs in the 1 μm regime, produced from Yb-based systems have already exceeded the 100 W – level, high power coverage of the interesting mid-infrared wavelength range remains yet to be demonstrated. Tm- and Ho-doped laser systems have recently shown operation at high average power levels in the 2 μm wavelength regime. However, frequency combs in this wavelength range have not exceeded the 5 W-average power level. In this work, we present a high power frequency comb, delivered by a Tm-doped chirped-pulse amplifier with subsequent nonlinear pulse compression. With an integrated phase noise of

Methods for long-distance time and frequency transfer over optical fibres have demonstrated excellent performances and are evolving rapidly. CLONETS is a European Union funded coordination and support action intended to facilitate the vision of a sustainable, pan-European optical fibre network for precise time and frequency reference dissemination.

High resolution and fast detection of molecular vibrational absorption is important for organic synthesis, pharmaceutical processes, and environmental monitoring, and is enabled by mid-infrared (mid-IR) laser frequency combs via dual-comb spectroscopy. Here, we demonstrate a novel and highly simplified approach to broadband mid-IR dual-comb spectroscopy via supercontinuum generation, achieved using unprecedented nanophotonic dispersion engineering that allows for ultra-broadband and flat-envelope mid-IR frequency combs. Our mid-IR dual-comb spectrometer has an instantaneous bandwidth covering the functional group region from 2800 – 3600 c m − 1 , comprising more than 100,000 comb lines, enabling parallel gas-phase detection with a high sensitivity, sub-Doppler spectral resolution, and a high speed. In addition to the traditional functional groups, their isotopologues are also resolved in this supercontinuum-based dual-comb spectroscopy. Our approach combines well established fiber laser combs, digital coherent data averaging, and integrated nonlinear photonics, each in itself a state-of-the-art technology, signaling the emergence of mid-IR dual-comb spectroscopy for use outside of the protected laboratory environment.