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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Dual-Comb Spectroscopy of Acetylene with a Single, Free-Running MIXSEL Generating two Frequency Combs
摘要： Dual-comb spectroscopy combines the advantages of conventional Fourier transform infrared spectroscopy (FTIR) with the measurement speed, stability and accuracy of multiheterodyne beat note detection. Two optical frequency combs (OFCs) with slightly different line spacing beat on a photodetector and convert the optical spectra down to the more accessible radio frequency (RF) domain. This enables an accurate broadband spectrometer without moving parts featuring short measurement time, however, it also requires two mutually locked OFCs with good noise performance which is challenging. Dual-comb modelocked optically pumped semiconductor disk lasers (SDLs) provide a great simplification. The modelocked integrated external-cavity surface emitting laser (MIXSEL) is a special type of ultrafast SDLs which integrates a semiconductor gain and a saturable absorber in a single epitaxial structure and allows for modelocking in a simple and straight cavity. Most recently we increased the modelocked optical bandwidth above 10 nm with pulse durations below 150 fs. With two intracavity birefringent crystals, the initially unpolarized beam is separated onto two spots on the MIXSEL chip, which can be individually pumped. The dual-comb MIXSEL is a straight linear cavity formed by the two end mirrors (i.e. MIXSEL chip and output coupler (OC) and emits two orthogonally polarized OFCs with a slight difference in line spacing from the same cavity with an intrinsically high mutual coherence. Here, we present dual-comb spectroscopy of acetylene with a single, free-running dual-comb MIXSEL at 1030 nm (290 THz). The laser provides more than 10 nm of optical bandwidth usable for spectroscopic interrogations and with a resolution of 2.73 GHz, we can clearly resolve the individual absorption lines with great precision. Without active stabilization and locking electronics, the overlay of the experimentally acquired dual-comb transmission follows line-by-line the characteristic acetylene transmission envelope as computed from the HITRAN 2016 database after an a posteriori wavelength calibration. Furthermore, the residuals between the observed traces and the HITRAN reference spectrum and its standard deviation of 0.028 attests good transmission intensity precision to our dual-comb spectrometer.
关键词： optical frequency combs,MIXSEL,acetylene,Dual-comb spectroscopy,HITRAN database
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - A Single Free-Running Dual-Comb MIXSEL for Fast and Precise Distance Measurements
摘要： Multiheterodyne techniques in science and technology promise unsurpassed precision in many fields of application such as dual-comb spectroscopy or light detection and ranging (LIDAR). Complexity, performance and cost can be greatly improved with dual-comb semiconductor disk lasers (SDL). Integration of the active semiconductor gain of a vertical external-cavity surface emitting laser (VECSEL) with the saturable absorber of a semiconductor saturable absorber mirror (SESAM) in the same epitaxial structure leads to the modelocked integrated external-cavity surface emitting laser (MIXSEL). The MIXSEL allows modelocking in a simple straight cavity. With two intracavity birefringent crystals, the initially unpolarized cavity beam is separated by polarization. When optically pumping two spots on the semiconductor chip, the dual-comb MIXSEL emits two orthogonally polarized optical frequency combs (OFCs) with a slight difference in pulse repetition rate which can be freely adjusted. The common cavity leads to an intrinsically high mutual coherence between the two OFCs, making the dual-comb MIXSEL the ideal source for dual-comb spectroscopy and other field-deployable multiheterodyne beatnote techniques.
关键词： semiconductor disk lasers,optical frequency combs,Multiheterodyne techniques,dual-comb spectroscopy,MIXSEL,SESAM,VECSEL,LIDAR
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Dual-Comb Spectroscopy using a Single Frequency-Shifting Loop
摘要： Dual-comb spectroscopy (DCS) is a multi-heterodyne interferometric technique that employs two optical frequency combs (OFCs) with different line spacing. When DCS is carried out with a pair of mode-locked OFCs, the need of a tight phase locking between them leads to sophisticated hardware and/or software implementations [1]. A strategy to simplify the DCS architecture, demonstrated with several comb modalities, is the use of a bidirectional laser cavity to produce two counter-propagating combs, each one having different line spacing [2,3]. Alternatively, but offering much more flexibility on the mode separation, electro-optic (EO) frequency combs can also be used for carrying out DCS. In that DCS scheme, both EO combs are fed by a single cw laser, which ensures by default a high degree of mutual coherence between them [4]. In the same vein, but comparatively much less exploited, frequency-shifting loops (FSLs) are also an easily implementable comb platform. Based on the recirculation of light in a loop containing an acousto-optic frequency shifter (AOFS), FSLs are capable of producing spectra with hundreds or even thousands of lines, without resorting to non-linear broadening or optimized fast driving electronics [5]. Recently, we have demonstrated DCS using two different FSLs [6]. However, this system requires the use of a low-bandwidth stabilization system to compensate for the uncorrelated fluctuations between the two combs, a requirement also found in other DCS schemes, and necessary for increasing the acquisition time (and, hence, the measurement signal-to-noise ratio) beyond the ms time scale. To improve the mutual coherence of the two OFCs, we present a bidirectional FSL that generates in the same optical loop two counter-propagating OFCs (called acousto-optic OFCs), with a tunable line spacing difference, as shown in Fig. 1a. The FSL is composed of three bidirectional elements: a frequency shifter that imparts a different frequency shift depending on the light direction, an optical amplifier (EDFA) and a tunable band-pass filter (BPF). The interference between the two acousto-optic OFCs produces a RF comb, whose bandwidth and flatness can be controlled through the parameters of the FSL (Fig. 1b). In order to test our setup, we performed molecular spectroscopy of a HCN absorption line, as can be observed in Fig. 1c. While much simpler, our system performs similarly to the technique that utilizes two different FSLs with a stabilization mechanism [6]. The presented bidirectional FSL is a compact and flexible scheme for DCS. Apart from avoiding duplication of the FSL, it provides common noise rejection between the two generated combs, allowing us to reach acquisition times up to the second scale. In addition, a pair of counter-propagating trains of optical pulses could also be generated by exploiting the temporal Talbot effect [5]. All these features make our system a powerful platform for multi-heterodyne interferometry, including molecular spectroscopy, distance ranging and fiber sensing.
关键词： Dual-comb spectroscopy,multi-heterodyne interferometry,acousto-optic frequency shifter,frequency-shifting loops
更新于2025-09-12 10:27:22
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Computational Doppler-limited dual-comb spectroscopy with a free-running all-fiber laser
摘要： Dual-comb spectroscopy has emerged as an indispensable analytical technique in applications that require high resolution and broadband coverage within short acquisition times. Its experimental realization, however, remains hampered by intricate experimental setups with large power consumption. Here, we demonstrate an ultrasimple free-running dual-comb spectrometer realized in a single all-fiber cavity suitable for the most demanding Doppler-limited measurements. Our dual-comb laser utilizes just a few basic fiber components, allows us to tailor the repetition rate difference, and requires only 350 mW of electrical power for sustained operation over a dozen of hours. As a demonstration, we measure low-pressure hydrogen cyanide within 1.7 THz bandwidth and obtain better than 1% transmittance precision over a terahertz in 200 ms enabled by an all-computational phase retrieval and correction algorithm. The combination of the setup simplicity, comb tooth resolution, and high spectroscopic precision paves the way for proliferation of frequency comb spectroscopy on a larger scale.
关键词： computational phase retrieval,Doppler-limited measurements,hydrogen cyanide,all-fiber laser,Dual-comb spectroscopy
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Retrieving the Phase Relation of a Quantum Cascade Laser Frequency Comb and Reconstructing its Emission Profile
摘要： In the direction of miniaturizing and expanding optical frequency comb (FC) operation in the infrared (IR), the most relevant results have recently been achieved with quantum cascade lasers (QCLs) [1–4]. By using broadband Fabry-P′erot QCLs [5] designed to have a low group velocity dispersion, FC generation was demonstrated in fully free-running operation (QCL-combs) [6,7]. Various techniques to characterize the emission of mid- and far-infrared QCL-combs have been recently developed [6, 8–12]. Here we demonstrate the possibility of monitoring the Fourier phases of the modes of a FC (sample FC). The proposed approach bases on dual-comb multi-heterodyne detection using a metrological FC as reference (LO-FC) and a subsequent Fourier transform analysis (see ?g. 1a), allowing a simultaneous retrieval of the modes phases (?g. 1b). The required stability is obtained by post-detection RF common frequency noise suppression. This approach is the most direct method for FCs characterization, being suitable for IR FCs. A mid-IR and a THz QCL-comb (sample FCs) have been characterized. As LO-FCs two difference-frequency-generated FCs have been used. The measurements consisted in series of seven consecutive acquisitions. A strong correlation among the modes and a remarkable phase stability over 10s of minutes have been evidenced (see ?g. 1c). For the THz QCL-comb all the emitted modes can be acquired, therefore it is possible to reconstruct the emission pro?le and the instantaneous frequency (?g. 1d and e), con?rming a substantial deviation with respect to typical FC pulsed operation. The observed standard deviations on the obtained phases are in the order of 8 ? 10° at tens-of-minutes timescale. Concerning the phase relation, the scattering of THz QCL-comb phases (Fourier phases) encompasses a range of 300°, a value which cannot be associated to short-pulses operation. The quadratic term found in the phase relation (?g. 1b) can be attributed to chirping in QCL-comb emission. The reconstructed emission pro?les are roughly the same from measurement to measurement over the 30 minutes. Noticeably, the QCL-comb emission deviates from a pulsed emission, even though its amplitude is deeply modulated during the round trip. The obtained instantaneous frequency con?rms that the THz QCL-comb operates in a hybrid amplitude-/frequency-modulated regime. The gained knowledge of the phase relation provides the basis for future implementation of programmable pulse shaping. The remarkable phase stability attained for the QCL-combs modes conclusively proves the high coherence characterizing their emission, demonstrating that these sources are potentially suitable for metrological applications.
关键词： Fourier phases,frequency comb,quantum cascade laser,dual-comb multi-heterodyne detection,metrological applications
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Frequency Comb Generation at 2 μm with Electro-Optic Modulators for Spectroscopic Applications
摘要： Mid-infrared (2–20 μm) gas sensing allows the detection of strong molecular absorptions with rather small absorption lengths (≤1 m). Various techniques can perform spectroscopic measurements in the mid-infrared but dual-comb spectroscopy (DCS) is one of the most powerful knowing its precision and real-time abilities [1]. However, setups used to perform DCS are in general complex since they require the phase locking of two independent femtosecond lasers at the known state of the art stability. This particular drawback can be bypassed if the combs are generated with electro-optic modulators (EOM) [2]. However, these equipments operate in the telecommunication wavelengths, generally near 1.55 μm where molecular absorptions are not very intense. Here, we experimentally demonstrate two different techniques of generating frequency combs with EOMs around 2 μm.
关键词： Spectroscopic applications,Frequency comb generation,Mid-infrared,Electro-optic modulators,Dual-comb spectroscopy
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Dual-Wavelength Dual-Comb Mode Locked Er-Doped Fiber Laser Based on Saganc Fiber Loop Mirror
摘要： We report an all-fiber dual-wavelength dual-comb mode locked fiber laser based on a Sagnac fiber loop mirror. Two asynchronous mode locked pulse trains with repetition rate difference of 218 Hz was realized.
关键词： fiber laser,Sagnac fiber loop mirror,mode locked,dual-wavelength,dual-comb
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - All-Polarization-Maintaining Dual-Color/Dual-Comb Yb:Fiber Laser
摘要： Dual-comb spectroscopy systems based on two pulse trains emitted from a single laser cavity benefit from passive mutual coherence between the two pulse trains, which leads to common-mode noise cancellation in the down converted radio-frequency (RF)-comb [1]. Due to their robustness, single cavity dual-color/dual-comb fiber lasers are promising candidates for such spectroscopy systems [2,3]. Here, we present a novel method to generate two pulse trains out of a single fiber laser cavity based on mechanical spectral filtering, which offers two key features: dynamical adjustment of the spectral separation between the two pulse trains and tuning of the difference in repetition rates. After demonstrating the concept in a 23-MHz nonlinear polarization evolution (NPE) mode-locked ytterbium (Yb) laser [4], we have now for the first time implemented this concept in a nonlinear amplified loop mirror (NALM) mode-locked all-polarization maintaining (PM) Yb:fiber laser operating at a repetition rate of 77 MHz, thus improving both the stability as well as the non-aliasing dual-comb bandwidth. The laser contains a free-space arm with a transmission grating compressor, in which the spectral components of the intra-cavity light are spatially dispersed (Fig.1(a)). By introducing a small beam block into the grating compressor, we split the spectrum into two separate regions. We show that these two spectral regions can be independently mode-locked, thus creating two pulse trains with slightly different repetition rates (Fig.1(b-d)). Due to the spatial distribution of the spectral components, we can vary the width of the spectral cut between the two spectra by rotating the beam block (Fig. 1(b), blue curves). Furthermore, adjusting the grating spacing (and thus the amount of dispersion) allows us to tune the difference in the repetition rate ?frep from 1-6 kHz (Fig. 1(e)). After spectral separation at the cavity output, the pulse centered around 1030 nm is amplified and broadened in a nonlinear fiber to create a spectral overlap with the 1060 nm-pulse (Fig. 1(f)). The overlapping spectrum is bandpass-filtered around 1055 nm and sent onto a photodiode (PD). An oscilloscope trace of the PD output shows interferograms (Fig. 1(f), inset) occurring with a periodicity of 1/?frep, which correspond to the Fourier-transform of the down-converted RF comb that is generated by the beating of both optical combs.
关键词： repetition rate tuning,polarization maintaining,Yb:fiber laser,spectral filtering,Dual-comb spectroscopy
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Computational High-Resolution Dual-Comb Spectroscopy with a Free-Running All-Fiber Laser
摘要： Dual-comb spectroscopy (DCS) has experienced a remarkable growth propelled by recent advances in fiber and semiconductor technology. A key enabler for DCS is mutual stability between two repetition-rate-mismatched frequency combs, which conventionally relies on feedback loops employing additional optics and electronics to synchronize a pair of sources. This limitation can be overcome in several ways, of which one of the most promising is the generation of two frequency combs in a single free-running fiber laser cavity [1–3]. To date, however, the only configuration proven to be compatible with Doppler-limited spectroscopy was the dual-color laser presented in Ref. [2] requiring external spectral broadening, thus adding an extra layer of complexity. Here, we report on the realization of a drastically simplified all-fiber dual-comb laser (AFDCL) with an unprecedentedly low number of components and battery-operation-compatible electrical power consumption (0.35 W) with excellent suitability for spectroscopy of Doppler-limited transitions (Fig. 1). A key feature of our solution relying on polarization-multiplexing [3] is that the laser cavity has an easily adjustable repetition rate difference ranging from sub-kHz to dozens of kHz obtained by varying the intracavity polarization state using polarization controllers (PC) and/or the length of the polarization maintaining fiber in the cavity, which is not possible in the dual-color or bidirectional schemes. Furthermore, we achieve uninterrupted operation times of dozens of hours, and a record-high repetition rate for an AFDCL exceeding 140 MHz to maximize the optical power per comb tooth. High-resolution molecular dual-comb spectroscopy in free-running mode is made possible thanks to a novel real-time compatible phase correction algorithm that marks a radical departure from the cross-correlation or cross-ambiguity function paradigm, hence considerably lowering the complexity of such procedures. As a demonstration, we measure P18-P27 lines of the 2ν3 band of H13C14N at 10 Torr with FWHM Doppler line widths of ~450 MHz within 200 ms (Fig. 1b,c) with better than 1% of precision in a 1 THz bandwidth.
关键词： high-resolution,free-running,molecular spectroscopy,Dual-comb spectroscopy,all-fiber laser
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - High-Power Dual-Comb Thin-Disk Oscillator
摘要： Dual-comb spectroscopy is a rapidly advancing spectrometric technique where the temporal interferograms generated with two asynchronous trains of pulses are recorded, and Fourier transformed to reveal the spectrum of an absorber in the beam path [1]. To date, best performance is achieved with systems involving complex active stabilization of two femtosecond erbium fiber lasers [1]. One way to simplify the technique is to generate a dual-comb output from a single laser cavity. However, there have been only a few demonstrations of such a scheme so far [2,3]. Here we present a dual-comb system based on a single thin-disk oscillator. The novel architecture effectively rejects common noise, with mutual coherence time exceeding one second without any active stabilization. Moreover, the system shows nearly an order of magnitude higher average and peak output powers compared to previous dual-comb demonstrations. Efficient nonlinear frequency conversion to the UV or mid-IR regions—of high interest to molecular spectroscopy—will thus be greatly facilitated.
关键词： thin-disk oscillator,high-power,Yb:YAG,Kerr-lens mode-locked,dual-comb spectroscopy
更新于2025-09-11 14:15:04