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Route from single-pulse to multi-pulse states in a mid-infrared soliton fiber laser
摘要： State-of-the-art ultrafast mid-IR ?ber lasers deliver optical solitons with durations of several hundred femtoseconds. The Er- or Ho-doped ?uoride gain ?bers generally used in these lasers have strong anomalous dispersion at ～3 μm, which generally forces them to operate in the soliton regime. Here we report that a pulse-energy clamping e?ect, caused by the buildup of intracavity nonlinearities, limits the shortest obtainable pulse durations in these mid-infrared soliton ?ber lasers. Excessive intra-cavity energy results in soliton instability, collapse and fragmentation into a variety of stable multi-pulse states, including phase-locked soliton molecules and harmonically mode-locked states. We report that the spectral evolution of the mid-IR laser pulses can be recorded between roundtrips through stretching their second-harmonic signal in a 25-km-length of single-mode ?ber. Using a modi?ed dispersive Fourier transform set-up, we were able to perform for the ?rst time spectro-temporal measurements of mid-IR laser pulses both in the pulsed state and during pulse collapse and fragmentation. The results provide insight into the complex nonlinear dynamics of mid-IR soliton ?ber lasers and open up new opportunities for obtaining a variety of stable multi-pulse mode-locked states at mid-IR wavelengths.
关键词： dispersive Fourier transform,soliton instability,multi-pulse states,pulse-energy clamping,mid-IR soliton ?ber lasers
更新于2025-09-16 10:30:52
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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) - Characterization of the Verdet Constant of Dy <sub/>2</sub> O <sub/>3</sub> Ceramics in the Two-Micron Spectral Range
摘要： High-power solid-state mid-IR lasers are being actively developed, as they possess the key properties for a vast number of technological applications [1] (e. g. lidar, gas sensing, or pump sources optical parametric oscillators) and are in a high demand for basic research as well [2]. These potentialities have recently led to intensive investigations of new mid-IR laser gain media [3,4] and other optical elements. One of the key components under investigation is an optical isolator (OI), a magneto-optical device enabling safe operation of a laser by preventing harmful back-reflections into the laser cavity. The development of high-power OIs is particularly challenging due to the severe thermal effects which arise because of the relatively high absorption of the currently available magneto-optical elements. Therefore, a lot of scientific effort is being put into the research of novel magneto-optical materials with the desired properties: high Verdet constant, low absorption and excellent thermal properties. All of these properties enable a reduction of the heat generated in the magneto-optical element. A large number of new magneto-optical materials for high-power OIs have been reported in the recent years. The vast majority of these reports targeted materials suitable for the wavelengths around 1 μm (corresponding to the neodymium and ytterbium doped gain media) in the task to find a better alternative to the most commonly used magneto-optical material for this spectral range – the terbium gallium garnet (TGG) [5]. In this manner, materials based on highly magnetically active rare-earth ions (e. g. Ce3+ [6], Tb3+ [7] or Ho3+ [8]) have been established as a possible next generation of magneto-optical materials for the visible and near-IR OIs. Some of these materials possess local transparency windows in the mid-IR as well, however, reports dealing with their magneto-optical characteristics in this region (or reports of any other suitable materials) were so far very rare. Nevertheless, Verdet constants of CeF3 crystal [9], DyxY0.95-xLa0.05O3 ceramics (with variable doping X = 0.7 – 0.9) [10] and EuF2 crystal [11] have been recently reported at the wavelength of ~1.94 μm, having ~7, ~10 - 14, and ~12 rad/Tm respectfully. We present broadband experimental characterizations of the Verdet constant of three novel material samples of Dy2O3-based ceramics in a broad spectral range 0.6 – 2.4 μm with the relative error of the measurement ~5%. An analytical approximation of the data is a challenging task due to the multiple resonances and absorption bands of Dy3+ ions within the measured range and is currently under investigation. The obtained values for the Verdet constant at 1.94 μm were 17.8, 22.2 and 26.8 rad/Tm predicting a high potential for Dy2O3 ceramics utilization in a high-power mid-IR OIs. The measured transmittances of our samples at 1.94 μm were equal to 54%, 72% and 76%.
关键词： mid-IR lasers,optical isolators,magneto-optical materials,Dy2O3 ceramics,Verdet constant
更新于2025-09-12 10:27:22
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Laser absorption spectroscopy of rare and doubly-substituted carbon dioxide isotopologues
摘要： Unambiguous detection of the clumped carbon dioxide isotopologue 13C16O18O with isotope ratio mass spectrometry is difficult due to isobaric interference on m/z = 47. We present an analytical technique based on direct absorption laser spectroscopy for precise, direct and simultaneous detection of all isotopologues involved in the isotope exchange reaction 12C16O2 + 13C16O18O ? 12C16O18O +13C16O2 and of 12C16O17O. The achieved precision of 2×10-5 for the 13C16O18O/13C16O2 and 12C16O18O/12C16O2 isotopologue ratios allows to determine the equilibrium constant K of the isotope exchange reaction with an external reproducibility of better than 2×10-5 (1σ) after 9 reference-sample comparisons. Each comparison requires 7 minutes. The isotopic composition of the pure gas can be simultaneously analyzed with a precision of 0.05‰ (1σ) for δ13C and δ18O, and 0.15‰ (1σ) for δ17O. The instrument deploys two interband cascade lasers (ICL) with center wavelengths of 4.3 μm and 4.4 μm. A custom-built optical cell has been designed for single pass and multi pass optical paths (pathlength ratio 1:100); it allows simultaneous detection of rare and abundant isotopologues. The setup is capable to analyze pure CO2 samples of ～100 μmol.
关键词： clumped isotope analysis,mid-IR lasers,tunable lasers,doubly substituted isotopologues,carbon dioxide,laser spectroscopy,laser absorption
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) - Annealing Influence on Structural and Luminescencent Properties of ZnSe:Fe
摘要： Zinc Selenide crystals doped with Iron are promising material to be used as an active media in tunable mid-IR lasers (4 ? 5 μm) [1]. The ZnSe:Fe lasing characteristics close to the theatrical maximum are obtained by optical excitation [2]. Nowadays other pumping methods are also being explored. Previously we have observed luminescence in the mid-IR spectral region with the maximum at the wavelength of 3.9 μm under electron-impact excitation. The present research is focused on the in?uence of annealing process in Zn atmosphere on defective-impurity compound (DIC) and intensity of mid-IR cathodoluminescence (CL). We studied DIC by two-photon confocal microscopy (TPCM) on Carl Zeiss LSM NLO 710 (commercially available equipment). The TPCM allows detecting edge luminescence (EL) (460-480 nm) and DIC (480 - 725 nm) as well as mapping luminescence distribution [3]. In the CL experiments, the crystals were excited by a pulsed electron gun with the accelerated electron energy of 36 kV [4]. A series of ZnSe single crystals doped with Fe by thermal diffusion from surface was subjected to the DIC and CL studies. The initial ZnSe plates were cut from boules grown from the melt by the Bridgman method with an addition of Tellurium. Iron concentrations varied from 0.01 to 14 wt.% as determined by XDR. The samples were observed by TPCM and CL before and after annealing in Zn atmosphere.
关键词： mid-IR lasers,ZnSe:Fe,two-photon confocal microscopy,cathodoluminescence,annealing
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) - Supercontinuum Generation in a As <sub/>2</sub> S <sub/>3</sub> -Silica Nanospike Waveguide Pumped by Tm-Doped Fiber Laser
摘要： The development of compact bright supercontinuum (SC) sources is of particular interest, especially in the mid-IR where is a lack of suitable sources [1,2]. Here we report first results on SC generation in a As2S3-silica dual nanospike waveguide [3, 4] pumped in different multi-pulse regimes by a high-power femtosecond Tm-doped fiber laser mode-locked by nonlinear polarization evolution [5-7]. The experimental set-up is sketched in Fig. 1a. The central wavelength of the laser is 1890 nm and its repetition rate is 13 MHz. By tuning the polarization controllers (PC1 and PC2) in the ring cavity [8], the laser could be configured to operate in different multi-pulse regimes, namely noise-like pulses, soliton bunches and soliton “rain”. The pulse duration is 931 fs in both soliton regimes. The coherence time of the noise-like pulses is 228 fs. The pulses were free-space launched into the As2S3-silica dual nanospike waveguide designed to improve the launch efficiency in and out of the waveguide (~20%). The central uniform portion of the hybrid nanospike has a core diameter of 1.1 μm, the group velocity dispersion (GVD) curve of which is plotted in the inset of Fig. 1a. The pump wavelength is in the anomalous dispersion region between two zero dispersion wavelengths. The measured SC spectra are shown in Fig. 1b for the regimes of soliton bunches (top) and noise-like pulses (bottom). The results from the soliton “rain” regime (not shown here) and the soliton bunches regime are similar. In the soliton regime, sidebands originating from self-phase modulation are observed for a launched peak power of ~90 W, with the spectrum spanning from 1650 nm to 2200 nm. The launched peak power of the solitons was estimated by the pulse duration and the laser characteristics after taking into account the coupling efficiency. The black-dashed line in Fig. 1b plots the simulated spectrum at the output end of the dual nanospike, agreeing reasonably well with experiment. In the preliminary simulation, a single pulse with the same peak power (90 W) was launched into the model. When pumping the waveguide by noise-like pulses the spectrum barely broadens, probably due to the smaller peak power of a single pulse in the packet. In summary, we have achieved spectral broadening in a As2S3-silica hybrid waveguide pumped in different multi-pulse regimes at 1890 nm. It appears that soliton-like regimes are preferable for SC generation. The system is promising for realizing all-fiber broadband SC sources using well-defined femtosecond pulses, as well as investigating different mechanisms of SC generation in multi-pulse regimes.
关键词： mid-IR,Tm-doped fiber laser,supercontinuum generation,As2S3-silica nanospike waveguide,multi-pulse regimes
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) - Extension of Mid-IR Lasing Spectral Region using Cr:ZnSe and Cr:CdSe Combined Active Medium
摘要： High intensity femtosecond solid-state lasers in mid-infrared (mid-IR) region are of significant interest for many applications such as laser processing, ultrafast spectroscopy, high-order harmonic generation, and laser plasma acceleration. Transition metal (TM) doped chalcogenides (Cr:ZnSe, Cr:CdSe, Fe:ZnSe etc.) are attractive laser media for high intensity mid-IR femtosecond lasers, since they have broad fluorescence spectrum and large stimulated-emission cross section in the mid-IR region [1]. Extension of lasing region by combining of fluorescence region of TM doped chalcogenides can contribute to generate mid-IR ultrashort pulses. Combined active medium method [2-4], by which multiple laser media are used inside a laser cavity simultaneously, is suitable for equipping lasing characteristics of multiple laser media on one laser oscillator. This method has high potential to oscillate ultrashort pulses directly from a solid-state laser, however the method has not been realized in the mid-IR region. In this study, we report on extension of mid-IR lasing region using Cr:ZnSe and Cr:CdSe combined active medium (CAM). We obserbed that wavelength tunability was extended when using Cr:ZnSe and Cr:CdSe CAM than when using Cr:ZnSe and Cr:CdSe indipendently. This is the first report that CAM technique based on Cr2+ doped chalcogenides was demonstrated in the mid-IR region.
关键词： Cr:CdSe,femtosecond lasers,combined active medium,mid-IR lasing,Cr:ZnSe
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) - All — Fiber Evanescent Wave Sensors for the Mid-Infrared Spectroscopy of Liquids
摘要： Methods of the mid-IR spectroscopy provide reliable tools for detecting chemical composition of gases and liquids. In the mid-IR spectral range (wavelengths of 3-25 μm), various molecules and functional groups have fundamental absorption bands with large absorption coefficients. Creation of materials and technologies for the remote sensors consisting of fiber-optic broadband sources of coherent mid-IR radiation, chalcogenide fibers for transmitting light to the sensing elements and spectrally-selective photodetectors is a problem of a high scientific priority. In this work, we develop the fiber-optic analytical spectroscopy for chemical analysis of aqueous solutions of acetone, ethanol, for determination of the fractional chemical composition of hydrocarbons. As a material base for the fiber-optic sensors, chalcogenide fibers with an extremely low content of impurities have been designed and fabricated by single- and double-crucible methods (including the REE-doped glass fibers). By using these fibers, technologies of fabrication of permanent fiber bends, tapers, microstructured fibers have been developed for using these structures in fiber lasers, supercontinuum generators, sensing elements. A theoretical approach based on electromagnetic theory of optical fibers has been applied for computer-aided design of the evanescent-wave sensors. A sensing element shaped as the U-bent fiber that was applied for chemical analysis of liquid consisting of a diesel oil and a fuel additive is shown. For chemical analysis, the absorption band at the wavelength of 7.83 μm, corresponding to esters, has been chosen. Output characteristics of the sensor were studied in experiment by variation of the fiber core diameter and the bend radius. In a computer model, it was shown that attenuation coefficients of evanescent modes propagating in the fiber bend grow with increase of the bend radius and with decrease of the fiber core diameter. This allows for enhancing sensitivity and decreasing the minimum detectable amount of an analyte. In fact, with an optimised sensing element, the minimum detected amount of the fuel additive was less than 0.1 vol.%.
关键词： evanescent-wave sensors,chalcogenide fibers,chemical analysis,fiber-optic sensors,mid-IR 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) - Picosecond Widely-Tunable Mid-IR Source for Gas Detection
摘要： Portable and remote sensing solutions to detect the nature of gases in the air are highly demanded. In particular for instance, for the measurement of fire smoke or uncontrolled discharge on risk sites or on an accident including a vehicle transporting hazardous substances [1]. Spectroscopic-based solutions would need a widely-tunable and powerful mid-infrared compact laser source that could be used on field and scan a large number of species. In a previous research from A Puiu et al. [2], the authors described an interesting system for acetone detection at 3.3 μm. The principle used was differential absorption (DIAL) based on a tunable mid-IR source from 3 to 3.45 μm. This source was based on an optical parametric oscillator (OPO) pumped by a Nd:YAG laser. This laser delivered 3.4 mJ at 20 Hz repetition rate and with 7 ns pulse duration. With a set-up based on a gas chamber and mid-IR detection unit for direct absorption measurements the authors demonstrated the capability of their system for detecting acetone concentrations in the range from 1 to 10 % which is the typical level of concentration expected at the vicinity of a bomb factory for instance. Such results are really impressive for a system that is potentially transportable. However, regarding this aspect, mainly because of the footprint and weight of the laser system, portability of the detection unit was a bit limited. Thus, in our case we explored a solution based on a fiber laser pumped OPO. The developed picosecond laser source exhibits short pulses and narrow linewidth (0.4 cm-1). This fiber laser is based on a mode-locked oscillator [3], a Fiber Bragg Grating (FBG) mounted on a piezo electric element for wavelength tuning and several fiber amplifiers. The OPO system was provided by the company LASERSPEC (Belgium) and permits to reach a spectrum ranging from 2700 to 3500 nm. A typical experimental set-up was prepared for characterizing this source for gas sensing [4]. The OPO laser beam was split in two. One beam was sent to a FTIR spectrometer and the other one to an 18-cm-long cell containing the gas under study (See Fig. 1). Acetone detection was demonstrated for various concentrations (Fig. 2). FTIR measurements are in good agreement. In conclusion, we present promising results on acetone with detection levels down to 1% at 3.3 μm (2970 cm-1) using an absorption spectroscopy system based on a widely-tunable compact fiber laser / OPO source.
关键词： mid-IR source,fiber laser,OPO,widely-tunable,picosecond,gas detection
更新于2025-09-12 10:27:22
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EXPRESS: External Cavity Quantum Cascade Laser-Based Mid-Infrared Dispersion Spectroscopy for Qualitative and Quantitative Analysis of Liquid-Phase Samples
摘要： Acquisition of classical absorption spectra of liquids in the mid-IR range with quantum cascade lasers (QCLs) is often limited in sensitivity by noise from the laser source. Alternatively, measurement of molecular dispersion (i.e., refractive index) spectra poses an experimental approach that is immune to intensity fluctuations and further offers a direct relationship between the recorded signal and the sample concentration. In this work, we present an external cavity quantum cascade laser (EC-QCL) based Mach–Zehnder interferometer setup to determine dispersion spectra of liquid samples. We present two approaches for acquisition of refractive index spectra and compare the qualitative experimental results. Furthermore, the performance for quantitative analysis is evaluated. Finally, multivariate analysis of a spectrally complex mixture comprising three different sugars is performed. The obtained figures of merit by partial least squares (PLS) regression modelling compare well with standard absorption spectroscopy, demonstrating the potential of the introduced dispersion spectroscopic method for quantitative chemical analysis.
关键词： liquid phase,Mid-infrared spectroscopy,QCL,quantum cascade laser,dispersion spectroscopy,mid-IR 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) - A 12.6 – 15 μm Mid-IR Source Based on Difference Frequency Generation in Orientation-Patterned GaAs
摘要： Tunable laser sources in the mid-infrared (mid-IR) spectral range have been of great interest for a variety of applications such as molecular spectroscopy and trace gas detection. Difference-frequency generation (DFG) based on nonlinear frequency conversion in nonlinear crystals has been an effective approach to realize tunable mid-IR laser sources [1]. Among nonlinear crystals, orientation-patterned (OP) GaAs has been highly attractive for mid-IR DFG laser sources due to its large nonlinear susceptibility, lack of birefringence, wide transparency range (0.9 – 17 μm), high thermal conductivity, and high laser-damage-threshold [2,3]. Here, we report the generation of broadly tunable mid-IR radiation across 12.65 – 15 μm based on the DFG approach using an OP-GaAs crystal.
关键词： mid-IR,difference-frequency generation,orientation-patterned GaAs,tunable laser sources,molecular spectroscopy,trace gas detection
更新于2025-09-11 14:15:04