Mid-infrared Laser Research Articles

5.3 W/265 μJ Mid-IR All-Fiber Er3+:ZBLAN Gain-Switched Laser Based on Dielectric Fiber Mirror and Fiber-Tip Protection

We report a 2.8 μm all-fiber high-power and high-energy gain-switched Er3+:ZBLAN laser based on dielectric fiber mirror and fiber-tip protection. The fiber pigtail mirror, specifically designed for dichroic operation (i.e., anti-reflection at 976 nm pump wavelength and high-reflection around 2.8 μm laser wavelength), shows high damage density of >10 MW/cm2. An anti-reflection protective film is coated on the input tip of Er3+:ZBLAN fiber and an AlF3 endcap is spliced to the output tip of Er3+:ZBLAN fiber for mitigating the fiber-tip photodegradation and high-power catastrophic failure at 2.8 μm. The compact all-fiber cavity is formed by efficiently connecting the Er3+:ZBLAN fiber with dielectric fiber mirror using the standard FC/PC fiber adaptor. When the 976 nm pump operates in pulsed regime, the all-fiber mid-infrared gain-switched laser can be attained with two states of single-pulse and pulse-burst output. The extracted maximum pulse energy is 4.8 μJ in the single-pulse state, and the shortest pulse width is 426 ns. The pulse-burst mode can generate a maximum average power of 5.291 W and burst energy of 264.55 μJ. This work may offer a promising way to realize the low-cost, all-fiber, high-power and high-energy gain-switched laser at MIR wavelengths.

Investigation of Thermal and Spectroscopic Properties of Tellurite-Based Glasses Doped with Rare-Earth Oxides for Infrared Solid-State Lasers.

The thermal and optical properties of 60TeO2-20K2TeO3-10WO3-10Nb2O5 (in mol%) glasses doped with Ho2O3, Er2O3, and Tm2O3 were explored in the present work. The thermal stability, refractive index n, extinction coefficient k, absorption coefficient α, and optical band gap of the glasses were evaluated. The UV-Vis-NIR absorption spectra, the Judd-Ofelt intensity parameter, the spectroscopic quality factor, and the emission and absorption cross-sections were calculated to investigate the effects of Er3+ and Tm3+, respectively, on the band spectroscopic properties of Ho3+ ions. The results showed that the maximum emission cross-section was approximately 8×10-21 cm2, and the values of the full width at half maximum (FWHM), quality factor (σe×FWHM), and gain coefficient of Ho3+: 5I7→5I8 were also reported. The value of the FWHM×σe was 1200×10-28 cm3, which showed greater gain characteristics than earlier study results. For 2 μm mid-infrared solid-state lasers, the glasses that were examined might be a good host material.

Modelling of long-wave mid-infrared ultrashort pulse generation via difference frequency generation.

In this paper, a model of generating mid-infrared (MIR) ultrashort laser pulse through difference frequency generation (DFG) is established. The pulse evolution relationship among the pump, signal, and idler pulses during the DFG process, as well as the effects of crystal length, pulse energy of the pump and signal lights, pulse width, and other factors on the characteristics of the MIR pulse are explored. Furthermore, through simulations from the time domain to the frequency domain, the spectral characteristics and angular distribution of MIR were analyzed. DFG experimental data are also presented to support the model.

Real-time monitoring of CH4 and N2O emissions from livestock using mid-infrared external cavity quantum cascade laser absorption spectroscopy

The largest share of greenhouse gas (GHG) emissions related to livestock originates from methane (CH4) and nitrous oxide (N2O) which have a far higher influence on global warming, it is therefore necessary to accurately monitor CH4 and N2O emissions to provide theoretical and practical basis for further estimating and regulating GHG emissions from livestock and improving livestock production performance. For the purpose of sensing CH4 and N2O emissions during livestock living process in real time, an optical sensor based on continuous-wave (CW) external cavity quantum cascade laser (EC-QCL) operating at room temperature was developed. CH4 and N2O absorption lines, located around 8 μm, of the ν4 and ν1 fundamental vibrational bands, respectively, were chosen for direct absorption spectroscopy, which allows for sensitive, selective and simultaneous measurement of CH4 and N2O concentrations. Use of a Herriot multi-pass cell with an effective path-length of 100 m, 1σ (SNR = 1) limits of detection of 26.8 ppbv, 20.3 ppbv and 0.01 % for CH4, N2O and H2O vapor were achieved, respectively. Field measurement of CH4 and N2O emissions from horses has been carried out in a stable over two weeks at the Vernaelde farm in Couderkerque Branche city, France. Concentrations of CH4 and N2O up to 10 times and 1.5 times higher than their levels in the local ambient air (∼ 2.12 ppmv and ∼ 427 ppbv) were observed, respectively.

Mid-infrared dielectric laser acceleration in a silicon dual pillar structure.

Dielectric laser accelerators use near-infrared laser pulses to accelerate electrons at dielectric structures. Driving these devices with mid-infrared light should result in relaxed requirements on the electron beam, easier fabrication, higher damage threshold, and thus higher acceleration gradients. In this paper, we demonstrate dielectric laser acceleration of electrons driven with 10 μm light in a silicon dual pillar structure. We observe the acceleration of 27 keV electrons by 1.4 keV, corresponding to a 93 MeV/m acceleration gradient. The damage threshold of the structures of 3.3 ± 0.6 GV/m peak field is significantly higher than for near-infrared accelerators. The dual pillar acceleration structure itself even survived 5.2 ± 0.9 GV/m, the highest field strength we could achieve with the current system. This together with the larger structure acceptance bodes well for future dielectric laser accelerators driven with mid-infrared light.

Narrowband mid-infrared optical parametric generator based on a type-II BaGa4Se7 crystal.

In this Letter, we first reported on a mid-infrared double-pass optical parametric generator (OPG) based on a single type-II phase-matching BaGa4Se7 (BGSe) crystal, pumped at 2.1 µm. The OPG achieved a maximum pulse energy of 55 µJ for generating narrowband mid-infrared laser pulses. The signal and idler lights exhibited center wavelengths of 4.04 and 4.33 µm, respectively, with bandwidths of 18.6 nm (11.4 cm-1) and 20.4 nm (10.9 cm-1). To improve the output performance, we utilized a cascaded scheme of type-I ZnGeP2 (ZGP) and type-II BGSe crystals. The spectral bandwidths of the signal and idler lights, nearing 4 µm, were narrower than 170 nm (90 cm-1), representing a significant improvement over the ZGP OPG. The cascaded OPG achieved a remarkable total optical-to-optical conversion efficiency (OOCE) of 14.9% and a maximum pulse energy of 0.329 mJ.

Mid-Infrared Supercontinuum Generation in Highly Nonlinear Chalcogenide Fibers

Interest in mid-infrared broadband laser light sources has surged due to applications in trace gas detection, free-space communications, and countermeasures. Progress in supercontinuum generation leverages fiber-based near-infrared and bulk-optic mid-infrared pump sources. In this paper, the Generalized Nonlinear Schrödinger Equation has been solved, using the Split Step Fourier Method, to simulate the pulse propagation and mid-infrared supercontinuum generation, inside a fiber composed of highly nonlinear As2Se3/As2S3 chalcogenide glass. The effect of various parameters, including fiber nonlinearity, Group Velocity Dispersion (GVD), input power and pulse-width, anomalous and normal dispersion pumping regime, etc. on the output supercontinuum bandwidth has been extensively studied. A tapered chalcogenide fiber is modeled to facilitate continuous simultaneous modification of the GVD and the Kerr nonlinearity parameter. Pumping the waveguides with 230-fs secant pulses at a peak power of 4.2-kW yields a mid-IR supercontinuum extending from [Formula: see text] to [Formula: see text] micrometers.

Spectral programmable mid-infrared optical parametric oscillator

A spectral programmable, continuous-wave mid-infrared (MIR) optical parametric oscillator (OPO), enabled by a self-developed high-power spectral tailorable fiber laser, was proposed and realized. While operating at a single-wavelength, the maximum idler power reached 5.53 W at 3028 nm, with a corresponding pump-to-idler conversion efficiency of 14.7%. The wavelength number switchable output was available from one to three. The single idler was tunable in a range of 528 nm (2852–3380 nm). In a dual-wavelength operation, the interval between two idlers could be flexibly tuned for 470 nm (53–523 nm), and the intensity of each channel was controllable. Triple-wavelength idler emission was realized, meanwhile exhibiting spectral custom-tailored characteristics. Furthermore, we balanced the parametric gain through the pre-modulating broadband multi-peak pump spectra, enabling a 10 dB bandwidth adjustment of the idler emission from 20 to 125 nm. This versatile mid-infrared laser, simultaneously featuring wide tuning, multi-wavelength operation, and broad bandwidth manipulation, has great application potential in composition detection, terahertz generation, and speckle-free imaging.

Methodology for the quantification of the absorption potential of greenhouse - and pollutant gases by climbing plants used in façade greening; a case study on ivy (Hedera helix)

How much do specific climbing plants contribute to the cleansing or absorption of harmful greenhouse and pollutant gases; often regarded as the main environmental threat in cities due to their adverse effects on human health? One of the main hurdles in the quantification of such ecosystem services is associated with the difficulty to obtain and design systems that provide detailed information on the interaction between various gases and the plant in question. To tackle these questions, two highly precise and accurate instruments, namely a mid-infrared laser absorption spectrometer (TDL) and a cavity-ring-down spectrometer (CRDS) were used to monitor the fate of gases when exposed to façade climbing plants like ivy. In a laboratory setting, a relaxation type of experiment was used consisting of a reaction chamber equipped with plant species and continuously flushed by synthetic air. This setup was used to determine the timescales of decay after short injections of the above-mentioned gases. After these injections, all gases followed simple exponential decay curves. N2O, a non-reactive (inert) tropospheric gas, was used as a reference to which all other gases were compared and thereby quantified. This paper focuses on the detailed description of methods and processes to analyse the gas-absorptive behaviour of plants when exposed to gaseous pollutants. For demonstration purposes, quantified absorption features of nitrogen oxide (NO2) are presented for ivy of the variety Hedera helix “Plattensee”. Results of this method of quantification showed that - as compared to N2O (control), - NO2 had a reduced residence time (time scale) of 100 s, while N2O resulted in a 600 s residence time (indicating no interference with the plant). This is equivalent to a 0.3 cm/s deposition velocity/ absorption rate of NO2 under light conditions.

Growth, thermal, spectroscopy and 2.8 μm laser performance of Er:LuYGG crystal

A novel mid-infrared (Er0.3Lu0.1Y0.6)3Ga5O12 laser crystal is successfully grown by the Czochralski method, the crystal structure, segregation coefficient, thermal performance, spectroscopy and 2.8 μm laser performance are studied systematically. The crystal possesses a pure garnet phase with a thermal conductivity of 4.54 W m−1 K−1. It exhibits a broader absorption band around 966 nm and some strong emission peaks at 2.6–3 μm, corresponding to the absorption cross-section of 1.39 × 10−21 cm2 at 966 nm and emission cross-section of 1.25 × 10−20 cm2 at 2822 nm, respectively. The level lifetimes of 4I11/2 and 4I13/2 are fitted to be 0.885 and 3.203 ms. A LD end-pumped Er:LuYGG laser has been demonstrated, achieving a maximum output power of 339 mW and a slope efficiency of 17.77 %. The primary laser wavelength is centered at 2824.76 nm. All the results indicate that the Er:LuYGG crystal is a novel and promising crystal material to realize the 3 μm laser.

Narrow bandgap two-dimensional Nb2SiTe4 as broadband saturable absorber for optical switch

Nb2SiTe4 is a novel narrow-bandgap (∼0.39 eV) two-dimensional material with a high optical absorption coefficient, high carrier mobility, and outstanding air stability, which shows great application potential in broadband optical switches. In this study, high-quality layered Nb2SiTe4 nanosheets were efficiently fabricated by the mechanical exfoliation method, and the basic characterizations were carried out comprehensively. Nondegenerate pump-probe technology was implemented to systematically explore the photocarrier dynamics in the Nb2SiTe4 nanosheets, which exhibit the ultrafast recovery time of Nb2SiTe4 (∼0.3 ps). Furthermore, broadband passively Q-switched lasers operating at 1.0, 2.0, and 2.8 μm with the shortest pulse width of 380, 549, and 218 ns were achieved based on Nb2SiTe4 saturable absorber. This work demonstrates the significant advantages of an optical switch based on Nb2SiTe4 saturable absorber, including a narrow output pulse width, wide working bandwidth, high damage threshold, excellent oxidation resistance, and a straightforward synthesis method, which underscore the immense potential of Nb2SiTe4 broadband optical switches in applications involving mid-infrared lasers.

Multiphoton-initiated laser writing of semiconductors using nanosecond mid-infrared pulses

The advent of more powerful mid-infrared nanosecond laser sources allows using them as attractive tools in material laser processing. For semiconductor bulk processing, laser intensities must remain modest to avoid detrimental nonlinear propagation and pre-focal plasma screening effects. Accordingly, nanosecond pulses are usually appropriate to locally initiate energy deposition by multiphoton absorption and subsequent modification, hardly achievable with ultrashort pulses. Employing a 2.8-μm 2.5-ns laser source, we explore the possibility to modify silicon and other semiconductors. With interactions initiated by three-photon absorption, we modify and determine the surface and bulk modification thresholds of Si, GaAs, and InP. For Si, compared to previous studies at telecom wavelengths, we report on a reduction of the energy threshold for volume modification with processing depth, and repeatable rear-surface modifications. Compared to Si, we find for GaAs and InP important fluctuations in the modification responses, which we attribute to an absorption mechanism initially triggered by a greater presence of defects. We also study germanium, as this narrower bandgap semiconductor very interesting for mid-infrared electro-optical applications is transparent at the newly introduced wavelength. Despite the ability to modify the surface, the bulk of Ge remains inaccessible in this two-photon regime, mainly attributed to beam aberrations and nonlinearities. Nonetheless, we demonstrate the ability to process Si chips integrating Ge layers. All these results showcase the potential of mid-infrared wavelengths to offer new degrees of flexibility for 3D laser processing technologies turned to silicon photonics and microelectronics packaging.

Experimental Study on Damage Effect of Mid-Infrared Pulsed Laser on Charge Coupled Device (CCD) and HgCgTe Detectors.

As the weak link in electro-optical imaging systems, photodetectors have always faced the threat of laser damage. In this paper, we experimentally investigated the damage mechanism of the photodetector induced by the out-of-band laser. The damage thresholds of the mid-infrared pulsed laser for Charge Coupled Device (CCD) and HgCdTe detectors were determined through damage experiments. The analysis of the damage phenomena and data for both CCD and HgCdTe detectors clearly demonstrated that out-of-band mid-infrared pulsed lasers could entirely incapacitate CCD and HgCdTe detectors. Our analysis of the damage process and data revealed that the primary mechanism of damage to CCD and HgCdTe detectors by mid-infrared pulsed lasers was primarily thermal. This study serves as a reference for further research on the mid-infrared pulsed laser damage mechanisms of CCD and HgCdTe detectors, as well as for laser protection and performance optimization in imaging systems.

Design of tensile-strained GeSn/SiGeSn structure for low threshold mid-infrared laser application

The plasticity of GeSn alloy energy band has promoted the development of silicon-based photoelectric integration and optical interconnection. A tensile-strained GeSn/SiGeSn double heterostructure laser wrapped with Si3N4 stress liner is designed and characterized theoretically. The triaxial tensile strain is introduced into the GeSn/SiGeSn heterostructure laser by the Si3N4 linear stressor. The lower threshold current density and higher optical gain of the GeSn/SiGeSn laser can be achieved by tuning the band structure and carrier distribution in the active region with tensile strain and Sn compositions. Compared with the relaxed device, the value of ne ,Γ/ne ,total for the Ge0.90Sn0.10/Si0.315Ge0.499Sn0.186 heterostructure laser wrapped with 300 nm Si3N4 linear stressor is increased to 30.6% at n e,total of 1018 cm−3, the laser λ can be extended to 3.44 μm, and the J th is reduced from 206 to 59 A/cm2.

Beam characterization of mid-infrared free electron laser to drive high-harmonic generation

The maximum energy of photons from high-harmonic generation (HHG) increases with the wavelength of the driving laser. A free electron laser (FEL) is a continuously tunable light source in the mid-IR wavelength range and it is useful for investigating the extension of the accessible photon energy in HHG. Recently, the undulator magnets of the IR FEL at the Laboratory for Electron Beam Research and Application (LEBRA), Nihon University, have been replaced, and then the output power of the FEL has increased. Here, we evaluate the pulse duration and focal beam size of the FEL and show that the LEBRA FEL with 2 and 3 μm laser wavelengths under a 44 MHz bunch repetition mode can drive HHG.

Acetone Gas Sensing Using a Hybrid Mid-Infrared Fluoride Fiber Laser

Acetone Gas Sensing Using a Hybrid Mid-Infrared Fluoride Fiber Laser

Sm3+ as effective deactivator for enhanced ∼3 μm laser emission in Er,Sm:SrLaAlO4 crystal

A promising mid-infrared (MIR) laser crystal with Er, Sm co-doped SrLaAlO4 (Er,Sm:SLA) crystal was successfully grown using the Czochralski (CZ) method. It was the first time that co-doped Sm3+ ion as deactivator for Er3+ activated ∼ 3.0 μm laser. The crystal structure, absorption spectra, emission spectra, and energy level lifetime were discussed in detail. The band structure and density of states were calculated by the density functional theory. The spectral parameters were calculated using Judd-Ofelt (J-O) theory and the deactivate effect of Sm3+ was systematically studied. The introduction of Sm3+ ions enhance the 2.7 µm mid infrared emission intensity by three times, and decrease the lifetime of 4I13/2 energy level of Er3+ ion from 4.35 ms to 0.98 ms. The lifetime ratio of upper and lower levels for 2.7 µm emission was calculated to be 0.63, which is 2.6 times of Er:SLA crystal and comparable to some commercial crystals. All the results indicate that the Sm3+ ion is an effective deactivator for ∼3 μm laser emission. The long upper level lifetime, as well as the large lifetime ratio, the broadening spectra characteristics and the appropriate emission cross-section show the Er,Sm:SLA crystal a good gain material for ultrafast and tunable lasers at ∼3.0 μm.

Mid-infrared tunable filter based on a femtosecond-written silica volume Bragg grating.

A silica volume Bragg grating (VBG) is used to filter the light of a mid-infrared (mid-IR) supercontinuum laser. The VBG with a 7 µm period was inscribed with 800 nm pulses with a 100 fs duration and the phase-mask technique over a glass thickness of 3 mm. Despite silica's absorption, the VBG allows obtaining a narrowband light source tunable from 2.9 to 4.2 µm with a full width at half maximum (FWHM) of 29 nm. This demonstrates the great potential of using femtosecond-written VBGs as highly tunable, yet selective, spectral filters in the mid-IR.

ZnO microwire lasing generated by mid-infrared laser pulses of various polarization

ZnO microwire lasing generated by mid-infrared laser pulses of various polarization

Dual-wavelength mid-infrared laser operation at 2.8 μm and 3.6 μm in Er3+ doped fluoride fiber

This study presents a pioneering experimental demonstration of dual-wavelength laser operation at 2.8 μm and 3.6 μm in an Er3+-doped ZrF4-BaF2-YF3-AlF3 double-cladding fluoride glass fiber, fabricated in-house. The achievement is realized through the implementation of a novel dual-wavelength pumping scheme utilizing 980 nm and 1150 nm lasers. This innovative scheme enables the excitation of the lower energy level of the 2.8 μm laser transition (4I11/2) to the upper energy level of the 3.6 μm transition (4F9/2) via an excited state absorption process, resulting in simultaneous emission at 2.8 μm and 3.6 μm. The maximum laser output powers at 2.8 μm and 3.6 μm are measured at 0.96 W and 0.32 W, respectively. This groundbreaking work marks the first experimental realization of dual-wavelength laser operation at 2.8 + 3.6 μm in Er3+-doped fluoride fiber, contributing significantly to the advancement of laser technology in this spectral range.