Mid-infrared Laser Research Articles

Fabrication and Mid-Infrared Laser Transmission Performance of Ultra-Low Loss Chalcogenide Glass Fibers

Fabrication and Mid-Infrared Laser Transmission Performance of Ultra-Low Loss Chalcogenide Glass Fibers

Photoacoustic Heterodyne CO Sensor for Rapid Detection of CO Impurities in Hydrogen.

Hydrogen (H2) fuel cells have been developed as an environmentally benign, low-carbon, and efficient energy option in the current period of promoting low-carbon activities, which offer a compelling means to reduce carbon emissions. However, the presence of carbon monoxide (CO) impurities in H2 may potentially damage the fuel cell's anode. As a result, monitoring of the CO levels in fuel cells has become a significant area of research. In this paper, a novel photoacoustic sensor is developed based on photoacoustic heterodyne technology. The sensor combines a 4.61 μm mid-infrared quantum cascade laser with a low-noise differential photoacoustic cell. This combination enables fast, real-time online detection of CO impurity concentrations in H2. Notably, the sensor requires no wavelength locking to monitor CO online in real-time and produces a single effective signal with a period of only 15 ms. Furthermore, the sensor's performance was thoroughly evaluated in terms of detection sensitivity, linearity, and long-term stability. The minimum detection limit of 11 ppb was obtained at an optimal time constant of 1 s.

Fabrication of PEEK Ag/AgI mid-infrared hollow fiber and transmission reliability study for CO2 laser radiation

Hollow fiber is a crucial means for delivery of mid-infrared laser radiation and has a wide range of applications in laser surgery and other fields. At present, there is still a lack of low-cost, highly flexible plastic hollow fiber that can reliably transmit mid-infrared laser with low loss. In this study, flexible Poly ether ether ketone (PEEK) tubing material was selected as the structural tube for establishing a robust plastic Ag/AgI mid-infrared hollow fiber. Fiber samples with inner diameters of 1.0, 1.5 and 2.0 mm were prepared using plasma treatment and dynamic chemical liquid deposition processes. The transmission losses for CO2 laser of the 1.0-, 1.5- and 2.0-mm-bore PEEK Ag/AgI hollow fibers increased from 0.40, 0.18 and 0.10 dB/m to 2.35, 1.60 and 1.05 dB/m, respectively, as they were bent at an angle from 0° to 180° with a radius of 15 cm. The hollow fibers could stably transmit CO2 laser in high (120 °C) and low (-78.5 °C) temperature environments. After undergoing 100 h of accelerated humidity-heat aging (85 °C, 85 % RH) and 10 cycles of high-low (-40 ∼ 85 °C) temperature cycling treatment, the transmission loss remained almost unchanged. The PEEK Ag/AgI hollow fiber exhibited high energy damage threshold and it could stably deliver a 10 ∼ 20 W CO2 laser beam for 20 min to 5 h when bent at a 25 cm radius and a 90° angle. The current research provides a possible approach for developing low-cost, highly flexible, low-loss and highly reliable mid-infrared hollow fibers. It is helpful to promote the applications of CO2 laser in laser medicine, intelligent manufacturing and sensing.

Four-dimensional laser absorption cinematography of species and temperature dynamics at 2 kHz in reacting flows.

A four-dimensional (4D) mid-infrared laser absorption imaging technique has been developed and demonstrated for quantitative, time-resolved, volumetric measurements of temperature and species concentration in dynamic combustion flows. This technique employs a dual high-speed infrared camera setup to capture turnable radiation from a quantum cascade laser near 4.85 µm to resolve rovibrational absorption transitions of carbon monoxide at two orthogonal projection angles. The laser is modulated with a customized waveform to adaptively resolve two target transitions with an increased density of data samples in proximity to the transition peaks, therefore ensuring accurate and quantitative spectral interpretation while minimizing the required frame rate. A 3D masked Tikhonov regularized inversion was performed to reconstruct spectrally resolved absorbance at every grid point of each frame, which enables subsequent interpretation of local gas properties in time. These methods are applied to achieve quantitative 4D cinematography of temperature and carbon monoxide in a propagating C2H4/O2 flame with a spatial pixel resolution of ∼70 µm and a temporal resolution of 2 kHz.

Dual-chirped optical parametric amplification of high-energy single-cycle laser pulses

We demonstrate how a scheme called advanced dual-chirped optical parametric amplification (DC-OPA) that employs two kinds of nonlinear crystal (BiB3O6 and MgO-doped lithium niobate) can generate high-energy, single-cycle mid-infrared laser pulses. In experiments, the advanced DC-OPA scheme achieved carrier-to-envelope phase-stable mid-infrared laser pulses with a bandwidth of over one octave (1.4–3.1 µm) and an output pulse energy of 53 mJ. The pulse duration was compressed to 8.58 fs, which corresponds to 1.05 cycles with a central wavelength of 2.44 µm and a peak power of 6 TW. To our knowledge, the obtained values for the pulse energy and peak power are the highest achieved for optical parametric amplification of single-cycle mid-infrared laser pulses. Moreover, owing to the energy scalability of the advanced DC-OPA scheme, the prospects of the multi-terawatt sub-cycle laser pulses are discussed.

High-power, single-frequency mid-infrared laser based on a hybrid Fe:ZnSe amplifier

This study proposes a high-power, single-frequency mid-infrared laser based on a quantum cascade laser (QCL) seeded Fe:ZnSe amplifier design. The Fe:ZnSe amplifier is injection-seeded with a 55-mW, 4.3-μm distributed feedback QCL and can produce 390 mW laser output with an extraction efficiency of 14%, a beam quality factor of M2 ∼ 1.1, and a spectral linewidth of 29.6 MHz. Further, this study presents a theoretical analysis predicting the laser performance of the optimized amplifier system. The prospects for further improvement in performance and extension of the tuning capability are discussed.

NH3 absorption line study and application near 1084.6 cm−1

Ammonia (NH3) holds significant importance as an industrial product, ambient trace pollutant, and a promising zero-carbon energy carrier, underscoring the critical need for accurate quantification in various applications. In this study, a mid-infrared quantum cascade laser (Mid-IR QCL) based tunable diode laser absorption spectroscopy (TDLAS) spectrometer was developed. It was coupled with two reactors, namely a gas cell and a shock tube and operated in three modes: low- and high-frequency (140 Hz and 10 kHz) scan modes and fixed-wavelength mode, tailored to the specific needs of each experimental scenario. The primary objects were NH3 line parameters measurement and absolute NH3 quantification. With the 140 Hz low-frequency scan mode, NH3-Ar pressure broadening coefficients of six transition lines near 1084.6 cm−1 were measured in a gas cell at 295 K and 1–11 mbar for the first time. These coefficients were subsequently employed to quantify the initial NH3 mole fraction in shock tube experiments, considering the substantial adsorption effect of NH3. Using the high-frequency scan mode (10 kHz), spectrally resolved NH3 absorption cross-sections were obtained in a shock tube across a pressure range of 1.46–3.25 bar and a temperature range of 1000–1800 K. This data, acquired for the first time, significantly contributes to the understanding of NH3 behavior in high-temperature environments. Additionally, potential interference from high-temperature water absorption near 1084.6 cm−1 was thoroughly examined. The high-temperature water absorption cross-section was measured over a pressure range of 0.99–3.02 bar and a temperature range of 1322–2905 K, utilizing a near-infrared water laser. Leveraging these comprehensive datasets, the study quantified the NH3 mole fraction during the NH3 oxidation process in the shock tube, employing the fixed-wavelength mode to achieve high time resolution. The quantified NH3 mole fraction was then compared to predictions from eleven recent chemical kinetic mechanisms, demonstrating the utility of the developed spectrometer in validating these mechanisms.

Spectroscopic properties and numerical analysis of novel erbium doped multi-component tellurite glasses

In this paper, Er3+ doped TeO2-ZnF2-BaF2-KF-Ta2O5 tellurite glasses with low hydroxyl content (∼0.03 × 10−19 cm−3) were investigated employing both glass composition and glass melting process optimization. The Raman spectra and physical properties were characterized to analyze the structure of the glasses. Under the pumping of 980 nm LD laser, intense up-conversion fluorescence at 1.5 and 2.7 μm of samples and their lifetimes were detected and analyzed, and the related transition mechanisms with gradient-varying Er3+ doping concentrations were discussed. The maximum absorption and emission cross section at 2.7 μm was calculated to be 6.4 × 10−21 cm2 and 6.8 × 10−21 cm2, correspondingly, which were higher than those of traditional tellurite glasses. Using the calculated and measured spectroscopic parameters of bulk tellurite glass, a dual-wavelength pumping model was established to verify the feasibility of mid-infrared laser output in similar tellurite glass fiber. Experimental results support the assertion that the Er3+ doped tellurite glasses hold promise as a candidate laser gain medium for mid-infrared fiber laser systems.

Growth and efficient laser emission of Er3+ doped LGGG single crystal at 2.8 μm

A novel kind of high-quality Er3+:LGGG crystal has been grown using the Czochralski method and exhibited excellent lasing performance for the first time at around 2818 nm in the mid-infrared spectral region. The J-O intensity parameters, spontaneous emission probability, branching ratio, and exited state lifetimes parameters have been calculated for the first time using the J-O theory, providing theoretical references for future analysis of the absorption and emission characteristics of Er3+:LGGG crystals. The fluorescence lifetimes of the upper (4I11/2) and lower (4I13/2) laser levels are 1.42 and 5.18 ms, respectively. Under 976 nm laser pumping, a continuous-wave laser output of 374 mW with excellent beam quality factors Mx2/My2 of 1.374/1.228 has been achieved by using the Er3+:LGGG crystal. These results indicate that Er3+:LGGG crystals are promising materials for generating 2.8 μm mid-infrared lasers.

Urban open-air chemical sensing using a mobile quantum cascade laser dual-comb spectrometer

Detection of airborne chemical releases in densely populated urban environments requires precise sensors with high temporal and spatial resolution capable of covering large areas. For this purpose, we present a mobile mid-infrared quantum cascade laser dual-comb spectrometer for identification and quantification of chemical plumes. Field tests with the remote sensor were conducted during daytime in the downtown Boston area over a five day period during which chemical releases were simulated by intermittently emitting non-toxic substances. Open-air sensing was performed with retroreflectors positioned at up to 230 m distance and with sensitivities in the ppm m range for one second of averaging time. The field campaign demonstrates a step toward a semiconductor dual-comb spectroscopic sensor in the mid-infrared fingerprint region, suitable for long-term deployments. These types of sensors will be valuable complements to existing optical sensors for urban hazardous gas leak monitoring, air quality assessments, and localization of clandestine chemical production.

Above 20 GHz high frequency operation of mid-infrared doughnut-shaped microcavity quantum cascade lasers

Microresonator-based high-speed single-mode quantum cascade lasers are ideal candidates for on-chip optical data interconnection and high sensitivity gas sensing in the mid-infrared spectral range. In this paper, we propose a high frequency operation of single-mode doughnut-shaped microcavity quantum cascade laser at ∼4.6 µm. By leveraging compact micro-ring resonators and integrating with grounded coplanar waveguide transmission lines, we have greatly reduced the parasitics originating from both the device and wire bonding. In addition, a selective heat dissipation scheme was introduced to improve the thermal characteristics of the device by semi-insulating InP infill regrowth. The highest continuous wave operating temperature of the device reaches 288 K. A maximum −3 dB bandwidth of 11 GHz and a cut-off frequency exceeding 20 GHz in a microwave rectification technique are obtained. Benefiting from the notch at the short axis of the microcavity resonator, a highly customized far-field profile with an in-plane beam divergence angle of 2.4° is achieved.

Rare-Earth-Doped Selenide Glasses as Laser Materials for the 5–6 μm Spectral Range

This paper provides an overview of mid-infrared lasers based on rare-earth-ion-doped selenide glasses. Laser action was demonstrated at the transitions between the first excited and the ground levels of Ce3+, Pr3+, Nd3+ and Tb3+ ions. The highest output parameters for bulk glass lasers (over 40 mJ of output energy) and wavelength tuning in the range of 4.6–5.6 microns were obtained with Ce3+-doped glass. The highest output parameters for fiber lasers (150 mW at 5.1–5.3 μm under continuous pumping) were demonstrated with Tb3+ ions. The longest lasing wavelengths for any glass laser and tunability within the 5.56–6.01 µm spectral band were shown with Nd3+ ions in a Tb3+-Nd3+ co-doped system.

Damage Mechanism of HgCdTe Focal Plane Array Detector Irradiated Using Mid-Infrared Pulse Laser

To investigate the damage threshold and mechanism of a mid-infrared HgCdTe focal plane array (FPA) detector, relevant experimental and theoretical studies were conducted. The line damage threshold of a HgCdTe FPA detector may be within the range of 0.59 Jcm−2 to 0.71 Jcm−2. The full frame damage threshold of the detector may be in the range of 0.86 Jcm−2 to 1.17 Jcm−2. Experimental results showed that when the energy density reaches 1.17 Jcm−2, the detector exhibits irreversible full frame damage and is completely unable to image. Based on the finite element method, a three-dimensional model of HgCdTe FPAs detector was established to study the heat transfer mechanism, internal stress, and damage sequence. When HgCdTe melts, we think that the detector is damaged. Under these conditions, the theoretical damage threshold calculated using the detector model is 0.55 Jcm−2. The difference between theoretical and experimental values was analyzed. The relationship between damage threshold and pulse width was also studied. It was found that when the pulse width is less than 1000 ns, the damage threshold characterized by peak power density is inversely proportional to pulse width. This relationship can help us predict the experimental damage threshold of an FPA detector. This model is reasonable and convenient for studying the damage of FPA detectors with a mid-infrared pulse laser. The research content in this article has important reference significance for the damage and protection of HgCdTe FPA detectors.

Widely tunable single-frequency Er-doped ZBLAN fiber laser with emission from 3.37 to 3.72 µm.

We demonstrate a widely tunable single-frequency Er-doped ZBLAN fiber laser operating on a 4F9/2→4I9/2 transition band. An uncoated germanium (Ge) plate serves as a narrow-bandwidth etalon and is inserted in the cavity to achieve a single longitudinal mode selection. Wavelength tuning from 3373.8 nm to 3718.5 nm was demonstrated by using a blazed diffraction grating at 3.5 µm. At the emission peak of 3465.6 nm, the laser yields over 100 mW single-frequency output power, with a 3 dB linewidth <6.9 MHz, and a slope efficiency (with respect to the incident 1990 nm pump power) of 20.3%. Such a tunable mid-infrared single-frequency fiber laser may serve as a versatile laser source in spectroscopy and sensing applications.

Bond-selective full-field optical coherence tomography.

Optical coherence tomography (OCT) is a label-free, non-invasive 3D imaging tool widely used in both biological research and clinical diagnosis. Conventional OCT modalities can only visualize specimen tomography without chemical information. Here, we report a bond-selective full-field OCT (BS-FF-OCT), in which a pulsed mid-infrared laser is used to modulate the OCT signal through the photothermal effect, achieving label-free bond-selective 3D sectioned imaging of highly scattering samples. We first demonstrate BS-FF-OCT imaging of 1 µm PMMA beads embedded in agarose gel. Next, we show 3D hyperspectral imaging of up to 75 µm of polypropylene fiber mattress from a standard surgical mask. We then demonstrate BS-FF-OCT imaging on biological samples, including cancer cell spheroids and C. elegans. Using an alternative pulse timing configuration, we finally demonstrate the capability of BS-FF-OCT on imaging a highly scattering myelinated axons region in a mouse brain tissue slice.

Mid-infrared pulsed Er:ZBLAN fiber laser producing mode-switchable cylindrical vector beams.

We demonstrate the generation of both continuous-wave (CW) and Q-switched cylindrical vector beams (CVBs) from a mid-infrared Er3+-doped ZBLAN (Er:ZBLAN) fiber laser at ∼ 2.8 µm. A customized S-waveplate is incorporated as the intracavity mode converter to achieve the mid-infrared CVBs. Switchable modes of CVBs between the radially and azimuthally polarized beam can be realized easily by manipulating the cavity conditions. A maximum output power of ∼250 mW is achieved for the CW CVBs. In the short-pulsed CVBs operation regime, both the active and passive Q-switching modes are realized with a pulse duration of hundreds of nanoseconds. The proposed mid-infrared cylindrical vector lasers can have significant potential for applications in biomedicine, optical trapping, material processing and optical communication.

Broadband 2.85 μm Luminescence Properties of Er3+/Dy3+ Co-Doped Fluorotellurite Glass

TeO2-BaF2-Er2O3-Dy2O3 laser glasses were prepared using the melt-quenching method. The bound water that can capture the excited state energy was reduced by physical and chemical methods. We did not observe a significant Er3+ emission peak at 2.7 μm in fluorescence spectra, which may be due to the efficient energy transfer process (ET2). Meanwhile, we found a broadband gain span of approximately 400 nm in fluorescence spectra at the 2.85 μm band, attributed to the ‘vector summation’ of the energy level radiation transition and the change of the glass network. Subsequently, we explored the structural properties of the glass. The results indicated that the Gaussian peak located at 250 cm−1 drifts toward 370 cm−1, which may be caused by the fracture or recombination of Te-O-Te and a decrease in the bridge oxygen content with the increasing concentration of Er2O3. The topology cage structure around the luminescence center of rare earth ions is changed and the stability of the optically active center is enhanced, finally contributing to the enhancement of luminescence. Meanwhile, the maximum σemi and gain coefficient of Dy3+ reach up to 7.22 × 10−21 cm2 and 7.37 cm−1, respectively. The comprehensive results show that the fluorotellurite glass designed in this study is expected to be a gain medium for mid-infrared lasers in remote sensing monitoring, military, and other fields.

Transient analysis of solar pyrolysis and hydrogen yield via interband cascade laser absorption spectroscopy of methane, acetylene, ethylene, and ethane

A mid-infrared laser absorption sensing method has been developed to measure species concentrations of four hydrocarbons and gas temperature over a range of temperatures in mixture compositions relevant to the pyrolytic decomposition of natural gas. The four measured species (methane, acetylene, ethylene, and ethane) are the most abundant hydrocarbons during the pyrolysis of natural gas, and provide a means to monitor decomposition progress and hydrogen yield through molar balance. In this work, time-division multiplexed signals of three distributed-feedback interband cascade lasers are used to make simultaneous measurements of select C-H stretch rovibrational transitions of the target hydrocarbons in the 3.00–3.34 μm range. The sensor was validated over a range of temperatures and pressures (300–1000 K, 0.03–1 atm) at relevant mixture compositions, with correction methods developed to mitigate cross-species interference. The sensor was demonstrated on a solar-thermal pyrolysis reactor, where time-resolved measurements of species mole fractions were performed across a range of insolation conditions to capture the transient response of the reactor.

Noisy soliton pulsation and its dynamics in a mid-infrared ultrafast fiber laser

We demonstrate the real-time dynamics of a unique pulsating soliton state featuring noisy behaviors in a mid-infrared ultrafast fiber laser at 2 μm. By virtue of the time-stretch dispersive Fourier transform method, the pulsating behaviors of the noisy solitons are investigated. We find that the noisy pulsating solitons are characterized by a special optical spectrum. The shot-to-shot spectra and pulse energy of these pulsating noisy pulses can evolve periodically with the roundtrips. Besides, the real-time optical spectra within a single period exhibit irregular fluctuations in terms of the spectral profile and intensity, suggesting that the pulsating solitons are made up of noisy wave packets with chaotic features. These results can further enrich the pulsating soliton dynamics and also give new insights into the nonlinear pulse dynamics of mid-infrared ultrafast fiber lasers.

Highly efficient octave-spanning long-wavelength infrared generation with a 74% quantum efficiency in a χ(2) waveguide

The realization of compact and efficient broadband mid-infrared (MIR) lasers has enormous impacts in promoting MIR spectroscopy for various important applications. A number of well-designed waveguide platforms have been demonstrated for MIR supercontinuum and frequency comb generations based on cubic nonlinearities, but unfortunately third-order nonlinear response is inherently weak. Here, we propose and demonstrate for the first time a χ(2) micrometer waveguide platform based on birefringence phase matching for long-wavelength infrared (LWIR) laser generation with a high quantum efficiency. In a ZnGeP2-based waveguide platform, an octave-spanning spectrum covering 5–11 μm is generated through optical parametric generation (OPG). A quantum conversion efficiency of 74% as a new record in LWIR single-pass parametric processes is achieved. The threshold energy is measured as ~616 pJ, reduced by more than 1-order of magnitude as compared to those of MIR OPGs in bulk media. Our prototype micro-waveguide platform could be extended to other χ(2) birefringence crystals and trigger new frontiers of MIR integrated nonlinear photonics.