mid-IR Laser Sources Research Articles

Carbon monoxide impurities in hydrogen detected with resonant photoacoustic cell using a mid-IR laser source

We report on a photoacoustic sensor system based on a differential photoacoustic cell to detect the concentration of CO impurities in hydrogen. A DFB-QCL laser with a central wavelength of 4.61 µm was employed as an exciting source with an optical power of 21 mW. Different concentrations of CO gas mixed with pure hydrogen were injected into the photoacoustic cell to test the linear response of the photoacoustic signal to the CO concentration. The stability of the long-term operation was verified by Allan-Werle deviation analysis. The minimum detection limit (MDL, SNR=1) results 8 ppb at 1 s and reaches a sub-ppb level at 100 s of integration time. Dynamic response of the system is linear and has been tested up to the concentration of 6 ppm. Saturation conditions are expected to be reached for CO concentration larger than 100 ppm.

Mid-IR narrow bandwidth tuneable laser source for the FAMU experiment

The FAMU (Fisica degli Atomi MUonici) collaboration aims to measure the proton Zemach radius through muonic hydrogen (μp) spectroscopy. The experimental setup relies on a custom-developed pulsed mid-IR laser source that can be tuned over a specific 6780-6790 nm wavelength range needed to ignite the hyperfine transition of the μp ground state 1S (also known as spin-flip transition). The excitation is observed as a distinctive muonic X-rays emission resulting from the oxygen impurity present in the hydrogen target. The mid-IR emission is produced by Difference Frequency Generation (DFG) in a non-linear crystal, pumped with a fixed wavelength 1064 nm Nd-YAG laser and a tuneable Cr:forsterite laser centred on 1262 nm. This setup produces more than 1.2 mJ at 6780 nm with a linewidth smaller than 30 pm. The experiment requires the laser to run continuously 24/7 in a restricted/radiation-controlled area and for this reason a specifically developed control software permits to remotely act on the laser. The characterization of a series of different non-linear crystals was performed during the development of the laser, resulting in the choice of BaGa4Se7.

Influence of antireflection Si coatings on the damage threshold of fused silica upon irradiation with mid-IR femtosecond laser pulses.

Recent progress in the development of high-power mid-IR laser sources and the exciting laser driven physical phenomena associated with the irradiation of solids via ultrashort laser pulses in that spectral region are aimed to potentially create novel capabilities for material processing. In particular, the investigation of the underlying physical processes and the evaluation of the optical breakdown threshold (OBT) following irradiation of bulk dielectric materials with mid-IR femtosecond (fs) pulses have been recently presented. In this Letter, we will explore the conditions that generate sufficient carrier excitation levels which lead to damage upon irradiation of a dielectric material (SiO2) coated with antireflection (AR) semiconducting films (Si) of variable thickness with fs pulses. Simulation results demonstrate that the reflectivity and transmissivity of the Si/SiO2 are thickness dependent which can be employed to modulate the damage threshold of the substrate. The study is to provide innovative routes for selecting material sizes that can be used for antireflection coatings and applications in the mid-IR region.

Frequency conversion of a chirped Ti:sapphire laser pulse to 11.4 μm wavelength with SrMoO4 Raman shifter and LiGaS2 DFG crystal

The simple mid-IR laser source based on femtosecond Ti:Sapphire laser and successive frequency conversion of its stretched up to 50 ps pulses in SrMoO4 Raman-active crystal and LiGaS2 second order nonlinear crystal is demonstrated. Energy of the mid-IR pulse at 11.4 μm wavelength was up to 250 nJ that was four times higher than the previous results for the similar setup. The influence of pump pulse intensity on spectral and energetic parameters of laser pulses after SrMoO4 and LiGaS2 crystals were studied in details.

Ionization dynamics and damage conditions in fused silica irradiated with mid-infrared femtosecond pulses

The employment of ultrashort laser sources at the mid-infrared (mid-IR) spectral region for dielectrics is expected to open innovative routes for laser patterning and a wealth of exciting applications in optics and photonics. To elucidate the material response to irradiation with mid-IR laser sources, a consistent analysis of the interaction of long wavelength femtosecond pulses with dielectric materials is presented. The influence of the pulse duration is particularly emphasized in specifying the laser parameters for which photoionization and impact ionization are important. Simulation results using pulses at 2.2, 3.2, and 5 μm are conducted to illustrate optimum conditions for the onset of damage on the solid that is related to the occurrence of the optical breakdown. The results predict that the damage threshold scales as ∼τpa (0.31≤a≤0.37) at all laser wavelengths. Given the significant effect of the induced excitation level on excitation of surface plasmons (SPs), which account for the formation of laser-induced periodic structures oriented perpendicular to the laser polarization, a correlation of the produced electron densities with SPs and the threshold of SP excitation (∼τpβ, 0.33≤β≤0.39) are also discussed in this as yet unexplored spectral region. The results are expected to guide development of an innovative approach to surface patterning using strong mid-IR pulses for advanced applications.

High-order harmonic generation in the water window from mid-IR laser sources

We investigate the harmonic response of neon atoms to mid-IR laser fields ($2000--3000$ nm) using a single active electron (SAE) model and the fully ab initio all-electron $R$ matrix with time dependence (RMT) method. The laser peak intensity and wavelength are varied to find suitable parameters for high-harmonic imaging in the water window. Comparison of the SAE and RMT results shows qualitative agreement between them as well as parameters such as the cutoff frequency predicted by the classical three-step model. However, there are significant differences in the details, particularly in the predicted conversion efficiency. These details indicate the possible importance of multielectron effects, as well as a strong sensitivity of quantitative predictions on specific aspects of the numerical model.

On-chip mid-IR octave-tunable Raman soliton laser.

Photonic chip-based continuously tunable lasers are widely recognized as an indispensable component for photonic integrated circuits (PICs). Specifically, mid-infrared (mid-IR) laser sources are of paramount importance in applications such as photonic sensing and spectroscopy. In this article, we theoretically investigate the propagation dynamics of mid-IR Raman soliton in Ge28Sb12Se60 chalcogenide glass waveguide. By carefully engineer the waveguide dispersion and nonlinear interaction, we propose a suspended chalcogenide glass waveguide device that allows an octave-tuning, from 1.96 µm to 3.98 µm, Raman soliton source. The threshold pump energy is in the low pico-Joule range. Our result provides a solution to continuously tunable on-chip mid-IR ultrafast laser sources.

Quasi-phase matching of high harmonics driven by mid-IR: toward the efficiency drop compensation

This paper presents a detailed investigation of the high-order harmonics generation quasi-phase matching in a series of gas jets interacting with a two-color laser field formed by the fundamental and the second harmonics of a mid-IR laser source. A quadratic growth of the enhanced harmonics efficiency as a function of a laser wavelength is presented. A power growth of the enhanced harmonics efficiency as a function of the width of the gas jets is also demonstrated. A simple relation connecting the position of the enhanced harmonics and the macroparamaters of the gas jets is introduced. Physical mechanisms lying behind the observed phenomena are also discussed.

Tunable mid-infrared laser sources for trace-gas analysis

We demonstrate advanced experimental approaches to photoacoustic gas detection with tunable mid-infrared (mid-IR) laser sources of different types. A gas analyzer for registration of various gas components based on a tunable narrow-linewidth optical parametric oscillator (OPO) was designed and investigated. Using this OPO, the possibility of measuring the trace concentration (∼2÷3 ppm) of methane (CH4) in air was experimentally shown. The gas detection capability was enhanced by introducing injection seeding into the OPO. Another gas analyzer was based on a quantum cascade laser (tunable within the range ∼7.6 ÷7.7 μm) and a resonant differential photoacoustic detector. Detection of the ultra-low concentration (∼0.3 ppm) of methane in air was achieved (the standard dispersion was (1σ) ≍ (10–11) ppb with an integration time of 10 s). We compare the presented approaches and outline their further development.

Diode-side-pumped watt-level high-energy Q-switched mid-IR Er:YLF laser.

We report on a powerful mid-IR diode-side-pumped tunable Er:LiYF4 (Er:YLF) laser electro-optically Q-switched with the help of a KTiOPO4 crystal. At a 20 Hz repetition rate, the laser pulses with output energy of 82 mJ and 13 ns duration at the wavelength of 2.67 µm are obtained. At higher repetition rates (up to 50 Hz), one can extract up to 20 mJ from the laser cavity. The developed mid-IR laser source demonstrates high peak (up to 6.3 MW) and average (up to 1.7 W) power. Realized wavelength tuning provides access for megawatt-peak power-level nanosecond laser pulses over the 2667-2851 nm wavelength region, which are highly demanded for mid-IR laser systems development and light-matter interaction study in the view of extreme-state creation in liquids and solids, paving the way to novel microprocessing techniques.

Mid-infrared 10-µJ-level sub-picosecond pulse generation via stimulated Raman scattering in a gas-filled revolver fiber

A sub-picosecond mid-infrared laser based on hollow-core silica fiber is demonstrated for the first time. By using deuterium-filled revolver fiber as an active medium, we realized efficient two-cascade Raman conversion 1.03 → 1.49 → 2.68 µm pumped by chirped pulses of a femtosecond ytterbium laser. The gas fiber Raman laser generates ∼920 fs pulses at 2.68 µm with output pulse energy as high as 10 µJ. It is shown that SRS can dominate other nonlinearities even in highly transient regime implemented in the mid-IR. The approach used may be applied to develop mid-IR laser sources of various types, such as frequency combs, supercontinuum and few-cycle pulse sources.

Review of mid-infrared mode-locked laser sources in the 2.0 μm–3.5 μm spectral region

Ultrafast laser sources operating in the mid-infrared (mid-IR) region, which contains the characteristic fingerprint spectra of many important molecules and transparent windows of atmosphere, are of significant importance in a variety of applications. Over the past decade, a significant progress has been made in the development of inexpensive, compact, high-efficiency mid-IR ultrafast mode-locked lasers in the picosecond and femtosecond domains that cover the 2.0 μm–3.5 μm spectral region. These achievements open new opportunities for applications in areas such as molecular spectroscopy, frequency metrology, material processing, and medical diagnostics and treatment. In this review, starting with the introduction of mid-IR mode-locking techniques, we mainly summarize and review the recent progress of mid-IR mode-locked laser sources, including Tm3+-, Ho3+-, and Tm3+/Ho3+-doped all-solid-state and fiber lasers for the 2.0 μm spectral region, Cr2+:ZnSe and Cr2+:ZnS lasers for the 2.4 μm region, and Er3+-, Ho3+/Pr3+-, and Dy3+-doped fluoride fiber lasers for the 2.8 μm–3.5 μm region. Then, some emerging and representative applications of mid-IR ultrafast mode-locked laser sources are presented and illustrated. Finally, outlooks and challenges for future development of ultrafast mid-IR laser sources are discussed and analyzed. The development of ultrafast mid-IR laser sources, together with the ongoing progress in related application technologies, will create new avenues of research and expand unexplored applications in scientific research, industry, and other fields.

Broadband tunable source of mid-IR laser radiation for photoacoustic spectroscopy

Control over volatile products of metabolic processes in human body in exhaled air is a promising method for noninvasive medical diagnostics. The mid-IR range (2–12 μm) is of great interest for diagnostic applications of the exhaled air spectral analysis. Laser optoacoustic spectroscopy is quite attractive for detecting a large set of gaseous substances; however, high-power sources of tunable radiation are required to increase the method sensitivity. We consider the possibility of using a parametric light generator based on a BaGa4Se7 crystal as a broadband tunable mid-IR laser source for laser optoacoustic spectroscopy.

Purification of Ge-As-Se ternary glasses for the development of high quality microstructured optical fibers

The production of chalcogenide microstructured optical fibers with low optical losses, due to the broad transparency window of these glasses in the mid-IR, can allow for new breakthroughs in various research fields, e.g. new mid-IR laser sources and mid-IR spectroscopy. In this framework, high purity chalcogenide glasses are needed in order to minimize absorption losses. In this study, Ge10As22Se68 samples were prepared using a double distillation method, using different combinations of chlorides and metals as getters for the physico-chemical elimination of carbon, oxygen and hydrogen impurities. Comparing the attenuation spectra of the different samples, the choice of the getters seems to be indeed a significant factor in the quality of the glass. A holey fiber has been realized by casting method using the best sample, showing that the method is suitable for this composition and that the attenuation before and after the casting are comparable.

Mid-infrared pulsed laser ultrasonic testing for carbon fiber reinforced plastics

Laser ultrasonic testing (LUT) can realize contactless and instantaneous non-destructive testing, but its signal-to-noise ratio must be improved in order to measure carbon fiber reinforced plastics (CFRPs). We have developed a mid-infrared (mid-IR) laser source optimal for generating ultrasonic waves in CFRPs by using a wavelength conversion device based on an optical parametric oscillator. This paper reports a comparison of the ultrasonic generation behavior between the mid-IR laser and the Nd:YAG laser. The mid-IR laser generated a significantly larger ultrasonic amplitude in CFRP laminates than a conventional Nd:YAG laser. In addition, our study revealed that the surface epoxy matrix of CFRPs plays an important role in laser ultrasonic generation.

Pulsed Laser Deposition of Epitaxial ZnSxSe1-x Thin Films for Waveguiding Applications in Mid-IR Active Multilayered Structures

ABSTRACTChromium doped II-VI semiconductors (such as ZnSe and ZnS) feature broad mid-IR emission in the 2-3 μm spectral range due to intershell transitions of the Cr2+ions. These materials show much promise for development of a tunable, electrically-pumped, mid-IR laser source. For integration into a mid-IR active multilayered structure, the ternary alloy ZnSxSe1-xis an attractive waveguiding material due to its lattice-matching ability and lower index of refraction with respect to the Cr2+:ZnSe active material. Epitaxial growth of each layer is desired to achieve the electronic and optical properties necessary for successful integration into a lasing device, so a study was conducted on the effects of sulfur content and growth temperature on the crystal quality of the resulting thin films. Several films of ZnSxSe1-xwere deposited by pulsed laser deposition (PLD) using a 248 nm KrF excimer laser source at varying growth temperatures and with various compositional parameters onto (100) GaAs substrates. The samples were analyzed via x-ray diffraction (XRD) and energy dispersive x-rays (EDX) to investigate the crystal quality and elemental content of the films for device integration. Film-substrate epitaxy was achieved and upper bounds to the defect density were calculated for several regimes of compositional parameter and growth temperature. From all samples produced, the lowest defect density of 2.2 x 1010cm-2was observed for the x=0.06 film grown at 450°C, while the lowest lattice mismatch between the substrate and epilayer of 0.059% was observed for the x=0.02 film grown at 450°C.

Forecast of intense near- and mid-IR laser radiation propagation along slant atmospheric paths

The effectiveness of the use of intense radiation from different near- and mid-IR laser sources propagating along high-altitude slant optical paths is numerically estimated on the basis of the optical model of the Earth’s atmosphere developed by the authors. Different laser sources, including chemical oxygeniodine laser (COIL), chain chemical DF laser, and carbon-monoxide (CO) laser are considered with different optical weather conditions taking into account linear and nonlinear optical effects. A COIL source is shown to be the most preferable in terms of the total laser power transmitted along a path, because of weak atmospheric attenuation and minimal effects of nonlinear factors. In addition, this laser source shows the best performance in terms of the mean radiation intensity at a receiver. Among chemical multiwavelength lasers, DF lasers lead in terms of the power transfer function.

Parametric generation and characterization of femtosecond mid-infrared pulses in ZnGeP2.

Ultrafast mid-infrared (IR) coherent radiation plays an important role in strong-field physics, wherein the use of longer wavelengths has reduced the optical intensities needed to drive light-matter interactions by orders of magnitude in comparison to near-IR radiation. Optimizing parametric interactions for generation and characterization of mid-IR pulses is an enabling step for those applications. We report on the production of >50 µJ femtosecond pulses centered at 5 µm in a two-stage optical parametric amplifier (OPA) based on ZnGeP2, a high-performance optical material in this spectral region. The OPA is pumped by an ultrafast 2-µm source. Amplified pulses have been characterized by parametric upconversion, enabling the use of standard silicon detectors. A numerical model of the system has been developed and tested to control dispersion, group-velocity mismatch, and off-axis parametric fluorescence. The source architecture is suitable for production of mJ-level mid-IR ultrafast pulses without the use of chirped-pulse amplification, where convenient pumping could be realized directly by mid-IR laser sources based on materials such as Cr:ZnSe or Cr:ZnS.

Multi-keV ultrahigh-order harmonics produced in gases with subrelativistically intense mid-IR laser pulses

Due to favorable wavelength scaling of the electron ponderomotive energy, high-order harmonic generation in gases is known to benefit from using long-wavelength femtosecond laser sources to produce high-energy photons. In this paper, using an analytical quantum-mechanical approach, taking into account the laser-induced depletion of atomic levels and the magnetic-field effects, we analyze the relative roles of these factors in limiting the generation efficiency and in shaping the spectral profile of the harmonic radiation produced with mid-IR laser pulses in various gaseous targets. Based on these calculations, we estimate the maximum width of the high-harmonic spectrum that can be obtained using the high-power mid-IR laser sources. The feasibility of multi-keV photon generation in gases irradiated by state-of-the-art mid-IR drivers is demonstrated.

Widely tunable, all-polarization maintaining, monolithic mid-infrared radiation source based on differential frequency generation in PPLN crystal

We present a difference frequency generation based (DFG) mid-infrared (mid-IR) laser source using an all-polarization-maintaining-fiber (all-PM) amplifier capable of simultaneous amplification of 1064 nm and 1550 nm signals. The amplifier incorporates a single piece of a standard erbium:ytterbium (Er:Yb) co-doped double-clad (DC) active fiber and a limited number of off-the-shelf fiber-based components. Excited by a single 9 W multimode pump, the amplifier delivered over 12.1 dB and 17.8 dB gain at 1 µm and 1.55 µm, respectively. Due to an all-PM configuration, the amplifier was exceptionally convenient for DFG of mid-IR radiation in periodically polled lithium niobate (PPLN) crystal, yielding an output power of ~200 µW in a wide spectral range spanning from 3300 to 3470 nm.