Mid-infrared Laser System Research Articles

Fluoride and chalcogenide glass fiber components for mid-infrared lasers and amplifiers: Breakthroughs, challenges, and future perspective

Since the early 1990s, when researchers began to explore rare-earth-doped mid-infrared glass fibers, fiber laser systems have emerged as promising high-brightness light sources with wavelengths beyond 2.5 μm for applications in spectroscopy and sensing, optical communications and ranging, and processing of complex materials and bio-tissues, to name a few. Despite a substantial research effort over the years, mid-infrared fiber lasers and amplifiers have yet to reach the maturity required for widespread and/or industrial use. The well-known advantages of fiber lasers over their bulk counterparts, namely superior stability and beam quality, compactness, cost-efficiency, flexibility, and maintenance-free operation, can only be fully harnessed in the mid-infrared wavelength range with the development of non-existent yet essential fiber-based components made of advanced fluoride or chalcogenide-glass materials. This Perspective reports on the recent significant achievements that have been made in the design and fabrication of in-fiber and fiber-pigtailed components for fully integrated mid-infrared fiber laser systems. Building upon a comprehensive overview of the mechanical, thermodynamic, and optical properties of fluoride and chalcogenide glass fibers, as well as their interaction with light, we aim to highlight current challenges and opportunities and provide an informed forecast of future advancements in mid-infrared all-fiber laser research.

Development and characterization of novel Fe2+:ZnSexS1-x solid solution laser ceramics for mid-infrared laser application

In this study, Fe2+:ZnSexS1-x (0.6 ≤ x ≤ 1) solid solution laser ceramics with cubic crystal structures were prepared for the first time via hot pressing sintering, using FeSe, ZnSe, and ZnS powders. The resulting ceramics exhibit a unique combination of the optical and physical properties of Fe2+:ZnSe and Fe2+:ZnS. An increase in the ZnS content led to a blueshift in the maximum absorption spectra of Fe2+ ions and an enhancement in Vickers hardness. These findings suggest that Fe2+:ZnSexS1-x solid solution ceramics could serve as promising gain media for mid-infrared solid-state lasers, offering a novel approach for the development of directly pumped mid-infrared laser systems.

Ultra-smooth processing of lithium niobate for outstanding mid-infrared transmittance.

The fabrication of anti-reflection (AR) subwavelength structures (SWSs) of lithium niobate (LN) is a challenging but rewarding task in mid-infrared LN laser systems. However, there are still some issues with the high-quality processing and fabrication of bifacial AR SWSs. Herein, a novel, to the best of our knowledge, approach to the fabrication of SWSs was proposed, which includes femtosecond laser ablation followed by wet etching and thermal annealing. The fabricated structures exhibit high surface quality (Ra = 0.08 nm) and uniformity. According to the experimental and simulated results, the transmittance of the mid-infrared AR SWSs with a period of 1.8 µm could be improved from 78% to 87% in the 3.6-5 µm band. Furthermore, the double-sided construction enabled a transmittance of up to 90%. The results have great potential in the promotion of the development of mid-infrared laser systems and LN-based photonics.

Unraveling the ultrafast dynamics of thermal-energy chemical reactions.

In this perspective, we discuss how one can initiate, image, and disentangle the ultrafast elementary steps of thermal-energy chemical dynamics, building upon advances in technology and scientific insight. We propose that combinations of ultrashort mid-infrared laser pulses, controlled molecular species in the gas phase, and forefront imaging techniques allow to unravel the elementary steps of general-chemistry reaction processes in real time. We detail, for prototypical first reaction systems, experimental methods enabling these investigations, how to sufficiently prepare and promote gas-phase samples to thermal-energy reactive states with contemporary ultrashort mid-infrared laser systems, and how to image the initiated ultrafast chemical dynamics. The results of such experiments will clearly further our understanding of general-chemistry reaction dynamics.

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.

Performance of the mid-infrared Q-switched LD side-pumped Er:YSGG MOPA laser.

We report on a laser-diode (LD)-pumped master-oscillator power amplifier (MOPA) mid-infrared laser system based on an LD side-pumped Er:YSGG seed laser that can operate in both free-running and Q-switched regimes. In the free-running mode of the seed laser, the maximum amplified single-pulse energy was 83.4mJ. In Q-switched mode of the seed laser, a maximum single-pulse energy of 7.8mJ was achieved at 100Hz repetition rate with the pulse width of 90ns, corresponding to the peak power of 86.7kW and the single-pass amplification factor of 1.66. The results indicate that the LD side-pumped MOPA structure is an effective way to realize a nanosecond ∼3µm mid-infrared laser with high repetition rate and high pulse energy.

Effects of the Processing Technology of CVD-ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe Polycrystalline Optical Elements on the Damage Threshold Induced by a Repetitively Pulsed Laser at 2.1 µm

Polycrystalline zinc selenide (ZnSe) and Cr2+ or Fe2+ doped ZnSe are key optical elements in mid-infrared laser systems. The laser-induced damage of the optical elements is the limiting factor for increasing the power and pulse energy of the lasers. In the present work, the optical damage of the ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe samples induced by a repetitively pulsed Ho3+:YAG laser at 2091 nm was studied. The probability of the optical damage and the laser-induced damage threshold (LIDT) were determined for the samples manufactured using different processing techniques. The highest LIDT was found in ZnSe samples annealed in an argon atmosphere. It was also found that the samples annealed in a zinc atmosphere or with hot isostatic pressing resulted in a decrease in the LIDT. The Cr2+-doped ZnSe had the lowest LIDT at 2.1 µm compared to Fe2+-doped or undoped ZnSe. The LIDT fluence of all tested ZnSe samples decreased with the increase in the pulse repetition rate and the exposure duration. The results obtained may be used to improve the treatment procedures of ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe polycrystals to further increase their LIDT.

Nonlinear pulse compression to 51-W average power GW-class 35-fs pulses at 2-µm wavelength in a gas-filled multi-pass cell.

We report on the generation of GW-class peak power, 35-fs pulses at 2-µm wavelength with an average power of 51 W at 300-kHz repetition rate. A compact, krypton-filled Herriott-type cavity employing metallic mirrors is used for spectral broadening. This multi-pass compression stage enables the efficient post compression of the pulses emitted by an ultrafast coherently combined thulium-doped fiber laser system. The presented results demonstrate an excellent preservation of the input beam quality in combination with a power transmission as high as 80%. These results show that multi-pass cell based post-compression is an attractive alternative to nonlinear spectral broadening in fibers, which is commonly employed for thulium-doped and other mid-infrared ultrafast laser systems. Particularly, the average power scalability and the potential to achieve few-cycle pulse durations make this scheme highly attractive.

Versatile few-cycle high-energy MID-IR OPCPA for nonlinear optics, spectroscopy and imaging

High-power, high-energy, ultrashort, mid-infrared (MID-IR) laser systems operating at high repetition rates are of considerable interest for many science applications, such as coherent vibrational spectroscopy, label-free imaging, time-resolved pump-probe and high-harmonic generation studies. We developed an optical parametric chirped-pulse amplifier (OPCPA) system employing a difference-frequency generation in a lithium gallium sulfide nonlinear crystal in the final amplifier stage, which provides in principle the possibility for passive carrier-envelop-phase (CEP) stability. The OPCPA efficiently down-converts a 1 μm 200 μJ Yb-YAG pump pulse into the MID-IR spectral range generating μJ-level pulses at a repetition rate of 200 kHz. Two modes of operations providing complimentary MID-IR pulse properties are presented. Depending on the envisaged application, one can switch between (a) a wavelength-tunable (4.2–11 μm) source and (b) a broadband source centered at ≈8.5 μm by controlling the group-delay dispersion of the signal pulse. The broadband, high-energy MID-IR pulses have a short pulse duration of 74±2 fs, which corresponds to only ≈3 optical cycles at the central wavelength of 8.5 μm.

Average-power (4.13 W) 59 fs mid-infrared pulses from a fluoride fiber laser system

We report a high-average-power mid-infrared ultrafast laser system consisting of a fluoride fiber mode-locked oscillator and a nonlinear amplifier. A backward pumping scheme was used in the amplifier to simultaneously realize pulse amplification and self-compression. The input signal polarization was demonstrated to play an important role in the self-compression process. Through the optimization of input polarization, a 4.13 W average-power 59 fs pulse at 2.8 µm was achieved, with an estimated pulse energy of 42.2 nJ and a peak power of 715 kW. To the best of our knowledge, this is the highest average-power pulse with sub-100-fs duration generated from a mid-infrared fiber laser system to date.

Design of a 10 W Level Dispersion-Managed High-Power Ultrafast Mid-Infrared Fiber Laser System

Design of a 10 W Level Dispersion-Managed High-Power Ultrafast Mid-Infrared Fiber Laser System

Development of Terawatt-Class High Power Mid-Infrared Laser Systems Using Optical Parametric Amplification

Development of Terawatt-Class High Power Mid-Infrared Laser Systems Using Optical Parametric Amplification

Development of a Minimally Invasive and Non-invasive Lipolysis Laser System for Effective Fat Reduction.

Introduction: Obesity is a global problem because it causes various complications. Methods for reducing fat for healthy life are being studied. In this study, we developed a minimally invasive and non-invasive lipolysis laser system for effective fat reduction. Methods: The laser had the wavelengths of 1980 nm and 2300 nm which have very good absorption of fat and water. We developed a minimally invasive laser system that breaks down fat by direct irradiation of fat tissue. This minimally invasive laser system uses a 808 nm diode laser and Nd:YVO4 to generate the 1064 nm wavelength, which is the pumping source of the nonlinear crystals. It is a mid-infrared lipolysis laser system having two wavelengths of 1980 nm and 2300 nm by controlling the temperature of nonlinear crystals. We also developed a non-invasive laser system that reduces fat with hyperthermia treatment by raising the temperature of adipocytes with a 1060 nm penetrating depth into the skin. In this non-invasive laser system, the In gallium arsenide (GaAs) diode laser is irradiated on the skin with an area of 4 × 8 cm2 through the hand-piece. The cooling system in the hand-piece protects the skin from burns. We studied the effectiveness and safety of each system through animal experiment. We studied the effects of lipolysis when these two systems were combined. Results: This research uses new wavelengths (1980 nm, 2300 nm) to increase the fat reduction effect with low energy (1.3 W). After using the 1060 nm (1.1 W/cm2) wavelength laser, when the 1980 nm and 2300 nm (1.3 W) laser were used, a lipolysis effect of about 35 % was obtained. Conclusion: We have developed a 1.3 W mid-infrared (1980 nm, 2300 nm) laser with good lipolysis effect with low power.

Development of Minimally Invasive Mid-infrared Lipolysis Laser System for Effective Fat Reduction

Development of Minimally Invasive Mid-infrared Lipolysis Laser System for Effective Fat Reduction

MXene and PtSe2 saturable absorbers for all-fibre ultrafast mid-infrared lasers

We report on the feasibility of MXene and platinum diselenide (PtSe2) as novel saturable absorbers for the development of wavelength stabilized passively mode-locked mid-infrared fibre laser systems. After evaluating the performance of individual absorbers in a test cavity, we demonstrate a linear all-fibre laser cavity that utilizes a high reflective chirped fibre Bragg grating for wavelength selective feedback. The observed mode-locked pulse train from this Er3+:ZBLAN fibre laser has a 37 MHz repetition rate with an average power of 603 mW and a spectral width of 721 pm. Our results show that MXene and PtSe2 are promising nonlinear materials for all-integrated ultrafast fibre laser cavities for the important mid-infrared spectral region.

Dispersive mirror characterization and application for mid-infrared post-compression

This paper presents a second harmonic assisted spectrally resolved interferometric technique that can overcome the limited spectral resolution of commercially available spectrometers in the mid-infrared. The discussed scheme was validated by measuring the group delay of several well-known and frequently used materials. Our main motivation was to characterize the spectral phase shift of newly designed and manufactured dispersive mirrors to be used for mid-infrared (MIR) post-compression. These mirrors were successfully implemented in the post-compression stage of our MIR laser system, where pulse duration was shortened below two optical cycles and the pulse peak power increased by 30.3% compared to the original output.

Broadband Nonlinear Photonics in Few-Layer Borophene.

In this paper, 2D borophene is synthesized through a liquid-phase exfoliation. The morphology and structure of as-prepared borophene are systemically analyzed, and the Z-scan is used to measure the nonlinear optical properties. It is found that the saturable absorber (SA) properties of borophene make it serve as an excellent broadband optical switch, which is strongly used for mode-locking in near- and mid-infrared laser systems. Ultrastable pulses with durations as short as 792 and 693 fs are successfully delivered at the central wavelengths of 1063 and 1560nm, respectively. Furthermore, stable pulses at a wavelength of 1878nm are demonstrated from a thulium mode-locked fiber laser based on the same borophene SA. This research reveals a significant potential for borophene used in lasers helping extending the frontiers of photonic technologies.

Investigation of ZnSe stability and dissolution behavior in As-S-Se chalcogenide glasses

Optical composite fibers based on active transition metal (TM)-doped semiconductor crystals are being investigated for use in mid-infrared (mid-IR) fiber laser systems. This study evaluates a candidate glass matrix system assessing its key physical properties and suitability for optical fiber drawing and examines the stability of TM-doped ZnSe crystals during processing. Results indicate that despite excellent refractive index matching between crystal and glass matrix and good fiber draw attributes, the stability of the crystalline dopant within the glass melt is severely impacted by melt conditions. The time and temperature dependence of this stability is mapped by X-ray diffraction (XRD) and second-harmonic generation (SHG) microscopy, illustrating how these tools can be used to track the phase stability and robustness throughout the melting process. Results show that in a range of sulfo-selenide based matrices, dissolution and re-precipitation of Zn-containing crystalline phases is a dominant mechanism.

Mid-infrared silicon photonic crystal fiber polarization filter based on surface plasmon resonance effect

In this paper, a novel silicon photonic crystal fiber (Si-PCF) polarization filter based on surface plasmon resonance effect is proposed for the first time. With the full-vector finite-element method, the mode coupling characteristics of the Si-PCF with the gold-coated film between the core mode and surface plasmon polariton mode are investigated, and the confinement losses are analyzed. The confinement losses of the Y-polarized core mode at the three resonant wavelengths 2.84, 3.29, and 4.53μm are 9235.9, 27097.5, and 97818.3 dB/m, respectively. The extinction ratio reaches -391 dB and the insertion loss is less than 1 dB when the Si-PCF length is 4 mm, along with the filter bandwidth of 2.75μm. Moreover, by modifying the fiber structure parameters, the filter bandwidth of the proposed three kinds of Si-PCF polarization filters can cover 2.75 to 7.80μm. It is believed that the proposed Si-PCF polarization filter has important applications in the mid-infrared laser and optical communication systems.

Determination of molecular contributions to the nonlinear refractive index of air for mid-infrared femtosecond laser-pulse excitation

Numerical simulations of the rotational contribution of oxygen and nitrogen molecules to the Kerr refractive index change in air are performed for ultrashort laser pulses in the near- and mid-infrared wavelength region. The calculated molecular response is parametrized by means of a damped harmonic oscillator model that is easily tractable in numerical simulations of long-distance propagation of ultrashort laser pulses. Our simulations show that pulses from available mid-infrared laser systems are long enough to be dramatically affected by the molecular response of air during propagation.