Search Results (334)

Optical klystrons have been developed in storage ring free-electron lasers (FELs) as insertion devices to increase the FEL gain in a straight section with limited length. By adjusting the magnetic field in the dispersion section of the optical klystron to shift the relative delay between the electron bunch and FEL pulse from an integer multiple of the FEL wavelength, FELs can oscillate at two wavelengths. The electron density of the electron bunch that interacts with the FEL pulse in a small-signal regime is modulated at the FEL wavelength period. When the FEL oscillates simultaneously at two wavelengths, the electron density of the electron bunch beats through the modulation with two periods. This beat generates long-wavelength coherent edge radiation at a bending magnet located in the straight section containing the optical klystron. Difference-frequency waves induced by dual-wavelength ultraviolet free-electron lasers generate a high-intensity mid-infrared monochromatic beam. Our findings will lay the foundation for the development of the difference-frequency waves of soft X-rays and extreme ultraviolet light using hard X-ray FELs. Full article

Diamond antireflection techniques are of high interest for optical windows operating at extreme conditions. Herein, diamond antireflective microstructures in mid-infrared (MIR) spectral range were theoretically designed and experimentally fabricated. Finite difference time domain (FDTD) simulations were used to optimize the transmission performance of the diamond microstructures. Based on the simulation results, the optimized microstructures were fabricated by femtosecond (fs) laser direct writing (1030 nm, 300 fs, 25 kHz) followed by wet etching. After wet etching, the laser-modified zones and the accumulated graphitized clusters were effectively removed, thereby achieving the desired depth. The influences of laser power and scanning strategy on the morphology evolution of diamond microstructures were investigated. It was found that at the optimal conditions, the transmittance of the diamond increased from 70.9% to 81.4% (single-side) over a broad spectrum from 8 to 22 μm. This work demonstrates a promising hybrid fs laser/wet etching technique for diamond antireflective microstructures in MIR spectral range. Full article

We demonstrate an all-polarization-maintaining (PM) mode-locked thulium-doped fiber laser operating in the net-normal-dispersion regime based on a figure-9 nonlinear amplifying loop mirror (NALM) configuration. A chirped fiber Bragg grating (CFBG) and a commercial PM dispersion-compensating fiber (PM-DCF) are incorporated into the figure-9 cavity, providing a large normal net dispersion and enabling stable dissipative-soliton mode-locking. Under stable dissipative-soliton operation, the laser delivers a maximum output power of 53.6 mW at a repetition rate of 12.31 MHz, corresponding to a pulse energy of 4.3 nJ. The output spectrum has a central wavelength of ~1952 nm with a 3 dB bandwidth of ~11 nm. The all-PM laser oscillator directly generates a fs pulse without extra-cavity compression, achieving a pulse duration of 545 fs at the CFBG arm. Moreover, stable fundamental mode-locking is verified by a high radio-frequency signal-to-noise ratio (SNR) exceeding 82 dB and a long-term root-mean-square (RMS) power fluctuation of 0.45% over two hours. To the best of our knowledge, this represents the highest output power generated from an all-PM-fiber figure-9 laser oscillator in the 2 μm band, alongside fs-pulse operation. This high-power, compact, stable and environment-insensitive fs-pulsed laser source shows great potential as an ideal seed for biomedical imaging and mid-infrared frequency combs. Full article

The 6.45 μm mid-infrared laser is highly promising for medical applications due to its efficient tissue ablation with minimal collateral damage. In this work, we demonstrate a stable and compact 10W-level, all-solid-state nanosecond laser source at 6.45 μm based on a Ho:YAG MOPA pumped ring-cavity ZnGeP2 optical parametric oscillator (ZGP OPO). The influence of spot size, phase-matching scheme, and crystal length on the output performance was systematically investigated. Using a 30 mm long Type I ZGP crystal, the system achieved optimal performance: a record-high average output power of 14.6 W at 6.45 μm with an optical-to-optical conversion efficiency of 17.57%, a peak power of 51.7 kW, and excellent power stability (1.45% fluctuation over 120 min at 11.7 W). To our knowledge, this represents the highest reported output power and conversion efficiency for an OPO in this spectral region, surpassing previous sources by an order of magnitude in average power and showing nearly double efficiency. This work provides a stable and reliable laser source tool for application research for techniques such as laser ablation. Full article

Mid-infrared (MIR) femtosecond lasers, resonant with the absorption bands of amide-related molecular groups in the range of 6.1 to 6.5 μm, have been demonstrated to be effective for tissue ablation. However, the flexible and stable delivery of such pulses to micrometer-scale tissue regions for controlled ablation remains challenging. Here, we utilize a silica-based anti-resonant hollow-core fiber (AR-HCF) to deliver high-power MIR femtosecond pulses with high temporal and spectral fidelity, featuring pulse durations of approximately 340 fs and peak power densities exceeding 1 GW/cm², for selective tissue ablation. Benefiting from the small numerical aperture of the AR-HCF, a relatively stable and consistent beam spot size can be maintained over a millimeter-scale propagation distance. Precise control of the ablation depth can be achieved by appropriately selecting the scanning parameters, with penetration depths reaching the sub-millimeter scale. Furthermore, for the first time, we systematically compare the tissue ablation performance of MIR femtosecond lasers at resonant wavelengths (6.4 and 6.1 μm) and a non-resonant wavelength (5.5 μm) under identical scanning conditions. An ablation depth ratio of more than 8:1 is observed, demonstrating the high efficiency and selectivity of the resonance-based ablation mechanism. These results establish flexible delivery of high-power MIR femtosecond pulses in tissue-resonant bands via silica-based AR-HCF as a powerful platform for selective, precise, and efficient tissue ablation, providing a promising approach for interventional and minimally invasive surgery. Full article

In this work, thermal imaging is employed to study the opto-thermal response of apples (Malus domestica Borkh.), assessing their post-harvest evolution through the estimation of thermal diffusivity. A non-destructive experimental procedure based on mid-wave infrared (MWIR) thermal camera (3–5 µm) and localized heating with a visible laser is developed, enabling spatially and temporally resolved surface temperature measurements. Temperature fields are recorded at different time points and radial distances from the heated spot. A theoretical model based on Fourier thermal diffusion equation is formulated to describe the spatio-temporal evolution of surface temperature. After validation on a reference sample, the method is applied to Golden and Red Delicious apples over a 28-day storage period at room temperature. Red Delicious apple exhibits higher mean diffusivity values without significant temporal changes, whereas a progressive increase in diffusivity is observed for Golden Delicious apples. These results show that thermal diffusivity is sensitive to post-harvest physiological changes in apple tissue and may be associated with intrinsic properties such as tissue density and water content. By relating laser-induced temperature fields to the estimation of thermal diffusivity, this approach enables the non-destructive, quantitative assessment of thermal diffusivity, showing potential for fruit maturity and quality assessment, which are of high importance in agri-food monitoring applications. Full article

Mid-IR flat/integrated optics require low-loss, programmable phase control. We investigate femtosecond laser direct writing (FLDW) in aluminogermanate glass (Corning 9754), first mapping the processing landscape to delineate no modification, Type I index increase, and spatial broadening regimes. We then operate in a non-accumulating regime that provides a broad, stable writing window. Quantitative-phase microscopy yields Δφ and a monotonic Δn with optically limited cross-sections compatible with low loss. Transmission spectroscopy shows high values (about 90% up to 4 µm) and no additional absorptions across the near-IR and mid-IR range. FTIR reveals a redshift of the Ge–O–(Ge/Al) stretching envelope from ≈1 µJ, correlating with the high Δn onset. s-SNOM at 925 cm⁻¹ resolves the written line as reduced near-field amplitude and decreased phase, confirming a local complex permittivity change consistent with densification-driven Type I tracks. Together, these results define practical conditions for on-demand mid-IR flat/GRIN/Fresnel optics by FLDW in this commercial mid-IR transparent glass. Full article

Whispering-gallery-mode (WGM) microcavities, with their ultra-high quality factors and deeply confined mode volumes, provide strong light–matter interaction and underpin a broad range of emerging photonic technologies. Their capabilities now span high-sensitivity sensing, ultra-low-noise microwave and frequency-comb generation, integrated quantum light sources, narrow-linewidth microlasers, and efficient nonlinear frequency conversion. As WGM devices advance toward greater practicality and integration, this paper reviews the research progress of WGM microcavity lasers across the visible to mid-infrared spectrum, which represents a key focus area, and discusses the challenges hindering their broader application. Full article

Diabetes is a developing global health concern that cannot be cured, necessitating frequent blood glucose monitoring and dietary management. Photoacoustic Spectroscopy (PAS) in the mid-infrared (MIR) region has recently emerged as a viable noninvasive blood glucose monitoring technique. However, MIR-PAS confronts significant challenges: (i) Water absorption, which reduces light penetration, and (ii) interference from other blood components. This paper systematically analyzes the background of photoacoustic signal generation and proposes a differential PAS (DPAS) in the MIR region for removing the background signals arising from water and other interfering components of blood, which improves the overall detection sensitivity. A detailed mathematical model with an explanation for choosing two suitable MIR quantum cascade lasers for this differential scheme is presented here. For single-wavelength PAS (SPAS), a detection sensitivity of $1.537$ µPa mg⁻¹ dL was obtained from the proposed model. Alternatively, $2.333$µPa mg⁻¹ dL detection sensitivity was found by implementing the DPAS scheme, which is about 1.5 times higher than SPAS. Moreover, DPAS facilitates an additional parameter, a differential phase shift between two laser responses, that has an effective correlation with the glucose concentration variation. Thus, MIR-based DPAS could be an effective way of monitoring blood glucose levels noninvasively in the near future. Full article

CO₂ laser processing has emerged as an efficient dry-finishing technique capable of inducing controlled chemical and morphological transformations in cotton and denim textiles. The strong mid-infrared absorption of cellulose enables localised photothermal heating, leading to selective dye decomposition, surface oxidation, and micro-scale ablation while largely preserving the bulk fabric structure. These laser-driven mechanisms modify colour, surface chemistry, and topography in a predictable, parameter-dependent manner. Low-fluence conditions predominantly produce uniform fading through fragmentation and oxidation of indigo dye; in comparison, moderate thermal loads promote the formation of carbonyl and carboxyl groups that increase surface energy and enhance wettability. Higher fluence regimes generate micro-textured regions with increased roughness and anchoring capacity, enabling improved adhesion of dyes, coatings, and nanoparticles. Compared with conventional wet processes, CO₂ laser treatment eliminates chemical effluents, strongly reduces water consumption and supports digitally controlled, Industry 4.0-compatible manufacturing workflows. Despite its advantages, challenges remain in standardising processing parameters, quantifying oxidation depth, modelling thermal behaviour, and assessing the long-term stability of functionalised surfaces under real usage conditions. In this review, we consolidate current knowledge on the mechanistic pathways, processing windows, and functional potential of CO₂ laser-modified cotton substrates. By integrating findings from recent studies and identifying critical research gaps, the review supports the development of predictable, scalable, and sustainable laser-based cotton textile processing technologies. Full article

We present E-CAHORS—a compact mid-infrared open-path diode-laser spectrometer designed for the simultaneous measurement of carbon dioxide, methane, and water vapor concentrations in the near-surface atmospheric layer. These measurements, combined with simultaneous data from a three-dimensional anemometer, can be used to determine fluxes using the eddy-covariance method. The instrument utilizes two interband cascade lasers operating at 2.78 µm and 3.24 µm within a novel four-pass M-shaped optical cell, which provides high signal power and long-term field operation without requiring active air sampling. Two detection techniques—tunable diode laser absorption spectroscopy (TDLAS) and a simplified wavelength modulation spectroscopy (sWMS)—were implemented and evaluated. Laboratory calibration demonstrated linear responses for all gases (R² ≈ 0.999) and detection precisions at 10 Hz of 311 ppb for CO₂, 8.87 ppb for CH₄, and 788 ppb for H₂O. Field tests conducted at a grassland site near Moscow showed strong correlations (R = 0.91 for CO₂ and H₂O, R = 0.74 for CH₄) with commercial LI-COR LI-7200 and LI-7700 analyzers. The TDLAS mode demonstrated lower noise and greater stability under outdoor conditions, while sWMS provided baseline-free spectra but was more sensitive to power fluctuations. E-CAHORS combines high precision, multi-species sensing capability with low power consumption (10 W) and a compact design (4.2 kg). Full article

Mid-infrared (MIR) supercontinuum (SC) sources are critical for spectroscopy, biomedical imaging, and environmental monitoring. However, conventional generation methods based on free-space experiments using optical parametric amplifiers (OPAs) and difference frequency generation (DFG) lasers suffer from narrow bandwidth and low power distribution in the MIR region. This paper presents a cascaded pumping technique using two soft-glass fibers. A picosecond thulium-doped fiber amplifier (TDFA) pumps a Germania-doped fiber (GDF) to generate an intermediate broadband spectrum, which then pumps a fluorotellurite fiber (TBY) with higher nonlinearity and a wider transmission window. Using this configuration, we achieved an Octave-Spanning SC generation covering 1–4 μm with 7.20 W output power. Notably, 32.8% of total power lies above 3.0 μm, with 11.2% beyond 3.5 μm, demonstrating excellent long-wavelength performance. In addition, we applied numerical simulation methods to investigate SC generation in GDF and TBY by solving the nonlinear Schrödinger equation. The close match between simulated and experimental results facilitates theoretical examination of how SC broadening occurs. This cascaded approach offers a feasible solution in terms of spectral band matching, material compatibility, and system integration potential. Full article

Polarization beam combining (PBC) is an important technology for enhancing laser brightness. The conventional bulk polarization beam combiners are Brewster plates and birefringent polarization prisms. However, in the mid- and long-wave infrared range, the beam combining performance is limited by the transmission and birefringent coefficient of the available materials. In this paper, a polarization beam combiner based on a reflection metasurface was proposed. The phases of incident beams with orthogonal linear polarizations were individually manipulated by the side lengths of the rectangular silicon pillar. A metasurface polarization beam combiner operating band was designed and fabricated. When the two beams at 4.6 μm with orthogonal linear polarizations were incident on the metasurface at angles of −13.3° and 13.3°, respectively, they were reflected in the 0°-direction. The overall beam combining efficiency was 88.9%. When both of the quantum cascade lasers used in the experiments were in the fundamental transverse Gaussian mode, the measured beam quality factors M² of the combined beam were 1.21 and 1.14 along the fast and slow axes, respectively. Both simulation and experimental results demonstrated that the proposed metasurface was an efficient polarization beam combiner with negligible wavefront distortion. It is a promising alternative to traditional bulk optics for the mid- and long-wave infrared. Full article

By employing graded-interfaces modeling, ~10 μm-emitting quantum cascade lasers (QCLs) are designed with previously found conditions for record-high wall-plug efficiency (WPE) operation of mid-infrared QCLs: direct resonant-tunneling injection from a prior-stage low-energy state into the upper-laser level, photon-induced carrier transport, and carrier-leakage suppression via the step-taper active-region (STA) approach. For devices with interface-roughness (IFR) parameters characteristic of optimized molecular-beam-epitaxy (MBE) growth, a maximum front-facet pulsed WPE value of 19.6% is projected for 60-stages STA-type devices. This results from several factors: 19 mV voltage defect at threshold, 72% voltage efficiency at the maximum WPE point, and ~93% injection efficiency due to strong carrier-leakage suppression. 2.7 W peak front-facet power is projected. For devices with our metal–organic chemical vapor deposition (MOCVD)-growth IFR parameters, the projected maximum pulsed WPE value is 17.1%, i.e., 1.7 times higher than the highest reported front-facet WPE value from ~10 μm-emitting MOCVD-grown QCLs. Studies regarding the WPE value variation with the stage number, while employing waveguide designs having the same empty cavity loss, reveal that the maximum WPE value remains almost the same for 50–60 stages devices. In turn, there is potential for obtaining significantly higher CW powers than from conventional ~10 μm-emitting QCLs. Full article

A 50.9-W all-fiber mid-infrared (MIR) supercontinuum (SC) laser with a conversion efficiency of over 76.7% is demonstrated in a ZBLAN (ZrF₄–BaF₂–LaF₃–AlF₃–NaF) fiber. The entire system consists of a broadband thulium-doped fiber amplifier (TDFA) operating at 1.9–2.6 μm and a piece of ZBLAN fiber. The system features an all-fiber architecture, which is achieved by directly splicing the pigtail fiber of the TDFA to the ZBLAN fiber. The system’s stability and reliability were ensured by the utilization of the water-cooled fusion splicing joint between the silica fiber and ZBLAN fiber, and an AlF₃ fiber endcap. When the seed pulse repetition rate (PRR) was 3 MHz and the pulse duration was 6 ns, a MIR SC laser with an average power of 50.9 W and a spectral range of 1.9–3.6 μm was obtained, with a corresponding power conversion efficiency (from the TDFA output to the SC laser output) of 76.7%. By adjusting the pulse duration to 4 ns, the generated SC laser exhibited a spectral range of 1.9–3.7 μm and an average power of 50.1 W, corresponding to a power conversion efficiency of 75.1%. Such a supercontinuum (SC) laser paves the way for the application of high-power SC lasers in a wide range of fields. Full article