Laser Crystal Research Articles

Pulse-by-pulse transient thermal deformation in crystal optics under high-repetition-rate FEL.

Time-domain modeling of the thermal deformation of crystal optics can help define acceptable operational ranges across the pulse-energy repetition-rate phase space. In this paper, we have studied the transient thermal deformation of a water-cooled diamond crystal for a cavity-based X-ray free-electron laser (CBXFEL), either an X-ray free-electron laser oscillator (XFELO) or a regenerative amplifier X-ray free-electron laser (RAFEL), by numerical simulations including finite-element analysis and advanced data processing. Pulse-by-pulse transient thermal deformation of a 50 µm-thick diamond crystal has been performed with X-ray pulse repetition rates between 50 kHz and 1 MHz. Results for temperature and thermal deformation have been compared with the results of transient analysis using a continuous wave (CW) power loading. Temperature and thermal deformation results from pulse-by-pulse transient analysis vary with time about the results for the CW case for the same average power. The variation amplitude increases with pulse energy and decreases with repetition rate. When the repetition rate increases to infinity, both temperature and thermal deformation converge to the results for the CW case. Two critical time scales for the operation of crystal optics in a CBXFEL are (1) first-turn time, i.e. the time for the XFEL pulse to complete the first turn around the cavity so that the crystal sees the recirculated XFEL pulse, and (2) period-end time, i.e.the time that the next electron bunch arrives for the amplification, so that the crystal outcouples the amplified FEL power. For the same average power, simulation results show that the crystal thermal deformation seen by the XFEL beam decreases with repetition rate at the first-turn time of a 300 m-long cavity and increases with repetition rate at the period-end time. For the wavefront preservation requirement of the crystal optics, a pulse-energy versus repetition-rate phase space has been established. The upper bounds of the pulse energy at both first-turn and period-end times decreases with repetition rate, especially at the period-end time. The upper bound of the thermal deformation of the crystal at the period-end time for any repetition frequency can be estimated from the CW case. For a water-cooled diamond crystal of dimension 5 mm × 5 mm × 0.05 mm, the time to reach a quasi steady-state is about 50 ms for temperature and 50 µs for thermal deformation.

A Study on the Neodymium Doped Yttrium Orthovanadate Laser

Abstract: When neodymium ions are added to yttrium orthovanadate, a solid substance known as neodymium-doped yttrium orthovanadate (Nd:YVO4) is created. Neodymium ions, which can be stimulated by visible or infrared light with a wavelength of 1064 nm, are the primary cause of Nd:YVO4's lasing characteristic, as is the case with all neodymium-doped laser crystals. Other noteworthy emission wavelengths are 1342 nm and 914 nm.

Analysis of Low-Threshold 1D Perovskite Photonic Crystal Laser

By using the bandgap effect and light localization effect, photonic crystal lasers can decrease the optical mode volume and lower the laser threshold, so satisfying the requirements for device shrinking and photonic integration. Given their wide range of potential applications in fields including light-emitting diodes and sensors, they are attracting considerable interest. The laser threshold is the minimum energy density required to cause laser oscillation and is a crucial specification for the practical application of laser devices. Perovskite materials, equipped with their exceptional optical gain characteristics, are well-suited for the development of low-threshold lasers. By combining them with photonic crystal lasers, it is possible to realize low-threshold or even threshold-free pumped lasers. This paper categorizes photonic crystal lasers according to their photonic crystal structures and examines the advancements in research on perovskite photonic crystal lasers in attaining low minimum thresholds. This work investigates the prospective capabilities of perovskite photonic crystal lasers, with the objective of achieving laser output that is low-threshold or near-zero-threshold, high-power, and of high quality.

Lasing in Crystals Based on 7‐Azaindole‐Phenylhydrazone Organoboron Compounds

AbstractThe development of efficient organic solid‐state lasers requires an in‐depth understanding between chemical structure, intermolecular interactions in the crystal phase, and optical and electronic properties. This study highlights these closed dependencies in novel 7‐azaindole phenylhydrazone derivatives and their corresponding boron complexes, by deploying a combined approach of experimental techniques and theoretical calculations (Density Functional Theory and Time‐Dependent Density Functional Theory) in the solvated and solid‐state phase. Notably, it is found that when these compounds, which are weakly emissive in solution, are processed into crystalline microfibers, they experience a sharp emission enhancement and exhibit laser action at low pump fluence thresholds. This is achieved by partially inhibiting structural relaxation, which drives non‐radiative decay, a critical factor for effective lasing, highlighting the potential of these materials for future optoelectronic applications.

Kaempferol restores the susceptibility of ESBLs Escherichia coli to Ceftiofur.

The development of extended-spectrum-beta-lactamase (ESBLs) Escherichia coli (E. coli) has become a global threat to public health. An alternative strategy to alleviate this is identifying potential natural compounds to restore antibiotic activity against ESBLs E. coli. This study aimed to find a possible compound to restore ESBLs E. coli sensitivity to ceftiofur. The synergistic effect of kaempferol and ceftiofur against ESBLs E. coli was investigated by checkerboard assays, time-kill, growth curves, and scanning electronic microscope. The impact of kaempferol with ceftiofur on the biofilm of ESBLs E. coli was evaluated by crystal violet staining and laser scanning confocal microscopy and this study also assessed the effect of kaempferol on the initial adhesion and aggregation of E. coli (SY20) by examining motility, adhesion, and surface characteristics. The RT-qPCR was used to determine the effect of kaempferol on the expression of genes related to the LuxS/AI-2 quorum sensing system in ESBLs E. coli, and the effect of kaempferol on AI-2 signaling molecules was determined by molecular docking and bioassay. The impact of kaempferol on the activity of blaCTX-M-27 protein was determined by RT-qPCR, molecular docking, and nitrofen experiments, the results were further verified by transcriptome analysis. The mouse infection model was established, and the inhibitory mechanism of kaempferol with ceftiofur on bacteria in vivo was further verified by HE staining and immunohistochemistry. Kaempferol with ceftiofur exerts synergistic antibacterial and bactericidal effects on ESBLs E. coli by influencing β-lactamase activity, biofilm formation, and LuxS/AI-2 QS system. In vivo, kaempferol protected the small intestinal villi from the damage of ESBLs E. coli. Furthermore, kaempferol fully restores the activity of ceftiofur in animal infection models by relieving the TLR4/NF-κb pathway. In conclusion, the sensitivity of ESBLs E. coli to ceftiofur in vitro and in vivo could be enhanced by kaempferol, which showed that kaempferol may be a kind of antibiotic adjuvant.

B-AsP as the saturable absorber for a mid-infrared 3 µm nanosecond laser

Black arsenic-phosphorus (B-AsP) has better stability than traditional black phosphorus (BP), and it was utilized to modulate a mid-infrared (mid-IR) 3 µm laser for what we believe to be the first time. The linear and nonlinear absorption characteristics of B-AsP at 3 µm were also investigated. The maximum continuous wave (CW) output power of the Er: SrF2 laser was 240 mW with an absorbed pump power of 2.87 W, resulting in a corresponding slope efficiency of 8.1%. During passively Q-switched (PQS) experiments, a laser pulse with a minimum duration of 188 ns was successfully generated at a repetition rate of 78 kHz, and the relevant single-pulse energy was 2.0 µJ. To the best of our knowledge, this is the narrowest passively Q-switched pulse for Er:SrF2 crystal laser. Our results indicate that B-AsP SA was a promising candidate to be the optical modulator in the mid-IR wavelength range.

Monocular Vision-Based 3D Reconstruction Method for Parts in Opto-Mechanical Assembly

Abstract In automated assembly, accurately capturing multi-dimensional parameters of parts is essential. Traditional methods include teaching methods or laser-based approaches, with the former relying on experience for pre-calibration and the latter being costly. This paper proposes a low-cost, monocular vision-based method for 3D reconstruction in opto-mechanical assembly. Taking the laser crystal component, including the laser gain medium and its heat sink, in a solid-state laser as an example, a monocular camera is firstly mounted on a robot and captures images of parts from specific angles. Due to the reflective properties of metal surfaces, some image information is lost. To address this problem, a 2D gamma function-based adaptive illumination correction algorithm is then proposed. Next, the improved SIFT algorithm is used to extract and match feature points from the collected images. Subsequently, the SFM approach generates a sparse point cloud, which is then densified using the CMVS/PMVS algorithm. Finally, the Poisson surface reconstruction algorithm is used to complete the 3D reconstruction of the laser crystal heat sinks. Experimental results indicate that the adaptive correction algorithm for non-uniform illumination images can extract more feature points and improve the number of matches. The reconstructed 3D model has high accuracy, providing important technical support for the next step in achieving automated opto-mechanical assembly.

Property optimization of Er/Yb-codoped LiNbO3 crystals for LNOI lasers and amplifiers

Lithium-niobate-on-insulator (LNOI) is regarded as an ideal platform for integrated photonics. As an essential part, active devices based on rare-earth (RE) doped LNOI have made significant progress, with erbium/ytterbium-codoped lithium niobate (Er/Yb-codoped LN) showing great potential. In this paper, a series of Er/Yb-codoped LN crystals were successfully grown by the Czochralski method, featuring a fixed Er3+ concentration with various Yb3+ doping levels and a fixed RE3+ (RE3+ = Er3+ + Yb3+) concentration. The absorption and emission spectra were measured, and the transfer efficiencies along with relative conversion efficiencies were also displayed. It was concluded that the optimal composition of codoped LN is ∼1.0 mol. % Er3+ and 1.0 mol. % Yb3+, which can enhance active devices by providing lower threshold power, reduced transmission loss, higher transfer efficiency, and improved conversion efficiency. These results will advance the development of high performance LNOI lasers and amplifiers.

Study on ablation behavior and mechanism for accurate determination of rare earth elements in CaF2 crystals by UV-LA-ICP-MS

Catastrophic ablation of CaF2 crystals is often observed in ultraviolet-laser ablation-inductively coupled plasma-mass spectrometry (UV-LA-ICP-MS) analysis, leading to variations in the volume of ablated material and resulting analytical errors in LA-ICP-MS microanalysis. Therefore, it is essential to understand the ablation behavior and the interaction mechanisms between the laser and CaF2 crystals. In this study, we examined the effects of crystal surface roughness and laser fluence on ablation behavior. The CaF2 crystal polished with 1500 mesh abrasive paper exhibited a stable signal profile, a regular ablation crater, and the formation of nanoparticles, which align with predictions from the thermo-mechanical coupling model. Both higher and lower roughness resulted in either unstable ablation or uncontrolled ejection of fragments; the latter occurred when the thermal stress from accumulated light energy significantly exceeded the compressive strength of CaF2. Consequently, a roughness of 1500 mesh at the bottom of the ablation craters was deduced. We also identified a laser fluence of 14 J·cm−2 as the threshold for effective LA-ICP-MS analysis of CaF2 crystals, based on consistent signal profiles, elemental fractionation index (EFI), and crater morphology as revealed by LA-ICP-MS and scanning electron microscope (SEM) analyses, along with theoretical calculations from the thermo-mechanical coupling model. The optimal roughness (1500 mesh) and fluence (14 J·cm−2), together with the thermo-mechanical coupling model, can serve as guidelines for UV-LA-ICP-MS settings in further quantitative analyses of CaF2 crystals.

Si-Ge Seed-Based Laser Crystallization of Amorphous Silicon for Monolithic 3D Upper Active Layer

Recently, there has been active progress in scaling semiconductor devices to reduce delay time and increase yield at the transistor level. However, this advancement is encountering a limitation in physical miniaturization. The monolithic 3D (M3D) integrated device technology is an emerging method to address this issue, which significantly enhances device packing density and minimizes via thickness [1]. One representation method for M3D integration technology involves depositing amorphous silicon (a-Si) onto the pre-existing lower device layer and then subjecting it to a thermal process to crystallize and form the upper active layer [2, 3]. However, achieving a highly crystalline silicon-based upper active layer with high performance necessitates a crystallization process conducted at elevated temperatures ranging from 700 to 900 °C. The primary constraint in achieving M3D integration technology is the requirement to utilize thermal processes below 450 °C to prevent damage to the lower device layer. When employing conventional thermal processes such as furnaces or rapid thermal processing to reach high temperatures, the duration of heat energy application is prolonged, and precise control over the depth of heat treatment becomes challenging. It can lead to thermal damage to the lower device layer. Furthermore, even after undergoing the crystallization process, the direction of crystal growth remains inconsistent, resulting in non-uniform electrical characteristics across different devices. This inconsistency poses challenges in realizing wafer-level M3D integrated device technology.In this work, we propose a method to create a highly crystalline upper active layer without damaging the lower device layer by employing Si-Ge seeds and laser crystallization. Single-crystal Si-Ge seeds, which induce growth in specific crystal orientations during laser crystallization, were formed at a low temperature of 450 °C using the selective etch growth (SEG) method. Following the deposition of 100 nm of a-Si onto the Si-Ge seed, laser crystallization was performed by scanning in a specific direction starting from the seeded area (Fig. 1). The laser used was a continuous wave (CW) laser with a wavelength of 532 nm. A flat-top line beam shape was utilized to ensure consistent crystallization across the irradiated region [4].As a result, the laser aimed at the seed area melts the interface between Si-Ge and a-Si. Subsequently, Si crystallization occurs following the atomic arrangement of single crystal Si-Ge during the cooling process [4]. The Si-Ge seed and the crystallized Si exhibited crystallinity with the same [110] orientation from transmission electron microscope (TEM) and fast Fourier transform (FFT) pattern analysis (Fig. 2). Following laser scanning in a specific direction, a long single-orientation Si crystal with a length of approximately 15 μm was obtained, preserving the specific crystallinity established from the seed. However, electron backscatter diffraction (EBSD) analysis confirmed that the flat-top line beam, larger than the 2 μm seed area, led to nucleation and crystal growth beyond the intended seed area at a-Si film. This resulted in collisions with grains originating from the seed (Fig. 3). We used a rectangular pattern to reduce nucleation in non-seed regions and prolong crystallization duration. Using this pattern, we successfully formed a single crystal active layer measuring 5 μm in width and 15 μm in length (Fig. 4).In conclusion, we successfully created a single crystal upper active layer using Si-Ge seed-based laser crystallization, a low-temperature process suitable for M3D integration structures. This crystallization method can be extended to create highly crystalline active layers in all layers by consistently generating single crystal seeds capable of inducing high crystallinity in each upper layer when stacking multiple layers in an M3D integrated structure.This work was supported by the National Research Foundation of Korea (NRF) grants funded by the Ministry of Science and ICT (MSIT) (RS-2023-00257003).[1] Y. Cheng et al., Integration, 85, 97-107 (2022)[2] A. H. T. Nguyen et al., Nano Convergence, 11(1), 5 (2024)[3] C. C. Yang et al., Japanese Journal of Applied Physics, 57(4S), 04FA06 (2018)[4] J. Baek et al., Applied Surface Science, 609, 155368 (2023) Figure 1

High-performance 320-nm continuous-wave solid-state laser

For the first time, to our knowledge, we realized a high-performance 320-nm continuous-wave (CW) laser with a fiber-coupled blue laser diode as the pump source. A V-shaped folded cavity is constituted by three mirrors, with a Pr3+:LiYF4 (Pr:YLF) as the laser crystal and a LiB3O5 (LBO) as the frequency doubling crystal, respectively. Under an absorbed pump power of 19.5 W, the maximum 320-nm output power reaches 4.26 W, corresponding to an optical conversion efficiency of 21.8% and a root-mean-square (RMS) power fluctuation of 0.61%, which give the best results of a 320-nm CW laser up to now. The excellent performance will make this ultraviolet laser source very suitable for practical applications, including semiconductor detection, spectral analysis, microscopic imaging, and biotechnology.

Application of confocal laser scanning microscopy to investigation of micro crystals in transparent amorphous media: Photoluminescence tomography and spectroscopy of CdZnSSe crystallites in historical silicate glass

Recently, photoluminescence tomography based on the confocal laser scanning microscopy with two-photon excitation has been developed to study the distribution of point and extended defects in the bulk of ZnSe laser crystals. This article presents the use of the tomography to investigate luminescent micro inclusions in transparent amorphous media such as silicate glass. Studies of CdZnSSe crystals synthesized in a silicate glass melt have been carried out using the tomography with both two-photon and single-photon excitation of luminescence. Zn-rich glass manufactured in the 19th century has been found to contain micron-sized crystals of CdξZn1−ξSζSe1−ζ (ξ≈0.5, ζ≈0.5) of hexagonal crystal system exhibiting intense photoluminescence. The photoluminescence band of these crystals has been found to peak at about 2.1 eV (∼590nm) at 300 K. Minor shifts in the maximum of bands and changes in their shape in individual crystals or at tomogram points within the crystal are associated with variations in their composition. Changes in the photoluminescence band shape and maximum due to the excitation of luminescence in CdZnSSe crystallites by laser radiation of different energies have also been observed in this study.

Growth and spectral properties of Er3+/Yb3+/Ce3+:YPO4 crystal

Er3+/Yb3+/Ce3+ tir-doped YPO4 crystals were successfully synthesized by high temperature solution method with Pb2P2O7 as flux. The growth, structures and spectral characterizations, including polarization absorption spectra, polarization fluorescence spectra and lifetime, were systematically discussed. It has broad absorption band around 973 nm with a full width at half maximum of 20.76 nm and 14.71 nm for π- and σ-polarizations, respectively, which is suitable for efficient pumping of InGaAs laser diodes. Based on J-O theory, spectral parameters such as oscillator strength, line strength, J-O intensity, fluorescence branching ratio, spontaneous transition rate and radiation lifetime were calculated systematically. In the polarization fluorescence spectra, four strong emission peaks were observed at 1505, 1537, 1561 and 1586 nm. The results show that Er3+/Yb3+/Ce3+:YPO4 crystal may be a promising laser crystal suitable for 1.5–1.6 μm.

Structure–luminescence property relationships of Yb3+-Doped Y2Mg3-xCax(SiO4)3 single crystals for 0.95–1.2 μm broadband emissions

This study successfully grew Yb3+-doped Y2Mg3-xCax(SiO4)3 (x = 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75) (Yb: YCMS) novel single crystals with multiple disordered structures. To the best of our knowledge, this is the first systematic report on the relationship between the luminescence properties (including emission intensity, emission peak position, full width half maximum, and fluorescence lifetime) and the local structure of the luminescent ions based on first-principles calculations. The wide half-height width of emission (103.10 nm@1047 nm) have been realized on the first-grown Yb: YCMS crystals. This study provides a novel solution for designing laser crystals with tunable optical properties. The comprehensive properties of Yb3+-doped YCMS crystals, such as ultra-wide emission bandwidth and high fluorescence lifetime, are promising gain materials for ultrafast laser applications.

Growth, first-principles calculations and optical properties of a novel near-infrared Ho: NLGW laser crystal

A rigid structure was constructed using an isotopic doping strategy, and a novel near-infrared 1 at% Ho3+: NaLa0.93Gd0.06(WO4)2 (Ho: NLGW) laser crystal with a size of Φ 18 mm × 30 mm was successfully grown by the Czochralski method. X-ray rocking curves and Rietveld refinement indicate that the grown crystal possesses high crystalline quality and crystallizes in the I41/a space group with lattice parameters: a = b = 5.3518 Å, c = 11.6438 Å and V = 333.5051 Å3. The Ho: NLGW crystal exhibits a low coefficient of thermal expansion (8.472 × 10−6 K−1), and the c-axis thermal conductivity increases from 1.235 W/(m × K) to 1.404 W/(m × K). The thermal properties of the Ho: NLGW crystal surpass those of other Ho3+-doped tungstate series and mainstream near-infrared laser crystals, suggesting that it is easier to obtain excellent laser gain. For revealing the excellent thermal properties, the elastic moduli of the NLW and NLGW crystals have been calculated by first principles. With the introduction of Gd3+, the structural stiffness of the NLW as a whole has been increased to optimize the mechanical properties in each axial direction and to obtain the reason for the larger Debye temperature. Finally, the transmission, absorption and near-infrared emission spectra of the Ho: NLGW crystal were investigated. The crystal exhibits a high transmittance of 88.5 % and an emission cross-section of 0.84 × 10−20 cm2 calculated according to the J-O theory. Experimental results indicate that the grown Ho: NLGW crystal can achieve large laser output more easily and are expected to be an excellent medium for 2 μm solid-state lasers.

Incorporating Er:YAP Microcrystals Into Tellurite Fiber Using Volumetric Interface Doping

AbstractIn this semi‐quantitative study, laser crystal microparticles which are potentially capable of generating mid‐infrared (MIR) light are incorporated into MIR transmitting optical fibers using a volumetric interface doping technique that combines interface doping with volumetric doping. Using confocal microscopy with a refractive index matching fluid, the Er:YAP microcrystals (MCs) inside the tellurite glass fiber are observed based on the detection of the green upconversion fluorescence emission of Er3+ ions, produced under excitation at 976 nm and localized at the central region within the fiber. The key outcome from this proof‐of‐concept study is that MC particles that are fused with the glass during the fiber drawing process survived heat treatment because the MC particles are exposed for a short time to a glass fluid with high viscosity of ≈105 Pa.s, which prevented the glass from exerting a dissolution effect. The survival of the MCs demonstrated the viability of the doping technique for fabricating fibers with exotic crystal‐glass combinations for applications including good refractive index matching across the pump and lasing bands of rare earth ions. This latter parameter provides significant particle size flexibility whilst minimizing additional loss from scattering especially at MIR wavelengths where the MC diameter‐to‐wavelength ratio becomes smaller.

Growth of YAG:Nd laser crystals by Horizontal Directional Crystallization in Protective Carbon‐Containing Atmosphere

AbstractLaser‐quality yttrium‐aluminum garnet single crystals doped with neodymium (YAG:Nd) of a concentration up to 1 at. % is grown by the method of horizontal directional crystallization from a molybdenum crucible in the protective reducing atmosphere based on argon, СО, and hydrogen. It is found that the content of carbon impurity in the grown crystals does not exceed 5·10−3 wt %, the content of molybdenum being on the level of 1.5·10−3 wt %. The optical quality of the crystals depends on the composition of the growth atmosphere and annealing. It is shown that, besides the bands of neodymium ion absorption, the crystals are characterized by the intense absorption in the UV edge of the spectrum at 370 nm wavelength, and by the wide absorption band with a maximum at 580 nm caused by formation of F and F+‐centers. The absorption at 370 and 580 nm can be eliminated by annealing. The structure perfection of the crystals is characterized by the rocking curve half‐width (β) which value varies within the limits of 10–14 arc. sec for (001) plane. Laser testing demonstrates the parameters comparable with those of YAG:Nd crystals grown by the Czochralski method from iridium crucible.

Modern developments in lasing with liquid crystals

A review of the recent developments in the field of lasing with liquid crystals (LCs) is presented. After an introduction into the principle of lasing the different relevant liquid crystal phases to the field are introduced, namely, the nematic and chiral nematic phase, Blue Phases, twist grain boundary and ferroelectric liquid crystals. The classic examples of liquid crystal lasing are shortly discussed, together with a variety of possibilities for tuning the lasing wavelength, before the modern trends in LC lasing are discussed in detail. These are particularly random lasers, where the effects of nanoparticles, quantum dots and solitons are highlighted, as well as localized surface plasmon resonance. Other modern laser systems that have attracted recent interest, white lasers, whispering gallery mode lasers and those with biological materials, for example, cellulose nanocrystals, are also introduced and the latest developments outlined.

Directional growth and composition design of the highly disordered Yb3+ doped Ca(Gd1-xLux)AlO4 crystals for ultrafast lasers

The unique disordered structure of the CaGdAlO4 crystal, combined with its exceptional thermal and spectral properties, has contributed to its growing popularity in the field of ultrafast lasers. In this work, high quality Yb3+ doped CaGdAlO4 crystals were directionally grown by the rapid and cost-effective micro-pulling down method for the first time. The anisotropic analysis determined [100]-orientation as the optimal growth direction due to its superior spectral, thermal and continuous-wave laser properties compared to that of [001]-orientation. Based on the optimized [100]-orientation, two novel crystals, Yb3+:CaGd1-xLuxAlO4 (x = 0.05 and 0.1), were designed by incorporating Lu3+ into Gd3+ site. Benefiting from the enhanced structure disorder induced by Lu3+ co-doping, the Yb3+:CaGd1-xLuxAlO4 crystals demonstrated superior spectral and pulsed laser performance compared to that of Yb3+:CaGdAlO4, featuring a broader emission spectrum, narrower pulse duration and higher peak power. The utilization of anisotropy and composition design strategies effectively enhanced the spectral and pulsed laser properties, providing a feasible way for the optimization of compact and high-performance laser devices.

Sol-Gel Pt-VO2 Films as Selective Chemoresistive and Optical H2 Gas Sensors.

In this work, VO2 (M1/R) thin films were exploited as H2 gas sensors. A flat film morphology, obtained by furnace annealing, was compared with a laser-induced nanostructured one. The combination of the environmentally friendly sol-gel approach with the ultrafast laser crystallization allows for significant reductions in energy consumption and related emissions during the fabrication of VO2 sensors. By decorating the sensors' surface with Pt nanoparticles (NPs), the sensor response was enhanced exploiting the hydrogen spillover effect. The Pt/VO2 sensors, tested at operating temperatures between 20 and 200 °C and for concentration of H2 from few ppm to 50000 ppm, offered a dual chemoresistive and optical sensing mode. Low operating temperatures of 150 °C were achieved, along with a detection limit as low as 2 ppm and a perfect baseline recovery. Both sensors guaranteed specific selectivity toward H2, without response to NO2 or humidity, and long-term stability over 500 h. The H2 sensing mechanism, for both the monoclinic and rutile VO2 phases, was investigated through in operando X-ray Diffraction and in situ X-ray Photoelectron Spectroscopy tests. The interaction was found to be based on the reversible formation of HxVO2 bronze, along with the reversible variations in the oxidation state of V.