Ultraviolet Laser Research Articles

High-efficiency 5-watt wavelength-tunable UV output from an Alexandrite laser

We investigate the performance of continuous-wave wavelength-tunable ultraviolet output from a diode-pumped Alexandrite laser by intra-cavity second harmonic generation. At 385 nm, ultraviolet output power of 5.05 W is achieved which is the highest continuous-wave ultraviolet power to date for intra-cavity frequency doubled diode-pumped Alexandrite lasers and highest optical-to-optical efficiency of 16.2% is achieved with respect to absorbed red pump power. An excellent ultraviolet wavelength tunable range, 38 nm, is achieved from 364 nm to 402 nm. Cavity mode analysis is performed for design of the resonator including cavity analysis and the modelling of output power from this wavelength tunable ultraviolet laser.

Demonstration of a kHz-repetition-rate extreme ultraviolet laser at 41.8 nm.

We demonstrate the operation of a plasma-based extreme ultraviolet (XUV) laser at a 1 kHz repetition rate driven by infrared pump pulses of less than 20 mJ. The 41.8 nm laser pulses were generated in a Xe plasma created by optical-field ionization by the L1 Allegra laser at ELI Beamlines. The output power of the XUV laser lies in the few microwatt range, and the energy efficiency of this pumping scheme opens the way for further scaling in repetition rate and average power.

Dynamic Monitoring the Friction Transmission of Mine Hoist Using Triboelectric Nanogenerators Self‐Powered Sensor Based on Different Surface Structures Embedded in the Friction Lining

The friction lining is a critical component of the friction hoist, serving as the driving force for lifting through its interaction with the wire rope. Monitoring the friction state between the wire rope and the friction lining is crucial as it directly impacts lifting capacity, work efficiency, and overall safety. By employing finite element simulation and creating surface microstructures on triboelectric nanogenerators (TENG) using ultraviolet laser, this study demonstrats that microstructure can improve voltage output. Compared with TENG without morphology, the voltage is increased by nearly seven times, reaching 2.28 V. Moreover, experiments revealed that embedding TENG at the optimal standard point of the friction lining enables effective monitoring of friction transmission under varied conditions, with the voltage signal showing synchronization with friction force. Notably, the voltage reached 520 mV under increasing specific pressures and stabilized around 670 mV with rising sliding speeds. This research represents a significant step toward real‐time monitoring of intelligent mining systems by dynamically observing friction transmission in mine hoists.

Femtosecond-laser-induced suprawavelength two-dimensional ZnO microstructures for multi-wavelength photodetector devices.

Herein, we report on two-dimensional (2D) suprawavelength crystalline ZnO microstructures induced by a single ultraviolet (UV) femtosecond laser beam (400 nm, 35 fs, 666 Hz) with significant absorption enhancement. The achieved absorption values of 90-99% and 75-80% in the UV and visible spectral regions, respectively, were approximately 1.16 and 12 times higher than those of the blank ZnO crystal. Furthermore, large-area 2D ZnO microstructures were fabricated to be used as photodetectors (PDs). The experimental results demonstrated that, compared with the blank ZnO, these 2D ZnO microstructures effectively enhanced the PD performance by nearly four times at 375 nm. More importantly, the ZnO microstructure exhibited great response value, ∼7.12 A/W at 532 nm as well as acceptable response at 660 and 808 nm, whereas the blank ZnO crystal showed almost no response. Raman analyses demonstrated that no change occurred after the femtosecond laser induced the microstructure on ZnO. Thus, the enhancement in photoelectric performance can be attributed to the strong absorption of the ZnO microstructure.

Ultraviolet spectral broadening by stimulated rotational Raman scattering on nitrogen pumped with signal laser injection

We present experimental results on kilojoule ultraviolet laser output with 1% spectral broadening. Through stimulated rotational Raman scattering (SRRS) with signal laser injection, we achieve effective spectral broadening in short-range propagation, with good retention of the original near-field distribution and time waveform. Theoretical calculations show that 2% bandwidth spectral broadening can be achieved by injecting 20 kW/cm2 signal light at 2.2 GW/cm2 flux of the pump laser. In addition, high-frequency modulation in the near field can be effectively avoided through replacement of the original random noise signal light by the controllable signal light. The SRRS in the atmospheric environment excited with signal laser injection can provide wide-band light output with controllable beam quality without long-distance propagation, representing an important potential route to realization of broadband laser drivers.

Ultraviolet laser induced periodic surface structures positively influence osteogenic activity on titanium alloys

Background/ObjectiveEndoprostheses might fail due to complications such as implant loosening or periprosthetic infections. The surface topography of implant materials is known to influence osseointegration and attachment of pathogenic bacteria. Laser-Induced Periodic Surface Structures (LIPSS) can improve the surface topography of orthopedic implant materials. In this preclinical in vitro study, laser pulses with a wavelength in the ultraviolet (UV) spectrum were applied for the generation of LIPSS to positively influence formation of extracellular matrix by primary human Osteoblasts (hOBs) and to reduce microbial biofilm formation in vitro.MethodsLaser machining was employed for generating UV-LIPSS on sample disks made of Ti6Al4V and Ti6Al7Nb alloys. Sample disks with polished surfaces were used as controls. Scanning electron microscopy was used for visualization of surface topography and adherent cells. Metal ion release and cellular metal levels were investigated by inductively coupled plasma mass spectrometry. Cell culture of hOBs on sample disks with and without UV-LIPSS surface treatments was performed. Cells were investigated for their viability, proliferation, osteogenic function and cytokine release. Biofilm formation was facilitated by seeding Staphylococcus aureus on sample disks and quantified by wheat germ agglutinin (WGA) staining.ResultsUV-LIPSS modification results in topographies with a periodicity of 223 nm ≤ λ ≤ 278 nm. The release of metal ions was found increased for UV-LIPSS on Ti6Al4V and decreased for UV-LIPSS on Ti6Al7Nb, while cellular metal levels remain unaffected. Cellular adherence was decreased for hOBs on UV-LIPSS Ti6Al4V when compared to controls while proliferation rate was unaffected. Metabolic activity was lower on UV-LIPSS Ti6Al7Nb when compared to the control. Alkaline phosphatase activity was upregulated for hOBs grown on UV-LIPSS on both alloys. Less pro-inflammatory cytokines were released for cells grown on UV-LIPSS Ti6Al7Nb when compared to polished surfaces. WGA signals were significantly lower on UV-LIPSS Ti6Al7Nb indicating reduced formation of a S. aureus biofilm.ConclusionOur results suggest that UV-LIPSS texturing of Ti6Al7Nb positively influence bone forming function and cytokine secretion profile of hOBs in vitro. In addition, our results indicate diminished biofilm formation on UV-LIPSS treated Ti6Al7Nb surfaces. These effects might prove beneficial in the context of long-term arthroplasty outcomes.

Self-frequency-doubling Yb:GdCOB laser intracavity-pumped Pr:YAP laser

Abstract We present for the first time a Pr:YAlO3 (Pr:YAP) laser emitting at 547 nm intracavity-pumped by a self-frequency-doubling Yb3+:Ca4GdO (BO3)3 (Yb:GdCOB) blue laser at 488 nm. We carried out a model to design the system properly, and the laser performance was experimentally investigated. Intracavity sum-frequency mixing at 547 and 488 nm was then realized in a CsLiB6O10 (CLBO) nonlinear crystal to reach the ultraviolet laser at 258 nm. We obtained a continuous wave output power of 575 mW at 258 nm with a pump source, which is a diode-pumped quasi-three-level Sr1-x La x -y Nd y Mg x Al12-x O19 (Nd:ASL) laser emitting 11.2 W at 902 nm.

Degradation mechanism during catastrophic optical damage in 385 nm GaN-based ultraviolet laser diodes

The failure mechanism of 385 nm GaN-based ultraviolet (UV) laser diodes (LDs) has been investigated. The degradation factors were studied by analyzing scanning electron microscopy (SEM), cathodoluminescence, and transmission electron microscopy (TEM) after aging. In degraded UV LD, degradation is easily observed on the anterior cavity facet, with holes found in the epitaxial GaN material, primarily concentrated in the quantum wells and waveguide regions of the LDs. This shows that the degradation may be closely related to the higher photon energy of the UV laser beam emitted by UV LDs. In the aging process of samples, emission of UV lasers leads to deterioration at the interface and in the semiconductor. This degradation leads to continuous heat accumulation and may create a positive feedback loop. Ultimately, this results in the failure of the UV LD. This study presents a possible major factor for the shorter lifetime of UV LD compared to blue LD. Therefore, it is very significant to improve the interface quality for extending the lifetime of UV LDs.

Optical and electrical degradation behavior of GaN-based UV-A laser diodes

The degradation mechanism of GaN-based ultraviolet (UV-A) laser diodes (LDs) is analyzed by studying the changes of their electrical and optical properties after aging process with the operation current below the threshold current (Ith). After aging treatment, Ith increases, the slope efficiency decreases, and the leakage current increases. In particular, the emission spectra of aged LD show significant broadening, with additional peaks on the shorter wavelength side. Both cathodoluminescence and deep level transient spectrum results indicate defects can develop around the active region of the LD, even when the operation current is below Ith. This leads to an increase in trap-assisted tunneling current and non-radiative recombination. The observed defects may result from the diffusion of water molecule in the environment from the cavity facet into the active region and formation of ON–CN and VGaON complex defects. These defects not only reduce the effective carrier concentration injected into the quantum well but also increase non-radiative recombination. These results will contribute to our understanding of the degradation mechanism of UV LDs and the preparation of long lifetime UV LDs.

Rate Coefficient and Branching Ratio for the Formation of Criegee Intermediate Syn-/Anti-CH3CHOO from CH3CHI + O2 and the Self-Reaction of Syn-/Anti-CH3CHOO Determined with Simultaneous IR/UV Probes.

A flow reactor coupled with a light-emitting diode at 286 nm, an infrared quantum-cascade laser near 11 μm, and an ultraviolet laser at 335 nm was implemented to probe the precursor CH3CHI2, syn-CH3CHOO, and anti/syn-CH3CHOO, respectively, in the reaction of CH3CHI + O2. The branching between syn- and anti-CH3CHOO was determined to be ≈80:20 from two methods. The concentration temporal profiles of anti-CH3CHOO, derived on comparison of infrared and ultraviolet profiles, yielded the rate coefficient for the self-reaction of anti-CH3CHOO, kself anti = (6 ± 2) × 10-10 cm3 molecule-1 s-1, ∼4 times the corresponding value, kself syn = (1.4 ± 0.3) × 10-10 cm3 molecule-1 s-1, for syn-CH3CHOO; the rate coefficient for the cross-reaction between syn-CH3CHOO and anti-CH3CHOO was estimated to be (2.1 ± 0.6) × 10-10 cm3 molecule-1 s-1. With determined concentrations of syn-CH3CHOO and self-reaction rate coefficients, the rate coefficient for the formation of CH3CHOO from CH3CHI + O2 was determined to be kform = (3.8 ± 0.7) × 10-12 cm3 molecule-1 s-1 at 298 K, ∼45% of previous reports.

Current-carrying properties of REBCO multi-filamentary tapes prepared by reel-to-reel ultraviolet picosecond laser cutting

Abstract REBCO high-temperature superconductors have been widely used in high magnetic field applications, because of their excellent critical current properties and high critical temperature. However, REBCO tape has an extremely large width-to-thickness ratio (typically in the range of 1000–10 000) which causes power dissipation to be too high in applications. One of the most effective ways to reduce AC loss is to divide the superconducting layer in the REBCO tape into filaments. The current-carrying properties degradation behavior of the prepared multi-filamentary tape is the focus of attention. In this study, REBCO multi-filamentary tapes are tested with different numbers of filaments (2-filament, 6-filament, and 10-filament) by cutting the copper-stabilizing layers and superconducting layers through a self-developed reel-to-reel ultraviolet picosecond laser cutting device. The findings indicate that the cut groove has a depth of approximately 30 μm and the width of the groove in the superconducting layer measures around 15 μm. Meanwhile, the research found that ultraviolet picosecond laser cutting does not cause substantial degradation in the I C. Under self-field conditions at 77 K, the I C decreases with the number of filaments, and the degradation of I C is less than 13% in a 10-filament tape, the corresponding decrease of J C is only about 10%. Similarly, at 4.2 K and under various high-field (10 T, 12 T, 14 T) conditions, the I C variation trends of REBCO high-temperature superconducting (HTS) multi-filamentary tapes and non-striated tapes are fundamentally similar, both decreasing as the applied vertical magnetic field increases. Furthermore, it was found that a constant tension of 50 MPa, 100 MPa, and 200 MPa had no effect on the current-carrying properties of the REBCO HTS multi-filamentary tapes.

Fluorescence imaging of plume-surface interaction in large-scale reduced pressure environments

Planar laser-induced fluorescence (PLIF) was applied for the first time in the 20-ft vacuum chamber at the Marshall Space Flight Center to visualize the plume-surface interaction (PSI) of a nitrogen jet seeded with nitric oxide (NO). A Mach 5.3 nozzle was used to simulate the exhaust of a landing spacecraft for two different jet stagnation pressures and one jet stagnation temperature. A flat plate was used to simulate the landing surface, and two different dimensionless altitudes were investigated. The chamber pressure was reduced such that both lunar-relevant environments at 0.01–28 Pa and Martian-relevant environments at ∼600 Pa were investigated. PLIF flow visualization was performed using a pulsed, tunable, ultraviolet laser, which entered the vacuum chamber through a window, and was directed to the test article using remote-controlled mirrors. Fluorescence at ultraviolet wavelengths was imaged using an intensified camera, which was placed inside a pressurized enclosure located inside the vacuum chamber. For the Martian-relevant condition, a Mach disk and stagnation bubble were observed at h/De = 10, whereas a pair of oblique stagnation shocks were observed at h/De = 3. Significantly complex flows, such as different stagnation shock behaviors, were observed for the lunar-relevant conditions based on the h/De and Reynolds number. The results presented here are the first NO-PLIF measurements of the PSI flowfield within rarefied environments. The unique information on jet expansion and plume structure will be useful to aid researchers in validating complex computational simulations and to inform engineering designs of extraterrestrial landing systems.

Discovery of Calcium Sulfate at different hydration states on Mars - Based on Perseverance SHERLOC Analysis

Organic matter on planets is often co-deposited with evaporites, and evaporation of lakes in the Jezero region of Mars may have led to the deposition of abundant organic matter and minerals such as sulfates, making sulfates important minerals for preserving the remains of potential life on Mars, especially in different hydration states, will help to invert the variability of the Martian environment and provide guidance for the exploration of life on Mars. Raman spectroscopy can detect the molecular composition of organic matter and acid anion information of the target of interest, thus enabling in situ analysis of life information and its living environment. In order to realize the detection of life remains on Mars, The Perseverance rover is equipped with SHERLOC in situ material detection payload, which adopts a 248.6nm deep ultraviolet (DUV) laser to simultaneously excite Raman and fluorescence signals of the target. In this paper, five scans in three modes (survey scan, HDR scan and detail scan) from two sites on Mars (Quartier and Bellegarde) were selected for preliminary analysis, and the presence of sulfate minerals at these two sites was confirmed. The detail scans at Quartier were analyzed in depth, and the presence of four calcium sulfate minerals, gypsum (CaSO4∙2H2O), bassanite (CaSO4∙0.5H2O), anhydrite (β-CaSO4) and gamma-calcium sulfate (γ-CaSO4)was inferred from the states of ν1 (SO4), ν3 (SO4) and hydrated peaks. The differences in the degree of hydration of calcium sulfate minerals suggest that there may have been active water activity on Mars. By comparing data collected by SHERLOC with spectra from spectral libraries, the composition of small-scale structures on Mars may be assessable. However, due to the complexity of the Martian geology, more accurate water activity will need to be combined with more detailed ions, temperatures, humidity, and other conditions for a more precise analysis.

A Nd-doped silica glass with high doping concentration, low hydroxyl content, and 900 nm fluorescence emission fabricated by laser additive manufacturing

The 900 nm wavelength laser is effective for atmospheric detection and various other applications.The frequency-doubled 450 nm deep blue laser can be used in maritime military, quantum optics, biomedicine, laser storage, laser display, and deep ultraviolet laser fields, among others. Although Nd3+ is considered the optimal medium for generating 900 nm lasers, competition with the 1060 nm emission wavelength must be addressed. In Nd-doped silica glass, without the introduction of aluminum, the emission intensity of the three-level transition is higher than that of the four-level transition. However, it can cause a concentration quenching between Nd3+, but co-doping with Al can effectively suppress it. As the Al/Nd ratio increases, the emission intensity at 1060 nm increases relative to that at 900 nm. By precisely adjusting the Al/Nd ratio, it is possible to suppress the 1060 nm emission while also inhibiting concentration quenching caused by Nd3+.

Translucent Si Solar Cells Patterned with Pulsed Ultraviolet Laser Beam

We report an application of a pulsed ultraviolet (UV) laser (λ = 355 nm) in producing translucent Si solar cells. This process efficiently generates a densely packed microhole array on a fully fabricated Si P‐N junction solar cell in just a few minutes. Herein, prototype cells with a nominal microhole diameter of 23 μm with a spacing between 60 and 300 μm are fabricated. High‐resolution electron‐beam microscopy reveals that the UV laser beam introduces amorphized silicon oxide (SiOx) in proximity to the patterned microholes via localized heating in air. Quantitative photovoltaic (PV) analysis shows a decline in the open‐circuit voltage (Voc) and the fill factor (FF) of the cells with the increase in the microhole density, likely due to the P‐N junction damage during the laser beam irradiation. Despite the reduction in Voc and FF, the solar cells retain a short‐circuit current density (Jsc) above 90% without post‐processing. The inherent microhole geometry associated with the laser beam profile allows multiple light scattering within the confined microhole structure, enhancing the translucency of the cells. While further development is required for optimization, these findings support the potential use of UV laser beams for fast and scalable production of translucent solar cells.

A failed search for concordancy across multiple isotopic systems in lunar impactites: Implications for testing the Late Heavy Bombardment hypothesis

Investigations of Apollo-returned samples radically altered our understanding of lunar history which has important implications for terrestrial habitability and Solar System evolution. Radiometric dating of those samples inspired the hypothesis that Moon experienced a Late Heavy Bombardment (LHB) at ∼3.9 Ga. The LHB concept has come under several recent challenges, including the concern that 40Ar/39Ar step-heating dates of Apollo impactites had been misinterpreted. Ultraviolet laser ablation (UVLAMP) 40Ar/39Ar dates – with their capacity for much higher spatial resolution and thus potential to avoid dating near-ubiquitous clasts in impact melt rocks – should in principle provide more interpretable results. Here we compare new ion microprobe 207Pb/206Pb accessory mineral dates for two Apollo 17 impactites for which UVLAMP 40Ar/39Ar dates had been previously obtained. Our results are consistent with a single accessory phase growth event for each sample, though the two samples yielded statistically different mean ages of ca. 3.974±0.013 and 3.928±0.003 Ga. Both can reasonably be interpreted as dating an impact event, but the 207Pb/206Pb dates are older than the associated 40Ar/39Ar dates by several hundred million years. We interpret that the age differences result from subsequent thermal disturbances. The discordancy between impact ages inferred from lunar impactites using two different radiometric systems suggests caution in acceptance of the LHB hypothesis without the benefit of both larger lunar datasets and more multichronometric studies. Even with such information, our capacity to know the lunar bombardment history is likely limited by compositional and thermal effects which appear to restrict growth of impact-produced accessory minerals to a small fraction of the lunar surface. Using currently available datasets, the LHB hypothesis may be effectively untestable.

Exploring photoionization of gas-phase free radicals with a widely tunable VUV laser at moderate spectral resolution

The VUv Laser for Considering Astrophysical and Isolated Molecules (VULCAIMs) setup [Harper et al., Phys. Chem. Chem. Phys. 24, 2777 (2022)] integrates a narrow-bandwidth tunable vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) nanosecond-pulsed laser system (6–16 eV) and a photoelectron spectrometer, designed for recording high-spectral-resolution (rotationally resolved) photoelectron spectra of gas-phase free radicals. This approach usually needs beforehand medium-resolution synchrotron data to guide the selection of specific spectral regions to be investigated at higher resolution with the VULCAIM setup. We present an upgraded version of the VUV laser system integrating an optical parametric oscillator for continuously scanned medium-resolution measurements (<3 cm−1) across the whole VUV and XUV spectral ranges. This innovation enables broader coverage without the need to access synchrotron facilities. Furthermore, rapid mode switching allows for maintaining optimized radical production conditions from mid-resolution to high-resolution operation mode, enhancing spectroscopy capabilities significantly. The new capabilities of the VULCAIM setup are illustrated on two showcases of photoionization studies: the nitric oxide (NO) stable molecular species and the benzyl (C6H5CH2) free radical produced by pyrolysis.

Ultraviolet laser-induced fragmentation of hydrocarbon fuel droplets

The present study aims to understand droplet fragmentation due to instabilities from the radiative heating process. We focus on the plasma-induced breakup mechanism of iso-octane and n-hexane droplets from the nucleation of holes through sheets and instabilities. The plasma generation inside the droplets leads to an intense explosion followed by fragmentation of the droplets. A droplet is suspended in the air using an acoustic levitator and exposed to ultraviolet nanosecond laser pulses. The droplet sizes used are in the range of 0.5–2 mm in diameter, and laser energies are 10–20 mJ per pulse. Initially, plasma formation followed by shock wave emission is observed during the impact of the laser pulse. Afterward, the droplet opens at one side and is stretched vertically to form a liquid sheet. The hole formation and its rapid growth result in the breaking of the thin liquid sheet. Small droplets and ligaments emerge from the circular edge of the sheet, which follows the well-known ligament distribution. This study reveals the detailed analysis of expansion dynamics, evolution of single and multiple holes, and instabilities associated with the liquid sheet. The results observed are categorized into four different mechanisms: (1) plasma formation followed by shock wave propagation, (2) droplet deformation, (3) sheet breakup through nucleation of holes followed by rapid growth, and (4) complete atomization.

Laser ablation for preventing coronary obstruction and maintaining coronary access in redo-TAVR: A proof of concept.

Redo-transcatheter aortic valve replacement (TAVR) is a promising treatment for transcatheter aortic valve degeneration, becoming increasingly relevant with an aging population. In redo-TAVR, the leaflets of the initial (index) transcatheter aortic valve (TAV) are displaced vertically when the second TAV is implanted, creating a cylindrical cage that can impair coronary cannulation and flow. Preventing coronary obstruction and maintaining coronary access is essential, especially in young and low-risk patients undergoing TAVR. This study aimed to develop a new leaflet modification strategy using laser ablation to prevent coronary obstruction and facilitate coronary access after repeat TAVR. To evaluate the feasibility of the leaflet modification technique using laser ablation, the initial phase of this study involved applying a medical-grade ultraviolet laser for ablation through pericardial tissue. Following this intervention, computational fluid dynamics simulations were utilized to assess the efficacy of the resulting perforations in promoting coronary flow. These simulations played a crucial role in understanding the impact of the modifications on blood flow patterns, ensuring these changes would facilitate the restoration of coronary circulation. Laser ablation of pericardium leaflets was successful, demonstrating the feasibility of creating openings in the TAV leaflets. Flow simulation results show that ablation of index valve leaflets can effectively mitigate the flow obstruction caused by sinus sequestration in redo-TAVR, with the extent of restoration dependent on the number and location of the ablated openings. Laser ablation could be a viable method for leaflet modification in redo-TAVR, serving as a new tool in interventional procedures.

Characterization of Micro-Holes Drilled Using a UV Femtosecond Laser in Modified Polyimide Flexible Circuit Boards.

Modified polyimide (MPI) flexible printed circuits (FPCs) are used as chip carrier boards. The quality of the FPC directly affects the reliability of the integrated circuit. Furthermore, micro-holes are critical components of FPCs. In this study, an ultraviolet (UV) femtosecond laser is used to drill micro-holes in double-layer flexible circuit boards with MPI as the substrate. The morphology of the micro-hole wall in the copper foil and MPI layer is observed, and the effects of the laser processing parameters on the diameter and depth of the micro-holes are analyzed. The drilling process and mechanism of micro-holes obtained using a UV femtosecond laser in MPI FPCs are discussed. The results show that the morphology of femtosecond laser-machined copper is closely related to the laser energy, and a periodic structure is observed during the machining process. Copper, MPI, and copper oxides are the most common molten deposits in micro-holes during drilling. The depth of the micro-holes increases with an increase in the energy of a single pulse, scanning time, and scanning overlap rate of the laser beam. However, the diameter exhibits no discernible alteration. The material removal rate increased significantly when laser processing was applied to the MPI resin layer.