Thin Laser Research Articles

Integration of Thin Laser Structured Micro Porous Layers in PEM Water Electrolyzers

Reduction of the Iridium loading of Proton Exchange Membrane (PEM) water electrolyzers is an important topic to reduce the capital costs and increase the sustainability. At high Iridium loadings (>1 mgIr cm-²) the interface between porous transport layer (PTL) and catalyst layer (CL) has influences on the electrochemical performance. However, this is significantly more important at low and especially ultra-low loadings: <1 mgIr cm-², < 0.1 mgIr cm-², respectively.At low catalyst loadings the electrical conductivity of such catalyst layers is significantly reduced, because of local inhomogeneity’s, e.g. not connected catalyst particles/agglomerates. There is a large mismatch between pore/particle sizes of both layers that lead to a bad electrical contact: commercial titanium PTLs have pore sizes of 30 µm [1], on the other hand catalyst particles are in the size of few nm [2]. Furthermore, the titanium tends to oxidize on the anode side, which leads to further increases of the resistances between PTL and CL. Because of these aspects protective, good conducting coatings on the PTL are used (often noble metals, e.g. Platinum, Iridium). Another favorable improvement is the integration of micro porous layers (MPL) to reduce the interface resistances [3]. However, it is not easy to manufacture such MPLs.In our approach we produce ultra thin MPLs with thicknesses of 10 µm. As base material we use titanium foils (grade 1) that are processed with laser precision machining to produce deterministically structured pores in the size of ≤ 5µm. These laser structured MPLs are integrated between PTL and CL.The experimental results show a significant improvement when using MPLs (Fig. 1a). The polarization behavior is clearly better because of the reduced resistances (Fig. 1b), which were measured by electrochemical impedance spectroscopy.This contribution deals with the improvement of the interface between PTL and CL by integrating thin MPLs to enable further reductions of Iridium loadings. By means of laser precision machining we can produce thin MPLs with deterministically structured pores. We will show the effect of different structural properties of the MPLs, such as pore sizes or pore distribution, on the electrochemical performance in combination with low loading CCMs.

Thin Film Stoichiometry and Defects Management for Low Threshold and Air Stable Near-Infrared Perovskite Laser.

While significant efforts have been devoted to optimize the thin-film stoichiometry and processing of perovskites for applications in photovoltaic and light-emitting diodes, there is a noticeable lack of emphasis on tailoring them for lasing applications. In this study, it is revealed that thin films engineered for efficient light-emitting diodes, with passivation of deep and shallow trap states and a tailored energetic landscape directing carriers toward low-energy emitting states, may not be optimal for light amplification systems. Instead, amplified spontaneous emission (ASE) is found to be sustained by shallow defects, driven by the positive correlation between the ASE threshold and the ratio of carrier injection rate in the emissive state to the recombination rate of excited carriers. This insight has informed the development of an optimized perovskite thin film and laser device exhibiting a low threshold (≈ 60 µJ cm-2) and stable ASE emission exceeding 21 hours in ambient conditions.

The effects of laser cane cues on the freezing of gait of Parkinson's disease patients: can increasing the laser light beam width play a role?

Freezing of gait can be seen in a significant number of people with Parkinson's disease. Disappointingly, the classic standard treatment of Parkinson's disease with dopamine replacement has not shown promising results in improving the freezing of gait. Hence the approach have shifted towards using non-invasive methods to address this problem. To assess the effect of laser cane as a visual cue on the freezing of gait of people with Parkinson's disease and further determine the effect of laser light beam width and color on the freezing of gait. 7 known Parkinson's Disease patients were enrolled in this study, all of whom had at least one episode of freezing at at least one clinical visit. These patients underwent gait analysis in 4 stages: walking without a cane, walking with a thin red light laser cane, a thick red light laser cane, and a green light laser cane. Using laser canes effectively improved nearly all parameters of walking, including right and left stride length, step length, the velocity of movement, and rotation time, compared to walking without a stick. Using different colors of laser cane didn't make any significant difference in improving the freezing of gait of our patients. Nevertheless, increasing the laser light beam width significantly improved almost all walking parameters. This is the first study assessing the effect of laser light beam width on freezing of gait in Parkinson's disease patients and shows promising results in regards to increasing the thickness of laser lights in order to improve walking parameters in Parkinson's disease patients more effectively. Furthermore, this is the second study to evaluate the effect of laser light color, contradicting the previous results by showing no significant correlation between the color of laser light and improvements in walking parameters.

A Wearable Thin-Film Hydrogel Laser for Functional Sensing on Skin.

Flexible photonics offers the possibility of realizing wearable sensors by bridging the advantages of flexible materials and photonic sensing elements. Recently, optical resonators have emerged as a tool to improve their oversensitivity by integrating with flexible photonic sensors. However, direct monitoring of multiple psychological information on human skin remains challenging due to the subtle biological signals and complex tissue interface. To tackle the current challenges, here, we developed a functional thin film laser formed by encapsulating liquid crystal droplet lasers in a flexible hydrogel for monitoring metabolites in human sweat (lactate, glucose, and urea). The three-dimensional cross-linked hydrophilic polymer serves as the adhesive layer to allow small molecules to penetrate from human tissue to generate strong light--matter interactions on the interface of whispering gallery modes resonators. Both the hydrogel and cholesteric liquid crystal microdroplets were modified specifically to achieve high sensitivity and selectivity. As a proof of concept, wavelength-multiplexed sensing and a prototype were demonstrated on human skin to detect human metabolites from perspiration. These results present a significant advance in the fabrication and potential guidance for wearable and functional microlasers in healthcare.

Experimental and numerical study on thin silicon wafer CO2 laser cutting and damage investigation

Experimental and numerical study on thin silicon wafer CO2 laser cutting and damage investigation

A high strength and flexible multilayered thin film laser induced graphene heater for thermal applications

Increasing demand for wearable sensors and heating elements has occurred recently. Herein, graphene has been observed as a biocompatible, cost effective, and multidimensional material catering to both sensing and heating applications. However, it still lacks essential features such as high temperature performance with low power usage, high strength, and robustness of thin films in tough environments such as heating elements in thermal socks. Hence, in this paper, we demonstrated laser induced graphene (LIG) as a suitable candidate for wearable thermal applications. LIG heaters were fabricated using a cost effective and environmentally friendly technique based on photothermal ablation of polyimide substrate using a 50 W CO2 laser. The heat flux of LIG heater was improved by stacking multiple films while their electrical connections are made in parallel. Upon joule heating, the heaters had excellent electrothermal performance, fast and stable response, achieving temperature of 195 °C using a relatively low DC voltage of 10 V. Most importantly, they showed good durability after bending, washing and repeated heating and cooling cycles. Due to these advantages, the LIG-based thin film heaters have potential as reliable and low-cost heating elements for variety of tough applications such as defrosting and wearable thermal pads.

The effect of surfactants and precursors on the structure and properties of ZnS:Cu nanocrystalline particles

Doped ZnS materials exhibit excellent optical and electrical properties, making them a superior material for alternating current (AC) thin film electroluminescent devices, solar panels, light-emitting diodes, laser diodes and other luminescent device designs and fabrications. This study involves the hydrothermal synthesis of nanocrystalline Cu-doped ZnS materials without a surfactant and using two surfactants – hexadecyltrimethylammonium bromide (HTAB) and sodium dodecyl sulfate (SDS). The structure, morphology and elemental content of the synthesized nanopowders were characterized by X-ray powder diffraction, X-ray absorption spectroscopy (XAS), scanning electron microscopy and energy-dispersive X-ray spectroscopy (EDX) techniques, while the optical properties were studied by photoluminescence (PL) spectroscopy. The sizes of the nanocrystallites in all the synthesized samples were below 20 nm. XAS results suggest that Cu ions substitute Zn ions in cubic zinc blende ZnS structure and are located in a locally distorted environment. The addition of a surfactant allows control of the morphology of the particles and their photoluminescent properties.

Preliminary tests on additive-manufactured Al-Sc specimens for the setup of a numerical model for Laser Shock Peening

Aluminum-Scandium alloys offer a great potential in aerospace applications due their high corrosion resistance and improved strength properties. Furthermore, these alloys have been qualified for laser additive manufacturing (AM), producing parts with static strengths rivalling their conventionally manufactured counterparts. However, laser processing also results in large residual stresses that can severely affect fatigue properties and result in geometric distortion. A proven method for reducing the fatigue-related problems in metallic structures is to drive compressive residual stresses into the affected area by means of Laser Shock Peening (LSP). This surface treatment is very effective in bulk structures, improving life performances of fatigue-sensitive aeronautical components, such as jet engines turbine blades or helicopter gearboxes. On the other hand, quite a limited number of studies has been presented on the effect of LSP on fatigue crack growth in thin components and laser AM structures. This work presents first the results of preliminary tensile tests on additive manufactured Al-Sc specimens. The tensile strengths of as-built and heat-treated samples are compared. Then, a reliable and computationally time-effective numerical model of laser peening is reviewed, referring to case studies investigated earlier. In view of applying LSP to additive manufactured Al-Sc components, the effects of different laser parameters and geometries are discussed. Finally, the possible drawbacks of the LSP treatment are addressed, in order to exploit its full potential in increasing the fatigue life of AM components.

Laser Scribing of Photovoltaic Solar Thin Films: A Review

The development of thin-film photovoltaics has emerged as a promising solution to the global energy crisis within the field of solar cell technology. However, transitioning from laboratory scale to large-area solar cells requires precise and high-quality scribes to achieve the required voltage and reduce ohmic losses. Laser scribing has shown great potential in preserving efficiency by minimizing the drop in geometrical fill factor, resistive losses, and shunt formation. However, due to the laser induced photothermal effects, various defects can initiate and impact the quality of scribed grooves and weaken the module’s efficiency. In this regard, much research has been conducted to analyze the geometrical fill factor, surface integrity, and electrical performance of the laser scribes to reach higher power conversion efficiencies. This comprehensive review of laser scribing of photovoltaic solar thin films pivots on scribe quality and analyzes the critical factors and challenges affecting the efficiency and reliability of the scribing process. This review also covers the latest developments in using laser systems, parameters, and techniques for patterning various types of solar thin films to identify the optimized laser ablation condition. Furthermore, potential research directions for future investigations at improving the quality and performance of thin film laser scribing are suggested.

Commentary: Evolution and practice patterns of thin flap sub-Bowman laser in situ keratomileusis in refractive surgery.

Commentary: Evolution and practice patterns of thin flap sub-Bowman laser in situ keratomileusis in refractive surgery.

Laser Iridotomy for Pupillary Block in Children with Endogenous Uveitis

Objective. Development of a differential approach to laser iridotomy in children with endogenous uveitis considering iris characteristics and the reaction of children’s eyes to different laser types.Patients and methods. Thirty-six laser iridotomies were conducted in 36 children aged 8–16 years with pupillary block. Nidek YAG laser was used in YAG (1064 nm) and SLT (532 nm) modes.Results. The frequency of hemorrhagic complications during surgery decreased to 19.4 % since 2009. The frequency of exudative reactions and proliferative syndrome with closure of laser coloboms in 1-6 months after surgery decreased to 33.3 % (25.7 % and 40.9 % respectively).Conclusion. We recommended the patented differential approach for effective nontraumatic laser iridotomy in children with endogenous uveitis. In a thin iris single-stage YAG laser perforation should be performed in maximum bombe and multiple perforation in cases of multi-chamber bombe. In a dense thick iris or in cases of former iridotomy closure two-stage approach should be performed. First, circular coagulation should be done in the form of a ring or spot at the site of the planned coloboma. Second, YAG-laser perforation should be done in 10–14 days. The iris vessels topography, reflexogenic zones, and the peculiarities of the iris reactions to the lasers in children with endogenous uveitis should be considered when choosing a place for a coloboma. The use of thermal coagulating lasers should be limited, especially on thin irises. Active anti-inflammatory therapy and eye monitoring are necessary after laser surgery. The differential approach is safe, effective, and can be recommended for implementation in the practice of pediatric ophthalmology.

Beam parameter product optimization of densely arranged multi‐emitter tunnel junction cascaded laser

AbstractA tunnel junction cascaded semiconductor laser with thin waveguide and narrowed spacing between adjacent emitters is designed in this work. It can be concluded theoretically that the spatial size of the spots arrangement in fast axis has a greater impact on the vertical beam parameter product (BPP) of the multi‐emitter cascaded laser than the divergence angle. The measured vertical BPP of the designed narrow emitter spacing (NES) laser has been reduced 42.5%, which implies that the beam quality performance of the laser has been improved and proves the feasibility of this method. Meanwhile, the slope efficiency of the thin waveguide NES laser can reach up to 3.55 W/A under 10 ns duration pulse current.

Monolithic Yb3+-doped thin film lithium niobate microring laser fabricated by photolithography-assisted chemo-mechanical etching technology

We demonstrate an on-chip microring laser on Y b 3 + -doped thin film lithium niobate (Yb:TFLN) fabricated by photolithography-assisted chemo-mechanical etching technology. Multiwavelength laser emissions around 1025 nm from the microring resonator pumped by a 980 nm laser diode are observed with the lasing threshold of 10 mW. Experimentally, up to 14 longitudinal modes are obtained from the fabricated Yb:TFLN microring laser, and this on-chip microring laser is a promising light source for multiple wavelength channels in optical communications and biosensors.

Non-destructive processing of silver containing glass ceramic antibacterial coating on polymeric surgical mesh surfaces.

Surgical meshes composed of bioinert polymers such as polypropylene are widely used in millions of hernia repair procedures to prevent the recurrence of organ protrusion from the damaged abdominal wall. However, post-operative mesh infection remains a significant complication, elevating hernia recurrence risks from 3.6% to 10%, depending on the procedure type. While attempts have been made to mitigate these infection-related complications by using antibiotic coatings, the rise in antibiotic-resistant bacterial strains threatens their effectiveness. Bioactive glass-ceramics featuring noble metals, notably silver nanoparticles (AgNPs), have recently gained traction for their wide antibacterial properties and biocompatibility. Yet, conventional methods of synthesizing and coating of such materials often require high temperatures, thus making them impractical to be implemented on temperature-sensitive polymeric substrates. To circumvent this challenge, a unique approach has been explored to deposit these functional compounds onto temperature-sensitive polypropylene mesh (PP-M) surfaces. This approach is based on the recent advancements in cold atmospheric plasma (CAP) assisted deposition of SiO2 thin films and laser surface treatment (LST), enabling the selective heating and formation of functional glass-ceramic compounds under atmospheric conditions. A systematic study was conducted to identify optimal LST conditions that resulted in the effective formation of a bioactive glass-ceramic structure without significantly altering the chemical and mechanical properties of the underlying PP-M (less than 1% change compared to the original properties). The developed coating with optimized processing conditions demonstrated high biocompatibility and persistent antibacterial properties (>7 days) against both Gram-positive and Gram-negative bacteria. The developed process is expected to provide a new stepping stone towards depositing a wide range of functional bioceramic coatings onto different implant surfaces, thereby decreasing their risk of infection and associated complications.

선택적 레이저 소결을 이용한 유연인쇄전자소자 제작

It is necessary to develop a low temperature process that can deposit and pattern metal on a heat sensitive substrate because most flexible printed electronics use high temperature sensitive materials such as plastic. The most commonly used photolithography process is not suitable for flexible printed electronics because the high temperature thermal treatment process and chemicals are not compatible with plastic. Recently research has been actively conducted on a method of minimizing thermal damage to plastic and high-resolution metal patterning by using selective laser sintering after forming a liquid metal nanoparticle thin film without using existing photolithography and vacuum deposition. In this review paper, we explore flexible printed electronics such as flexible thin film transistors and flexible transparent conductors using selective laser sintering of nanomaterials and discuss future development directions.

Ultimate figures of merit broadband self-powered obliquely deposited antimony thin film laser detectors

Fabrication of a fast and high detectivity infrared detector operating at room temperature represents a big challenge. Due to the small energy gap of the semiconducting materials used for infrared detectors, the noise becomes considerable factor and the possibility of operating the detector at room temperature is very limited. A study of the figures of merit antimony thin films detector grown by oblique angle deposition technique is presented. Polycrystalline antimony thin films were thermally evaporated on the glass substrates at a angles of 0, 10, 30, and70°. The aim was to develop a wideband (0.649–10.6) µm self-powered laser detectors; operating at room temperature. The deposition angle had a decisive role in the detector specifications, namely, its detectivity, responsivity, linearity, and response time. At θ = 70° deposition angle; maximum detectivity and fastest response were achieved. The variation of rise time with deposition angle was linear, and the rise time was around 50 ns at 70°. The antimony detectors showed about the same specific detectivity ~ 109 Jones at 300 k for the wavelength range of 1.064–10.6 µm.

Thin active region HgCdTe-based quantum cascade laser with quasi-relativistic dispersion law.

HgCdTe is promising as a material to solve a problem of the development of semiconductor sources with an operational frequency range of 6-10 THz due to the small optical phonon energies and electron effective mass. In this study, we calculate the dependence of the metal-metal waveguide characteristics on the number of cascades for the 3-well design HgCdTe-based quantum cascade laser at 8.3 THz. It is shown that four cascades are sufficient for lasing at a lattice temperature of 80 K due to the large gain in the active medium. The results of this study provide a way to simplify the fabrication of thin active region HgCdTe-based quantum cascade lasers for operation in the range of the GaAs phonon Reststrahlen band inaccessible to existing quantum cascade lasers.

Flexible random laser from a porous polymer film

Flexible random lasers have attracted a great deal of interest due to their potential in light-weight, flexible optical sensors and devices. Among many alternatives, flexible thin film random lasers are very interesting because they can be easily fabricated via a simple solution-based process. Herein, we demonstrate a dye-doped porous polyvinyl alcohol film that can work as a flexible random laser source under optical pumping. The film is fabricated by a drop cast technique and has a nearly circular shape with a diameter of ∼5 mm. Owing to the inverted photonic glass structure that is air voids in the polymer matrix, light emission from dye molecules is multiple scattering and lasing emission is achieved. In the central area, the film laser works reliably with the lasing threshold of ∼166μJ/mm2 and lasing wavelength of around 595 nm. In the edge area, the lasing properties are more fluctuated indicating that the structure may not be uniform. It is found that the lasing wavelength in the edge area is 4.5 nm red-shifted compared to that in the central area of the film. Interestingly, the thin film laser can operate well under bending conditions with a minor change in the lasing wavelength.

Thin Film Photodetectors Based on Zinc Oxide Nanoinks

Zinc oxide (ZnO) has many useful properties for electronics and optoelectronics including wide band gap, large exciton binding energy, low-cost, ease of processing and availability [1]. This has led to increased interest and development of thin film electronics, transparent conductors, solar cells, light-emitting diodes, lasers, photodetectors and various sensors based on ZnO materials [2, 3]. The high surface areas and tunable properties of ZnO nanostructures make them particularly suitable for applications such as sensing and photonic devices [4, 5].In this work, we present results on nanostructured ZnO thin film photodetectors fabricated using nanoparticle inks (nanoinks) obtained via planetary ball milling (PBM) of bulk powders. PBM [6] is an emerging solution-based nanofabrication approach that can quickly produce nanoink suspensions at low-cost by nanoscale grinding, without complex processing and suitable for thin film coating of various materials on different substrates [7]. The thin film photodetector devices were fabricated by depositing PBM ZnO nanoink onto flat insulating glass substrates followed by contact formation as shown schematically in Fig. 1a: PBM was performed using ZnO powder in ethylene glycol (EG) or deionized (DI) water solvent (a.k.a. colloidal grinding) with zirconia grinding beads. The grinding speed and time were varied between 200 and 1000 rpm and 10 min. and 60 min., respectively. A few μL of the resulting ZnO nanoink was used to coat the substrate surface and dried at ~ 100 °C. Lastly, two electrical contacts to the resulting films were made using silver paint and copper tape. Analysis of ZnO films after deposition showed they consist of nanostructured particles with sizes reaching below 100 nm, as displayed in the scanning electron microscopy (SEM) and atomic force microscopy (AFM) images in Fig. 1b, depending on grinding conditions (speed, time).The optical properties of the ZnO thin films were evaluated via photoluminescence measurements (Fig. 1c), which, in addition to interband transitions in the UV, displayed longer wavelength emission peaks due to surface and bulk defect states. Such deep level states are dependent on grinding parameters and thus allow the accessible spectrum for the nanostructured ZnO films to be extended into the visible region in a tunable manner. Two-terminal photoconductance data of the ZnO PBM nanoink thin film devices were obtained using a probe station and precision source-measure unit, with and without illumination, under ambient atmosphere and at room temperature. Fig. 1d shows current vs. voltage curves obtained for a typical photodetector device, which display current increasing proportional to incident light intensity. This behavior can be explained by electron-hole pair creation and desorption of surface oxygen species (leading to vacancies that act as donors) upon photon absorption, which leads to an increase in conductance. This is consistent with previous studies where ZnO thin films have been used for photoconductive sensor applications, validating PBM nanoink as a suitable synthesis technique for the active material in photodetectors.Compared to standard ZnO thin films, the PBM nanoink method allows both particle dimensions and surface states to be tailored and optimized for different photodetector applications in a straightforward manner by adjusting grinding conditions. In particular, both UV and visible light detection can be tuned via the solution-based ZnO nanoink approach presented without additional material/chemical processing. Such PBM nanoinks thus offer the potential of realizing low-cost photodetectors and multifunctional thin film coatings for applications in optoelectronics, imaging, environmental monitoring and communications.

Enhancing TEM00-Mode Solar Laser With Beam Merging and Ring-Array Concentrator

Abstract It is reported here a large improvement in numerically calculated TEM00-mode side-pumped solar laser efficiency, and brightness figure-of-merit by pumping two thin Nd:YAG laser rods simultaneously with a ring-array solar energy primary concentrator. Two side-pumping configurations were investigated. A single-rod configuration was used to pump a typical single thick laser rod with the full collection area of the ring-array concentrator, and a dual-rod to pump two thin laser rods simultaneously. A three-folding-mirror laser beam merging technique was used, enabling the emission of only one laser beam from the two rods. For the dual-rod single laser beam configuration, 27.50 W continuous-wave TEM00-mode solar laser output power was numerically achieved, corresponding to 16.10 W/m2 TEM00-mode solar laser collection efficiency, 1.70% solar-to-laser power conversion efficiency, 25.00 W brightness figure-of-merit, and 1.54% brightness conversion efficiency, being 1.46, 1.30, 1.75, and 1.40 times, respectively, higher than the previous numerical records, and also 2.04, 1.60, 3.87, and 2.03 times, respectively, more than the previous state-of-the-art experimental records.