mW Laser Research Articles

The safe lowest effective power of subthreshold micropulse laser treatment in Chinese patients with acute or chronic central serous chorioretinopathy

PurposeTo assess the safe, lowest effective laser power of subthreshold micropulse laser (SML) for treating acute and chronic central serous chorioretinopathy (CSC) in Chinese patients.MethodsPatients were distinguished with acute or chronic CSC based on focal or diffuse retinal pigment epithelium (RPE) leakage on fundus fluorescein angiography (FFA), with or without widespread RPE decompensation. Patients were categorized into five groups and treated with 577 nm yellow SML according to 50% titration power. The change of best-corrected visual acuity (BCVA) and central macular thickness (CMT) were set as primary outcomes. A linear regression model assessed the correlation between different factors and outcome indicators.ResultsA total of 103 patients with 127 eyes (61 with acute CSC and 66 with chronic CSC) were enrolled. The baseline characteristics were balanced between the five groups (all p > 0.05). The decrease of CMT and the improvement of BCVA were related to the CMT at baseline (all p < 0.05). We found that the lowest effective laser power for acute CSC was 425 mW (−225.50 μm vs. −171.24 μm vs. −114.50 μm vs. −130.54 μm vs. −68.00 μm, p < 0.001), showing a significant CMT reduction at this power, but no significant increase in BCVA (−0.15 ± 0.10 logMAR vs. −0.20 ± 0.16 logMAR vs. −0.14 ± 0.11 logMAR vs. −0.17 ± 0.30 logMAR vs. −0.11 ± 0.14 logMAR, p > 0.05). For chronic CSC, the lowest effective laser power was 375 mW (p = 0.01), the change of CMT was significant in 375 mW (−93.91 ± 109.06 μm, −119.32 ± 105.56 μm, −88.67 ± 67.26 μm, −60.89 ± 106.86 μm, and −99.11 ± 157.32 μm, p = 0.04). The change of BCVA was similar trend (−0.54 ± 0.66 logMAR vs. −0.17 ± 0.23 logMAR vs. −0.10 ± 0.21 logMAR vs. −0.02 ± 0.30 logMAR vs. 0.05 ± 0.19 logMAR, p < 0.001).ConclusionIn this study, our results suggested 425 mW and 375 mW laser power is the lowest effective SML power for treating acute and chronic CSC in Chinese patients respectively, And the power of SML for chronic CSC requires lower power than acute CSC.

Fabrication of high-quality surface microtextures on GaN by femtosecond laser direct writing

Gallium nitride (GaN), as a third-generation semiconductor, is highly attractive due to its exceptional physical and chemical properties. Laser direct writing offers an efficient method for the precise processing of hard and brittle materials. In this work, various types of surface microtexture were processed on GaN epilayers using a femtosecond laser with a wavelength of 1030 nm. The effects of the laser energy, single-pulse interval, number of pulses, and number of scan passes on groove machining were investigated with a view to achieving high-quality micromachining. The depth, width, surface morphology, and roughness of the grooves were analyzed using scanning electron microscopy, laser scanning confocal microscopy, and atomic force microscopy. Damage and stress were characterized at the microscale using Raman spectroscopy. High-quality precision machining of different types of periodic surface microtexture at 40 mW laser power was achieved by controlling the process parameters and laser trajectory. Finally, an initial exploration was conducted to examine vector-light-based micro- and nanostructure processing. The findings demonstrate the potential of femtosecond lasers for efficient micromachining of hard and brittle materials without the creation of heat-affected zones or microcracks. The high-quality textured structures achieved through this processing technique have broad and promising applications in optoelectronic devices and tribology.

The negative differential resistance of nitrogen implanted TiO2

The microstructure and negative differential resistance (NDR) effect of nitrogen implanted rutile TiO2 were investigated by measuring the XPS, Raman spectra and current voltage curves. It was found that the light illumination has large influence on the NDR effect. Under the illumination of 60 mW laser light, a large NDR with a small electric field (1250 V/cm) is obtained. This electric field is about three orders smaller than that reported in literature (1×106 V/cm). The electric field induced tunneling is the possible mechanism of electric transport at higher field region. The NDR is thought to be related to the light and nitrogen dopant induced reaction including the destroying of water, the scavenging of electron, and the surface oxidation transform of non-stoichiometric TiO2−x to stoichiometric insulating state. The results of this paper are not only useful in understanding the mechanism of NDR, but also useful in providing an effective method in manipulation NDR.

Raman laser intensity and sample clarification on biochemical monitoring over Zika-VLP upstream stages

In the current biopharmaceutical scenario, constant bioprocess monitoring is crucial for the quality and integrity of final products. Thus, process analytical techniques, such as those based on Raman spectroscopy, have been used as multiparameter tracking methods in pharma bioprocesses, which can be combined with chemometric tools, like Partial Least Squares (PLS) and Artificial Neural Networks (ANN). In some cases, applying spectra pre-processing techniques before modeling can improve the accuracy of chemometric model fittings to observed values. One of the biological applications of these techniques could have as a target the virus-like particles (VLP), a vaccine production platform for viral diseases. A disease that has drawn attention in recent years is Zika, with large-scale production sometimes challenging without an appropriate monitoring approach. This work aimed to define global models for Zika VLP upstream production monitoring with Raman considering different laser intensities (200 mW and 495 mW), sample clarification (with or without cells), spectra pre-processing approaches, and PLS and ANN modeling techniques. Six experiments were performed in a benchtop bioreactor to collect the Raman spectral and biochemical datasets for modeling calibration. The best models generated presented a mean absolute error and mean relative error respectively of 3.46 × 105 cell/mL and 35 % for viable cell density (Xv); 4.1 % and 5 % for cell viability (CV); 0.245 g/L and 3 % for glucose (Glc); 0.006 g/L and 18 % for lactate (Lac); 0.115 g/L and 26 % for glutamine (Gln); 0.132 g/L and 18 % for glutamate (Glu); 0.0029 g/L and 3 % for ammonium (NH4+); and 0.0103 g/L and 2 % for potassium (K+). Sample without conditioning (with cells) improved the models' adequacy, except for Glutamine. ANN better predicted CV, Gln, Glu, and K+, while Xv, Glc, Lac, and NH4+ presented no statistical difference between the chemometric tools. For most of the assessed experimental parameters, there was no statistical need for spectra pre-filtering, for which the models based on the raw spectra were selected as the best ones. Laser intensity impacts quality model predictions in some parameters, Xv, Gln, and K+ had a better performance with 200 mW of intensity (for PLS, ANN, and ANN, respectively), for CV the 495 mW laser intensity was better (for PLS), and for the other biochemical variables, the use of 200 or 495 mW did not impact model fitting adequacy.

(Invited) Optical Probes for Resonance-Enhanced Gold Growth on Nanooptical Substrates

We investigate light-stimulated growth of gold metal lines to technically mimic the growth of long-range axonal connections for neuromorphic computing architectures. Photocatalytic gold growth from an aqueous gold chloride precursor solution (HAuCl4) on a photoactive titanium dioxide layer is used. It is known that local gold growth may be obtained by UV illumination through a shadow mask [1]. To obtain a wavelength and angle dependent growth of metal lines – and thus stimulus-dependent resistances – we suggest to employ a nanooptical template. Inspired by the typical number of 2 to 10 connections to a node found, e.g., in the neuronal system of the biological species Hydra, we decided on the implementation of a hexagonal design. The edges are formed by periodic grating nanostructures with 10 to 20 periods and a grating pitch of 170 nm to 210 nm for excitation in the UV. In order to investigate the resonant optical enhancement, we employ optical probes. It is well known that colloidal quantum dots show enhanced fluorescence emission on photonic crystal surfaces due to resonant excitation and resonant outcoupling [2]. In our initial experiments for investigation of the resonant enhancement, we use 4,4’-Bis(2,2-diphenylvinyl)-1,1’-biphenyl (DBVBi) as the emitter material. Its absorption maximum matches the excitation laser at 355 nm and fluorescence in the visible spectrum around 455 nm may be monitored with our camera and spectrometer setup.The nanostructure master was fabricated by electron-beam lithography (Kelvin Nanotechnology Ltd.) according to our design. We transfer the nanostructure pattern onto 1.1 mm thick soda-lime glass substrates by UV-nanoimprint lithography. Subsequently, a 100 nm titanium dioxide layer is deposited. The 150 nm emissive DBVBi layer is then added by thermal evaporation. The samples are characterized optically with a camera setup and magnifying optics on an in-plane rotatable xy-stage. We use a Cobolt Zouk 355 nm 10 mW laser to excite the emissive layer. The output power of the laser is set to 2 mW and its output beam is widened with a collimating lens setup to a diameter of approximately 1.5 mm². The widened beam is essential to obtain a homogeneous excitation. We observe the successful resonant excitation by the higher emission intensity of DPVBi in specific regions of the nanostructure at specific excitation angles. Already for 10 periods of the grating structure resonance effects are observed. A stronger enhancement is obtained for 20 periods. Further, the enhancement depends on the grating pitch as connections with nanograting pitches below 190 nm are no longer visible. They do not meet the criteria for resonant excitation.This method of using optical probes on the nanooptical template works well for initial characterization of the resonance enhancement at different excitation angles. Now the setup is ready for performing gold growth under different excitation conditions. Without the additional emissive layer, the waveguide thickness change needs to be compensated with an increased titanium dioxide layer thickness. For online monitoring of the resonant enhancement during growth optical probes may be employed below the photoactive titanium dioxide layer. It is expected that the resonance enhancement is reduced with the addition of gold due to the increased absorption and thus reduced quality factor as was previously studied in the context of nanostructured OLEDs [3].We acknowledge funding by the DFG (German Research Foundation) with the CRC 1461- Neurotronics (Project-ID 434434223 – SFB 1461).[1] S. Veziroglu et al. (2018). Photocatalytic growth of hierarchical au needle clusters on highly active TiO2 thin film. Advanced Materials Interfaces, 5(15), 1800465.[2] N. Ganesh et al. (2007). Enhanced fluorescence emission from quantum dots on a photonic crystal surface. Nature nanotechnology, 2(8), 515-520.[3] J. Buhl et al. (2023). Resonance‐Based Directional Light Emission from Organic Light‐Emitting Diodes: Comparing Integrated Nanopatterns and Color Conversion Waveguide Gratings. Advanced Photonics Research, 4(2), 2200143. Figure 1. (Left) Fluorescence image of optical probe layer on nanooptical substrate for 355 nm laser excitation. (Middle) Schematic of nanooptical substrate with grating pitch (in nm) and number of periods given. Same colors represent identical grating features. (Right) Field emission scanning electron microscopy (FESEM) image of one node with 6 connections. Figure 1

The effect of different parameters of low-level laser used in the treatment of oral mucositis, on the viability and apoptosis of oral squamous cell carcinoma cells: Invitro study.

Oral mucositis is a complication of chemo/radiotherapy. To assess the impact of various power levels of diode-laser on the survival and expression of apoptosis-related genes in oral cancer cells, it is crucial to consider the potential existence of malignant cells within the treatment region and the reliance of laser effectiveness on its specific characteristics. Cal-27 cells were cultivated and exposed to a 660 nm-diode-laser at power levels of 20, 40, and 80 mW, alongside non-irradiated control cells. Viability and expression of Bax and Bcl-2 mRNA were assessed with Methyl Thiazolyl Tetrazolium (MTT) and Real-time Polymerase Chain Reaction (RT-PCR), respectively. The results were analyzed using one-way ANOVA and Tukey post-hoc test (p < 0.05). A significant reduction in viability was found only in the 20 mW group compared to controls (p = 0.001). Cell survival was significantly lower in cells receiving 20 mW laser than those treated with 40 and 80 mW (p < 0.05). None of the laser groups showed significant changes in BcL-2, but Bax was significantly lower in cells receiving 40 and 80 mW (p < 0.05), compared to controls. Laser irradiation at 660 nm (2 J/cm2, 30 s) significantly reduced the viability of oral cancer cells when using 20 mW power. These specifications align with the recommendation that the lowest possible laser dose should be applied for treating cancer patients. The exact mechanism of cell death following laser therapy with these specifications requires further investigation.

Long-Term Continuous Gas Diagnostics For Fuel Cell Systems: Development Of An Automatized Raman Metrology

Knowledge of the composition of gas flows in fuel cell systems is crucial for their understanding. In current research, this data is rarely recorded inline and in real-time due to the lack of suitable metrology. Here, we present an optical gas sensor. Green light (532 nm) from a 450 mW laser excites Raman scattering. A spectrometer analyzes the scattered light and a Python software extracts gas composition data automatized and in real-time. We designed a measurement cell that allows optical inline access to gas flow systems and is easy to implement. Therefore, common signal enhancement methods with more complex setups can not be applied. Literature data on scattering cross sections does not offer a reliable basis for calibration what constitutes the need for a gas conditioning system that allows fast preparation of well defined mixtures. We used it to present two principles of calibration. First, calibration based on relative scattering cross sections is the more stable possibility, because it is still valid in cases where laser power and integration time are changed. However, in consequence the results for one species are not independent from the other species. A poor signal, e.g. following from a low mole fraction in a single component, will introduce uncertainty in all components. We avoid that problem through direct linear correlation of signal strength of one species to its partial pressure, which is the second calibration variant. In this case, there is an influence of laser power and integration time. The additional information on overall pressure can be used in model systems, where the presence of undetected components can be ruled out. We can compare that information to pressure measurements to do plausibility checks on the Raman results in real-time. We apply the sensor in fuel cell system research, where measurement intervals of one second yield results of sufficient precision. Increasing integration time can further decrease the uncertainties where favorable. The measurement and data evaluation routines work stable and constant enough to monitor gas compositions in longterm operation. To date, the sensor can measure mixtures of nitrogen, oxygen, hydrogen and water vapor.

Behaviour quantification of Sm3+ in borotellurite glass phosphors for warm-colour illumination

Lighting in unconventional environments is closely related to eye health and circadian rhythms, making it essential for warm-colour light sources to align with technological advancements in solid-state lighting. Herein, warm light in spectral region over 550 nm is realised in Sm3+ doped multicomponent borotellurite (MBT-Sm) glass phosphors as colour converters for LEDs/LDs and their luminescent behaviours are quantified in detail. MBT-Sm glass phosphors standout for their high transparency and the large absorption/emission cross-section, with high quantum efficiency of 84.1 % and quantum yield of 19.15 % under violet LED excitation, and a high luminous flux of 3.33 lm under 50 mW laser. Remarkably, it not only possesses superior colour performance with the correlated colour temperature below 2000 K and colour purity up to 99.8 %, but also shows excellent heat resistance of luminescence. MBT-Sm glass phosphors show promising applications as colour conversion materials in innovative lighting technology.

Exploring the role of impedance spectroscopy in assessing 405nm laser-induced inactivation of saccharomyces cerevisiae.

Impedance spectroscopy was employed to assess the electrical properties of yeast following 405nm laser irradiation, exploring the effects of visible, non-ionizing laser-induced inactivation as a more selective and safer alternative for photoinactivation applications compared to the use of DNA targeting, ionizing UV light. Capacitance and impedance spectra were obtained for yeast suspensions irradiated for 10, 20, 30, and 40min using 100 and 200 mW laser powers. Noticeable differences in capacitance spectra were observed at lower frequencies (40Hz to 1kHz), with a significant increase at 40min for both laser powers. β-dispersion was evident in the impedance spectra in the frequency range of 10kHz to 10MHz. The characteristic frequency of dielectric relaxation steadily shifted to higher frequencies with increasing irradiation time, with a drastic change observed at 40min for both laser powers. These changes signify a distinct alteration in the physical state of yeast. A yeast spot assay demonstrated a decrease in cell viability with increasing laser irradiation dose. The results indicate a correlation between changes in electrical properties, cell viability, and the efficacy of 405nm laser-induced inactivation. Impedance spectroscopy is shown to be an efficient, non-destructive, label-free method for monitoring changes in cell viability in photobiological effect studies. The development of impedance spectroscopy-based real-time studies in photoinactivation holds promise for advancing our understanding of light-cell interactions in medical applications.

Effect of the Photoexcitation Wavelength and Polarization on the Generated Heat by a Nd-Doped Microspinner at the Microscale.

Thermal control at small scales is critical for studying temperature-dependent biological systems and microfluidic processes. Concerning this, optical trapping provides a contactless method to remotely study microsized heating sources. This work introduces a birefringent luminescent microparticle of NaLuF4:Nd3+ as a local heater in a liquid system. When optically trapped with a circularly polarized laser beam, the microparticle rotates and heating is induced through multiphonon relaxation of the Nd3+ ions. The temperature increment in the surrounding medium is investigated, reaching a maximum heating of ≈5 °C within a 30 µm radius around the static particle under 51 mW laser excitation at 790 nm. Surprisingly, this study reveals that the particle's rotation minimally affects the temperature distribution, contrary to the intuitive expectation of liquid stirring. The influence of the microparticle rotation on the reduction of heating transfer is analyzed. Numerical simulations confirm that the thermal distribution remains consistent regardless of spinning. Instead, the orientation-dependence of the luminescence process emerges as a key factor responsible for the reduction in heating. The anisotropy in particle absorption and the lag between the orientation of the particle and the laser polarization angle contribute to this effect. Therefore, caution must be exercised when employing spinning polarization-dependent luminescent particles for microscale thermal analysis using rotation dynamics.

Enhanced upconversion emission in Nd, Yb, Er and Ho tetra-doped Y2O3 phosphor

Yb3+, Nd3+, Er3+ and Ho3+ tetra ions doped Y2O3 upconversion phosphors have been prepared by the combustion route. Crystalline phase purity and cubic phase of prepared samples have been confirmed from powder X-ray diffraction study. Absorbance of samples over spectral range 200–1100 nm has been measured by diffuse reflectance spectroscopy. All samples exhibit large band gaps. Scanning electron micrograph analysis reveals spherical morphology of particles and sizes around 200 nm. Upconversion emission has been studied under a 980 nm diode laser excitation with 166 mW laser power. The Ho3+, Nd3+ and Yb3+ co-doped Y2O3 phosphor show very high emission intensity of a green band centred at around 550 nm and another moderate intensity red band centred on 667 nm, while reverse is the case for Er3+, Nd3+ and Yb3+ co-doped Y2O3 phosphor. Er3+, Ho3+, Nd3+ and Yb3+ co-doped Y2O3 phosphor show enhanced high emission intensity in both green and red bands. These two bands are not visible in Nd3+ and Yb3+ co-doped Y2O3 phosphor but show weak upconversion emission at 549, 568 and 799 nm. Owing to the high emission intensity of green band, Ho3+, Nd3+ and Yb3+ co-doped Y2O3 phosphor may find potential applications in medical and security, while Er3+, Ho3+, Nd3+ and Yb3+ co-doped phosphor showing enhanced upconversion in green and red bands may find applications in white light generation.

Diagnosis of multiple gases using a multi-pass ring cavity to enhance Raman scattering

Spontaneous Raman scattering is widely used to enable simultaneous concentration measurements of all relevant species with overcomes whose signal is weak and susceptible to fluorescence interference. A multi-pass ring-cavity scheme is proposed to enhance Raman scattering signal. The Raman spectra of CO2, N2, O2 and H2O in the air are acquired under condition of low excitation power which is 200 mW laser of 532 nm. Compared with the results obtained by single collection without ring cavity, the Raman signal level is enhanced 40 times and the signal-to-noise ratio is improved by 43 times at maximum. Power of pump is taken into consideration to analyze its impact on signal. A limit of detection (3σ criterion standard) of 83 ppm for CO2 is calculated for the multi-pass ring-cavity. The limit of detection of 14 ppm for CH4 is also estimated by the theoretical ratio of cross section values of CO2 and CH4. When power of excitation is low, high level of signal of multi-species gases is acquired with fine detection sensitivity through ring cavity.

Super-Resolution Diamond Magnetic Microscopy of Superparamagnetic Nanoparticles.

Scanning-probe and wide-field magnetic microscopes based on nitrogen-vacancy (NV) centers in diamond have enabled advances in the study of biology and materials, but each method has drawbacks. Here, we implement an alternative method for nanoscale magnetic microscopy based on optical control of the charge state of NV centers in a dense layer near the diamond surface. By combining a donut-beam super-resolution technique with optically detected magnetic resonance spectroscopy, we imaged the magnetic fields produced by single 30 nm iron-oxide nanoparticles. The magnetic microscope has a lateral spatial resolution of ∼100 nm, and it resolves the individual magnetic dipole features from clusters of nanoparticles with interparticle spacings down to ∼190 nm. The magnetic feature amplitudes are more than an order of magnitude larger than those obtained by confocal magnetic microscopy due to the narrower optical point-spread function and the shallow depth of NV centers. We analyze the magnetic nanoparticle images and sensitivity as a function of the microscope's spatial resolution and show that the signal-to-noise ratio for nanoparticle detection does not degrade as the spatial resolution improves. We identify sources of background fluorescence that limit the present performance, including diamond second-order Raman emission and imperfect NV charge state control. Our method, which uses <10 mW laser power and can be parallelized by patterned illumination, introduces a promising format for nanoscale magnetic imaging.

Near infrared low-level laser effect on electron radiation therapy of non-melanoma human squamous cell cancer: An in-vitro study

PurposeThe aim is to assess the efficacy of combined electron-laser radiation therapy on non-melanoma Squamous cell carcinoma (SCC) cancer cells in an in-vitro model. Material and methodsThe human SCC cancer line (TSCC-1) was purchased from the Iranian Biological Resources Center (IBRC) and cultured according to the standard protocol. The groups of this study were control; only electron radiation; only Low-Level Laser Therapy (LLLT); and combined laser-electron radiation. Irradiation with a 980 nm 50 mW laser was performed in a single session with energy doses of 1 and 1.5 J/cm2. Electron radiation was carried out using a Varian accelerator with a radiation dose of 2 and 4 Gy. 24 h after laser treatment of cancer cells, combined electron irradiation was performed. MTT and flow cytometry bioassays were performed and analyzed to check their effectiveness. ResultsThe cell viability assay for irradiation with 980 nm 50 mW NIR laser in a single session with an irradiation time of 20 and 30 s in combination with 2 and 4 Gy electrons showed a significant difference (P-value <0.01). Flow cytometry test of the electron-radiated samples showed that the sum of early and late apoptosis was the highest. However, for the combination of electron-laser radiation of 30 s with 2 and 4 Gy electrons, the maximum percentage of apoptosis and necrosis was obtained close to the electron alone. Except for the control group, the quantitative interval of induced necrosis of all the groups evaluated by electron alone, laser alone, and combined electron laser was almost equivalent. ConclusionsThis study showed that the physical parameters of a 980 nm NIR LLLT might not have a synergy effect on treatment response in combination with an electron ionizing beam on SCC cancer cells. It is critical to consider the effect of light irradiation parameters for combination therapy in more extensive studies.

High energy laser &amp; systems to neutralise stellar coronal mass ejections (CME) plasma

With CME plasma and shockwave travelling at 600+ km/sec, active methods such as high energy electron lasers (HEL) and mirrors are effective at making contact with ionised atoms in CME. Electrons pulsed from kW to MW laser(s) could polarise ionised atoms such as Fe16+, O7/8+, Mg, He2+,etc to fill valence pairs. As high-FIP atoms are electromagnetically trapped with a higher susceptibility from lower e- density and temperatures, CME plasma clouds can be neutralised, separated, and reduced in velocity trajectory around planet. Study outlines interactions between Electron Laser and CME plasma cloud, orbital geometry, build of high energy lasers, subsystems, as well as recoils, and cloud charge dynamics with e- interactions to neutralise CME particles. Additional space-based systems are designed such as mirrors in closer orbit to align lower velocity light beams. In approaching higher electron recombination and FIP ionisation of laser-plasma ion cluster density, max absorption of e- to CME could be approached with similar beam, CME, mirror angles and alignment, where e- couple and fill valence shells. Models evaluate efficacy of coherent laser beams of charged electrons, X-rays, infrared (IR), and/or electron/radio Hz to polarize CME column charge densities, with optimal CME scatter geometry and time window. Low cost ground experiments are discussed. Models suggest every ~1 km gap laser creates when CME t=8.255min creates a 10,067 km gap for Earth to orbit through. Such a HEL laser, reflecting mirrors, and space systems could neutralize plasma CME Cloud within 92.818M mi (Sun-Earth distance) and mitigate effects and trillion dollar costs from Carrington-type CME flares, and supernovae.

Chemical States of Water in Anion Exchange Membrane for Fuel Cells Using Raman and Coherent Anti-Stokes Raman Spectroscopies

Purpose Low membrane durability remains a major challenge in anion exchange membrane fuel cells (AEMFCs). This is despite the AEMFCs’ proven potential to eliminate the dependency of Fuel cells on Pt catalysts and bring about the mass commercialization of the technology. This problem can be effectively addressed through combined optimization of the AEMFCs’ operating conditions during evaluation, followed by finetuning of the membrane chemistry to address any observed weaknesses. After synthesis, water distribution is the primary operation condition determining a given AEM’s performance and lifespan [1]. This is partly because water affects the ionic conductivity and, thus, maximum current density, which is known to play a significant role in the longevity of membranes. Therefore, establishing the water distribution during power generation for any given membrane is highly desirable. For this to happen, suitable and reliable techniques must exist to measure and compare the water distribution in situ and operando. In this paper, we used in-house assembled Raman spectroscopy and coherent anti-Stokes Raman scattering spectroscopy (CARS) systems to measure the water in an operational AEMFC for the first time. CARS comes with a high time resolution of 0.1 s, which is essential in the transient response study of FCs. Experimental Method QPAF-4 membrane film (Fig. 1) of the thickness of 30 µm and IEC of 2.0 meq g-1 was solution cast as reported [2]. The cell was then assembled, as reported [3]. An airtight transparent quartz window 200 μm thick was mounted at the cathode endplate for optical access to the QPAF-4 membrane through a 500 mm pinhole in the GDE. A thin Pt disk was placed on the opposite side of the membrane to reflect the signal to the spectrometer through the ×50 objective lens used. For Raman spectroscopy, a 632 nm, 1 mW laser with 5.5 min total exposure was used. For CARS, an 11 mW 785nm pump laser and 16 mW Stokes laser with 200 ms total exposure were used. The flow rate was 100 ml min-1 for all gases. The cell temperature was maintained at 60 °C. The relative humidity of the gas varied from 30% to 100% in steps of 10% RH. The system was allowed to stabilize for 3 hours at each humidity level before measurement. Results and discussion Figures 2 and 3 show the normalized in situ spectra recorded at the center of the membrane at different relative humidity values using CARS and Raman, respectively. The peak positions are comparable. However, the OH peak in CARS is taller relative to C=C than in Raman. CARS signal intensity is generally stronger than Raman [3]. Within the CARS peak, the purely OH portion of the signal is more prominent relative to the rest of the peak than in Raman. This is attributed to the fact that the Infrared laser associated with the stokes light (817-1144nm) of CARS is known to be more sensitive to OH vibration than the lower wavelength laser (632nm) used in Raman [4]. Conclusion We successfully developed a 785nm CARS system capable of operando water measurement in AEMFCs. The results from this technique are comparable to those from micro-Raman spectroscopy but with better signal intensity and time resolution. This increases the number of practical methods available to researchers interested in measuring water content in AEMFCs allowing for faster development of the technology. The water distribution results during power generation will be discussed at the conference. With CARS, higher temporal/time resolution is achieved, which is advantageous when cell response needs to be studied.

(Invited) Direct Laser Induced Gold Wiring of 2D Materials with Sub-Μm Resolution

One of the most influential technologies of our modern world are integrated electronics. Almost all parts of our daily life include some bearing with any kind of electrical technologies. The fabrication methods itself, for integrated miniatured electrical devices have had not much innovation in terms of production. Several processing steps still mainly consist of different kinds of lithography. This situation may change with new challenges on the production of smaller quantities with specialized functions, or the use of temperature critical or atomically thin surfaces, where the thermal evaporation of metals damages the sample.For some decades now, printing of all types of electronics have gained great attraction. While lithography is a time-consuming multi-step process (including resist preparation, illuminating, developing, evaporation and lift-off) with expensive and harmful photoresists and harsh environmental conditions (high-vacuum and thermal treatments), ink printing allows for direct and simple application of the desired structures [1]. Two main types of inks are typically applied: colloidal solutions of metal nanoparticles [2, 3] or metal-organic precursor solutions [4]. In both cases, thermal curing after deposition is required to achieve metallic conduction. To this end, laser writing is often advantageous over thermal sintering due to the overall lower thermal stress applied to the material, particularly on flexible, thermally sensitive substrates [5] whereas metal nanoparticles suffer from a relatively high photothermal stability and the need for a large laser power to achieve sufficient sintering [3]. In contrast, metal-organic precursor solutions feature a relatively low metal content (≤34 wt-%)10, and undergo large volume contractions during laser writing. These challenges have so far prevented the definition of metallic gold contacts with diffraction-limited feature sizes by ink printing and laser writing.Here, we introduce atomically-precise, metalloid Au32(nBuP12Cl8) nanoclusters (Au32NCs) [6] as an ink for resistless, direct laser writing of metallic gold micro- and nanostructures. The unique advantages of this ink over Au nanoparticles or typical metal-organic Au precursors are their high photosensitivity in combination with a large gold content of 70 wt-%. This allows for writing gold structures with feature sizes of 250 nm and line spacings < 200 nm using 1.86 mW laser power at 488 nm with a scan speed of 0.1 mm/s. We apply this method on a wide range of substrates, including flexible polymer membranes, find metallic conductance with conductivities ~ 1 × 106 S/m and demonstrate that defining such Au contacts on two-dimensional semiconductors results in fully functional optical switches and field effect transistors made out from 2D materials.[1] Raut NC. et al., Jour. Mat. Chem. C 2018, 6(7): 1618-1641.[2] Ko E. et al., Nanotechnology 2007, 18(34): 345202.[3] Hong S. et al., ACS Nano 2013, 7(6): 5024-5031.[4] Schoner C et al., Thin Solid Films 2013, 531: 147-151.[5] Skylar-Scott MA et al., PNAS 2016, 113(22): 6137-6142.[6] Kenzler S et al., Angew. Chem. Int. Ed. 2019, 58(18): 5902-5905. Figure 1

High-power, single-frequency mid-infrared laser based on a hybrid Fe:ZnSe amplifier

This study proposes a high-power, single-frequency mid-infrared laser based on a quantum cascade laser (QCL) seeded Fe:ZnSe amplifier design. The Fe:ZnSe amplifier is injection-seeded with a 55-mW, 4.3-μm distributed feedback QCL and can produce 390 mW laser output with an extraction efficiency of 14%, a beam quality factor of M2 ∼ 1.1, and a spectral linewidth of 29.6 MHz. Further, this study presents a theoretical analysis predicting the laser performance of the optimized amplifier system. The prospects for further improvement in performance and extension of the tuning capability are discussed.

Photothermal Conversion Efficiency of Silver and Gold Incorporated Nanosized Apatites for Biomedical Applications.

The aim of this research was to investigate the photothermal ability of nanocrystalline hydroxyapatite (nHAp) incorporated with silver and gold. It was studied by using a recently developed technique evaluating the photothermal conversion efficiency. The heating performance of aqueous dispersions was examined under 445 and 532 nm excitation. The largest increase in temperature was found for the 2% Ag-nHAp and reached above 2 °C per mg/mL of sample (445 nm) under 90 mW laser continuous irradiation and an external light-to-heat conversion efficiency of 0.11 L/g cm. The obtained results have shown a new functionality of nanosized apatites that has not been considered before. The studied materials have also been characterized by XRPD, TEM, BET, and UV-Vis techniques. Finally, in this work, a new idea for their application was proposed: photothermal therapy.

Nonlinear effects in optical trapping of titanium dioxide and diamond nanoparticles

Optical trapping in biophysics typically uses micron-scale beads made of materials like polystyrene or glass to probe the target of interest. Using smaller beads made of higher-index materials could increase the time resolution of these measurements. We characterized the trapping of nanoscale beads made of diamond and titanium dioxide (TiO2) in a single-beam gradient trap. Calculating theoretical expectations for the trapping stiffness of these beads, we found good agreement with measured values. Trap stiffness was significantly higher for TiO2 beads, owing to notable enhancement from nonlinear optical effects, not previously observed for continuous-wave trapping. Trap stiffness was over 6-fold higher for TiO2 beads than polystyrene beads of similar size at 70 mW laser power. These results suggest that diamond and TiO2 nanobeads can be used to improve time resolution in optical tweezers measurements.