Graphitisation of Waste Carbon Powder with Femtosecond Laser Annealing

Graphitisation of structural characteristics and improvement in electrical conductivity was reported onto waste carbon powder through femtosecond laser annealing. Raman spectroscopy on the carbon powder pre- and post-annealing showed a shift from amorphous-like carbon to graphitic-like carbon, which can be explained by the three-stage model. Electrical I-V probing of the samples revealed an increase in conductivity by up to 90%. An increase in incident laser power was found to be correlated to an increase in conductivity. An average incident laser power of 0.104 W or less showed little to no change in electrical characteristics, while an average incident laser power of greater than 1.626 W had a destructive effect on the carbon powder, shown through the reduction in powder. The most significant improvement in electrical conductivity has been observed at laser powers ranging from 0.526 to 1.286 W. To conclude, the graphitisation of waste carbon powder is possible using post-process femtosecond laser annealing to alter its electrical conductivity for future applications.

Фотопреобразователь лазерного излучения на основе GaInP с КПД 46.7% на длине волны 600 nm

GaInP-based laser power converters (LPC) structure grown by MOVPE and device chip design have been optimized for operation under high-power lasers of the green-red spectral range. Light IV curves records have shown the performance of the LPC up to 40-50 W/cm2 of incident power densities. The highest level data were obtained for 532 nm, 600 nm, and 633 nm power laser lines: 44.3%, 46.7%, and 40.6% under 13-16 W/cm2, respectively. LPC demonstrated an efficiency of more than 40% at elevated up to 40-50 W/cm2 of the incident laser power density.

Experiments And Simulations of Thermometric Lateral Flow Immunoassay For Point-of-Care Testing

Temperature sensing is a promising method of enhancing the detection sensitivity of lateral flow immunoassay for point-of-care testing. A temperature increase of more than 100 °C can be readily achieved by photoexcitation of reporters like gold nanoparticles (GNPs) or colored latex beads (CLBs) on the strips with a laser power below 100 mW. Despite its promise, processes involved in the photothermal detection have not yet been well-characterized. Here, we provide a fundamental understanding of this thermometric assay by combining experiments and simulations using non-fluorescent CLBs as the reporters deposited on nitrocellulose membrane. By measuring the dependence of temperature rises on the number density of membrane-bound CLBs, we determined a 1.5-fold enhancement of the light absorption at 520 nm by the beads (diameter of 0.4 μm). The enhancement, however, was compromised by a 5-fold reduction of the incident laser power due to multiple scattering of the light in this highly porous medium. The limit of detection was measured to be 1 × 105 particles/mm2. In line with previous studies using GNPs as the reporters, the CLB-based thermometric assay provides a 10× higher sensitivity than color visualization, as demonstrated with the immunoassay for nucleocapsid proteins of the SARS-CoV-2 virus.

Pulsed-laser source characterization in laboratory seismic experiments

The present study aimed to characterize the properties of a laser-generated seismic source for laboratory-scale geophysical experiments. This consisted of generating seismic waves in aluminum blocks and a carbonate core via pulsed-laser impacts and measuring the wave-field displacement via laser vibrometry. The experimental data were quantitatively compared to both theoretical predictions and 2D/3D numerical simulations using a finite element method. Two well-known and distinct physical mechanisms of seismic wave generation via pulsed-laser were identified and characterized accordingly: a thermoelastic regime for which the incident laser power was relatively weak, and an ablation regime at higher incident powers. The radiation patterns of the pulsed-laser seismic source in both regimes were experimentally measured and compared with that of a typical ultrasonic transducer. This study showed that this point-like, contact-free, reproducible, simple-to-use laser-generated seismic source was an attractive alternative to piezoelectric sources for laboratory seismic experiments, especially those concerning small scale, sub-meter measurements.

Simulation of the Thermal Aberration of Fused Silica Reflective Optics Under High-power Laser Irradiation

The output beam quality of high-power laser systems is limited by laser-induced thermal aberration of fused silica reflective optics. A numerical model for the simulation of thermal aberration was proposed and verified by the experimental results. Simulations on the thermal aberration of fused silica optics under 3~10 kW laser irradiation with laser beam diameters of 5 mm ~ 45 mm were carried out with the verified model. The simulation results showed that the peak-valley (PV) value of thermal aberration increases with increasing incident laser power under the same incident laser spot size and reduces with increasing incident laser spot size under the same incident laser power. There are the same PV values of thermal aberration under different incident power or power densities. An analytic formula of thermal aberration PV as a function of incident laser power and beam spot size was proposed. The analytic results are in good agreement with the simulations. With these conclusions, the thermal aberration of fused silica optics under high incident power and power density can be evaluated by that under low incident power and power density. It is helpful for the design of high-power laser systems to obtain reasonable output beam quality.

Fabrication and Characterization of Near Infrared Molybdenum Disulfide/Silicon Heterojunction Photodetector by Drop Casting Method

In this work, a highly efficient, molybdenum disulfide (MoS2) based near infrared (NIR) heterojunction photodetector is fabricated on a Si substrate using a cost-effective and simple drop casting method. A non-stoichiometric and inhomogeneous MoS2 layer with a S/Mo ratio of 2.02 is detected using energy dispersive X-ray spectroscopy and field emission scanning electron microscope analysis. Raman shifts are noticed at 382.42 cm-1 and 407.97 cm-1, validating MoS2 thin film growth with a direct bandgap of 2.01 eV. The fabricated n-MoS2/p-Si photodetector is illuminated with a 785 nm laser at different intensities, and demonstrate the ability of the photodetector to work in both regions, the forward biased and reverse biased from above 1.5 V and less than -1.0 V. The highest responsivity, R is calculated to be 0.52 A/W while the detectivity D* is 4.08 x 10^10 Jones for an incident light intensity of 9.57 mW/cm2. The minimum rise and fall times are calculated as 1.77 ms and 1.31 ms for an incident laser power of 9.57 mW/cm^2 and 6.99 mW/cm^2 respectively at a direct current bias voltage of 10 V. The demonstrated results are promising for the low-cost fabrication of a thin MoS2 film for photonics and optoelectronic device applications.

Silicon twisted cone structure produced by optical vortex pulse with structure evaluation by radiation hydrodynamic simulation

We demonstrate a radiation hydrodynamic simulation of optical vortex pulse-ablated microcone structures on silicon (Si) substrates. Doughnut-shaped craters were formed by single pulse irradiation on the Si substrate, and a twisted cone structure with a height of 3.5 µm was created at the center of the irradiation spot by the circularly polarized optical vortex pulse. A two-dimensional (2-D) radiation hydrodynamic simulation reproduced the cone structure well with a height of 3 µm. The central part of the incident laser power was lowered from the initial profile due to plasma shielding over the laser pulse duration for an inverted double-well laser profile. The acute tip shape of the silicon surface can survive over the laser irradiation period.

Effects of Fabrication Parameters on the Properties of Parts Manufactured with Selective Laser Sintering: Application on Cement-Filled PA12

Selective laser sintering (SLS) becomes a promising technology for manufacturing complicated objects with small to moderate numbers from a wide range of polymeric and metallic powders. However, the fabrication parameters in the SLS process need to be tailored for each end-use fabricated product. Hence, it becomes extremely important to investigate the effects of fabrication parameters on the mechanical and morphological properties of SLS parts. For this purpose, the present experimental work is devoted to evaluating the effects of some important fabrication parameters, that have not received proper attention in the published literature, on the properties of cement-filled polyamide 12 (PA12) parts manufactured with the SLS technique. The effect of scanning vector length on the tensile, compressive, and flexural strength of manufactured PA12/white cement parts is investigated. Also, the end-of-vector (EOV) effect on the edge geometry of manufactured parts is studied. Moreover, the effect of incident laser power (LP) on the surface quality of fabricated SLS PA12/white cement parts is qualitatively evaluated. The results from this work revealed that the scanning vector length significantly affects the mechanical properties of SLS parts provided that the load is applied along the scanning vector direction. Also, it is noticed that excessive exposure to laser energy at layer edges can deteriorate the part’s edge and in some cases can cause localized heating and burning of the part’s edge and, eventually, can result in surface microcracks. Finally, the experiments confirmed that increasing the laser power can enhance the surface roughness of manufactured parts; however, excessive increase in laser power causes localized burning and initiation of surface microcracks.

A tunable positive and negative photoconductive photodetector based on a gold/graphene/p-type silicon heterojunction

Fast switching of positive and negative photocurrents of a device under the modulation of different incident laser power densities.