Solar-pumped lasers (SPLs) rely primarily on solar energy without the need for electrical power, which directly converts sunlight into laser. In this work, three end-side-pumping configurations were numerically investigated using a Ring-Array Concentrator (RAC) with an effective collection area of 0.785 m(2). The first configuration employed a single Nd:YAG rod (4 mm diameter, 16 mm length), achieving a collection efficiency (CE) of 49.1 W/m(2), a solar-to-laser conversion efficiency (SLCE) of 4.9%, and a slope efficiency of 6.1% under 1000 W/m(2) solar irradiance. However, thermal stress reached 182.5 N/mm(2), close to the fracture limit. To overcome this, a second configuration using four thin Nd:YAG rods (2 mm diameter, 16 mm length each) was designed, distributing the concentrated solar energy among four rods. This configuration achieved a total laser power of 43.9 W (CE = 55.9 W/m(2), SLCE = 5.59%, slope efficiency = 6.45%), while significantly reducing thermal stress to 44.92 N/mm(2) and maximum temperature to 326.6 K. Finally, to maximize efficiency, the active material was replaced with Ce:Nd:YAG (0.1 at. % Ce, 1.1 at.% Nd) while maintaining the same four-rod geometry. Under 890 W/m(2) solar irradiance, this configuration produced a record total laser power of 56.4 W (14.1 W per rod), corresponding to a CE of 71.3 W/m(2), an SLCE of 8.09%, and a slope efficiency of 9.33%, which are 1.73, 1.74, and 1.22 times higher, respectively, than the previous records by Liang et al. (41.25 W/m(2) and 4.64%) using three Ce:Nd:YAG rods. Thermal stress remained within safe limits at 75.79 N/mm(2). These results demonstrate that the four-thin-rod Ce:Nd:YAG configuration with an RAC concentrator offers an optimal balance between high efficiency and acceptable thermal stress, providing a practical and scalable solution for high-power solar lasers.
This study presents the design and analysis of a highly sensitive surface plasmon resonance (SPR) biosensor based on a graphene-SiO2 hybrid structure. Utilizing a prism-coupled configuration, the sensor incorporates a SiO2 dielectric layer and a few-layer graphene film deposited on a gold film to substantially enhance the localized electromagnetic field and biomolecule capture efficiency at the sensing interface. The effects of key structural parameters-including the number of graphene layers, SiO2 thickness, and gold film thickness-on sensor performance were systematically investigated. An optimized sensitivity of 220 degrees/RIU was achieved with a five-layer graphene configuration at an analyte refractive index of 1.39, representing a 175% improvement over conventional SPR sensors. Electromagnetic field analysis revealed that localized field enhancement near the graphene edges is the primary mechanism driving this sensitivity improvement. The proposed sensor exhibits excellent responsiveness and stability across a broad refractive index range of 1.33-1.39, providing a high-performance platform for precise biochemical detection.
Underwater optical wireless communication (UOWC) offers high-bandwidth alternatives to acoustic systems but faces severe attenuation and scattering in varying water conditions. This paper investigates the efficacy of optical code-division multiple-access (OCDMA) employing zero cross-correlation (ZCC) codes for UOWC transmission links. Comprehensive simulations evaluate system performance across five water types-pure sea, clear ocean, coastal ocean, Harbor I, and Harbor II-using log(BER), Q-factor, and eye diagrams as metrics. Results demonstrate robust performance at data rates of 2.5, 5, and 10 Gbps, with maximum achievable ranges of 102 m (pure sea), 42 m (clear ocean), 19.5 m (coastal ocean), 8.5 m (Harbor I), and 4.8 m (Harbor II) while maintaining a Q-factor >= 4 dB and log(BER) <=-5 which is commonly used as a practical forward-error-correction benchmark in simulation studies. Q-factor and log(BER) versus range graphs reveal ZCC codes' resilience to multi-user interference and channel impairments, outperforming traditional schemes in turbid waters. Eye diagrams confirm signal integrity at optimal ranges. These findings validate ZCC-OCDMA as a promising multiplexing solution for short-to-medium-range UOWC applications, such as underwater sensor networks.
This study examines four-wave mixing (FWM) enhancement in tapered optical fibers operating at 1-& micro;m wavelength, achieved by depositing an Nb2CTx-ZnO composite onto the fiber surface. Tapers with waist diameters of 30 & micro;m, 40 & micro;m, and 50 & micro;m were fabricated using the flame-brush technique. The composite coating significantly boosted the nonlinear response, with the 30 & micro;m taper showing the greatest improvement, a 22.5% increase in FWM conversion efficiency. The generated idler wave remained stable throughout a 60-minute test. These results advance the development of efficient, compact nonlinear photonic devices for applications in the 1 & micro;m spectral band.
Single-junction solar cells are fundamentally limited by the Shockley-Queisser efficiency ceiling due to incomplete utilization of the solar spectrum. In this work, we propose and numerically optimize a monolithic tandem solar cell based entirely on tungsten diselenide (WSe2) using SCAPS-1D simulation software. The top cell employs germanium-incorporated WSe2 (WSe2:Ge) as the wide-bandgap absorber (Eg approximate to 1.6 eV), while the bottom cell uses pristine WSe2 as the narrow-bandgap absorber (Eg approximate to 1.0 eV). A Cu2O hole transport layer and ZnO electron transport layer are used to facilitate charge extraction. Systematic optimization of absorber layer thicknesses yields current-matched operation (Jsc = 18.53 mA/cm & sup2;) at top and bottom cell thicknesses of 1.08 mu m and 1.62 mu m, respectively. The optimized monolithic tandem structure achieves an open-circuit voltage (Voc) of 0.743 V, short-circuit current density (Jsc) of 43.18 mA/cm & sup2;, fill factor (FF) of 84.82%, and a power conversion efficiency (PCE) of 21.94% under standard AM1.5G illumination. This efficiency surpasses previously reported single-junction WSe2 solar cells and demonstrates the potential of same-material monolithic tandem architectures using earth-abundant, non-toxic transition metal dichalcogenides. The results provide a theoretical foundation for experimental realization of high-efficiency WSe2-based tandem photovoltaics.
