Applied Physics B最新文献

Ytterbium (Yb) is used in cold-atom systems, including magneto-optical traps and optical lattice clocks. However, the long-term operation of such systems may be associated with substantial degradation of optical transmittance through vacuum chamber viewports due to Yb adsorption. Here, we show that coating the surface with tetracontane effectively suppresses such adsorption.

This study presents a comprehensive theoretical investigation into the linear optical properties of CdS@Ag core–shell quantum dots (CSQDs) embedded in various dielectric matrices. Using a quasi-static approximation and a Lorentz–Drude model for the silver shell, we examine how structural parameters core radius, shell thickness and host matrix permittivity modulate the optical response, including plasmonic field enhancement, refractive index behavior, absorption/scattering cross-sections and extinction cross-sections. Key findings reveal that increasing shell thickness significantly boosts both the local field enhancement factor and the absorption cross-section ((sigma _{text {abs}})), particularly in low-index hosts like PMMA. In contrast, increasing the core size results in a red-shift of the plasmon resonance while reducing field localization, highlighting a geometric trade-off between spectral tunability and optical intensity. Host permittivity also plays a crucial role: PMMA yields sharper and more intense plasmonic resonances, whereas (text {SiO}_2) and (text {Al}_{2} text {O}_3) broaden and blue-shift the spectral response due to enhanced dielectric screening. These results offer valuable design guidelines for optimizing CSQDs in applications such as nanophotonic circuits, nonlinear optical switching, and plasmon-enhanced sensors.

The gold (Au) mining industry requires rapid and cost-effective quantitative analysis techniques to enhance detection efficiency and reduce operational costs. Compared to conventional Au detection methods, laser-induced breakdown spectroscopy (LIBS) offers distinct advantages, including rapid analysis capabilities, minimal sample preparation requirements, and simultaneous multi-element detection, which makes it a widely adopted technique in material analysis. Additionally, it meets the demand for more efficient detection methods in Au mining. This study employed LIBS to detect and analyze trace Au in gold ore samples. The characteristic spectral lines used in the subsequent calculation of the experiment were determined in the experimental preparation stage. The systematic optimization of experimental parameters was used to calculate the relative standard deviation (RSD) of the sample and determine the optimal ratio of laser energy to binder for effective sample breakdown. Based on this condition, the transverse magnetic field intensity and spectral collection delay time were adjusted, and the influence of transverse magnetic field strength on the signal-to-noise ratio (SNR) of Au spectral lines under varying delay conditions was investigated. Compared with the condition of no constraint and no delay, the limit of detection (LOD) of Au decreased from 52.52 to 23.29 mg/kg under a 0.4 T constant magnetic field and 2.4 μs. Through hardware enhancements, including the replacement of conventional focusing lenses with microscopic objectives, the spectral data of Au samples with different gradient concentrations were obtained. The LOD was reduced to 5 mg/kg by calculation and data fitting. Finally, plasma temperatures and electron densities across different magnetic field intensities were calculated to determine local thermodynamic equilibrium (LTE) conditions, while the effect of magnetic confinement on the enhancement of plasma spectral lines was theoretically explained.

Laser-induced fluorescence spectroscopy was used to determine the concentration of cobalt ions in aqueous solution, in which CH-90 resin was used to chelate the ions to transform the liquid samples into solid ones. The experimental results showed that the fluorescence emission of the ions was significantly enhanced after excited by a low-power semiconductor laser at the wavelength of 447 nm. The limit of detection of 1.0 ng/L was achieved, which was 10,000 times lower than the permissible Co(Ⅱ) content of 0.01 mg/L in drinking water. The fluorescence intensity was proportional to the concentration of cobalt ions with a linear correlation coefficient of R² = 0. 998. The method greatly improved the sensitivity of detection for cobalt element in aqueous solutions.

Ultrafine soot particles emitted from combustion devices and biomass burning are a major particulate pollutant for human health and a major climate forcer. Unprecedented efforts have been made to understand the mechanism of soot formation and the physical, chemical, and optical properties of soot particles at different stages of maturity. Pulsed laser-induced incandescence (pLII) has become a powerful tool for in-situ measurements of soot volume fraction and primary particle size and to investigate the effects of pulsed laser irradiation on soot absorption properties. Experimental studies have confirmed that a high-power laser pulse can enhance the absorption of young soot particles through laser-induced annealing. Previous studies have ascribed the observed changes in soot absorption by pulsed laser irradiation to thermal annealing. In this study, a numerical study was conducted to model the effect of pulsed laser irradiation on the absorption efficiency of soot of different maturities to reproduce the results of a recent double-pulse pLII experiment. The numerical results based on thermal annealing models proposed in the literature failed to capture the enhanced peak LII signals of laser-heated young soot compared to those of un-preheated soot. By assuming the laser-induced annealing of soot particle is attributed to both thermal and photon mechanisms, the modified LII model can reproduce the experimentally observed enhancement in the peak LII signal of laser irradiated soot of different maturities. The findings of this study serve as indirect evidence to support the conjecture that the photon mechanism plays an important role in laser-induced annealing of young soot.

In this paper, a self-calibration photoacoustic (PA) spectroscopy analysis technique based on the idle transmitted light intensity was proposed to resolve the key influence of incident light power on PA signal. To demonstrate this proposed gas sensing technique, methane (CH₄) was selected as the target gas, a photoacoustic spectroscopy (PAS) gas sensor system based on near-infrared distributed feedback (DFB) diode laser emitting at 1653 nm was developed by combining wavelength modulation spectroscopy (WMS) with second harmonic (2 F) signal detection method. Instead of the expensive optical power meter, a low-cost photodetector (PD) is used to measure the transmitted light signal and serves as the reference signal for the normalization of the PA signal. The experimental results show that the measured WMS-PA-2 F/PD signals have a good immune to the large dynamic fluctuations of the incident light power. The Allan-Werle deviation analysis indicated that a detection limit of 42.1 ppb can be achieved with an average time of 244 s, corresponding to the corresponding normalized noise equivalent absorption coefficient (NNEA) of 3.63 × 10^− 9 ({text{c}text{m}}^{-1}text{W}/text{H}text{z}).

We propose a quantum model involving two superconducting qubits (SQs) interacting with a single-mode microwave cavity, influenced by a Kerr nonlinear medium and Ising interaction, within the framework of time-varying coupling (T-VC). The Hamiltonian of the system is determined, and we compute the density operator for both the full system and its subsystems. Physically, the Kerr medium introduces nonlinearity while the Ising interaction between SQs facilitates tunable SQs coupling. The interplay of these mechanisms allows for fine-tuned quantum control, crucial for maintaining coherence and managing decoherence processes. We examine the time evolution of key quantum properties, including SQ–SQ entanglement, SQs–cat field entanglement, and quantum Fisher information, as functions of system parameters. Finally, we investigate the dynamic relationships among these quantum measures, revealing mechanisms that can maximize entanglement and coherence under various parameter regimes.

In this paper, a V₂GeC saturable absorber (SA) is prepared and used to modulate a Tm:YAP laser. In continuous wave (CW) mode, an output power of 2.48 W at 1940.5 nm was achieved with a 15.39 W pump power, corresponding to an optical–optical conversion efficiency of 16.1%. Under passively Q-switched (PQS) mode, an average output power of 663 mW at 1937.4 nm was acquired with an optical–optical conversion efficiency of 4.3%, and a pulse width of 416.7 ns at 129.00 kHz was acquired in the laser stable operation, corresponding to a per pulse energy of 5.1 µJ. These experimental results demonstrate the effective modulation capabilities of the V₂GeC SA in near-infrared laser systems.

This study explores the application of Laser-Induced Grating Spectroscopy (LIGS) for non-intrusive measurements of temperature and water vapour concentration in premixed flames of air with blends of hydrogen and methane under high-pressure conditions. Employing a swirl-stabilized burner, the research demonstrates the capabilities of tracer-free LIGS, using thermal and electrostrictive gratings generated by a 1064 nm Nd:YAG laser, to measure local temperatures and water molar fractions. The study also includes an extension of the thermoacoustic model for characteristics LIGS signals, built in order to extract the relative concentration of water vapour from the ratio of second (thermal) to first (electrostrictive) peak magnitudes. Experiments are conducted in non-sooting flames, leveraging a high-pressure optical chamber (HPOC) with pressures up to 3 bar. The study evaluates mixtures of methane and hydrogen (100%, 70%, and 40% CH(_{4})) and identifies key relationships between LIGS signal characteristics, frequency distributions, and combustion dynamics. Results show excellent agreement between measured temperatures and adiabatic flame temperatures, alongside measurements of water vapour molar fractions. The spatial temperature and water vapour maps are related to the complex mixing and recirculation patterns associated with the flame’s shear and recirculation zones. The results establish LIGS as a robust diagnostic tool for combustion analysis, with potential applications in advancing hydrogen-rich energy systems.

In this work, we explored the impact of indium composition (x) on the structural and optical characteristics of In_xAl_1-xAs layers within the context of quantum cascade laser (QCL) structures grown on InP (100) substrates using the Metal Organic Vapor Phase Epitaxy method. The quality of the In_xAl_1-xAs QCL is notably influenced by the growth with low indium composition, evident in terms of crystallinity, interface sharpness, and optical properties. The properties of the InAsP layer at the InP/In_xAl_1-xAs junction are particularly sensitive to the indium composition. A drop below 0.52 in indium composition leads to a substantial lattice mismatch between the In_xAl_1-xAs layer and the InP substrate, typically exceeding [3 8]%. This mismatch induces defects or traps within the bandgap, significantly impacting carrier localization in this system. Our study demonstrates that cultivating In_xAl_1-xAs with a low indium concentration results in a strained (lattice-mismatched) In_xAl_1-xAs layer. This finding is significant as it can be leveraged to balance strain in high indium content InGaAs layers, particularly in the context of applications involving quantum cascade lasers.