Applied Physics B最新文献

Biological silk is a natural optical waveguide with humidity-sensitive properties. The refractive index (RI) is a critical parameter that determines the optical properties of waveguides and is greatly affected by humidity. In this article, we propose an optical method for real-time measuring the RI of micron-scale biological silks at different humidity. We employ a section of single-mode fiber (SMF) and a section of biological silk to configure an F-P cavity structure. By recording the spectrum and diameter of the silk under different humidity, we can obtain the relationship among free spectral range (FSR)、diameter, and relative humidity (RH). Based on this relationship, we calculate the variation of RI with humidity. We measure three materials in the 30–80% RH range. The measurement results indicate that during this process, the RI of spider egg sac silk (SESS) ranges from 1.491 ± 0.003 to 1.412 ± 0.009, mulberry silk is 1.551 ± 0.009 to 1.473 ± 0.005, and radial silk is 1.549 ± 0.005 to 1.479 ± 0.003. The relative uncertainty in the range ± 5 × 10^− 3 to ± 7 × 10^− 3 is achieved for these challenging samples. This rapid and convenient measurement method provides a new perspective for applying biological silks.

We have investigated the second-order nonlinear susceptibility associated with difference frequency generation in singly electron charged CdSe/ZnS, CdSe/ZnSe, CdSe/MgS & CdSe/MgSe quantum dots via intersublevel transitions in the conduction band. The confined energy levels in the dots are calculated in the effective-mass approximation by solving the three-dimensional Schrodinger equation. The second-order nonlinear susceptibility coefficients in the conduction band DFG processes are then determined using density matrix approach. As the dot radius increases, the DFG susceptibility spectrum shifts towards lower energy side. Also, we observe that, the peak height of the DFG spectrum increases slightly with increasing dot radius. For CdSe/ZnS, CdSe/ZnSe, CdSe/MgS quantum dots the second order nonlinear susceptibility associated with DFG is found to be one order higher (≈10⁻¹⁰ m/V) in contrast to that of the bulk CdSe (≈10⁻¹¹ m/V). We observed that second-order nonlinear difference frequency generation processes depend on the polarization state of incident photon beam, dot size and the surrounding matrix.

This research introduces a novel application of three-dimensional (3D) combustion thermometry through the thermally-assisted volumetric laser-induced fluorescence, namely the TAVLIF technique. The TAVLIF method is designed to provide quantitative 3D temperature diagnostics using a single dye-laser system, combining the advantage of tomographic imaging with the thermally-assisted LIF approach. The technique employs the A²Σ⁺←X²Π (0, 0) band Q₁(7) transition to excite OH radicals within a controlled Bunsen burner flame. Following excitation, the fluorescence emitted from the resonant (0, 0) and non-resonant (1, 0) vibrational bands is captured sequentially by an intensified camera, facilitating the reconstruction of the 3D fluorescence field. Utilizing the axisymmetric and stable properties of the burner flame, we reconstruct the 3D distribution of fluorescence signals from both bands. The resulting 3D temperature field is determined by the ratio of fluorescence intensities between the two bands, employing a novel ternary model calibrated experimentally to relate temperature to fluorescence ratio. After accounting for acquisition errors such as reflection and scattering of excitation light, as well as reconstruction and temperature calculation errors, the relative error remains below 6%. This research demonstrates the cost-effectiveness (only one dye laser system), accuracy, and reliability of the TAVLIF technique in diagnosing 3D temperature fields within combustion processes.

We derive the required formalism to evaluate the complex (frequency-dependent) dielectric function and optical conductivity to capture their changes due to doping, temperature and frequency. Subsequently, we apply our microscopic theory to the experimental data obtained from La(_{2-x})Ca(_{x})CuO(_{4}) superconductor and semimetallic WTe(_2) to derive the physical mechanisms of complex dielectric and optical conductivity. We find that the frequency-dependent optical conductivity function that changes as a result of doping, temperature and frequency is influenced by the plasmon density, plasmon-plasmon and plasmon-polariton scattering rates. However, for the semiconducting La(_{2})CuO(_{4}) compound, plasmon density is the dominant contributor to optical conductivity, prior to scattering rate effect at a higher frequency range. In addition, the plasmon density and the stated scattering rates are found to vary distinctly at different frequency ranges, which define the optical conductivity curves for La(_{2-x})Ca(_{x})CuO(_{4}) and WTe(_2) when the temperature, chemical composition and photon energy are systematically varied. As usual, we find that the effects of temperature, Ca-doping and changing frequency on optical conductivity data consistently obey the physics derived from the Ionization Energy Theory (IET) and its method.

This paper investigates the interaction of an ultra-short, high-intensity laser with a near-critical density hydrogen target, offering valuable insights into how laser intensity, plasma density, and target thickness influence the generation of high-energy proton beams. We report that optimizing target parameters at a fixed laser intensity results in a significantly greater increase in proton energy compared to simply increasing the laser intensity from (6 times 10^{20}) to (6 times 10^{21} mathrm{W/cm}^2). Specifically, simulation results show that the maximum proton energy rises from 45 to 94 MeV with optimized target parameters, whereas it only increases from 45 to 68 MeV with higher laser intensity on a near-critical density target of thickness 100 nm. By carefully selecting the laser and target parameters, we successfully exploit the Directed Coulomb Explosion (DCE) mechanism for ion acceleration, where both Radiation Pressure Acceleration (RPA) and Coulomb Explosion (CE) contribute to achieving such high proton energies. The optimal density and thickness are found to satisfy the condition for DCE proposed by Brantov et al. (IEEE Trans Plasma Sci 44:364–368, 2015) and the energy obtained matches with the theoretically predicted energy for DCE (Bulanov et al. in Phys. Rev. E-Stat. Nonlinear Soft Matter Phys. 78: 026412, 2008). Protons with energies around 100 MeV hold significant potential for practical applications, including cancer therapy, fusion energy, and other advanced technologies.

This research aims to explore the fractional cubic–quintic–septimal Schrödinger equation. It improves optical signal transmission by controlling dispersion and nonlinear influences. Step-index optical fibers have structured refractive indices. They are frequently used in soliton-based research. Here, two robust integration architectures, the Sardar subequation and the (G'/(bG'+G+a)) expansion methods, are implemented to investigate novel soliton solutions with a comparative analysis of the (beta -)fractional and (M-)truncated derivatives that expose practical insights into how different fractional definitions affect system dynamics, memory effects, and solution behaviors in complicated models. By utilizing multiple graphical techniques, the study highlights how fractional parameters affect system behavior, memory properties, and soliton formation. The findings hold significant relevance for the mathematical physics community and are especially crucial for advancements in telecommunications.

An unprecedented fiber narrow-band filter is proposed, which is composed of a phase-shifted fiber grating with an anti-symmetric refractive index distribution and a uniform fiber grating. The anti-symmetric refractive index distribution is obtained by performing a one-sided exposure on both sides of the few-mode fiber, where the two exposure positions differ by half period of the grating. By introducing an anti-symmetric refractive index distribution, coupling resonance occurs in the (hbox {LP}_{01}) and (hbox {LP}_{11}) modes in the two-mode fiber, and the reflected light and transmitted light are separated into (hbox {LP}_{11}) mode and (hbox {LP}_{01}) mode, respectively. To achieve a narrow-band reflection spectrum, the (pi ) phase is introduced into an anti-symmetric refractive index grating, and its transmitted light is reflected through a uniform grating. Single-mode fiber and taper-coupled fiber are introduced to select (hbox {LP}_{01}) mode selection, and the (hbox {LP}_{11}) mode is cutoff. Finally, the laser linewidth characteristics of the proposed structure are analyzed by co-simulation with semiconductor gain chips. Simulation results show that the proposed structure can improve the linewidth of single-longitudinal mode lasers, which has very important potential applications in the fields of Lidar, coherent communication and sensing.

Sensitive detection of trace gas molecules is critically important for various scientific and industrial applications. We present a wavelength-modulated cavity-enhanced two-photon absorption spectroscopy (WM-CETPAS) technique that integrates the Doppler-free precision of two-photon absorption with the noise suppression capability of wavelength modulation. This approach achieves both high sensitivity and high selectivity in molecular detection. As a demonstration, we measured (^{13})CO(_2) in gas mixtures, confirming that the WM-CETPAS method enables real-time detection without interference from other molecular species. The method provides an opportunity to be a powerful tool for various applications, such as isotope analysis, environmental monitoring, and industrial process control.

The optical properties of soot are crucial in estimating its climate impact through direct radiative forcing. Soot light absorption is typically quantified by the mass absorption cross-section (MAC_λ) or the absorption function E(m_λ), which are wavelength dependent. Light absorbed by soot can be predicted from its MAC_λ using mass-concentration measurements, or from its E(m_λ) using material density and an optical model accounting for soot-aggregate morphology. Recent work has shown that the soot MAC_λ shows a size dependency, due to a size-dependent degree of graphitization. We therefore hypothesized here that a similar size dependency may be observed for E(m_λ), which we quantify here. To test this hypothesis, we present a novel approach to obtain size-resolved MAC_λ and E(m_λ) of soot from a gas turbine engine by combining pulsed laser-induced incandescence signals with total mass-concentration measurements. E(m_λ) was found to vary with soot-particle size, with values ranging between 0.23 to 0.31 for the smallest (≈ 0.13 fg) and largest (≈ 3 fg) particles measured. To our knowledge, these measurements are the first to demonstrate that E(m_λ) not only varies between soot samples, but also within a population of soot particles, which impacts the interpretation of optical diagnostics and prediction of the radiative properties of soot.

A new hydrogen chloride (HCl) laser absorption diagnostic was developed and combined with a shock tube to obtain HCl time-history profiles behind reflected shock waves. An interband cascade laser was used to access the R(8) transition lines of the two isotopes H³⁵Cl and H³⁷Cl in the fundamental (1 (leftarrow) 0) band at the specific wavelengths of 3045.06 and 3042.74 cm⁻¹ near 3.3 μm, respectively. Spectroscopic parameters were obtained using HCl in 99.5% Ar, focusing on the line strengths and Ar-broadening effects, and were compared with theory from the literature. Experimental calibration of the HCl absorption coefficient and its dependence over a wide range of temperatures and pressures were obtained (i.e. 1261—1759 K, 0.25—0.42 atm, and 2390—3736 K, 1.26—2.00 atm). Measurements of the line strengths, Ar-broadening parameters at 296 K, and temperature-dependence exponents for the R(8) transition lines of H³⁵Cl and H³⁷Cl were validated against these results and can be summarized as follows:

1. 1)

   For H³⁵Cl:({S}_{12}left({T}_{0}right)) = 2.099 (pm) 0.084 cm⁻²-atm⁻¹, ({gamma }_{H35Cl-Ar}left({T}_{0}right)) = 0.0110 (pm) 0.0005 cm⁻¹-atm⁻¹, and ({n}_{H35Cl-Ar}) = 0.4 (pm) 0.01.

2. 2)

   For H³⁷Cl:({S}_{12}left({T}_{0}right)) = 0.708 (pm) 0.028 cm⁻²-atm⁻¹, ({gamma }_{H37Cl-Ar}left({T}_{0}right)) = 0.0105 (pm) 0.0005 cm⁻¹-atm⁻¹, and ({n}_{H37Cl-Ar}) = 0.3 (pm) 0.01.

The new HCl laser probe shows promising results for future measurements to better understand the combustion chemistry of propellants containing chlorine.