Applied Physics B最新文献

We propose an efficient scheme to manipulate the Goos-Hänchen (GH) shift of the reflected beam in a metal-clad waveguide structure, where a cold atomic ensemble with four-level ladder-type configuration acts as the substrate. Due to the quantum interference in the two decay pathways from the two upper closely lying levels, spontaneously generated coherence (SGC) is generated. It is demonstrated that the reflected GH shift is sensitively dependent upon the SGC effect. The controllable GH shift originates from the competition between the internal damping and radiation damping. Furthermore, in the presence of SGC, the magnitude, sign, and position of the GH shift can be effectively controlled via adjusting the intensity and detuning of the trigger field. Our scheme may have potential applications in all-optical switching and optical sensor.

Coal is still the main primary energy source worldwide despite being a major source of carbon dioxide and other emissions. In order to improve combustion efficiency, to reduce pollutant emission and for pricing purposes, a rapid tool for coal analysis is desirable. In this work, we demonstrate that laser-induced breakdown spectroscopy (LIBS) can provide a comprehensive analysis of high-grade coals using anthracite and bituminous as examples. LIBS is capable of detecting elements such as C, Fe, Na, Mg, Mn, Ti, Si, and Al, but also of some toxic elements such as Ba and Sr. The result of the LIBS elemental analysis is confirmed by X-ray fluorescence spectroscopy. In addition, we show the determination of the coal rank, which is a measure of the state of coalification, from the H/C line intensity ratio in the LIBS spectra. Proximate analysis has been performed to specify the quality of the different coal samples and has been correlated with the results obtained by the LIBS technique. Multivariate techniques for data analysis such as Principal Component Analysis and Hierarchy Clustering Analysis were employed to differentiate the coal samples. The results obtained from LIBS show good agreement with the state-of-the-art proximate analysis.

We report a piezoelectric (PZT) tube photoacoustic spectroscopy (PAS) gas sensing system, in which a PZT tube serves as both an acoustic resonator and a transducer. To suppress the external disturbance and fully use the internal surface of the PZT tube, we investigate the radial modes for PAS sensing. By exciting its 003-radial mode, the signal-to-noise ratio is more than one order of magnitude higher than that of its commonly used 100 longitudinal mode. We take water vapor as an example to demonstrate its sensing performance, achieving a minimum detection limit of 0.32 ppm, corresponding to a normalized noise equivalent absorption (NNEA) coefficient is 5 × 10^− 9 cm^− 1·W·Hz^− 1/2, and the R-square value of the concentration response fitting is 0.9998. A method to efficiently determine the resonant frequency is studied, which can effectively improve the stability of the sensor system when dealing with external disturbances. With a high acoustic coupling efficiency, simple structure and less disturbance by radial resonant mode, this proposed PZT-PAS technique would promote the PAS application for practical sensitive gas sensing.

In this work, we provide a simplified theoretical analytical estimation of the quantum cascade laser build-up time, accurately taking into account the main effects: the QCL overheating during the pump pulse and the photon mode filling effect. The non-trivial interplay of the mentioned effects brings about a variety of possible experimental build-up time behaviors. The latter range from decreasing curvature for low-power devices to non-monotonous function for devices performing at high power.

A portable ultraviolet (UV) laser absorption diagnostic was developed to measure temperature and O₂ concentration in high-temperature environments. The diagnostic uses two wavelengths (225.0150 nm/44,441.48 cm⁻¹; 225.0447 nm/44,435.62 cm⁻¹) to probe absorption features with components arising from two different lower vibrational levels of the Schumann–Runge system ((B^3 Sigma _u^-leftarrow X^3 Sigma _g^-)). To ascertain the position of the features, absorption cross-section measurements were collected at a variety of wavelengths from 225.0000 to 225.0460 nm in a reflected shock tube. After identifying spectral peak locations, the temperature dependence of the absorption cross-section at each peak was measured from 1500 to 5000 K. Experimental measurements motivated changes to an existing spectroscopic model, enabling accurate temperature-dependent cross-section predictions at both wavelengths within experimental uncertainty. Diagnostic validation data shows accurate predictions of temperature and O₂ mole fraction across a wide range of conditions (T = 1600–4500 K; P= 0.15–0.90 atm; (chi _{O_2}) = 2–100%). The average measurement error was 4% for both temperature and mole fraction. The diagnostic was also used to track O₂ dissociation as a function of time behind reflected shock waves and showed good agreement with an in-house coupled vibration-dissociation model.

The division of focal plane (DoFP) polarimeter is a vital tool for polarization imaging due to its compact structure and stable performance. However, its detection accuracy is significantly influenced by fabrication and integration errors of the micro-polarizer array (MPA). To address this, we establish a clear relationship between the accuracy of DoFP polarimeter and error sources, including the integration alignment, integration distance, integration angle, transmission axis angles, and extinction ratio of the MPA. Using a novel mathematical model based on the finite difference time domain method, we quantitatively analyze the impact of these errors on polarization detection accuracy. Our results demonstrate that as the detection accuracy improves from 10^− 1 to 10^− 2 and 10^− 3, the required fabrication accuracy of MPA’s transmission axis angles and the integration accuracy both increase by approximately one order of magnitude. Additionally, to achieve same accuracy improvements, the extinction ratio of the MPA exhibits nonlinear growth, increasing by about 2.5 times and 20 times, respectively. These findings provide a critical foundation for error control and quantitative performance assessment in DoFP polarimeters, advancing their application in various fields.

Laser-induced breakdown spectroscopy (LIBS) offers several advantages, including simultaneous multi-element detection, a simple structure, rapid detection speed, and no impact on sample morphology. Recent advancements in LIBS technology have focused primarily on signal enhancement and improved data analysis, with imaging techniques serving as the main method for exploring plasma characteristics. In this study, we investigate the application of a femtosecond (fs) double-pulse scheme to enhance the analytical performance of LIBS under varying polarization and wavelength conditions. Our results show that combining double pulses with polarization allows for the study of the plasma expansion process. This research presents new insights into the development of LIBS by adjusting the relationship between the polarization state and wavelength, offering a relatively simple method for improving LIBS technology.

When a linearly chirped fiber Bragg grating is subjected to transverse force, there will be some axial extension in the applied area. If the area is the same order of magnitude as the fiber diameter, the influence of the axial expansion cannot be neglected that an extra phase shift is produced in the structure of the grating. The transmission peak of new corresponding spectral is closely related with the location of the phase shift. We consider also the birefringence in the applied area of the grating with transverse force. In this study, based on the mechanical analysis of space elasticity, we present a theoretical sensing model of transverse force in small area by measuring the polarization dependent loss. The results show that the force is exponentially related to the transmission coefficient and linearly related to the peak value of the polarization dependent loss. The peak wavelength of the polarization dependent loss spectrum corresponds to the location and the magnitude of the transverse force. Therefore, we can measure and locate the transverse force with small applied area. In practical applications, the sensitivity of the transverse force measurement can be enhanced effectively by fixing the length of the forced region during packaging. And it can be connected in series forming a transverse force sensor network to locate the sensing position accurately.

The holmium-doped yttrium aluminum perovskite (Ho:YAP, (hbox {Ho:YAlO}_{3})) is a promising material for high-power mid-infrared solid-state lasers. This study presents detailed temperature-dependent spectroscopic properties of Ho:YAP, including 2 (upmu)m polarisation-resolved absorption and emission spectra, as well as the upper-laser-level lifetime, measured across a wide temperature range (4–300 K). For experimental validation, three Ho:YAP crystals with different orientations ((mathbf {{a}})-, (mathbf {{b}})-, and (mathbf {{c}})-cut) were employed as the gain medium in cryogenically cooled (78–300 K), multi-watt, resonantly pumped microchip lasers operating near 2.1 (upmu)m. Similarly to other quasi-three-level laser media, Ho:YAP demonstrated a significant reduction in the laser threshold with decreasing temperature, alongside a simultaneous drop in effective absorption. The maximum output power was achieved at approximately 200 K. The orientation of the crystal primarily influenced the emission wavelength, while the lasers consistently exhibited linearly polarised output and fundamental-mode beam profiles. These findings confirm Ho:YAP as a versatile material for efficient laser operation in the mid-infrared region, even under cryogenic conditions.