Applied Physics B最新文献

Self-mixing interference (SMI) has emerged as a powerful non-contact vibration sensing technique, leveraging the inherent coupling between laser emission and external optical feedback. However, conventional SMI systems often face limitations in signal resolution and measurement accuracy, particularly when probing low-amplitude vibrations or low-reflectivity targets. This study proposes a frequency modulation (FM) approach, FM-SMI, to enhance the capabilities of SMI setups. By intentionally modulating the laser frequency of 20 kHz, the FM-SMI technique induces a segmentation of the interference signal, effectively increasing the temporal resolution and facilitating the detection of finer vibration details. Comprehensive experiments involving oscillating speakers and rotating silicon wafers validate the superior performance of the FM-SMI system. Notably, the frequency-modulated signals exhibit stability and robustness, even under low-amplitude vibration conditions or when targeting low-reflectivity surfaces. The enhanced signal quality, coupled with numerical processing techniques, enables precise extraction of vibration characteristics, including amplitude variations and surface topographies. The proposed FM-SMI approach demonstrates its potential as a versatile tool for high-precision, non-contact vibration measurements across diverse applications, such as, non-destructive testing and the characterization of vibration induced by the rotational systems.

The detailed analysis of the effect of light and heavy holes on the generation of terahertz (THz) radiation in GaAs in a magnetic field is given. It is shown that taking into account the motion of light holes leads to a relative increase in the field strength of the THz pulse by several times. Such an increase manifests itself at times comparable to or greater than the inverse plasma frequency of electrons and is accompanied by a relative increase in the spectral density of radiation at low frequencies. In the frequency range from 0.1 to 10 THz, the affect of heavy holes is weak and resulted in a small change in the spectral energy density at frequencies slightly higher than 0.1 THz, which leads to a relative increase in the THz field strength at the last stage of generation.

WSe₂ and CuO belong to transition metal chalcogenides (TMDs) and transition metal oxides (TMOs), respectively, and both are semiconductor materials that have been applied in production in many fields. In this work, WSe₂/CuO heterojunction nanocomposites were prepared by simple and non-toxic liquid phase exfoliation (LPE) and vacuum filtration methods, and WSe₂/CuO heterojunction saturable absorber (SA) devices were prepared by film transfer technology. The morphology and purity of the WSe₂/CuO heterojunction were studied. In addition, the WSe₂/CuO heterojunction SA was applied to a passively Q-switched (PQS) solid-state laser for the first time, generating a stable pulse output with a Watt-level output power, a maximum average output power of 2.32 W, a repetition frequency of 68.68 kHz, and a minimum pulse width of 752.8 ns. Our research results illustrate the great potential and broad application prospects of WSe₂/CuO composites in the field of photonic devices.

Nanoparticle-enhanced laser-induced breakdown spectroscopy (NELIBS) represents a promising tool for detecting trace elements. This work improves NELIBS by substituting metal nanoparticles with nano-silica particles to achieve rapid detection of Cs elements at low concentrations. This substitution effectively prevents cluster formation and simplifies the experiment preparation process. The research optimizes factors such as target movement speed, nanoparticle concentration, and nanoparticle size to identify the optimal experimental parameters. Comparative analysis of the 3D morphology of laser ablation areas with and without nanoparticles reveals that evenly distributed nano-silica particles on the target surface provide the most effective colloidal particle lens array (CPLA) effect, and increasing the roughness of the target surface thereby enhancing the quality of laser ablation. With a laser frequency of 10 Hz, optimal characteristic spectral signals are achieved when the target movement speed exceeds 2 mm/s. Under conditions of a concentration of 0.1 mg/mL and an average particle size of 50 nm, the greatest enhancement effect on Cs element LIBS characteristic spectral signals is observed. Consequently, the limit of detection (LOD) and the limit of quantitation (LOQ) of elemental Cs by LIBS technology are reduced to 0.45 mg/L and 1.51 mg/L, respectively, facilitating real-time detection of Cs element at low concentrations. In addition, the nano-silica particles have also had a certain enhancement effect on the spectral signal of elemental properties in the target, proving that enhancing the LIBS characteristic spectral signal using nano-silica particles is a feasible method.

Tracer based planar laser-induced fluorescence (PLIF) has emerged as a powerful in-situ measurement technique with a considerable spatial and temporal resolution for Internal combustion (IC) engines. In PLIF, the emitted fluorescence signals from a tracer molecule are processed to determine distribution of temperature, fuel, residual gases, etc. However, it is imperative to have a thorough understanding of the tracer physical properties and its fluorescence intensity dependencies on excitation wavelength, pressure, temperature and bath gas composition existing inside the combustor for accurate quantitative interpretation. This work consists of a series of two articles providing a detailed review of the existing literature of fluorescence characteristics of various molecules used as tracers in IC engine applications. Due to the overwhelming usage of organic compounds in IC engine environment, the work is restricted to them. Part A of this work is focussed on non-aromatic compounds whereas part B will focus on aromatics (toluene, anisole, naphthalene, 1-methylnaphthalene and fluoranthene). Due to a large energy gap between the excited singlet and triplet states of aromatics, they are highly sensitive to oxygen quenching effects than ketones. Absorption cross-section might increase or decrease with temperature but is insensitive to pressure changes. Fluorescence quantum yield of aromatics show a very strong reduction with increase in temperature but might either increase or decrease with increasing pressure. The pressure sensitivity is found to increase with the number of atoms in a bath gas molecule. Fluorescence spectra are found to undergo redshift with temperature which can be used to measure temperature using 2 colour thermometry. The large fluorescence quenching by oxygen can also be used to directly measure fuel–air ratio using FARLIF methodology. Towards the end several IC engine studies are reviewed to discuss various aspects of mixture formation and temperature distribution.

Identifying the types of materials such as plastics, microplastics, and oil pollutants is essential for understanding their effects on marine life. We propose a new methodology for the real-time detection and identification of microplastics in aquatic environments. Our experiments are based on a compact Laser Induced Fluorescence (LIF) device, with machine learning techniques applied to classify the materials. A 405 nm CW laser excitation source effectively induces fluorescence spectra in the visible spectrum from material samples that are either floating or submerged in water. We examine known plastic pollutants in seawater, including polyethylene (PE), polypropylene (PP), polystyrene (PS) and polyethylene terephthalate (PET), as well as maritime fuels, lubricating oils, and other organic substances that are abundant in the marine environment. Our two-step identification process first employs machine learning algorithms to distinguish microplastics from other organic materials with a high degree of accuracy (97.6%). Subsequently, the type of plastic is determined with an accuracy of 88.3% in a second application of machine learning techniques.

Computational methods have been established as cornerstones in optical imaging and holography in recent years. Every year, the dependence of optical imaging and holography on computational methods is increasing significantly to the extent that optical methods and components are being completely and efficiently replaced with computational methods at low cost. This roadmap reviews the current scenario in four major areas namely incoherent digital holography, quantitative phase imaging, imaging through scattering layers, and super-resolution imaging. In addition to registering the perspectives of the modern-day architects of the above research areas, the roadmap also reports some of the latest studies on the topic. Computational codes and pseudocodes are presented for computational methods in a plug-and-play fashion for readers to not only read and understand but also practice the latest algorithms with their data. We believe that this roadmap will be a valuable tool for analyzing the current trends in computational methods to predict and prepare the future of computational methods in optical imaging and holography.

We demonstrated a wavelength discretely tunable laser with outputs at 572.6 nm, 589.1 nm, 603.8 nm, and 611.8 nm using external cavity Ng-cut KGW Raman conversion and intracavity frequency mixing. The multiple visible wavelengths were generated by utilizing this specially cut KGW crystal and the g[mm]g Raman configuration, as well as the temperature-dependent phase-matching characteristic of the LBO crystal. The maximum output powers at 572.6 nm, 589.1 nm, 603.8 nm, and 611.8 nm were measured to be 227 mW, 175 mW, 258 mW, and 103 mW respectively, with nearly fundamental Gaussian beam profiles. This work provides a monolithic setup capable of producing tunable yellow-red laser outputs through Raman and (chi ^2) frequency conversions for various applications such as air detection, optogenetics, biomedicine, and chemical analysis.

Investigations of structured laser beams formation are one of the attractive areas of laser research in recent years. Compared to solid-state lasers, dye lasers were rarely in demand in these studies. Here we present several transverse mode selection experiments in a pulsed Rhodamine 6G dye laser ((lambda) = 580 nm) with a plano-spherical resonator under hollow beam pumping by 20 ns pulses of 532 nm radiation from the Nd:YAG laser 2-nd harmonic. Along with high-order vortex and petal Laguerre–Gaussian modes, a whole family of non-planar geometric modes of different structures was obtained at the frequency degenerate states of this dye laser resonator. The ensemble of geometric modes in the related degenerate resonator configurations is illustrated by fractal frequency spectrum calculations. The experiments performed show that a dye laser represents a fairly simple and convenient object for testing various mode selection techniques. Dye lasers operating in the visible and near-infrared spectral regions can complement the range of solid-state laser sources currently used for obtaining and studying structured laser beams, which have many applications in scientific research and applied problems.