This study presents an analytical investigation of terahertz (THz) radiation generation resulting from the beat-wave interaction of amplitude-modulated Gaussian laser beams with metallic spherical and cylindrical nanoparticles (NPs) under an externally applied static magnetic field. This scheme involves the resonant excitation of THz radiation through the beat-wave of two lasers in the presence of ponderomotive nonlinearities, which drive a nonlinear current density acting as the primary source of THz emission. The analytical model incorporates the spatial and temporal variations of the ponderomotive force arising from the amplitude modulation, thereby enhancing the nonlinear current response. The incorporation of the magnetic field significantly enhances laser-metal coupling and alters the surface plasmon resonance conditions of the NPs' electrons, leading to much stronger THz emission. The study systematically examines the influence of magnetic field strength, NP radius and interparticle spacing, and modulation index of the incident laser on the THz amplitude. Results indicate that the THz field strength increases with enhanced magnetic field and larger NP radius, while decreased interparticle spacing promotes stronger near-field interactions, further amplifying the emission. The combined use of spherical and cylindrical NPs introduces multiple plasmonic resonance modes, enabling more efficient energy conversion. This work provides important insights into the optimization of NP-based THz sources for applications in spectroscopy, imaging and wireless communication.

This study explores the enhancement of twisted terahertz (THz) radiation power by using a novel approach leveraging a relativistic electron beam modulated by twisted lasers. The modulated beam propagates through a helical magnetic wiggler and ion channel guiding that induces a transverse modulation in the electron density. The magnetic wiggler deflects the electron trajectories resulting in the emission of THz photons with a twisted phase structure. Our numerical results reveal a significant increase in THz power with rising ion channel frequency, peaking at a critical point where resonance is approached. Furthermore, we observe that maximum THz power is tunable with introduction of ion channel density and relativistic electron beam velocity. In present study, ion channeling also improves the twisted THz radiation power to the order of ∼ 10−2corresponding to beam energy of 1.64MeV approximately, which increase by nearly order of magnitude compared to previously reported values.

This communication proposes an analytical model that exhibits terahertz (THz) radiation generation from spatially corrugated noble-metal spherical and cylindrical nanoparticles (NPs) placed under the influence of an externally applied static magnetic field. This scheme involves the resonant excitation of THz radiation through the beat-wave of two lasers in the presence of ponderomotive nonlinearities. Effect of magnetic field as well as laser intensity profiles, which include super, cosh, flat-top and ring-shaped Gaussian profiles, have been investigated. The incorporation of the magnetic field induces substantially more dynamic laser-metal coupling and influences the surface plasmon resonance condition associated with electrons of the NPs, thereby leading to stronger THz emission. Our results also demonstrate that the spatial profile of the laser affects the THz output, as it impacts the excitation and dynamics of the NPs. Additionally, we find that both the shape, size and interparticle-separation of NPs play crucial roles in enhancing THz generation. Furthermore, we explore the effects of varying other parameters like electric field strength and beam waist of incident lasers. These findings provide valuable insights for the design and optimization of THz sources based on NP systems, offering new avenues for applications in spectroscopy, imaging, communication and biomedical sciences.

The significance of the Normalized Difference Vegetation Index (NDVI) variations in India lies in its implications for ecosystem health, agricultural productivity, and climate change monitoring. This study aims to assess the NDVI patterns across India with different spatial/temporal scales. The spatial and temporal NDVI variations were examined through geospatial methods using satellite data from Moderate Resolution Imaging Spectroradiometer (MODIS) from 2000 to 2010 across India. It was discovered that the time series of India's annual averaged NDVI from 2001 to 2010 shows a positive trend with a slope of $0.003 / \text{yr}$. It also suggests that NDVI values were lower in arid regions like Rajasthan and Gujarat, while they were greater in the western Himalayas, north-eastern states, and coastal areas. The study also found that, as a result of increased vegetation growth, NDVI values increased during the monsoon months (June to September) and declined during the dry winter months. It has also been discovered that changes in land use and cover, along with variations in temperature and rainfall, have a major influence on NDVI patterns. The understanding of the spatial and temporal variation of NDVI over the Indian climate region is crucial for ecosystem management, agricultural planning, and climate change mitigation. The findings of this study can serve as a valuable reference for policymakers, land managers, and researchers working towards sustainable land use practices, conservation efforts, and climate adaptation strategies in India.

This work presents a theoretical analysis of the generation of twisted terahertz (THz) radiation using laser-bunched relativistic electron beams in a magnetic wiggler. By employing a laser-bunched relativistic electron beam, which introduces a transverse modulation to the electron beam density, and a magnetic wiggler, which induces a transverse deflection to the electron trajectories, the generation of twisted THz radiation is achieved. The interaction between the modulated electron beam and the magnetic field leads to the emission of THz photons with a twisted phase structure. The findings of this study provide valuable insights into the generation and manipulation of twisted THz radiation contributing to the advancement of THz technology and its diverse applications.

The long-term spatiotemporal vegetation dynamics with climate variables is essential for effectively managing environmental assets. This study presented the long-term spatio-temporal trends of vegetation dynamics and its association with rainfall/temperature in Koppen climate regions from 2000 to 2022. Linear regression (LR) and the Mann-Kendall (MK) test used to analyse the inter-annual and seasonal long-term spatiotemporal trend of vegetation dynamics across the Koppen climate regions during 2000–2022. The parameters (slope, Sen’s slope, Pearson correlation coefficients, Z value, p-value, Kendall Tau, etc.) from the LR and MK test with Sen’s slope are quantifying the significance of vegetation dynamics trends, and their association strengths with climate variables. The statistically significant and strong upward trend of inter-annual NDVI dynamics are found across the Indian region (growth rate of 0.0034/yr) and Koppen climate regions (growth rate ranges for five climate regions is 0.0029/yr–0.0043/yr and for Mountain Climate Region is 0.0011/yr). The statistically significant and strong upward trend found in seasonal NDVI growth for the monsoon, post monsoon, and winter seasons. However, the statistically significant and weak upward trend found in the pre-monsoon season for the Indian region and most of the climate regions. A significant positive association of vegetation dynamics observed with the rainfall across all seasons and climate regions, except the Mountain Climate Region. However, an inverse association of vegetation dynamics observed with temperature across all climate regions, except in a few cases. These findings have significant impacts, influencing decisions in land management, conservation, and strategies for regional climate resilience.

This communication deals with the analytical study of terahertz (THz) generation via frequency-difference mechanism using two circularly symmetric Gaussian laser beams with slightly different frequencies omega 1 and omega 2 and wave vectors k -> 1 and k -> 2 simultaneously propagating through a mixture of spatially corrugated noble-metal nanoparticles. The mixture, consisting of spherical nanoparticles (SNPs) and cylindrical nanoparticles (CNPs), is placed in a host medium under the influence of an externally applied static magnetic field. The two co-propagating laser beams impart a nonlinear ponderomotive force on the electrons of the NPs, causing them to experience nonlinear oscillatory velocity. Furthermore, the consequent nonlinear current density excites THz radiation at the beat frequency omega (=omega 1-omega 2). Magnetic fields influence the surface plasmon resonance condition associated with electrons of the nanoparticles due to enhancement in ponderomotive nonlinearities, thereby causing an increment in the amplitude of the generated THz field. It is observed that the generated THz radiation has a strong dependence on the shape and size of the NPs in addition to the magnetic field strength. CNPSs provide greater THz amplitude than SNPs due to additional resonance modes, and combining both kinds of nanostructures further enhances the amplitude. THz radiation plays an important role in biomedical and pharmaceutical fields, communications, security and THz spectroscopy.

In this study, the temporal variation of Equivalent Black Carbon (eBC) and its source apportionment is studied using a yearlong (Dec. 2020-Nov. 2021) multiwavelength Aethalometer (AE-33 model) measurements over Varanasi, located in the central Indo-Gangetic Basin (IGB). Results suggest that mean mass concentrations of eBC vary in the range between 0.46 +/- 0.13 to 11.22 +/- 5.09 mu g m(-3) with an annual mean value of similar to 3.57 +/- 2.39 mu g m(- 3) during the study period. A strong temporal variation in eBC and its components i.e., eBCff (eBC from fossil fuel), and eBCbb (eBC from biomass burning) are found which shows a large variation on different temporal scales with an average value during winter (6.21 +/- 3.56 mu g m(-3)), summer (5.09 +/- 3.61 mu g m(-3)), monsoon season (1.52 +/- 1.03 mu g m(-3)), and post-monsoon (3.75 +/- 2.68 mu g m(- 3)). The diurnal variation of eBC shows two different maxima between 07:00-08:00 a.m. and 08:00-10:00 p.m. An inverse relationship between eBC concentration and all meteorological parameters (temperature, wind speed, and boundary layer height) is found except relative humidity. The concentration of eBC increases with respect to RH (up to 70 %) suggesting hygroscopic growth while for higher RH (>70 %) value, eBC concentration decreases and indicates the possible wet scavenging processes in the atmosphere. Source apportionment of eBC using the "Aethalometer Model" reveals that eBCff is dominant over eBCbb in total eBC loading during the study period. Cluster analysis of HYSPLIT (Hybrid Single Particle Lagrangian Integrated Trajectory) model computed five days airmass back-trajectory suggests that airmass reached at Varanasi passes through a highly dense fire count region over the northwestern IGB and surrounding which could be the most responsible for the black carbon loading over the study region.

This communication proposes an analytical model that investigates the nanoparticle-based nonlinear absorption phenomenon associated with an obliquely incident p-polarized laser beam on a metallic surface. In this scheme, the surface is ingrained with noble-metal spherical nanoparticles (SNPs) and cylindrical nanoparticles (CNPs) in the presence of an external static magnetic field. The absorption of laser energy in the presence of nanoparticles (NPs) is attributed to surface plasmon resonance and enhanced magnetic-field effects. The absorption phenomenon was significantly enhanced by the incorporation of nanostructures and a magnetic field. The ellipticity characterizing parameter, which significantly influences resonant frequency of different nanometric structures have also been analysed and discussed. The effects of varying the magnetic field intensity, incident angle, size, and spacing of the NP were examined to determine their influence on the anomalous absorption of the laser. Furthermore, a direct dependency was found between the absorption coefficient and transmission coefficient of the incident laser, as well as the dimensions of the NPs. Several applications have direct relevance to this study, including biosensors such as DNA sensors and immunosensors, photothermal therapy, photoacoustic imaging, optoelectronic devices, solar cells, and surface-enhanced Raman spectroscopy.

A network of CNTs embedded on a dielectric substrate is used to transmit two laser beams with frequencies _1 and _2 and wave vectors k_1 and k_2 respectively. These laser pulses cause a localized plasma to develop when they contact with nanotubes. As a result, electrons develop oscillatory velocities. By applying ponderomotive pressure to the electrons, it causes oscillations in the charge density at 2_1 and _1-_2 frequencies. At the frequency 2_1-_2 , which is in the terahertz (THz) region, the laser exerts a ponderomotive force on the free electrons of carbon nanotubes causing a nonlinear current density. Each nanotube functions as an oscillating electric dipole that emits THz radiation. We establish the governing equation for THz efficiency and its dependence on laser incidence angle, amplitude, nanotube size, and CNT spacing. We obtain maximum peak of THz power at incident angle _0≈ 23.5^^∘ . The terahertz power of carbon nanotubes is highly dependent on their radius and length, so as these parameters increase, their terahertz power increases as well. Whereas on decreasing separation between the nanotubes, THz efficiency increases.

An amplitude modulated Laguerre-Gaussian (LG) laser beam carrying orbital angular momentum (OAM) is considered for terahertz radiation using non-uniform plasma vortex channel under relativistic conditions. The suggested approach involves the exchange of angular momentum between a non-uniform vortex plasma and a laser beam. During the interaction of non-uniform vortex plasma with photons, the laser angular momentum changes and twisted terahertz radiation is generated. The resultant THz radiation is shown to be substantially dependent on the beam width parameter and non-uniformity in the plasma channel. The amplitude of THz increases with beam focusing and the orbital angular momentum parameter. Due to higher amplitude of THz this study is useful in THz applications like, detection of counterfeit drugs, explosive material, analyze and identify defects in materials, medical imaging and communication.

An analytical model is presented that deals with THz generation by nonlinear mixing of two Gaussian laser beams with different frequencies ω1 and ω2 and wave vectors k1→ and k2→simultaneously propagating through an array of spatially corrugated noble-metal nanoparticles placed in the presence of a static magnetic field where ponderomotive nonlinearities are operative. The two co-propagating laser beams exert a nonlinear ponderomotive force on the plasma electrons, causing them to acquire nonlinear oscillatory velocity. This velocity leads to the generation of nonlinear macroscopic current density at the beat frequency ω (ω1-ω2) which further gives rise to strong terahertz radiation. The beat frequency lies in the THz region and density ripple provides the necessary phase-matching conditions. The externally applied magnetic field enhances the nonlinear coupling between the electric field of the lasers and causes resonant interaction of the laser beam with electrons of the NPs. THz radiations being non-invasive and biologically innocuous, play an important role in medical imaging, biomedical and pharmaceutical fields, and THz spectroscopy.

A theoretical study has been proposed where a p-polarised laser is irradiating a metallic surface topped with nanotubes at oblique incidence in the presence of static magnetic field. Interaction between incident laser and metallic surface stimulates the electrons of the nanotubes, causing them to excite and resonate at the plasma frequency. Incorporating external magnetic field with the system of nanotubes significantly enhances the absorption phenomenon. The absorption coefficient thus obtained is found to have direct dependence on the transmission coefficient of the incident laser as well as on dimensions of the nanotubes. Increasing the magnetic field strength along with the angle of incidence is found to produce more sharp absorption peaks. The result was also carried out for different materials. Due to their large surface-to-volume ratio of nanotubes, the carried-out study has a straight relevance in various biomedical applications like DNA sensor, immunosensors among other sensors, electrochemical sensors due to their excellent catalytic properties, in photothermal therapy and in photoacoustic imaging.

Abstract This communication deals with the analytical study of terahertz (THz) generation via beat-wave mechanism of two circularly symmetric Gaussian laser beams with frequencies \({\omega }_{1}\) and \({\omega }_{2}\) and wave vectors \({\overrightarrow{k}}_{1}\) and \({\overrightarrow{k}}_{2}\)simultaneously propagating through a mixture of spatially corrugated noble-metal nanoparticles (NPs). The mixture, consisting of spherical and cylindrical nanoparticles, is placed in argon gas under the influence of a static magnetic field. The two co-propagating laser beams impart a nonlinear ponderomotive force on electrons of the NPs, causing them to experience nonlinear oscillatory velocity. Further, the consequent nonlinear current density excites terahertz radiation at the beat frequency \(\omega (={\omega }_{1}-{\omega }_{2})\). Magnetic field influences the surface plasmon resonance condition associated with electrons of the nanoparticles due to enhancement in ponderomotive nonlinearities, thereby causing an increment in the amplitude of generated THz field. It is observed that the generated THz radiation has a strong dependence on the shape and size of the NPs in addition to the magnetic field strength. Cylindrical nanoparticles provide greater THz amplitude than spherical nanoparticles due to additional resonance modes, and combining both kinds of nanostructures further enhance the amplitude. THz radiations play an important role in biomedical and pharmaceutical fields, communications, security and THz spectroscopy.

A nonlinear analytical model is developed for the absorption of a p-polarized laser that is obliquely incident on a metal surface embedded with metallic nanoparticles under the influence of an external magnetic field. The model suggests that the absorption coefficient is proportional to the angle of incidence and cube of nanoparticle-radius, but inversely proportional to the square of interparticle separation. Obtained results show that the laser absorption by the nanoparticles is substantially amplified due to plasmon resonance in the presence of an external magnetic field. The absorption coefficient has a sharp peak at surface plasma resonance ω = ω p / 3 , where ω p is the plasma frequency and it shows explicit dependence on the amplitude transmission coefficient T A of the incident wave. Absorption coefficient is obtained for gold nanoparticles for different incident angles, radii and interparticle separations and this study is of direct relevance in high performance optoelectronic devices, solar cells and nanomedicines.

The dust storm is a common atmospheric phenomenon that modifies the optical, physical, and radiative properties of aerosols and plays a crucial role in the global radiation budget, and hence global climate change. The present chapter proposes different remote sensing techniques, such as moderate resolution imaging spectroradiometer true-color images, AErosol RObotic NETwork, cloud-aerosol LIDAR, and infrared pathfinder satellite observation (CALIPSO) to study the various properties of dust particles during dust storms over Indo-Gangetic Basin. In addition, Hybrid Single-Particle Lagrangian Integrated Trajectory model is used for the event confirmation and source identification of dust storms.

Nanofluids are currently regarded a new growing area of research with numerous advantages over conventional heat transport fluids in heat transfer applications. Because, nanofluids possess a better thermophysical characteristics. Hence, they can perform better when compared to traditional working fluids. The thermo-physical characteristics of zinc oxide nanoparticles disbanded water (ZnO/water) nanofluid was evaluated in this study by altering the volume proportions of nano-ZnO particles and temperature experimentally. The volume proportion of ZnO/water nanofluids was adjusted from 0.01 to 0.2 in four different (0.01, 0.05, 0.1 and 0.2) fractions. Using a field emission scanning electron microscope, the surface properties of ZnO nanoparticles were investigated. The results evidenced that the absolute viscosity, thermal conductivity, and density of the water was augmented by 1.43%, 37.0%, and 1.57%, respectively through the diffusion of 0.2 vol% of nano-ZnO particles in water. In contrast, the specific heat of water was lessened by 2.7% with 0.2 vol% of nano-ZnO particles in water. Copyright (C) 2022 Elsevier Ltd. All rights reserved.Selection and peer-review under responsibility of the scientific committee of the International Conference on Design, Manufacturing and Materials Engineering.

This paper presents an analytical investigation of terahertz generation by self-focused amplitude modulated Gaussian laser beam at modulation frequency in non-uniform plasma channel. Due to intensity variations transverse to the propagating laser, a ponderomotive is generated. Attempts have been made to derive ponderomotive force, which generates transient transverse nonlinear current. The analytical expression for beam width parameter and amplitude of THz radiation have been derived. The self-focusing of amplitude modulated Gaussian laser beam in non-uniform channel and its effect on generated THz amplitude have been studied. It is observed that increase in the value of non-uniformity, self-focusing enhances and shifts towards lower value of propagation distance which further enhance the THz amplitude. In this study, we obtained a normalized power of the order of 10−4times the original power supplied by the laser beam by self-focusing the laser beam.

A new method utilizing holographic interferometry technique is described to conceal information in security holograms for enhancing their anti-counterfeiting ability. This concealed information can only be imitated if security hologram is illuminated through correct decoding wavefront generated through a key hologram. In decoding process, three spatially separated focus spots emerge at predefined positions which upon divergence further generate interferometric fringes modulated with concealed information in them. When security hologram is perfectly aligned, interferometric fringes disappear and concealed information becomes visible. The advantage of encoding through this technique lies in the fact that relative repositioning of key and security hologram becomes much easier and also additionally brings multifold improvement in the security level of the verification systems.

The current work examines the enactment of a traditional single sloped type of solar still in the presence of crude wax as an organic phase changing material (PCM) and a low mass of nano-zinc oxide (ZnO) particles disbanded crude wax as NDPCM in terms of daily potable water output. To accomplish this goal, three identical solar stills were planned and constructed. Among these, one was an unchanged traditional still (Normal Still), another still was combined with crude wax based PCM (CW Still), and a third still was amalgamated with NDPCM (NDPCM Still). Earlier, the NDPCM was formed by combining 1.0 percent mass of zinc oxide nanoparticles with enough quantity of crude wax. The tests were carried-out in March 2021 at 11.0168° N, 76.9558° E. The results indicated that the addition of crude wax and specifically, the NDPCM increased the output of clean water by 50.24 percent and 65.17 percent, respectively.