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Accepted papers to appear in an upcoming issue

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Heralded single-photon source based on ensemble of Raman-active molecules

Ivan Panyukov, Vladislav Shishkov, and Evgeny Andrianov

DOI: 10.1364/JOSAB.457400 Received 01 Mar 2022; Accepted 01 Jul 2022; Posted 01 Jul 2022  View: PDF

Abstract: Light with high mutual correlations at different frequencies can be used to create heralded single-photon sources, which may serve as the basic elements of existing quantum cryptography and quantum teleportation schemes. One of the important examples in natural systems of light with high mutual correlations is the light produced by spontaneous Raman scattering on an ensemble of molecules. In this paper, we investigate the possibility of using Raman light to create a heralded single-photon source. We show that when using Stokes scattered light for postselection of an anti-Stokes scattered light, the latter may posses the single-photon properties. We analyze the influence of the various negative factors on the characteristics of such a heralded single-photon source, which include a time delay between Stokes and anti-Stokes photons, the finiteness of the correlation radius of an external source, and background radiation. We show that the high purity of the single-photon source is preserved even when the flow of uncorrelated photons exceeds the flow of correlated photons in the scattered Raman light by an order of magnitude.

Analysis of wander and spreading of optical beam by using oceanic turbulence optical power spectrum

Yalçin Ata, Yahya Baykal, and Muhsin Gökçe

DOI: 10.1364/JOSAB.463808 Received 11 May 2022; Accepted 29 Jun 2022; Posted 29 Jun 2022  View: PDF

Abstract: Variance of beam displacement, short-term and long-term spreading of Gaussian beam propagating in the presence of underwater turbulence are examined by using the Oceanic Turbulence Optical Power Spectrum (OTOPS). Analytical expressions for both beam wander displacement variance and beam spreading are presented. Results show that underwater turbulent channel causes deflection from the on-axis mean irradiance and brings significant wander and spreading effects to the propagating Gaussian beam wave. The variations of beam wander, short- and long-term spreading are obtained depending on the underwater medium parameters such as the average temperature, average salinity concentration, temperature-salinity gradient ratio, temperature and energy dissipation rates. In particular, the real values of average temperature and salinity concentration of turbulent water are used to obtain results. In addition, the effect of propagation distance, Gaussian beam source size and wavelength are shown. Results demonstrate that underwater turbulent channel brings displacements in the centroid and spreading of the optical beam.

Extra-cavity manipulation from traditional scalar to flexible vector solitons

Zhichao Wu, shuhao hua, Chaoyu Xu, Yuzhen Zhao, jianxing pan, Dan Luo, Jing Zhang, and Tianye Huang

DOI: 10.1364/JOSAB.462989 Received 04 May 2022; Accepted 28 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: Soliton manipulation is considered as an effective way to generate complicated and controllable vector solitons. Here, we experimentally acquire flexible vector solitons deriving from standard scalar solitons by route-assisted and birefringence-enhanced structures along the laser output port. These vector solitons with weak interaction between two polarized components possess tunable pulse numbers, intensities and intervals. These results would be significant complement for soliton polarization dynamics as well as a valuable soliton light source for various practical applications.

Design and simulation of hybrid coated LPG-TFBG-FBG three-parameter sensor for ocean environment

Yuxuan Yan, Zhengtian Gu, Huiping Jiang, Zhengyuan Li, Jinyi Wu, and Ying Wang

DOI: 10.1364/JOSAB.459329 Received 23 Mar 2022; Accepted 27 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: Based on the demand for monitoring CTDs(Conductivity, Temperature, and Depth) in the ocean, a hybrid coated made up of a long period fiber grating, a tilted fiber Bragg grating and a fiber Bragg grating structure (LPG-TFBG-FBG) was proposed, which could eliminate the mutual interference of CTDs in the measurement. Firstly, according to the coupled mode theory and phase matching conditions, the coupling equation of each segment of grating is deduced. Next, through the difference iterative method, the total transfer matrix of coated LPG-TFBG-FBG is obtained. Then, in order to improve the sensitivity of the structure and make the demodulation more accurate and convenient, the structure of the grating is optimized. The tilt angle of the TFBG is selected to improve the coupling efficiency of the second-order cladding mode, and the thickness of the film is chosen to increase the sensitivity of the sensor. Besides, the grating period is determined in order to separate the resonance peaks from each other to facilitate observation and detection, and the length of each segment of grating is determined in order to minimize the transmittance at each resonance wavelength. On this basis, the transmission spectrum of the structure is simulated and three peaks formed by coupling the forward core mode with the forward cladding mode in LPG( ),the backward high-order cladding mode in TFBG( ) and the backward cladding mode in FBG( ) are investigated. Furthermore, the sensing characteristics of SRI, temperature, and water pressure of the peaks are analyzed, and the three peaks show different sensitivity to environmental parameters. Therefore, a three-parameter matrix equation is established, and the three parameters can be measured simultaneously without interference. The simulation results of the response of the three transmission peaks to three parameters show good performance in both bandwidth (less than 5nm) and linearity (all larger than 0.99). The maximum sensitivities of three transmission peaks to SRI, temperature, and water pressure are -343nm/RIU, -1318.7 pm/℃, and -9.5 nm/Mpa, respectively. Finally, the condition number of the parametric demodulation matrix is 39.421, indicating the inversion of the resonant wavelength offset has high precision. The proposed coated LPG-TFBG-FBG structure has good linearity, high sensitivity and novel structure, which makes this structure have great application potential in the fields of multi-parameter sensing and segmented sensing.

Plasmonically enhanced composite vortex beam generation using ultra-thin dielectric fork gratings

Nirjhar Kumar, Ankit Arora, and Ananth Krishnan

DOI: 10.1364/JOSAB.460366 Received 13 Apr 2022; Accepted 27 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: We experimentally demonstrate a simple method for the generation of composite vortex beams using resonant ultra-thin dielectric fork gratings (UFGs) of thicknesses an order of magnitude less than the incident wavelength. The degradation in the diffraction efficiency of these gratings at reduced dielectric thicknesses was computationally shown to be compensated by introducing a thin continuous gold layer (Au, 30 nm) between the grating and the substrate. At the resonance wavelength, the diffraction efficiency of UFGs with Au was ∼ 4 times higher when compared to that of UFGs without Au, which was attributed to the plasmon-induced transmission enhancement. UFGs were fabricated with the optimized geometric parameters using electron beam lithography. These gratings showed lattice-plasmon resonance at the wavelength corresponding to the grating vector, resulting in vortex beams with a specific wavelength and polarization selectivity. Further, hybrid UFGs were designed by replacing a central concentric circular region of a UFG with another UFG of a different topological charge. These hybrid UFGs resulted in the formation of composite vortex beams, indicating that the relative spatial phase imparted to the lattice plasmon by hybrid gratings was preserved in the leaked radiation. These results can help in designing integrated, ultra-thin, low aspect ratio optical phase-singularity structures for enhanced optical sources, detectors, and sensing applications

Performance of free-space optical communication system employing receive diversity techniques in anisotropic atmospheric non-Kolmogorov turbulence

Yalçin Ata, Yahya Baykal, and Muhsin Gökçe

DOI: 10.1364/JOSAB.461245 Received 12 Apr 2022; Accepted 27 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: In this paper, we aim at investigating the effect of receive spatial diversity on the performance of a free-space optical communication (FSOC) system operating in an anisotropic non-Kolmogorov weak turbulent atmosphere. Results to observe the mitigating effects of diversity techniques on turbulence are obtained for different receive diversity techniques, namely selection combining (SC), equal gain combining (EGC), and maximum ratio combining (MRC). The Gaussian beam is used as the transmit laser with binary phase-shift keying (BPSK) modulation. It is found that the spatial diversity technique used at the receiver causes significant performance improvement in the performance of an FSOC system under the conditions of anisotropic non-Kolmogorov atmospheric turbulence. It is also observed that BER performance improves in more anisotropic turbulent medium.

Generation of polygonal Perfect Optical Vortex Array by Optical Pen

Guanxue Wang, Ji Guo, Ziyan Li, Xiangyu Kang, Keyu Chen, xiaojie sun, Yue Li, and Xiumin Gao

DOI: 10.1364/JOSAB.464570 Received 20 May 2022; Accepted 26 Jun 2022; Posted 28 Jun 2022  View: PDF

Abstract: Perfect optical vortex (POV) has generated a large number of applications in classical to quantum physics because its diameter is independent of topological charge (TC). Previous reported POVs still show a lack of controllable size, shape, and amplitude which may hinder their applications. In this paper, a combined phase is used to create complex polygonal perfect optical vortex (PPOV) arrays. The size, number, position, shape, and amplitude of the PPOVs in the array are controllable, where the shape can be an arbitrary symmetric polygon. We investigate the transmission characteristics of the PPOV arrays. The generation of PPOV arrays will bring further provides more flexibility in optical micro-manipulation, quantum entanglement, optical communication, and other fields.

Upper hybrid wave excitation and particle acceleration by resonant beating of two hollow Gaussian laser beams in magnetized plasma

Gunjan Purohit

DOI: 10.1364/JOSAB.455660 Received 09 Feb 2022; Accepted 24 Jun 2022; Posted 24 Jun 2022  View: PDF

Abstract: This paper investigates the excitation of the upper hybrid wave by resonant beating of two intense hollow Gaussian relativistic laser beams in a magnetized plasma. Hollow laser beams are taken in this study because they have the same power at different beam orders. The interaction of two intense hollow laser beams at the frequency difference (∆ω ≈ ω1 – ω2) and wave number (∆k = k1 – k2) excites the upper hybrid wave in the magnetized plasma. The excited upper hybrid wave accelerates the electrons to higher energies. The acceleration of electrons has also been studied. This study is carried out under a higher-order paraxial region, where the dielectric constant and the eikonal are expanded to the fourth power of the radial distance. Analytical expressions are obtained for the beam width parameter of the hollow Gaussian laser beams, the electric field of the upper hybrid wave, and the energy gain by the electrons. The effects of various laser and plasma parameters (such as beam order, plasma frequency and electron cyclotron frequency) on the electric field of the upper hybrid wave and the energy gain of electrons have been explored. The results are compared with paraxial region and the Gaussian profile of laser beams. Numerical analysis has been performed for well-established laser and plasma parameters.

Enhanced solar photocurrent using a quantum dot molecule

Jefferson Lira, Jose Villas Boas, Liliana Sanz de la Torre, and Augusto Miguel Alcalde Milla

DOI: 10.1364/JOSAB.462403 Received 26 Apr 2022; Accepted 23 Jun 2022; Posted 24 Jun 2022  View: PDF

Abstract: We present a detailed study on the influence of coherent tunneling on the photovoltaic properties of a semiconductor molecule driven by solar radiation. The connection between the power delivered by the QDM and quantum coherence is not simply proportional but depends on an interplay between the interdot coherent tunneling, the interaction of the system with thermal phonon reservoirs, and the resonance between the QDM and conduction bands. We explored numerically various parameter regimes and found that the maximum power delivered by the molecule is up to 30\% greater than the power delivered by a single quantum dot device. The calculated photovoltaic conversion efficiency is presented in terms of accessible experimental parameters and, as expected, is constrained by the second law.

Temperature-induced stochastic resonance in Kerr photonic cavities for frequency conversion

Bertrand Braeckeveldt and Bjorn Maes

DOI: 10.1364/JOSAB.458237 Received 11 Mar 2022; Accepted 20 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Driven non-linear photonic cavities are widely studied because they exhibit many interesting effects, such as non-reciprocity, thermal effects and frequency conversion. Specifically, adding noise to a modulated non-linear system can lead to stochastic resonance (SR), which corresponds to periodic transitions between stable states. In this work, we study the outgoing power and spectra from a non-linear driven photonic cavity coupled to an external port. Using a Langevin framework, we show that the system temperature induces SR in the bistable regime, which we study in detail to exploit for enhanced frequency conversion. In this way, the thermal fluctuations of the system itself can function as a driver for effective sideband generation, enabling conversion efficiencies of up to 40%. We extensively explore various regimes in order to understand and maximize the process.

Machine Learning Based Beam-Steering in Hybrid Plasmonic Nano-antenna Array

Korany Mahmoud and Ahmed Montaser

DOI: 10.1364/JOSAB.458574 Received 14 Mar 2022; Accepted 20 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: In this paper, different beam-steering techniques have been introduced using 8 × 8 hybrid plasmonic nano-antenna array operating at 1550 nm. Two conventional techniques of switched-beam antenna arrays and phased array antennas have been considered for implementing beam-steering. For a switched-beam antenna, the beam-steering is achieved by switching between the feed antenna elements, whereas, the feed antenna array is attached to the back surface of a fishnet achromatic-metalens to collimate the rays. In phased array antenna, the beam is steered by estimating the appropriate feeding phases of the 64 elements using deep neural network (DNN) either with or without lens. Finally, a hybrid technique based on activating only subset of antenna elements in the existence of the lens is proposed to steer the pattern in a certain direction. By predicting the proper feeding phases of the antenna array elements, the neural network with back-propagation technique and weighted hybrid gravitational search algorithm-particle swarm optimization approach is used to beam-steer. Furthermore, the DNN is applied to assign the required active subset elements for directing the main beam toward the desired direction. Several sample examples are provided to beam-steer the pattern in numerous directions to assess the correctness of the strategies.

Quantum imaging and metrology with undetectedphotons: a tutorial

Gabriela Barreto Lemos, Mayukh Lahiri, Radek Lapkiewicz, Sven Ramelow, and William Plick

DOI: 10.1364/JOSAB.456778 Received 22 Feb 2022; Accepted 20 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: We present a tutorial on the phenomenon of induced coherence without induced emission, and specifically its application to imaging and metrology. It is based on a striking effect where two nonlinear crystals, by sharing a coherent pump and one of two output beams each, can induce correlations between the other two individual, non-interacting beams. This can be thought of as a type of quantum-erasure effect, where the ``welcher-weg'' (which-way), or in this case ``which-source'' information is erased when the shared beams are aligned. With the correct geometry this effect can allow an object to be imaged using only photons which have never interacted with the object -- in other words the image is formed using undetected photons. Interest in this and related setups has been accelerating in recent years due to a number of desirable properties, mostly centered around the fact that the fields for detection and imaging (since separate) may have different optical properties, entailing significant advantages to various applications. The purpose of this tutorial is to introduce researchers to this area of research, to provide practical tools for setting up experiments as well as understanding the underlying theory, and to also provide a comprehensive overview of the sub-field as a whole.

GOAT - A Multi-purpose optical simulation tool

Thomas Weigel, Gustav Schweiger, and Andreas Ostendorf

DOI: 10.1364/JOSAB.459574 Received 28 Mar 2022; Accepted 20 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Some solutions for the calculation of optical problems already exist. Many of them are isolated solutions, very complex or expensive. Therefore, there is a need for easy-to-use, flexibly adaptable program packages. For this reason, we present here a programming library for the simulation of optical problems, which is based on geometrical optics, due to its high flexibility. Special attention was paid to a flexible adaptability to different problems and an easy usability. The program package is freely available as an open source project implemented in C++ and can be downloaded from the GitHub platform.

Excellent long-wavelength pass filters of CsPbBr3 and CsPb(Cl/Br)3 quantum dots glasses by Cu2+ quenching strategy

Linke Song, Xizhen Zhang, Mengqi Lin, Lizhu Guo, Sai Xu, jiashi sun, jinsu zhang, and Baojiu Chen

DOI: 10.1364/JOSAB.461587 Received 20 Apr 2022; Accepted 20 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Perovskite CsPbBr3 quantum dots (QDs) glasses doping Cu2+ are reported for excellent long-wavelength pass filters. Transmittance, optical density (OD), PL, PLE and PL decay are used to investigate filter properties and quenching mechanism. At low Cu2+ molar concentration of 0, 0.0025%, 0.005% and 0.01%, the filters exhibit good properties in transmittance and OD. Transition wavelength is 518, 513, 513 and 512 nm respectively. Shape and position of transmittance and OD are almost not changed. As Cu2+ concentration increases, PL intensity is monotonously quenched. PL decay is obviously faster. Quenching mechanism is dynamic quenching, that is electron transfer from QDs to Cu2+. In comparison with initial intensity, the intensity decreases by a factor of 7.6, 12.8, and 18.8 respectively. Oxidation and reduction atmospheres are introduced and the dynamic quenching mechanism is further confirmed. At high Cu2+ concentration of 0.013%-0.02%, quenching mechanism is static quenching. Double-anion CsPb(Cl/Br)3 QDs glasses of different Cu2+ concentrations extend operation wavelength to blue light region. For Cu2+ concentration of 0, 0.005% and 0.01%, the transition wavelength is 470, 472 and 473 nm for CsPb(Cl/Br)3 (NaCl as Cl source) QDs glasses, whereas it is 430, 426 and 445 nm for CsPb(Cl/Br)3 (PbCl2 as Cl source) QDs glasses respectively.

Numerical analysis of beam self-cleaning in multimodefiber amplifiers

Mesay Jima, Alessandro Tonello, Alioune Niang, Tigran Mansuryan, Katarzyna Krupa, Daniele Modotto, Annamaria Cucinotta, Vincent COUDERC, and Stefan Wabnitz

DOI: 10.1364/JOSAB.463473 Received 09 May 2022; Accepted 20 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Recent experimental results have reported the observation of beam self-cleaning or, more generally, nonlinear beam reshaping in active multimode fibers. In this work we present a numerical analysis of these processes, by considering the ideal case of a diode-pumped signal amplifier made of a graded-index multimode fiber with uniform Yb doping. Simulations confirm that beam cleaning of the signal may take place even in amplifying fibers, that is the absence of beam energy conservation. Moreover, we show how the local signal intensity maxima, which are periodically generated by the self-imaging process, may influence the population inversion of the doping atoms, and locally saturate the amplifier gain.

The robustness of symmetry-protected BICs in dielectric metasurfaces

Bing Meng, Chunjie Feng, Li Chen, Xiaoying Qu, xinfeng Wang, and Chaobiao Zhou

DOI: 10.1364/JOSAB.465997 Received 06 Jun 2022; Accepted 19 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: Optical metasurfaces with high Q-factors have attracted a lot of attention due to their sharp spectral feature and signifcant field enhancement. The exaction of symmetry-protected bound states in the continuum (SP-BICs) is an efficient way to achieve the high Q-factor resonator. While the experimental Q-factors of the resonant quasi SP-BICs metasurface are currently not high. In this work, we numerically demonstrate the robustness of SP-BIC in silicon metasurfaces. The two SP-BICs are transformed into quasi SP-BICs by breaking the in-plane symmetry of the structure, the resonance properties of these quasi SP-BICs are discussed with far-feld radiation and near-field distribution. Moreover, the effects of different period, size, substrate refractive index, and shape factors on the SP-BICs are explored, and the Q-factors of quasi SP-BICs always exhibit the same inverse quadratic dependence on asymmetry parameters, which demonstrates the robustness of the SP-BIC. Our results may provide a theoretical support for the experimental realization of ultra-high Q-factors quasi SP-BICs.

Semi-analytical model of optical cavity-assisted photon-nucleon coupling

Fei He and Ka-Di Zhu

DOI: 10.1364/JOSAB.455609 Received 04 Feb 2022; Accepted 17 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: We propose a semi-analytical method to evaluate the photon-nucleon interaction. Our method is based on adding an optical cavity to the neutron decay process. This model is an extension of the classical Fermi's beta decay model, which satisfactorily considers the effects of optical cavities on nuclear decay. The numerical simulation results show that this model may explain the neutron lifetime problem in the present experiment. Finally, we discuss the discrepancy in current methods of measuring neutron lifetime, which may be caused by different experimental setups.

Dephasing effect of Rydberg states on trap loss spectroscopy of cold atoms

Yifei Cao, Wenguang Yang, Hao Zhang, Weibin Li, Linjie Zhang, Liantuan Xiao, Suotang Jia, and Mingyong Jing

DOI: 10.1364/JOSAB.459064 Received 23 Mar 2022; Accepted 17 Jun 2022; Posted 21 Jun 2022  View: PDF

Abstract: In this paper, we investigate the asymmetry of trap loss spectra of ultra cold atoms during the excitation of Rydberg states. It is shown that the profile of trap loss spectrum is affected by the density of Rydberg atoms as well as dephasing rate of Rydberg states. The splitting of trap loss spectrum is shown at the higher dephasing rates of Rydberg states. A three-level model, where the dephasing rates mainly ascribe to a random collision of Rydberg atoms, reasonably explains the experimental results.

Thermally induced polarization distortions in uniaxial crystals

Evgeniy Mironov and Oleg Palashov

DOI: 10.1364/JOSAB.461456 Received 15 Apr 2022; Accepted 16 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: The polarization distortions of high-power laser radiation, which arise when it passes through a solid-state optical element cut from a uniaxial crystal, are studied theoretically and experimentally. The theoretical analysis is carried out taking into account the anisotropy of all physical properties of the crystal for an optical element with an arbitrary orientation of the crystallographic axes. Experimental verification shows convincing agreement with theoretical concepts. The problem of minimizing polarization distortions for optical elements cut in a direction close to the direction of the optical axis is considered

Passive blind quantum computation with heralded single-photon sources

Gen-Le Piao, HUA-WEI YUAN, Chunhui Zhang, Xiao Ma, HuaJian Ding, Xingyu Zhou, Jian Li, and Qin Wang

DOI: 10.1364/JOSAB.449003 Received 17 Nov 2021; Accepted 15 Jun 2022; Posted 17 Jun 2022  View: PDF

Abstract: Blind quantum computation (BQC) is one of the most promising alternatives to solve the shortage of quantum resources in the implementation of quantum computation. However, in most reported studies on decoy-state BQC, the source intensities are actively modulated, which, unfortunately, would result in side-channel leakage and undermine the system security. In this paper, we present a passive decoy-state BQC scheme with a heralded single-photon source, which circumvents this problem skillfully, improving the system security. Moreover, numerical simulation results show that our passive scheme can even outperform other active schemes in the generation efficiency of blind states when using the state-of-art equipment.

Design of Compact Si Photonic Directional Coupler Introducing Hetero-Cladding Approach

MADHUSUDAN MISHRA and Nikhil Das

DOI: 10.1364/JOSAB.454041 Received 18 Jan 2022; Accepted 13 Jun 2022; Posted 13 Jun 2022  View: PDF

Abstract: The present work proposes a new approach of hetero-cladding for silicon photonic waveguides and outlines its contribution towards realization of a compact directional coupler. The proposed hetero-cladding comprising ferroelectric BaTiO3 (BTO) and SiO2 helps control the distribution of modes and evanescent modes in the structure. The results show very small and identical coupling lengths for both TE and TM modes with reduced device cross-section, which promises for a huge reduction in the footprint of both conventional and programmable photonic integrated circuits (PICs). This concept could also be utilized to design compact, low loss and energy-efficient waveguide based other optical devices.

On the Optimization of Underwater Quantum Key Distribution Systems with Time-Gated SPADs

Amir Hossein Fahim Raouf and Murat Uysal

DOI: 10.1364/JOSAB.451237 Received 13 Dec 2021; Accepted 09 Jun 2022; Posted 10 Jun 2022  View: PDF

Abstract: In this paper, we study the effect of various transmitter and receiver parameters on the quantum bit error rate (QBER) performance of underwater quantum key distribution. We utilize a Monte Carlo approach to simulate the trajectories of emitted photons transmitting in the water from the transmitter towards receiver. Based on propagation delay results, we first determine a proper value for bit period to avoid the intersymbol interference as a result of possible multiple scattering events. Then, based on the angle of arrival of the received photons, we determine a proper field-of-view to limit the average number of received background noise. Finally, we determine the optimal value for the single photon avalanche diode (SPAD) gate time in the sense of minimizing the QBER for the selected system parameters and given propagation environment.

Investigation of number density, temperature and kinetic energy of nanosecond laser induced Zr plasma species for self-generated electric and magnetic fields in axial expansion of plume

Tayyaba Sajid, Shazia Bashir, Mahreen Akram, Maira Razzaq, Mubashir Javed, and Khaliq Mahmood

DOI: 10.1364/JOSAB.454320 Received 19 Jan 2022; Accepted 02 Jun 2022; Posted 07 Jun 2022  View: PDF

Abstract: The number density, temperature and kinetic energy of laser induced Zr plasma species have been evaluated experimentally under ultra-high vacuum condition as a function of 1 to 4cm axial distances of plume at laser irradiances ranging from 4.5 GWcm-2 to 11.7 GWcm-2. Zr plasma parameters have been evaluated using Time Of Flight (TOF) measurements by utilizing Faraday Cup (FC) as diagnostic technique. The amplitudes of signals as well as number density and temperature are strongly dependent upon laser irradiance and axial distances. With increasing laser irradiance Laser Induced Plasma (LIP) parameters show increasing trend, however a decreasing trend is obtained with increasing axial distances. LIP electron and ion number density vary from 3.13 x 1013 to 6.81 x 1013cm-3 and 1.84 x 1013 to 4.41 x 1013 cm-3 respectively. The electron temperature varies from 1.54 eV to 125 eV whereas kinetic energy of ions varies from 1.20 keV to 34 keV respectively. The maxima of Zr plasma parameters are achieved away from the target surface. In order to correlate the charge particle distribution and their energies with Self-Generated Electric and Magnetic Field (SGEMFs) the measurements have been done by employing electric and magnetic probes respectively. The signal profiles of SGEMFs reveal the quadrupolar distribution which is attributed to two oppositely generated dipoles whose contribution is strongly dependent upon axial distances and laser irradiances. The strength of both SGEMFs show an increasing trend with increasing laser irradiance and a decreasing trend is obtained with increasing probe-target distance. For overall plume axial expansion, LIP electric and magnetic fields vary from 30V/m to 3140 V/m and 0.2 T to 0.4 T respectively. Similar trends of SGEMFs and axial gradients of electron-ion number density confirm that the quadrupolar structure of plasma corresponds to the electron-ion charge separation. This charge separation is due to the spatially evolved number density and temperature gradients in plasma and their optimization will be helpful to use LIP as a powerful source of electric and magnetic fields in ion acceleration