Atomic, Molecular, Optical, and Plasma Physics Division focuses on fundamental interactions of atoms, molecules, optical media, and charged particles to laser lights, x rays, or other novel sources of electric and magnetic fields. These fundamental interactions are important to understand natural phenomena such as solar flares, the birth of stars, and lightning, as well as to advance modern technology such as the development of efficient light bulbs, plasma televisions, lasers, and modern infrastructures for quantum computers. We will have one invited talk from an expert in the field and several contributed talks from young scholars.
Laboratory Astrophysics with Highly Charged Ions
Highly Charged Ions (HCIs) may be considered ideal mini laboratory in which one can study the physics of matter and light in an environment of high internal electric field that cannot be recreated with standard lab equipment. While HCIs are rare on Earth, they are commonplace in the universe, in particularly in the high temperature and pressure environments of stars and solar winds. Understanding how to read the photon signature from interactions of HCIs with neutral gases in the universe gives information on the density, temperature and constituents of both. Additionally, their ultra-strong fields make HCIs ideal mini laboratories in which to test physical theories in extreme conditions. This talk will present our current work on characterizing the HCI beam at Clemson. Then I will briefly discuss our near-term plans for charge exchange.
Investigation of Laser Ablation as a Function of Pulse Length in Silicon at 1015 W/cm² Intensities
Tirtha Raj Joshi*¹, E. N. Hahn², T. Cordova², R. E. Turner², J. E. Garay², R. B. Spielman¹ and F. N. Beg¹
¹Laboratory for Laser Energetics, University of Rochester, Rochester, NY 14623-1299
²University of California San Diego, La Jolla, CA 92093
Thermomechanical shocks (TMS) caused by high x-ray intensities in the upper atmosphere have become a major threat for exoatmospheric objects orbiting in space such as satellites. We have implemented high laser fluxes and fluences as a surrogate for x-ray irradiation to generate thermomechanical shocks at multi-Mbar levels and have studied the underlying physics of laser–matter interactions. The effect of laser pulse lengths
on energy coupling into silicon has beeninvestigated in experiments on the OMEGA EP Laser System at the University of Rochester’sLaboratory for Laser Energetics. We used three-layer planar targets consisting of 50-um silicon,25μm copper, and 500μm quartz layers where the Si layer was irradiated at a fixed intensity of 1015W/cm2 with varying pulse lengths of 100-ps, 500-ps, 1-ns, and 10-ns duration. Analytical and theoretical predictions show that the ablation pressure of laser-produced plasma and hot-plasma blowoff scales with laser intensity and pulse length. Analytical predictions of ablation pressures, ignoring pulse-length scaling, are in good agreement with the measurements for pulse length τ= 10 ns, but in disagreement for τ <1 ns. Coronal plasma densities and ablation temperatures have been inferred as a function of the pulse lengths via 4w angular filtered refractometry and x-ray spectroscopy, respectively. Radiation-hydrodynamics simulations are used to generate simulated plasma density and plasma temperature profiles. Comparisons of measurements with the radiation hydrodynamic simulations and analytical solutions reveal that there exists a critical time necessary for the ablation pressure to accumulate near the target surface and that shock decay and multiple wave effects strongly dictate the evolving shock profile that propagates within the laser-shocked target as ultimately measured by rear-surface diagnostics [1] These results clearly demonstrate that the laser pulse length plays a pivotal role in plasma ablation and strong shock generation for laser impulse studies.
1. E. N. Hahn et al., “Laser-Pulse-Length–Dependent Ablation and Shock Generation in Silicon at 1015W/cm2 Intensities,” to be submitted to Physical Review Letters.
The project or effort depicted was or is sponsored by the Department of the Defense, Defense Threat Reduction Agency under the MSEE URA, HDTRA1-20-2-0001. The content of the information does not necessarily reflect the position or the policy of the federal government, and no official endorsement should be inferred. The experiment was performed under the LaserNetUS Program.
Session Schedule
Please look below for detailed schedule.
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Abstract Number: ANPA2022_0134 Presenting Author: Tirtha Raj Joshi (Invited) Presenter's Affiliation: Laboratory for Laser Energetics, University of Rochester, Rochester, NY 14623-1299 Title: Investigation of Laser Ablation as a Function of Pulse Length in Silicon at 10^15 W/cm^2 Intensities Show/Hide Abstract Thermomechanical shocks (TMS) caused by high x-ray intensities in the upper atmosphere have
become a major threat for exoatmospheric objects orbiting in space such as satellites. We have
implemented high laser fluxes and fluences as a surrogate for x-ray irradiation to generate
thermomechanical shocks at multi-Mbar levels and have studied the underlying physics of laser�matter interactions. The effect of laser pulse lengths on energy coupling into silicon has beeninvestigated in experiments on the OMEGA EP Laser System at the University of Rochester�sLaboratory for Laser Energetics. We used three-layer planar targets consisting of 50-um silicon,25-um copper, and 500-um quartz layers where the Si layer was irradiated at a fixed intensity of 10^15 W/cm^22 with varying pulse lengths of 100-ps, 500-ps, 1-ns, and 10-ns duration. Analytical and theoretical predictions show that the ablation pressure of laser-produced plasma and hot-plasma blowoff scales with laser intensity and pulse length. Analytical predictions of ablation pressures, ignoring pulse-length scaling, are in good agreement with the measurements for pulse length tau= 10 ns, but in disagreement for tau<=1 ns. Coronal plasma densities and ablation temperatures have been inferred as a function of the pulse lengths via 4w angular filtered refractometry and x-ray spectroscopy, respectively. Radiation-hydrodynamics simulations are used to generate simulated plasma density and plasma temperature profiles. Comparisons of measurements with the radiation hydrodynamic simulations and analytical solutions reveal that there exists a critical time necessary for the ablation pressure to accumulate near the target surface and that shock decay and multiple wave effects strongly dictate the evolving shock profile that propagates within the laser-shocked target as ultimately measured by rear-surface diagnostics [1] These results clearly demonstrate that
the laser pulse length plays a pivotal role in plasma ablation and strong shock generation for laser impulse studies.
1. E. N. Hahn et al., �Laser-Pulse-Length�Dependent Ablation and Shock Generation in
Silicon at 10^15 W/cm2 Intensities,� to be submitted to Physical Review Letters.
The project or effort depicted was or is sponsored by the Department of the Defense, Defense
Threat Reduction Agency under the MSEE URA, HDTRA1-20-2-0001. The content of the
information does not necessarily reflect the position or the policy of the federal government, and
no official endorsement should be inferred. The experiment was performed under the
LaserNetUS Program
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Abstract Number: ANPA2022_0135 Presenting Author: Roshan Chalise Presenter's Affiliation: Central Department of Physics, Tribhuvan University, Nepal Title: Enhancing agricultural productivity with atmospheric pressure plasma Show/Hide Abstract Atmospheric pressure plasma have wide variety of applications in different fields to
improve the quality of human life such as food safety (inactivation of microbial contamination,
bacteria free food), health (cancer treatment, wound healing, blood coagulation, dental treatment), micro-fabrication (etching, chemical vapor deposition), agriculture (insecticide, sterilization, germination, growth enhancement, fertilizers), environmental science (treatment of polluted air and water), etc. Recent advances made in production of gliding arc discharge, dielectric barrier discharge and plasma using local resources, their characterization using electrical and optical methods, and their applications by gliding arc discharge and dielectric barrier discharge in agricultural as well as for various purposes of applications will be presented. It is observed that direct treatment of seeds (coriander seed and mushroom) by gliding arc plasma causes change in contact angles of the treated seeds. The seeds become more hydrophilic and they can absorb more water such that their germination is faster. Plasma activated water is produced by exposing the gliding arc plasma in water, which is then used for irrigation for various agricultural products. The plasma activated water has decreased the ph of water and increased the conductivity. Also, direct treatment of atmospheric pressure dielectric barrier discharge plasma, contact angle of Nepali Kagaj, Palpli Dhaka and Zno thin film is declined, and activation of E. coli in water is also declined
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Abstract Number: ANPA2022_0136 Presenting Author: Santosh Dhungana Presenter's Affiliation: Kathmandu University Title: Characteristics of Plasma Activated Water (PAW) Generated from Gliding Arc Discharge (GAD) and Its Applications on Enhancement of Seed Germination of Radish Show/Hide Abstract In recent decades, generation of plasma activated water (PAW) from non-thermal atmospheric pressure plasma sources has received enormous attention due to their diverse applications. The research described in this paper is mainly focused on the preparation and characterizations of plasma activated water (PAW) produced from gliding arc discharge (GAD) and its use in the enhancement of seed germination of radish. The physical and chemical parameters of the PAW are investigated using multi-parameter probe and UV-visible spectrometer. There were significant differences in physical parameters like pH and conductivity, and chemical parameter like concentration of nitrates, nitrites, ammonia in untreated and plasma treated samples (PAW). But no significant differences in temperature and total dissolved oxygen (TDO) were found. In order to determine the effects of PAW on seed germination, different germination parameters were calculated on radish (Raphanus sativus) which indicates that PAW can enhance the seed germination of radish.
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Abstract Number: ANPA2022_0137 Presenting Author: Chandra Adhikari Presenter's Affiliation: Department of Chemistry, Physics and Materials Science, Fayetteville State University, Fayetteville, NC 28301 Title: Magic wavelength for two-photon 1S�nS transitions in deuterium Show/Hide Abstract When the optical dipole trap or the optical lattice clock is used for trapping atoms, an ac Stark shift resulting from an applied fields or laser becomes significantly larger than the target precision for the transition frequency. To cancel this shift, one needs to use the light of a special wavelength called the magic wavelength. In this work, we investigate the magic wavelength for two-photon 1S�nS transitions in a deuterium atom, where nS is an excited state with n >1, as well as 2S�nS transitions, where the lower level is the metastable 2S state. At the magic wavelength the transition frequency is independent of the intensity of the trapping laser field. Experimentally feasible magic wavelengths of transitions with small slopes in the atomic polarizabilities are determined; these are the most stable magic wavelengths against variations of the laser frequency. We also analyze the stability of the elimination of the ac Stark shift at the magic wavelength against tiny variations of the trapping laser frequency from the magic value.
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Abstract Number: ANPA2022_0138 Presenting Author: Shiva Bikram Thapa Presenter's Affiliation: Central Department of Physics, Tribhuvan University, Nepal Title: Dust charge fluctuation and ion acoustic wave propagation in dusty plasma with two temperature groups of electron: q-nonextensive hot and Maxwellian cold electrons Show/Hide Abstract The dispersion relation of ion acoustic wave in four-component plasma with Maxwellian low-temperature electron, non-extensive high-temperature electron, ions and dust particulates is derived considering Landau damping. The dust charging process with the modified damping as well as instabilities is studied. The dust charging mechanism depends upon various dusty plasma parameters such as hot electron density, non-extensivity and hot to cold electron temperature ratio. The dust charging coefficient is plasma species dependent and its nature varies greatly when the hot electron density is considerably large. The damping rate due to dust charge fluctuation including the instability of IAWs explicitly depends upon the magnitude of dusty plasma parameters. We have carried out the numerical analysis of ion acoustic Landau damping and investigated its dependence on hot to cold electron temperature ratio. The ion acoustic Landau damping becomes dominant in the high wave number limit where ions can behave as resonant particles.
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Abstract Number: ANPA2022_0139 Presenting Author: Num Prasad Acharya Presenter's Affiliation: Central Department of Physics, Tribhuvan University, Nepal Title: Dynamics of dust particles in active magnetized plasma sheath with non- thermal electrons Show/Hide Abstract We have investigated the effects of non-thermal electrons on the magnetized dusty plasma
sheath in the presence of electron impact ionization source and sink terms using fluid model.
The set of governing fluid equations have been solved for given initial conditions, whereas
the dust charging equations have been solved using Newton-Raphson method to find the dust
charge at every position in the sheath region. The magnitude of potential monotonically
increases towards the wall and in terms of magnitude, the potential drop in the sheath region
increases from 246 to 332 as the non-thermal electron distribution approaches to Boltzmann
distribution. The particle densities decrease towards the wall; however, the decreasing rate of
electrons is much faster than that of ions and dust particles. The peak value appears on the
space charge density profile in between 6.0 to 13.0 electron Debye lengths from the sheath
entrance and it decreases towards the wall after that peak value. The non-thermal electron
distribution affects the flow of velocity of ions and dust particles in the sheath region. The
dust is negatively charged close to the sheath entrance due to higher attachment rate of
electrons and this decrease as the non-thermal electron distribution approaches to Boltzmann
distribution. As the dust particles flow towards the wall, the attachment rate of ions increases
and this dominates over the electrons attachment rate close to the wall. The obtained results
are useful to understand the plasma-wall interaction mechanism which is crucial in various
applications such as in sputtering, etching, electronic industry, fusion devices, plasma
processing, and many more.
References
[1] T. Sheridan and J. Goree, Phys. Fluids B 3, 2796 (1991).
[2] X. Zhao, B. Zhang and C. Wang, Phys. Plasmas 27 (11), 113705 (2020)
[3] R. A. Cairns, A. A. Mamun, R. Bingham, R. Bostrom, R. O. Dendy, C. M. C. Nairn and P.
K. Shukla, Geophys. Res. Lett. 22, 2709 (1995).
[4] P. Shukla and A. Mamun, Introduction to Dusty Plasma Physics (Institute of Physics Publishing Ltd, Bristol,
(2002).
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Abstract Number: ANPA2022_0140 Presenting Author: Tika R Kafle Presenter's Affiliation: JILA, University of Colorado Boulder Title: Generation of deep UV light in a gas filled anti-resonant hollow core fiber Show/Hide Abstract Coherent beams in the ultraviolet (UV) and deep ultraviolet (DUV) region of the spectrum have broad applications in science and technology, for high-resolution imaging and photoelectron spectroscopies. However, traditional approaches based on non-linear optical frequency up-conversion in crystals suffer from damage (e.g., due to color-center formation), and have limited spectral range and conversion efficiency too. Here we demonstrate a simple approach for bright DUV generation at 257 nm by making use of four-wave mixing in a gas-filled anti-resonant hollow core fiber. The use of a gas medium mitigates damage issues, while the efficient fiber throughput and non-resonant condition enhances the conversion efficiency. Finally, the flexibility of tuning the repetition rate, as well as the excellent beam quality, makes it possible to scale coherent light into the deep UV and vacuum regions.
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Abstract Number: ANPA2022_0148 Presenting Author: Joan Marler (Invited) Presenter's Affiliation: Clemson University, Department of Physics and Astronomy, Clemson, SC, USA Title: Laboratory Astrophysics with Highly Charged Ions Show/Hide Abstract Highly Charged Ions (HCIs) may be considered ideal mini-laboratory in which one can study the physics of matter and light in an environment of high internal electric field that cannot be recreated with standard lab equipment. While HCIs are rare on Earth, they are commonplace in the universe, in particularly in the high temperature and pressure environments of stars and solar winds. Understanding how to read the photon signature from interactions of HCIs with neutral gases in the universe gives information on the density, temperature and constituents of both. Additionally, their ultra-strong fields make HCIs ideal mini laboratories in which to test physical theories in extreme conditions. This talk will present our current work on characterizing the HCI beam at Clemson. Then I will briefly discuss our near term plans for charge exchange cross sections combined with x-ray spectroscopy of HCIs and astrophysically relevant neutral targets.
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Abstract Number: ANPA2022_0149 Presenting Author: Tikaram Neupane Presenter's Affiliation: Chemistry and Physics Department, The University of North Carolina at Pembroke, Pembroke, NC 28372 Title: Crossover from Reverse Saturable Absorption to Saturable absorptions of Two-Dimensional TMDC Show/Hide Abstract The tunable bandgap presence in TMDCs plays a key role in the nonlinear absorption process where the monolayer has a direct bandgap and the bilayer and multilayer have an indirect bandgap. The bandgap of the monolayer is wider than that of the bilayer/multilayer. This absorption process is described by Jablonski diagrams which may include two-step absorption with one-photon for each step, two-photon absorption to the real final state through a virtual intermediate state. In the one-photon excitation, the electric dipole transition from the initial to the final state is allowed due to different parities. This implies that the ground-state absorption cross-section is higher than the excited-state absorption cross-section which results in saturable (negative) absorption; SA). However, in the two-photon excitation case, the electric dipole transitions from the initial to the final state are allowed due to the same parities between them via an intermediate state. It insinuates that the excited state absorption cross-section is higher than the ground state which consequences reverse saturable (positive) absorption; RSA). Therefore, the tunable bandgap corresponding to the number of layers switches RSA to SA or vice versa. The atomic layers with SA are utilized for laser Q-switch and mode-locker, while the atomic layers with RSA are utilized for optical power limiters. Acknowledgment: This work is supported by the College of Arts and Sciences at UNCP, funding # 101012.
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