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Effects of background gases and pressure in pulsed laser deposition of Al-doped ZnO
摘要： Background gases (O2, He or Ar) with the pressure from ~ 10?3 Pa to 133.3 Pa are used in 355 nm laser deposition of Al-doped ZnO at room temperature. The effects of these gases and pressure on plasma formation are studied by optical emission spectroscopy (OES) and time of flight (TOF) measurement. The OES results show that the emission intensity of the species in O2 and Ar decrease slightly and then increase exponentially above ~ 5 Pa. The emission intensity in Ar is the highest, followed by emission in O2 whilst the emission in He is low and weakly depend on background gas pressure. TOF measurements indicate that the ion velocity decrease with increasing O2 and Ar pressure at about 5–10 Pa. The ion velocity is highest in He while the ion velocities in O2 and Ar are similar. Thin-film samples deposited in different gas at 2.6 Pa are amorphous, but those deposited at 133.3 Pa are crystalline and exhibit different morphologies and optical properties depending on type of gas. Samples deposited in O2 are highly transparent but those deposited in He and Ar contain nano and micron-sized structures with <50% transmittance. In addition, Zn crystallites are detected by X-ray diffraction.
关键词： Pulsed laser deposition,Background gases,Aluminum-doped zinc oxide,Pressure,Laser produced plasma,Nanostructured films
更新于2025-09-23 15:21:01
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Evaluation of electron temperature and electron density of laser-ablated Zr plasma by Langmuir probe characterization and its correlation with surface modifications
摘要： The plasma parameters of laser-ablated Zirconium (Zr) using a Langmuir probe technique have been investigated by employing a Q-switched Nd:YAG laser (532 nm, 6 ns) at various irradiances ranging from 8.6 to 15.5 GW/cm2. All the measurements have been performed under an ultra-high vacuum condition while keeping the probe at a fixed distance of 4 mm from the target. By varying the biasing voltages from 1 to 75 V, the corresponding values of electric currents are measured by the probe on the oscilloscope. Laser-induced Zr plasma parameters such as electron temperature, electron number density, plasma potential, Debye length, and thermal velocity have been evaluated from I–V characteristic curves of Langmuir probe data. It is found that both the electron temperature and thermal velocity of Zr plasma reveal an increasing trend from 18 to 41 eV and 2.8 × 108 to 4.3 × 108 cm/s, respectively, with increasing laser irradiance which is attributed to more energy deposition and enhanced ablation rate. However, the electron number density of Zr plasma exhibits a non-significant increase from 6.5 × 1014 to 6.7 × 1014 cm?3 with increasing irradiance from 8.6 to 10.9 GW/cm2. A further increase in irradiance from 12 to 15.5 GW/cm2 causes a reduction in the number density of Zr plasma from 6.1 × 1014 to 5.6 × 1014 cm?3 which is attributed to the formation of thick sheath, ambipolar electric field, and laser-supported detonation waves (Shock front). Scanning electron microscope analysis has been performed to reveal the surface morphology of irradiated Zr. It reveals the formation of cracks, ridges, cones, and grains. It was observed at high irradiances the ridges are vanished, whereas cones and cracks are dominant features. By controlling plasma parameters, surface structuring of materials can be controlled, which has a vast range of applications in the industry and medicine.
关键词： electron temperature,Langmuir probe,laser-produced plasma,plasma parameters,Electron number density
更新于2025-09-23 15:19:57
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Investigation of picosecond thermodynamics in a laser-produced plasma using Thomson scattering
摘要： The picosecond evolution of the plasma conditions in a laser-produced plasma was measured using a Thomson-scattering diagnostic. The picosecond resolved Thomson spectra was enabled by a pulse-front-tilt-compensated spectrometer. The Thomson spectra revealed a transition in the plasma conditions from an initially cold evolving plasma to a quasi-stationary equilibrium plasma. The equilibrium temperature was found to match the generalized heat equation’s predicted scaling Te ∝ n2/5 and Te ∝ I 1/5. The plasma evolution was compared to Raman gain bandwidth calculations and showed a time-dependent resonance detuning that would limit the transfer e?ciency of a Raman plasma ampli?er in the linear regime.
关键词： laser-produced plasma,Thomson scattering,picosecond thermodynamics,Raman plasma amplifier,plasma conditions
更新于2025-09-19 17:13:59
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Efficient absorption of laser light by nano-porous materials with well-controlled structure
摘要： The absorption of high-power nanosecond laser pulses in a porous matter is investigated through theoretical and numerical calculations. The effects of structural properties of the porous target such as size of pores and thickness of solid elements on the laser absorption are investigated. The time and space-dependent absorption coefficient of the laser created partially homogenized plasma is used in a plasma hydrodynamic code to reproduce the laser absorption and plasma formation processes in a porous matter. It is observed that the structural characteristics of the porous material can be optimized to significantly increase the laser energy absorption. For porous targets with pore sizes in the range 30–60 nm a value around 1000 nm could be desirable for the wall thickness to increase the laser absorption efficiency to more than 90%. The results can be advantageous in production of efficient laser absorber targets which are desirable in advanced applications such as inertial confinement fusion and laser-plasma x-ray sources.
关键词： laser produced plasma,laser–matter interaction,plasma absorption coefficient,porous targets
更新于2025-09-19 17:13:59
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Multiple structure formation and molecule dynamics in transient plasmas generated by laser ablation of graphite
摘要： Transient plasmas generated by ns - laser ablation of graphite in air have been investigated by complementary optical diagnosis techniques to study complex multiple structures generated in carbon laser produced plasmas (C-LPP) during the expansion phase. The overall emission was investigated by ICCD fast camera imaging and revealed the structuring of C-LPP into four distinct structures with di?erent evolutions. The dynamic of the C-LPP was analyzed on various expansion directions in order to understand the formation of the main CN dominant structure and of lateral “?aps” with dominant C2 emission. The kinetic and thermal energies of the resulted atoms, ions and molecules were investigated by means of space-and time-resolved optical emission spectroscopy and using the Boltzmann plot and Stark broadening approaches. The e?ect of the background gas pressure on the formation of molecular carbon structures is discussed and an optimum range of working pressure which maximizes the generation of C2 is found. Based on the acquired data a scenario for the complex carbon structures generation in C-PLL as function of the background gas is proposed.
关键词： Complex carbon structures,ns-laser produced plasma,molecule dynamics,Graphite,Multiple plasma structuring,ICCD fast camera imaging
更新于2025-09-16 10:30:52
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High Energy and Short Pulse Lasers || Brilliance Improvement of a Laser-Produced Soft X-Ray Plasma
摘要： The brilliance of a laser-produced soft X-ray source is enhanced for gaseous target concepts. In contrast to solid or liquid target materials, these sources are clean and versatile but provide a comparably low conversion efficiency of laser energy into EUV and soft X-ray radiation. The basic idea is to induce supersonic effects in the gas jet, leading to a local increase of the particle density, and thus, to a larger number of possible emitters. Typically, the target gas is expanded into a vacuum environment and the density rapidly drops in all directions. In the present approach, a low pressure helium atmosphere is used to generate shock waves in the supersonic nozzle flow. Passing through these structures, the target gas is recompressed, and the particle density is raised. By focusing the laser beam into such regions, a higher number of gas atoms can be ionized resulting in a brighter and smaller plasma.
关键词： soft X-ray,supersonic jet,barrel shock,laser-produced plasma
更新于2025-09-16 10:30:52
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Characterization of radiative and kinetic properties of laser produced plasmas for efficient extreme ultraviolet nanolithography sources
摘要： Increasing extreme ultraviolet (EUV) photon power in laser-produced plasma (LPP) sources is critically important for e?cient future nanolithography devices. Enhancing the lifetime of the optical collector system in these devices is another important challenge for reliable and economically feasible devices. In this work, various mechanisms a?ecting ion acceleration in LPP were investigated to predict the maximum ion energies and ?ux arriving at the collecting mirror surfaces. Plasma evolution produced by an Nd:YAG laser from Sn targets was studied in detail to predict the dynamics of EUV producing ions and their contribution to the EUV power. The multiphysics fully 3D integrated HEIGHTS computer package was used in this analysis. HEIGHTS simulations of detail plasma evolution and ion kinetic energies were compared with various worldwide experimental data. Excellent agreement was shown regarding the range of ion kinetic energies and their angular distribution as well as recombination processes and their e?ect on the temporal output of EUV photons. Spatial and charge distributions were predicted for EUV producing ions and ionic debris. The analysis showed that mainly two Sn ions, i.e., Sn XII and Sn XIII, determine the EUV source intensity and spatial location. It was also shown that reducing the laser spot size and increasing the pulse duration allow a signi?cant reduction in ion kinetic energies that is important for a longer lifetime of the optical collection system.
关键词： laser-produced plasma,ion acceleration,extreme ultraviolet,nanolithography,EUV photon power
更新于2025-09-12 10:27:22
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Higher-order harmonic generation of laser radiation due to relativistic plasma resonance at nonrelativistic laser intensity
摘要： The well-known plasma resonance (transformation into plasma waves) at a critical density in an inhomogeneous plasma easily becomes relativistic nonlinear even at nonrelativistic laser intensities because the generated electrostatic ?eld is signi?cantly increased. Therefore, the widely used theory of harmonic generation by plasma resonance in a laser-produced plasma should be re-examined. We formulate the corresponding analytical theory of higher-order harmonic generation by nonrelativistic intense laser radiation propagating in a spatially inhomogeneous plasma. We ?nd the spectral and angular characteristics of the harmonic radiation ?eld and demonstrate the role of relativis- tic nonlinearity at plasma resonance in forming the harmonic spectra. The applicability range of the developed theory is determined by the plasma wave-breaking condition in the vicinity of the critical plasma density, which we analyze explicitly. The proposed theory is compared with the standard perturbation approach. Because the latter corresponds to low laser intensities, this comparison clearly shows the failure of the theory of harmonic generation via linear plasma resonance. The presented relativistic theory, which is applicable up to the laser intensity corresponding to plasma wave breaking, demonstrates the formation of a smooth power-law energy spectrum of higher-order laser harmon- ics in contrast to the standard perturbation theory. A spectral modulation of harmonics is also shown, which is a unique feature of relativistic nonlinearity.
关键词： laser-produced plasma,harmonic generation,wave-breaking condition,relativistic nonlinearity,plasma resonance
更新于2025-09-11 14:15:04
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ions
摘要： Laser-produced Sn plasma sources are used to generate extreme ultraviolet light in state-of-the-art nanolithography. An ultraviolet and optical spectrum is measured from a droplet-based laser-produced Sn plasma, with a spectrograph covering the range 200–800 nm. This spectrum contains hundreds of spectral lines from lowly charged tin ions Sn1+?Sn4+ of which a major fraction was hitherto unidenti?ed. We present and identify a selected class of lines belonging to the quasi-one-electron, Ag-like ([Kr]4d 10 nl electronic con?guration), Sn3+ ion, linking the optical lines to a speci?c charge state by means of a masking technique. These line identi?cations are made with iterative guidance from COWAN code calculations. Of the 53 lines attributed to Sn3+, some 20 were identi?ed from previously known energy levels, and 33 lines are used to determine previously unknown level energies of 13 electronic con?gurations, i.e., 7p, (7, 8)d, (5, 6)f , (6–8)g, (6–8)h, (7, 8)i. The consistency of the level energy determination is veri?ed by the quantum-defect scaling procedure. The ionization limit of Sn3+ is con?rmed and re?ned to 328 908.4 cm?1, with an uncertainty of 2.1 cm?1. The relativistic Fock-space coupled-cluster (FSCC) calculations of the measured level energies are generally in good agreement with experiment but fail to reproduce the anomalous behavior of the 5d 2D and nf 2F terms. By combining the strengths of the FSCC calculations, COWAN code calculations, and con?guration interaction many-body perturbation theory, this behavior is shown to arise from interactions with doubly excited con?gurations.
关键词： Sn3+ ions,energy-level structure,nanolithography,laser-produced plasma,extreme ultraviolet light
更新于2025-09-09 09:28:46