Generation Of Extreme Ultraviolet Radiation Research Articles

Simulation of extreme ultraviolet radiation of laser induced discharge plasma

Extreme ultraviolet (EUV) light source is an important part of EUV lithography system in semiconductor manufacturing. The EUV light source requires that the 4p<sup>6</sup>4d<sup><i>n</i></sup>-4p<sup>5</sup>4d<sup><i>n</i>+1</sup> + 4d<sup><i>n</i>-1</sup>4f transitions of Sn<sup>8+~13+</sup> ions emit thousands of lines which form unresolved transition arrays near 13.5 nm. Laser-induced discharge plasma is one of the important technical means to excite target into an appropriate plasma condition. Laser-induced discharge plasma has a simple structure and a low cost. It also has important applications in mask inspection, microscopic imaging, and spectral metrology. In the design and production process, there are many factors that can influence the conversion efficiency, such as current, electrode shape, and laser power density. The simulation method is a convenient way to provide guidance for optimizing the parameters. In this paper, a completed radiation magneto-hydrodynamic model is used to explore the dynamic characteristics of laser-induced discharge plasma and its EUV radiation characteristics. To improve the accuracy, a more detailed global equation of state model, an atomic structure calculation model including relativistic effect and a collision radiation model are proposed simultaneously. The simulation reconstructs the discharge process effectively, which is divided into five stages in the first half cycle of current, including expansion of laser plasma, column formation of discharge plasma, diffusion of discharge plasma, contraction of discharge plasma, and re-diffusion of discharge plasma. It is revealed that the pinch effect during the current rising time exerts a significant influence on the generation of EUV radiation. The conversion efficiency of EUV radiation is still low under our existing conditions, and hopefully a higher rising rate of current can improve the conversion efficiency in the future work.

Simulation of extreme ultraviolet radiation of laser induced discharge plasma

Extreme ultraviolet (EUV) light source is an important part of EUV lithography system in semiconductor manufacturing. The EUV light source requires that the 4p<sup>6</sup>4d<sup><i>n</i></sup>-4p<sup>5</sup>4d<sup><i>n</i>+1</sup> + 4d<sup><i>n</i>–1</sup>4f transitions of Sn<sup>8+~13+</sup> ions emit thousands of lines which form unresolved transition arrays near 13.5 nm. Laser-induced discharge plasma is one of the important technical means to excite target into an appropriate plasma condition. Laser-induced discharge plasma has a simple structure and a low cost. It also has important applications in mask inspection, microscopic imaging, and spectral metrology. In the design and production process, there are many factors that can influence the conversion efficiency, such as current, electrode shape, and laser power density. The simulation method is a convenient way to provide guidance for optimizing the parameters. In this paper, a completed radiation magneto-hydrodynamic model is used to explore the dynamic characteristics of laser-induced discharge plasma and its EUV radiation characteristics. To improve the accuracy, a more detailed global equation of state model, an atomic structure calculation model including relativistic effect and a collision radiation model are proposed simultaneously. The simulation reconstructs the discharge process effectively, which is divided into five stages in the first half cycle of current, including expansion of laser plasma, column formation of discharge plasma, diffusion of discharge plasma, contraction of discharge plasma, and re-diffusion of discharge plasma. It is revealed that the pinch effect during the current rising time exerts a significant influence on the generation of EUV radiation. The conversion efficiency of EUV radiation is still low under our existing conditions, and hopefully a higher rising rate of current can improve the conversion efficiency in the future work.

Multipass cell post-compression at 515 nm as an efficient driver for a table-top 13.5 nm source

We present a table-top, efficient and power scalable scheme enabling the effective generation of extreme ultraviolet radiation up to 100 eV photon energy. Therefor ultrashort pulses (< 20fs) in the visible spectral range (515 nm) are used to drive high harmonic generation (HHG) in helium. This allows for a significant efficiency boost compared to near-infrared (NIR) drivers, enabled by the favourable scaling of the single-atom response of λ-6 [1]. The experimental realization of a mulitpass cell delivering 15.7 fs pulses with a peak power close to 25 GW at 515 nm and an overall efficiency (IR to compressed green pulse) of >40 %. In conjunction, preliminary HHG results will be presented, paving the way for mW-class HHG sources at 13.5 nm.

Compensation of laser propagation effects within solids for high harmonic generation of extreme ultraviolet radiation

High harmonic generation (HHG) from solids offers a convenient means of producing coherent extreme ultraviolet (EUV) radiation. However, the achievable harmonic yield is greatly affected by propagation effects that the driving laser pulse experiences with spatiotemporal distortion when passing through solids. Here, we intend to optimize EUV harmonics generated from crystals by pre-shaping the driving laser pulse via spectral phase modulation through a genetic algorithm. Our experimental results obtained from MgO, sapphire and quartz crystals demonstrate EUV yield improvements, without increasing the incident laser fluence, up to an order of magnitude along with cut-off extension and selective harmonic enhancement. As a practical tool of compensating laser propagation effects, our method is expected to facilitate solid-based HHG applications such as high-energy photon spectroscopy and multi-petahertz signal processing.

Electric Field-Induced High Order Nonlinearity in Plasmonic Nanoparticles Retrieved with Time-Dependent Density Functional Theory

The nonlinear response of metallic nanoparticles is obtained from quantum time dependent density functional theory calculations. Without any aprioristic assumption our calculations allow us to identify high-order harmonic generation in canonical plasmonic structures such as spherical single particles and dimers. Furthermore, we demonstrate that under currently available experimental conditions, the application of an external polarizing field to the nanoparticles allows to actively control even-order harmonic generation in otherwise symmetry forbidden situations. Our quantum calculations provide quantitative access to the high-order response of metallic nanoantennas, which is of utmost importance in the design, control, and exploitation of optoelectronic devices as well as in the generation of extreme ultraviolet radiation.

Bow-tie nano-antenna assisted generation of extreme ultraviolet radiation

We report on the generation of extreme ultraviolet radiation utilizing the plasmonic field enhancement in arrays of bow-tie gold optical antennae. Furthermore, their suitability to support high-order harmonic generation is examined by means of finite-difference time-domain calculations and experiments. Particular emphasis is paid to the thermal properties, which become significant at the employed peak intensities. A damage threshold depending on the antenna length is predicted and confirmed by our experimental findings. Moreover, the gas density in the vicinity of the antennae is characterized experimentally to determine the number of atoms contributing to the measured radiation, which is almost an order of magnitude larger than previously reported.

RECENT PROGRESS AND PERSPECTIVES OF PLASMA HARMONICS

We review recent achievements of high-order harmonic generation in the plasma plumes produced during laser ablation of various materials. These studies have demonstrated the attractiveness of a new approach in coherent extreme ultraviolet radiation generation. We also present the general ideas of potential goals of plasma harmonic studies and perspectives of the development of this relatively new field of nonlinear optics.

Generation of EUV radiation by plasmonic field enhancement using nano‐structured bowties and funnel‐waveguides

Recent experimental data of high‐order harmonic generation (HHG), obtained by use of the plasmonic field enhancement of nanostructure bowties and funnel‐waveguides, are presented. Emphasis is laid on reproduction of previous experimental results and also elucidation of the fundamental limitations associated with the nanostructure thermal damage, small laser‐gas interaction volume, and atomic line emission in the plasmon‐driven HHG process. In addition, the dominance of coherent harmonics is quantitatively verified by implementing a two‐beam interference experiment using a pair of funnel‐waveguides. This study proves that funnel‐waveguides are a superior plasmonic device capable of providing not only high thermal immunity but also sufficient atom emitters to produce practically usable extreme‐ultraviolet (EUV) radiation in a reproducible manner.

Relativistic frequency upshift to the extreme ultraviolet regime using self-induced oscillatory flying mirrors

Coherent short-wavelength radiation from laser–plasma interactions is of increasing interest in disciplines including ultrafast biomolecular imaging and attosecond physics. Using solid targets instead of atomic gases could enable the generation of coherent extreme ultraviolet radiation with higher energy and more energetic photons. Here we present the generation of extreme ultraviolet radiation through coherent high-harmonic generation from self-induced oscillatory flying mirrors—a new-generation mechanism established in a long underdense plasma on a solid target. Using a 30-fs, 100-TW Ti:sapphire laser, we obtain wavelengths as short as 4.9 nm for an optimized level of amplified spontaneous emission. Particle-in-cell simulations show that oscillatory flying electron nanosheets form in a long underdense plasma, and suggest that the high-harmonic generation is caused by reflection of the laser pulse from electron nanosheets. We expect this extreme ultraviolet radiation to be valuable in realizing a compact X-ray instrument for research in biomolecular imaging and attosecond physics.

Numerical and theoretical study of the generation of extreme ultraviolet radiation by relativistic laser interaction with a grating

The generation of harmonics by the interaction of a femtosecond, relativistic intensity laser pulse with a grating of subwavelength periodicity was studied numerically and theoretically. For normal incidence, strong, coherent emission at the wavelength of the grating period and its harmonics is obtained, nearly parallel to the target surface, due to relativistic electron bunches emanating from each protuberance. For oblique incidence (30°), only even harmonics of the grating periodicity are seen, but with an even higher intensity. This is due to constructive interference of the emission from the grating protuberances. The emission along the grating surface is composed of trains of attosecond pulses; therefore there is no need to use a filter. An efficiency greater than 10−4 is obtained for the 24th harmonic. The conversion efficiency is fairly constant when the similarity parameter S=ne/(a0nc)(∝neλL/IL1/2) is held fixed, and is optimum when S≃4. Here, ne and nc are the electron density and the critical density; a0=eEL/(meωLc) is the quiver momentum in the laser field EL normalized to mec.

Generation of extreme ultraviolet radiation with a Bessel–Gaussian beam

The generation of few high-order harmonics in the extreme ultraviolet is enhanced by focusing the fundamental femtosecond laser beam with a combination of lens and axicon in an infinite gas cell. We show that this combination leads to an improvement in the phase-matched generation of harmonics in the cutoff region, with a higher photon flux and a better spatial beam profile. A high atom density through the use of a high gas pressure can be used and the absorption limit of the harmonic generation is obtained for an interaction length of a few millimeters.

Generation of high flux, highly coherent extreme ultraviolet radiation in a gas cell

We report the generation of extreme ultraviolet radiation with high photon flux (1010–1012 photon/cm2 s), high spatial coherence (up to 0.95), and good spatial beam profile by high-order harmonic generation in various noble gases (argon, neon, and helium) in a gas cell. The photon flux was determined using an extreme ultraviolet spectrometer equipped with a charge-coupled device camera and the spatial coherence was determined from Young double-slit interference fringes. The high-order harmonic emission is confined to just a few orders because of the small phase mismatch in the cut-off region that allows macroscopic phase matching to be satisfied for just a few harmonics in this region. The efficiency and spatial beam profile are studied as a function of gas pressure and geometrical configuration.

Phase-matching for generation of few high order harmonics in a semi-infinite gas cell

Small phase-mismatch between the fundamental and high order polarization in the cut-off region, allowing macroscopic phase-matching to be satisfied for these harmonics can be used for generation of extreme ultraviolet radiation with high flux, high coherence and few harmonic orders in a semi-infinite argon gas cell.

Compact electron‐accelerator system using laser‐induced photoelectrons and DISKTRON electrostatic accelerator

A new type of relativistic electron acceleration facility is being developed by the Laser Science Research Group at The Institute of Physical and Chemical Research. It utilizes laser‐induced photoelectrons accelerated by a compact DISKTRON electrostatic accelerator, which makes it possible to generate a controllable bright short‐pulsed electron beam up to the energy of 1 MeV with a low emittance (<2×10−5 mrad) and high current density (∼500 A/cm2) without any guiding field. The characteristics of the entire facility and some of the key components are described in detail. The experimental results which confirm the possibilities of increasing quantum efficiency of metal photocathodes by geometric alteration are reported. Observation of laser undulator effects in the visible wavelength was demonstrated in the facility. The coming use of the system includes a far‐infrared/submillimeter free‐electron laser using a microwiggler and generation of extreme ultraviolet radiation by the laser undulator.

Third harmonic generation of extreme ultraviolet radiation in a nitrogen continuous free jet zone of silence

The interpretation of third harmonic generation, as obtained by crossing and focusing a pulsed laser beam on the axis of a continuous supersonic jet of nitrogen, is discussed and treated quantitatively. The geometry of the laser modes, as well as the inhomogeneity of the free jet zone of silence surrounded by the shock wave structure and the background gas, are taken into account. In this way, the variation of the phase matching factor is calculated in terms of the axial distance from the nozzle to the laser focus. This makes it possible to obtain the free jet characteristics from careful measurements of two-photon resonant, or nonresonant, frequency conversion rates. Thus the variations along the jet axis of the number density and the rotational temperature (decreasing down to 6 K), are obtained in good agreement with theoretical predictions.

Generation of extreme ultraviolet radiation at 79 nm by sum frequency mixing

High brightness tunable coherent extreme ultraviolet (XUV) radiation at 79 nm with a peak power of ∼200 mW has been generated in H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> gas by sum frequency mixing of two quanta from a high spectral brightness ArF* (193 nm) source with one quantum from a tunable dye laser (∼436 nm). Spectroscopic application of this radiation has been demonstrated by observation of a broad (∼160 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) autoionizing structure in Ar and narrow (∼2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ) autoionizing features in D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> . An analysis is given which identifies the dominant molecular states involved in the nonlinear susceptibility of the medium (H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> ). The frequency independent tuning behavior of the 79 nm output power observed over ∼300 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> is related to the molecular structure and response of the nonlinear medium in the intense optical field.