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We have observed soft X-ray spectra from highly charged ions of seven different lanthanide elements with atomic numbers ranging from 60 to 70 in laser-produced plasmas (LPPs) using CO2 and Nd:YAG laser systems, the wavelengths of which are 10.6 μm and 1.064 μm, respectively. The spectral feature drastically changes between the two types of LPPs due primarily to the difference in opacity. Narrowband quasicontinuum features arising from n = 4–4 transitions, the centre wavelength of which systematically moves to shorter wavelength as the atomic number (Z) increases, are observed in the CO2 LPPs, accompanied by sharp peaks coinciding with the strongest resonance lines of Pd-like ions for lower Z elements. In contrast, the quasicontinuum bands are broader and smoother in the Nd:YAG LPPs, appearing with bands of n = 4–5 transitions on the shorter wavelength side. The results are also discussed based on comparisons with atomic structure calculations for ions with outermost 4d and 4f subshells.

Soft x-ray and extreme ultraviolet (XUV) spectra from lead (Pb, Z=82) laser-produced plasmas (LPPs) were measured in the 1.0–7.0 nm wavelength region employing a 150-ps, 1064-nm Nd:YAG laser with focused power densities in the range from 3.1×1013 W/cm2 to 1.4×1014 W/cm2. The flexible atomic code (FAC) and the Cowan's suite of atomic structure codes were applied to compute and explain the radiation properties of the lead spectra observed. The most prominent structure in the spectra is a broad double peak, which is produced by Δn=0, n=4–4 and Δn=1, n=4–5 transition arrays emitted from highly charged lead ions. The emission characteristics of Δn=1, n=4–5 transitions were investigated by the use of the unresolved transition arrays (UTAs) model. Numerous new spectral features generated by Δn=1, n=4–5 transitions in ions from Pb21+ to Pb45+ are discerned with the aid of the results from present computations as well as consideration of previous theoretical predictions and experimental data.

Laser-produced medium element plasma sources are being considered as strong candidates for in vivo photographic imaging of biological samples in laboratory-scale water-window soft X-ray microscopes. We explored spectral changes in the emission from dual-laser-produced zirconium (Zr) plasmas in the water-window soft X-ray spectral region. The emission was enhanced at a delay time of 5 ns between the pre- and main-laser pulses and found to possess a source size of $$38\,\upmu \hbox {m }\times 68\,\upmu \hbox {m}$$ very similar to that obtained without any pre-pulse. We also investigated the decrease in emission observed at longer delay times, in the context of the collisional-radiative (CR) model-calculated absorption coefficient.

We produced 3–15 ns pulses at 10.6 μm wavelength to investigate efficient extreme ultraviolet and soft X-ray sources. A master oscillator power amplifier (MOPA) laser operating at a repetition rate of 10 Hz was built on transversely excited atmospheric (TEA) CO2 mediums. A scheme of a pulse-width tunable CO2 laser was proposed. The amplification by a 14-pass amplifier provided output energies of 150 and 60 mJ per pulse at durations of 15 ns and 3 ns, respectively. An initial observation of Gd plasmas produced by the CO2 laser shows that the spectral efficiency around 6.7 nm was improved by short laser pulses irradiation.

Soft X-ray (SXR) spectra from hafnium and tantalum laser produced plasmas were recorded in the 1–7 nm region using two Nd:YAG lasers with pulse lengths of 170 ps and 10 ns, respectively, operating at a range of power densities. The maximum focused peak power density was 2. 3 × 1014 W cm-2 for 170 ps pulses and 1. 8 × 1012 W cm-2 for 10 ns pulses, respectively. Two intense quasicontinuous intensity bands resulting from n = 4 - n = 4 and n = 4 - n = 5 unresolved transition arrays (UTAs) dominate both sets of experimental spectra. Comparison with calculations performed with the Cowan suite of atomic structure codes as well as consideration of previous experimental and theoretical results aided identification of the most prominent features in the spectra. For the 10 ns spectrum, the highest ion stage that could be identified from the n = 4 - n = 5 arrays were lower than silver-like Hf25+ and Ta26+ (which has a 4d 104f ground configuration) indicating that the plasma temperature attained was too low to produce ions with an outermost 4d subshell, while for the 170 ps plasmas the presence of significantly higher stages was deduced and lines due to 4d–5p transitions were clearly evident. Furthermore, we show an enhancement of emission from tantalum using dual laser irradiation, and the effect of pre-pulse durations and delay times between two pulses are demonstrated.

We demonstrate intense emission in the water-window soft x-ray spectral region by controlling the spectral behavior through changing the balance between emissivity and self-absorption in an expanding plasma. The number of photons obtained from a dual laser irradiated target with a 150-ps pre-pulse was maximized at 3.8 × 1014 photons/sr in λ = 2.34 − 4.38 nm at a pulse separation time of 7 − 10 ns. Enhancement of the number of photons is attributed to efficient coupling with the main laser pulse while maintaining a tiny source size.

We describe the production of mid-infrared (mid-IR) short carbon dioxide (CO2) laser pulses with variable durations from 3 to 15ns at a maximum pulse energy of 150 mJ/pulse using a germanium (Ge) substrate semiconductor switch and a multipass amplifier. The results clearly show the spectral profiles possess all of the desired characteristics as well as the possibility of obtaining an energy conversion efficiency close to the theoretical upper limit. It is also shown that it is necessary to irradiate with pulse durations less than 10ns to optimize efficient EUV emission using Sn and Gd targets.

We demonstrated the upper limitation to the number of shots, i.e., target lifetime, together with the number of photons emitted in the water-window soft x-ray spectral region from a number of targets used as sources in this spectral region, for multi-shot irradiation at the same position on the target surface. The spectra involved result from unresolved transition arrays originating from n=3–n=4 transitions in medium-Z element plasmas and from n=4–n=4 transitions originating in high-Z plasmas. The output flux was maintained for the highest number of shots in the case of the high melting point element molybdenum, and the total output in the water window was 7.7×1013 photons/sr at a laser power density of 1.2×1014 W/cm2.

We produced a 3–15-ns CO 2 laser pulse with 1011 W/cm2 for an efficient extreme ultraviolet (EUV) source by rare earth element of Gd. The EUV emission was observed a sharp spectral structure at 6.79 nm.

A broadband and high-power water window soft x-ray source based on laser-produced high-Z plasmas has a great potential for bio-nanoimaging technologies. Here, we characterized the feature of multiply ionized Au, Pb and Bi plasmas.

The effect of sub-ns duration and sub-mJ energy laser pulse on 13.5 nm extreme ultraviolet (EUV) source diameter and conversion efficiency has been investigated. It was demonstrated that an in-band EUV source diameter as low as 18 μm has been produced due to short scale length of the picoseconds duration laser plasma. Such EUV source is suitable for high brightness and high repetition rate metrology applications.

We evaluate the EUV emission an d the spatial distributions of the plasma parameters by use of the two -dimensional (2-D) radiation hydrodynamic simulation in the microplasma high -brightness EUV source. The expected EUV source size, which is attributed to the expanding microplasma by the hydrodynamic motion, was evaluated to be 15 µm at the laser pulse duration of 150 ps [full width at half -maximum (FWHM)]. The numerical simulation suggests that the high brightness EUV source should be produced by use of a dot target based microplasma with the source diameter less than 20 µm. The em ission at 13.5 nm was attributed to Sn charge states between Sn 7+ and Sn 12+ with the UTA spectral structure. Keywords: Extreme ultraviolet, high-brightness source, Sn, dot target, 2-D radiation hydrodynamic simulation 1. INTRODUCTION Extreme ultraviole t (EUV) lithography, which is required for high volume manufacturing (HVM) of integrated circuits having node sizes of 22 nm or less, is significant promising technology as the next generation imaging solution after a 193 -nm dry and/or immersion lithograph y by use of the ArF excimer laser [1]. CO

We demonstrate efficient enhancement of soft X-ray (SXR) emission from molybdenum plasmas produced using dual pulse irradiation, in which 10-ns and 150-ps pre-pulses were followed by a 150-ps main pulse. The number of photons was observed to be 5.3 × 1016 photons/sr, which corresponded to a conversion efficiency of 1.5%/sr in λ = 2.34–4.38 nm region at a pulse separation time of 1 ns with the 150-ps pre-pulse. The conversion efficiency became 1.3 times as large as that produced by a single pulse. The results indicate the advantage of dual pulse irradiation using sub-ns pre-and main pulses to produce the bright plasmas required for applications such as laboratory based SXR microscopy.

We characterized the spectral structure of the soft X-ray emission and determined the plasma parameters in laser-produced highly charged platinum plasmas. The spectral structure observed originated from Pt21+ to Pt34+ ions, emissions from which overlapped to produce a high output flux in the carbon-window soft X-ray spectral region. Using dual laser pulse irradiation, we observed the maximum output flux, which was 20% larger than that obtained under single-laser irradiation, and the evolution of a strongly absorbed spectral structure, which was attributed to the effects of both opacity and long-scale length of the expanding pre-plasma.

The unresolved transition arrays (UTAs) emitted from laser produced bismuth (Bi) plasma sources show potential for single-shot live cell imaging. We have measured extreme ultraviolet spectra from bismuth laser produced plasmas in the 1-7 nm region using a lambda = 1064 nm Nd: YAG laser with a pulse duration of 150 ps. Comparison of spectra obtained under different laser power densities with calculations using the Hartree-Fock with configuration interaction Cowan suite of codes and the UTA formalism, as well as consideration of previous predictions of isoelectronic trends, are employed to identify lines and a number of new features in spectra from Bi XXIII to Bi XLVII. The results show that Delta n. =. 0, n = 4-4 emission from highly charged ions merges to form intense UTAs in the 4 nm region and Delta n - 1, n - 4-5 resonance transitions UTAs dominate the 1-3 nm region of the Bi spectrum.

The extreme ultraviolet (EUV) emission and its spatial distribution as well as plasma parameters in a microplasma high-brightness light source are characterized by the use of a two-dimensional radiation hydrodynamic simulation. The expected EUV source size, which is determined by the expansion of the microplasma due to hydrodynamic motion, was evaluated to be 16 μm (full width) and was almost reproduced by the experimental result which showed an emission source diameter of 18–20 μm at a laser pulse duration of 150 ps [full width at half-maximum]. The numerical simulation suggests that high brightness EUV sources should be produced by use of a dot target based microplasma with a source diameter of about 20 μm.

XUV spectra of ns- and ps-laser produced platinum (Pt) plasmas in the 1-7 nm wavelength region, where Delta n = 1 n = 4-5 and Delta n = 0 n = 4-4 transitions dominate the observed emission, were investigated experimentally and theoretically. Ab initio calculations using the Hartree-Fock with configuration interaction (HFCI) Cowan suite of codes and the unresolved transition array (UTA) formalism, as well as consideration of previous predictions of isoelectronic trends, together with spectra obtained under different laser power densities are all employed to identify lines and a number of new features in spectra from Pt XX to Pt XLII. The possible reasons for the main differences between the ns- and ps-laser plasmas spectra are also demonstrated. This work extends previous analyses of the XUV spectra of laser produced gold, tungsten, tantalum, hafnium and rhenium plasmas in the 1-7 nm wavelength range.

We have characterized the spectral structure and the temporal history of the laser-produced high-Z multi-charged ion plasmas for the efficient water window soft x-ray sources. Strong unresolved transition array emission was observed due to 4d–4f and 4f–5g transitions from Au, Pb, and Bi plasmas in the 280–700 eV photon energy region. The temporal behavior of the emission was essentially similar of that of the laser pulse with a slight delay between different transitions. These results provide feedback for accurate modeling of the atomic processes with the radiative hydrodynamic simulations.

We demonstrated the generation of the intense radially polarized mid-infrared optical vortex at a wavelength of 10.6 μm by use of a passive axially symmetric zinc selenide (ZnSe) waveplate with high energy pulse throughput. The phase of the radially polarized optical vortex with the degree of polarization of 0.95 was spirally distributed in regard to the angle. The converted laser beam energy of about 2.6 mJ per pulse was obtained at the input pulse energy of 4.9 mJ, corresponding to the energy conversion efficiency of 56%.

We report on the usefulness of germanium (Ge) and gallium (Ga) plasmas as potential extreme ultraviolet (EUV) sources at both 6.x and 13.5 nm, wavelengths of interest for lithography and metrology applications. Spectra from plasmas produced using neodymium-doped yttrium-aluminum-garnet (Nd:YAG) lasers with pulse durations of 170 ps and 7 ns [full width at half-maximum] and a compact electron beam ion trap have been used to determine the charge states responsible while theoretical calculations using atomic structure Cowan and HULLAC codes enabled the identification of structure in the Ge spectrum arising from strong transitions of the type 3d – 4p and 3d – 4f. Transitions of the type 3d – 4f in Ge10+ and Ga11+ were found to lie in the 6.x nm region, while 3p−3d transitions from a range of stages in both elements contribute in the 13.5 nm region. We also studied the emission spectra of galinstan plasmas, and the results imply that galinstan might provide a promising candidate for EUV applications that explo...

Extreme ultraviolet spectra of highly-charged rhenium ions were observed in the 1–7 nm region using two Nd:YAG lasers with pulse lengths of 150 ps and 10 ns, respectively, operating at a number of laser power densities. The maximum focused peak power density was 2.6 × 1014 W cm−2 for the former and 5.5 × 1012 W cm−2 for the latter. The Cowan suite of atomic structure codes and unresolved transition array (UTA) approach were used to calculate and interpret the emission properties of the different spectra obtained. The results show that n = 4-n = 4 and n = 4-n = 5 UTAs lead to two intense quasi-continuous emission bands in the 4.3–6.3 nm and 1.5–4.3 nm spectral regions. As a result of the different ion stage distributions in the plasmas induced by ps and ns laser irradiation the 1.5–4.3 nm UTA peak moves to shorter wavelength in the ps laser produced plasma spectra. For the ns spectrum, the most populated ion stage during the lifetime of this plasma that could be identified from the n = 4-n = 5 transitions was Re23+ while for the ps plasma the presence of significantly higher stages was demonstrated. For the n = 4-n = 4 4p64dN-4p54dN+1 + 4p64dN−14f transitions, the 4d-4f transitions contribute mainly in the most intense 4.7–5.5 nm region while the 4p-4d subgroup gives rise to a weaker feature in the 4.3–4.7 nm region. A number of previously unidentified spectral features produced by n = 4-n = 5 transitions in the spectra of Re XVI to Re XXXIX are identified.

The characteristics of soft x-ray emission from optically thin high-Z plasmas of gold, lead and bismuth were investigated with the large helical device. Compared to optically thicker laser-produced plasmas, significantly different spectral structures were observed due to the difference in opacities and electron temperatures. Peak structures appearing in unresolved transition arrays were identified by calculations using atomic structure codes. The main contributors of discrete line emission in each case were Pd-, Ag-, and Rh-like ion stages. The present calculations point to the overestimation of contributions for 4p–4d transitions based on intensity estimates arising purely from gA distributions that predict strong emission from 4p–4d transitions. Understanding of such spectral emission is not only important for the completion of databases of high-Z highly ion charge states but also the development of promising high brightness sources for biological imaging applications.

We have investigated the effect of irradiation of solid Sn targets with laser pulses of sub-ns duration and sub-mJ energy on the diameter of the extreme ultraviolet (EUV) emitting region and source conversion efficiency. It was found that an in-band EUV source diameter as low as 18 μm was produced due to the short scale length of a plasma produced by a sub-ns laser. Most of the EUV emission occurs in a narrow region with a plasma density close to the critical density value. Such EUV sources are suitable for high brightness and high repetition rate metrology applications.

Bright narrow band emission observed in optically thin plasmas of high-Z elements in the extreme ultraviolet spectral region follows a quasi-Moseley's law. The peak wavelength can be expressed as λ=(21.86±12.09)×R∞−1×(Z−(23.23±2.87))−(1.52±0.12), where R∞ is the Rydberg constant. The wavelength varies from 13.5 nm to 4.0 nm as the atomic number, Z, increases from Z = 50 to Z = 83. The range of emission wavelengths available from hot optically thin plasmas permits the development of bright laboratory-scale sources for applications including x-ray microscopy and x-ray absorption fine structure determination.