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Attosecond Pulse Shaping by Multilayer Mirrors
摘要： The emerging research field of attosecond science allows for the temporal investigation of one of the fastest dynamics in nature: electron dynamics in matter. These dynamics are responsible for chemical and biological processes, and the ability to understand and control them opens a new door of fundamental science, with the possibility to influence all lives if medical issues can thereby be addressed. Multilayer optics are key elements in attosecond experiments; they are used to tailor attosecond pulses with well-defined characteristics to facilitate detailed and accurate insight into processes, e.g., photoemission, Auger decay, or (core-) excitons. Based on the investigations and research efforts from the past several years, multilayer mirrors today are routinely used optical elements in attosecond beamlines. As a consequence, the generation of ultrashort pulses, combined with their dispersion control, has proceeded from the femtosecond range in the visible/infrared spectra to the attosecond range, covering the extreme ultraviolet and soft X-ray photon range up to the water window. This article reviews our work on multilayer optics over the past several years, as well as the impact from other research groups, to reflect on the scientific background of their nowadays routine use in attosecond physics.
关键词： attosecond,X-ray,extreme ultraviolet (EUV),soft X-ray,multilayer,mirror
更新于2025-09-23 15:23:52
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Effect of Oxygen on Thermal and Radiation Induced Chemistries in a Model Organotin Photoresist
摘要： Organotin photoresists have shown promise for next generation lithography due to their high extreme ultraviolet (EUV) absorption cross sections, their radiation sensitive chemistries, and their ability to enable high-resolution patterning. To better understand both temperature and radiation induced reaction mechanisms, we have studied a model EUV photoresist, which consists of a charge-neutral butyl-tin cluster. Temperature programmed desorption (TPD) showed very little outgassing of the butyl-tin resist in ultrahigh vacuum, and excellent thermal stability of the butyl groups. TPD results indicated that decomposition of the butyl-tin resist was first order with a fairly constant decomposition energy between 2.4 and 3.0 eV, which was determined by butyl group desorption. Electron stimulated desorption (ESD) showed that butyl groups were the primary decomposition product for electron kinetic energies expected during EUV exposures. XPS was performed before and after low energy electron exposure to evaluate the compositional and chemical changes in the butyl-tin resists after interaction with radiation. The effect of molecular oxygen during ESD experiments was evaluated and it was found to enhance butyl group desorption during exposure, and resulted in a significant increase in the ESD cross section by over 20%. These results provide mechanistic information that can be applied to organotin EUV photoresists, where a significant increase in photoresist sensitivity may be obtained by varying the ambient conditions during EUV exposures.
关键词： X-ray photoelectron spectroscopy,electron stimulated desorption,Extreme ultraviolet lithography,organotin photoresist,temperature programmed desorption
更新于2025-09-23 15:23:52
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Coherent Tabletop EUV Ptychography of Nanopatterns
摘要： Coherent diffraction imaging (CDI) or lensless X-ray microscopy has become of great interest for high spatial resolution imaging of, e.g., nanostructures and biological specimens. There is no optics required in between an object and a detector, because the object can be fully recovered from its far-field diffraction pattern with an iterative phase retrieval algorithm. Hence, in principle, a sub-wavelength spatial resolution could be achieved in a high-numerical aperture configuration. With the advances of ultrafast laser technology, high photon flux tabletop Extreme Ultraviolet (EUV) sources based on the high-order harmonic generation (HHG) have become available to small-scale laboratories. In this study, we report on a newly established high photon flux and highly monochromatic 30 nm HHG beamline. Furthermore, we applied ptychography, a scanning CDI version, to probe a nearly periodic nanopattern with the tabletop EUV source. A wide-field view of about 15 × 15 μm was probed with a 2.5 μm?diameter illumination beam at 30 nm. From a set of hundreds of far-field diffraction patterns recorded for different adjacent positions of the object, both the object and the illumination beams were successfully reconstructed with the extended ptychographical iterative engine. By investigating the phase retrieval transfer function, a diffraction-limited resolution of reconstruction of about 32 nm is obtained.
关键词： high-order harmonic generation,ptychography,lensless X-ray microscopy,Extreme Ultraviolet,Coherent diffraction imaging
更新于2025-09-23 15:21:21
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A precision polishing method for Wolter-I type optical mandrel
摘要： In the application of the 13.5-nm extreme ultraviolet (EUV) collector optics of the discharge produced plasma (DPP) source, the Wolter-I structure based on the X-ray grazing incidence optical design is usually adopted. The requirement of the surface roughness of this collector optics is demanding, which should reach to several nanometers. Currently, the mandrel replication is the main fabrication technology of this collector optics. Obviously, the requirement of the surface roughness of the mandrel used for the replication process should reach to the same level of the collector optics. However, the fabrication of the Wolter-I mandrel with high surface quality requirement still faces great challenge. In this paper, we propose a method that applies an elastic spherical tool to polish the surface of the Wolter-I mandrel, in which the shape of the elastic sphere can be changed relatively easily to accommodate the aspherical surface of the Wolter-I mandrel. A mathematical model regarding the movement trace of the polishing tool was established. Based on this model, the contact force between the polishing sphere and the aspherical surface can be controlled to point from the center of the polishing sphere in the normal direction to the polishing point. The influence of the polishing parameters on the material removal thicknesses is simulated and analyzed. The polishing experiments of ellipsoid and hyperboloid are carried out considering the difference of the diameter of each radial section on the Wolter-I mandrel surface. The proposed method is proved to reduce the surface roughness of the mandrel coated with chemically deposited nickel-phosphorous (NiP) alloy after diamond turning effectively. The root mean square (RMS) roughness of the mandrel surface after polishing can be reduced to 1.56 nm. It indicates that this method is suitable for further polishing of nickel-plated Wolter-I mandrel after ultra-precision turning. As a result, the manufacturing precision and efficiency of the Wolter-I mandrels can be improved by using the proposed polishing approach in this study, and the manufacturing cost can be reduced accordingly.
关键词： Optical mandrel,Wolter-I,Aspherical,Extreme ultraviolet,Replication manufacturing
更新于2025-09-23 15:21:21
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Beam optimization in a 25 TW femtosecond laser system for high harmonic generation
摘要： It has been demonstrated in the past that high fluxes of extreme ultraviolet (XUV) light could be obtained by driving high harmonic generation (HHG) with high energy lasers. However, the peak intensity at the focal point of a femtosecond laser with more than 100 mJ can be too high for phase-matched HHG in gases. We propose a method to optimize the spatial profile at focus by adding customized wavefront terms. An XUV pulse energy of 5.6 μJ was obtained from HHG when a larger off-focus spot of a 500 mJ Ti: Sapphire laser beam was applied in an argon gas cell.
关键词： wavefront correction,extreme ultraviolet,femtosecond laser,high harmonic generation,Ti: Sapphire laser
更新于2025-09-23 15:21:01
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Intense circularly polarized attosecond pulse generation from solid targets irradiated with a two-color linearly polarized laser
摘要： A method for the production of intense circularly polarized (CP) attosecond pulses from relativistic laser-solid interactions is proposed, where a two-color linearly polarized (LP) laser is used. The polarization, photon frequency, and other properties of the obtained attosecond pulse can be controlled by adjusting the ratio of the dichromatic driving LP field in different harmonics, which is much easier and more efficient than those previously using CP driving lasers. Both one- and two-dimensional particle-in-cell simulations show that a CP attosecond extreme-ultraviolet pulse with an intensity of 1.4 × 1019 W/cm2 and a duration of about 120 as is obtained by a two-color LP laser at intensities in the fundamental and second harmonics of, respectively, 1.5 × 1022 and 6.4 × 1021 W/cm2, which can be applied for the detection of the magnetic and chiral properties of materials.
关键词： relativistic laser-solid interactions,attosecond pulse,two-color linearly polarized laser,circularly polarized,extreme-ultraviolet pulse
更新于2025-09-23 15:21:01
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Angular dispersion enhanced prebunch for seeding ultrashort and coherent EUV and soft X-ray free-electron laser in storage rings
摘要： Prebunching is an effective technique to reduce the radiation saturation length and to improve the longitudinal coherence and output stability in storage-ring-based free-electron lasers (FELs). A novel technique is proposed which uses angular dispersion to enhance the high-harmonic bunching with very small laser-induced energy spread. This technique can effectively reduce the radiation saturation length without significantly reducing the peak power of the FEL. Numerical simulations demonstrate that this technique can be used for the femtosecond generation of 100 MW scale level, fully temporal coherent extreme-ultraviolet and soft X-ray radiation pulses through a 10 m-long undulator based on a diffraction-limited storage ring.
关键词： angular dispersion,free-electron lasers,prebunching,storage rings,high-harmonic bunching,radiation saturation length,ultrashort,extreme-ultraviolet (EUV)
更新于2025-09-23 15:21:01
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Synthesis and Property of Tellurium-Containing Polymer for Extreme Ultraviolet Resist Material
摘要： Synthesis, physical properties, and resist properties of tellurium containing polymer with pendant adamantyl ester groups poly(Re-co-Te)-AD were examined, relevant to the application of resist material for extreme ultraviolet laser photolithography (EUVL) system. A tellurium containing polymer with pendant hydroxyl groups poly(Re-co-Te) was synthesized by the condensation reaction of resorcinol (Re) and tellurium tetrachloride (TeCl4), followed by the condensation reaction with adamantyl bromo acetate to give a corresponding polymer poly(Re-co-Te)-AD. Their physical properties (solubility, film-forming ability, thermal stability) and resist properties (thickness loss property after soaking in 2.38 wt% TMAH aq. solution, out-gassing on EUV exposure tool, and resist sensitivity under EUV exposure tool) were also examined.
关键词： Adamantyl ester,Synthesis,Resist,Extreme ultraviolet,Tellurium
更新于2025-09-23 15:21:01
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Generation of coherent phonons by coherent extreme ultraviolet radiation in a transient grating experiment
摘要： We investigate the excitation of coherent acoustic and optical phonons by ultrashort extreme ultraviolet (EUV) pulses produced by a free electron laser. Two crossed femtosecond EUV (wavelength 12.7 nm) pulses are used to excite coherent phonons at a wavelength of 280 nm, which are detected via diffraction of an optical probe beam. Longitudinal and surface acoustic waves are measured in BK-7 glass, diamond, and Bi4Ge3O12; in the latter material, the excitation of a coherent optical phonon mode is also observed. We discuss probing different acoustic modes in reflection and transmission geometries and frequency mixing of surface and bulk acoustic waves in the signal. The use of extreme ultraviolet radiation will allow the creation of tunable GHz to THz acoustic sources in any material without the need to fabricate transducer structures.
关键词： transient grating experiment,optical phonons,acoustic waves,extreme ultraviolet radiation,coherent phonons
更新于2025-09-23 15:21:01
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Vacuum Arc Plasma Heated by Sub-Terahertz Radiation as a Source of Extreme Ultraviolet Light
摘要： This paper presents the results of the ?rst experimental studies of the interaction of a powerful sub-terahertz radiation with expanding highly inhomogeneous plasma of vacuum arc discharge. The tantalum plasma of a vacuum arc discharge additionally heated by the focused sub-terahertz radiation of a gyrotron, the radiation power is up to 250 kW, and the wavelength is 1.2 mm. Characteristics of the light emission in the extreme ultraviolet range are presented.
关键词： gyrotron,vacuum arc plasma,Extreme ultraviolet light,sub-terahertz radiation
更新于2025-09-23 15:21:01