XUV Region Research Articles

Precision spectroscopic measurements of few-electron atomic systems in extreme ultraviolet region

<sec>Precision spectroscopic measurements on the few-electron atomic systems have attracted much attention because they shed light on important topics such as the “proton radius puzzle” and testing quantum electrodynamics (QED). However, many important transitions of few-electron atomic systems are located in the vacuum/extreme ultraviolet region. Lack of a suitable narrow linewidth light source is one of the main reasons that hinder the further improvement of the spectral resolution.</sec><sec>Recently, narrow linewidth extreme ultraviolet (XUV) light sources based on high harmonic processes in rare gases have opened up new opportunities for precision measurements of these transitions. The recently implemented XUV comb has a shortest wavelength of about 12 nm, a maximum power of milliwatts, and a linewidth of about 0.3 MHz, making it an ideal tool for precision measurements in the XUV band. At the same time, the Ramsey comb in the XUV band can achieve a spectral resolution of the kHz range, and may operate throughout the entire XUV band.</sec><sec>With these useful tools, direct frequency spectroscopy and Ramsey comb spectroscopy in the XUV region are developed, and precision spectroscopic measurements of few-electron atomic systems with these methods are becoming a hot topic in cutting-edge science. In this paper, we provide an overview of the current status and the progress of relevant researches, both experimentally and theoretically, and discuss the opportunities for relevant important transitions in the extreme ultraviolet band.</sec>

Two-XUV-photon double ionization of neon

Two-XUV-photon double ionization of Ne, induced by an intense few-pulse attosecond train with a \ensuremath{\sim}4 fs envelope duration is investigated experimentally and theoretically. The experiment is performed at ELI-ALPS (Extreme Light Infrastructure Attosecond Light Pulse Source) utilizing the recently constructed 10 Hz gas phase high-order harmonic generation SYLOS GHHG-COMPACT beamline. A total pulse energy up to \ensuremath{\sim}1 \ensuremath{\mu}J generated in argon in conjunction with high-reflectivity optics in the XUV region allowed the observation of the doubly charged state of Ne induced by 40 eV central XUV-photon energies. The interaction of the intense attosecond pulse train with Ne is also theoretically studied via second-order time-dependent perturbation theory equations of motion. The results of this work, combined with the feasibility of conducting XUV-pump--XUV-probe experiments, constitute a powerful tool for many potential applications. Those include attosecond pulse metrology as well as time-resolved investigations of the dynamics underlying direct and sequential double ionization and their electron correlation effects.

Interaction of Electron Beams and Polarized Radiation in a Two-Beam Free-Electron Laser

Recent research has focused on shorter pulses, new spectral ranges, higher photon fluxes, and the production of photons with a variety of polarizations. A time-dependent three-dimensional free-electron laser oscillator code was developed for a two-beam free-electron laser system with an elliptically polarized undulator. Characteristics of the interaction of the electron beams and polarized radiation in the XUV region were studied using this code. The code utilized an optical field using the spectral method in the paraxial approximation by a fast Fourier transformation, a Gaussian modal expansion for the optical field, and Newton–Lorentz force equations for particle tracking. As the emittance was increased, the degrees of polarization of the single-beam system with an elliptically polarized undulator and the two-beam system with a planar undulator were decreased significantly compared to those of a two-beam system with an elliptically polarized undulator in the XUV regions. The radiation intensities, the evolutions of the radiation power for wavelength, and the time in the two-beam system were increased significantly compared to those of a single-beam system. The statistical simulation result for the distribution of the number of shots in the degrees of polarization in the two-beam system was much better than that of the case with the single-beam system.

A comparison of the UV and HI properties of the extended UV (XUV) disk galaxies NGC 2541, NGC 5832 and ESO406-042

We present a UV study of 3 extended UV (XUV) galaxies that we have observed with the UVIT and the GMRT. XUV galaxies show filamentary or diffuse star formation well beyond their optical disks, in regions where the disk surface density lies below the threshold for star formation. GALEX observations found that surprisingly 30% of all the nearby spiral galaxies have XUV disks. The XUV galaxies can be broadly classified as type 1 and type 2 XUV disks. The type 1 XUV disks have star formation that is linked to that in their main disk, and the UV emission appears as extended, filamentary spiral arms. The UV luminosity is associated with compact star forming regions along the extended spiral arms. The star formation is probably driven by slow gas accretion from nearby galaxies or the intergalactic medium (IGM). But the type 2 XUV disks have star formation associated with an outer low luminosity stellar disk that is often truncated near the optical radius of the galaxy. The nature of the stellar disks in type 2 XUV disks are similar to that of the diffuse stellar disks of low surface brightness galaxies. The star formation in type 2 XUV disks is thought to be due to rapid gas accretion or gas infall from nearby high velocity clouds (HVCs), interacting galaxies or the IGM. In this paper we investigate the star formation properties of the XUV regions of two type 2 galaxies and one mixed XUV type galaxy and compare them with the neutral hydrogen (HI) emission in their disks. We present preliminary results of our UVIT (FUV and NUV) observations of NGC 2541, NGC 5832 and ESO406-042, as well as GMRT observations of their HI emission. We describe the UV emission morphology, estimate the star formation rates and compare it with the HI distribution in these type 2 and mixed XUV galaxies.

Tuning the electronic band structure of metal surfaces for enhancing high-order harmonic generation

High-harmonic generation (HHG) from the condensed matter phase holds promise to promote future cutting-edge research in the emerging field of attosecond nanoscopy. The key for the progress of the field relies on the capability of the existing schemes to enhance the harmonic yield and to push the photon energy cutoff to the extreme-ultraviolet (XUV, 10-100eV) regime and beyond toward the spectral "water window" region (282-533eV). Here, we demonstrate a coherent control scheme of HHG, which we show to give rise to quantum modulations in the XUV region. These modulations are shown to be caused by quantum-path interferences and are found to exhibit a strong sensitivity to the delocalized character of bulk states of the material. The control scheme is based on exploring surface states in transition-metal surfaces and, specifically, tuning the electronic structure of the metal surface itself together with the use of optimal chirped pulses. Moreover, we show that the use of such pulses having moderate intensities permits us to push the harmonic cutoff further to the spectral water window region and that the extension is found to be robust against the change in the intrinsic properties of the material. The scenario is numerically implemented using a minimal model by solving the time-dependent Schrödinger equation for the metal surface Cu(111) initially prepared in the surface state. Our findings elucidate the importance of metal surfaces for generating coherent isolated attosecond XUV and soft-x-ray pulses and for designing compact solid-state HHG devices.

Femtosecond Single Cycle Pulses Enhanced the Efficiency of High Order Harmonic Generation.

High-order harmonic generation is a nonlinear process that converts the gained energy during light-matter interaction into high-frequency radiation, thus resulting in the generation of coherent attosecond pulses in the XUV and soft x-ray regions. Here, we propose a control scheme for enhancing the efficiency of HHG process induced by an intense near-infrared (NIR) multi-cycle laser pulse. The scheme is based on introducing an infrared (IR) single-cycle pulse and exploiting its characteristic feature that manifests by a non-zero displacement effect to generate high-photon energy. The proposed scenario is numerically implemented on the basis of the time-dependent Schrödinger equation. In particular, we show that the combined pulses allow one to produce high-energy plateaus and that the harmonic cutoff is extended by a factor of 3 compared to the case with the NIR pulse alone. The emerged high-energy plateaus is understood as a result of a vast momentum transfer from the single-cycle field to the ionized electrons while travelling in the NIR field, thus leading to high-momentum electron recollisions. We also identify the role of the IR single-cycle field for controlling the directionality of the emitted electrons via the IR-field induced electron displacement effect. We further show that the emerged plateaus can be controlled by varying the relative carrier-envelope phase between the two pulses as well as the wavelengths. Our findings pave the way for an efficient control of light-matter interaction with the use of assisting femtosecond single-cycle fields.

Computation of Refractive Index Values of Inert Gases at Near Infrared and XUV Region based on Mathematica Software

In this study, refractive indices in the visible, near infrared and extreme ultraviolet (XUV) region are calculated based on Mathematica software. Atomic scattering factors are simulated for high photon energy range (20-60eV). By using the atomic scattering factors, the real and imaginary part of index of refraction values are plotted as a function of photon energy. The aim of this work is to present a computational program, which calculates the index of refraction of the inert gases at different wavelength regions. The refractive indices of gases, namely helium (He), neon (Ne), argon (Ar) and xenon (Xe) in the near infrared and XUV region are computed by using a Mathematica software. The applications of the index of refraction are discussed through the paper. The Mathematica program calculating the refractive indices is presented in the Appendix.

Extreme Ultraviolet Frequency Comb with More than 100 μW Average Power below 100nmSupported by the National Natural Science Foundation of China (Grant Nos. 11674356 and 11527807), and the Strategic Priority Research Program of the Chinese Academy of Sciences (Grant No. XDB21010400).

Extreme ultraviolet (XUV) frequency comb is a powerful tool in precision measurement. It also brings many new opportunities to the field of strong field physics since high harmonic generation related phenomena can be studied with high repetition rate. We demonstrate the generation of an XUV frequency comb with the aid of intra-cavity high harmonic generation process. The setup is driven by a high power infrared frequency comb, and an average power of 4.5 kW is reached in the femtosecond enhancement cavity. With Xe gas as the working media, harmonics up to the 19th order are observed. Power measurement indicates that as much as 115.9 μW (1.3 mW) are generated at ∼94 nm (∼148 nm). The shortest wavelength we can reach is ∼55 nm. The coherence of the generated light is tested with an optical-heterodyne-based measurement of the third harmonic. The resulted line width is ∼3 Hz. In addition, with this system, we also observe a strong suppression of below threshold harmonics from O2 compared to that from Xe. These results suggest that the current system is ready for precision spectroscopic measurements with few-electron atomic and molecular systems in XUV region as well as the study of strong field physics with an unprecedented 100MHz repetition rate.

Generation of even and odd harmonics in the XUV region with controlling the relative delay and polarization of two-color fields

Abstract We report high harmonic generation in the extreme ultraviolet (XUV) region by using two-color laser fields at the wavelengths of 800 nm and 400 nm. With a Ti: sapphire femtosecond laser at a 10 Hz repetition rate efficient high harmonic generation was obtained in an argon gas medium with the IR field (ω) and its second harmonic (2ω) with parallel and perpendicular polarizations. The relative delay between the pulses is controlled via a Michelson interferometer arrangement. In addition to the odd high harmonic spectrum with frequencies (2n+1)ω, where n - integer number, also even spectral components 2nω are obtained, when the fields of the two colors are temporally overlapped and interact with the argon gas. Due to this overlap, the yield of odd harmonics can be increased as well. The calculations of electron trajectories within the semi-classical approach show differences in the action of the fields with parallel and perpendicular polarizations. For the former, there exist broad time intervals for returning electrons, and in the latter case there are only narrow intervals for possible solutions for each of the electron returns to the parent ion for a fixed phase difference between the ω and 2ω fields. By varying the relative delay between the two laser fields it is possible to spectrally enrich and enhance the produced XUV radiation or suppress it. The conclusions of the semi-classical approach were confirmed by calculations of the harmonic intensities within the strong field dipole approximation.

Development and prospect on driving laser for attosecond pulse

<p indent="0mm">Attosecond light source is a new type of light source that was born at the beginning of the 21st century, which has a short pulse, broad spectrum, high temporal and spatial coherence and wide tunability, thus being widely employed in various research fieds. From ultrafast motion of electrons in atoms to charge transfer in biological macromolecules, attosecond pulses is currently the only tool that can track and capture these ultrafast dynamics. Attosecond pulse enables us to investigate ultrafast dynamics of micro-world both in nanometer and attosecond scales. However, the mechanism of attosecond pulse generation is completely different from general ultrafast lasers. Instead, attosecond pulse is generated by a highly nonlinear interaction between strong ultrafast femtosecond laser and matter, which is called high-order harmonic generation (HHG). The mechanism of HHG can be understood by a classical three step model. First, an electron is ionized from an atom by a strong laser electric field through tunnel ionization. Then the free electron is accelerated by the laser field and gains energy. Finally, the electron recombines with the parent ion when the laser field changes its sign with emission of a photon, whose energy equals its kinetic energy gained in the laser field plus ionization potential of the atom. Apparently, HHG is strongly affected by the laser waveform. Several key parameters of driving laser, such as wavelength, intensity, and carrier envelope phase strongly affect the process of HHG. Thus, the characteristics of attosecond pulses are determined by the driving laser. The rapid development of attosecond pulse technology strongly depends on the development of driving laser technology. In the beginning, chirped pulse amplification (CPA) technology greatly promoted the development of attosecond light sources. The femtosecond CPA systems based on Ti:sapphire crystal has been the main driving laser to generate attosecond light pulses. The driving laser wavelength is in the near infrared region near <sc>800 nm,</sc> which generally has a pulse duration of multiple optical cycles. By employing post-compression technology to shorten pulse durations of CPA systems to few-cycle, isolated attosecond pulses in the extreme ultraviolet (XUV) can be generated, which is called the first generation of attosecond light source. Recently, optical parametric amplification (OPA) systems have been widely used as driving laser due to its flexible wavelength tunability. Using OPA, longer driving laser wavelength up to the midinfrared (MIR) can be obtained, which pushes the attosecond pulses to the soft X-ray region, and has been called the second generation of attosecond light sources. Due to broad spectrum and higher photon energy, attosecond pulses have a shorter duration in the soft X-ray region compared with XUV region, given that the temporal chirp is properly compensated. In 2017, reseachers generated soft X-ray isolated attosecond pulses, which was driven by mid-infrared pulses centered at <sc>1.8 µm.</sc> These attosecond pulses, whose duration reaches 53 as and spectrum surpasses carbon K-edge, provide a tool for studying the ultrafast dynamics of diamond, graphene and other carbon materials. In this paper, we start with the principle of attosecond pulses generation based on HHG. Then, we introduce different technologies and their development for obtaining driving laser pulses for HHG. Finally, we introduce prospect on development of driving laser pulses for attosecond pulses generation.

High repetition rate ultrafast laser technology for drivinghigh-order harmonic generation

The interaction of ultra-intense and ultrafast laser pulses with matter has paved the way for generation of ultrashort pulses in the attosecond timescale and coherent radiation in the extreme ultraviolet (XUV) and soft X-ray region at a table-top size. On one hand, it provides attosecond temporal resolution and atomic spatial resolution for ultrafast electron dynamics in atoms, molecules and condensed matters; on the other hand, it inspires the great potential of optical frequency comb (OFC) in precise measurements of transition frequencies and hyperfine splitting, a verification of basic physical constants such as the Rydberg constant, and the research on precise optical atomic clocks. With the expansion of the above-mentioned scientific researches, the repetition rate of the driving source has become the key factor to break through the measurement accuracy obstacles. Therefore, the research on high-repetition rate ultrafast laser technology for driving high-order harmonic generation (HHG) commences. In this paper, the high repetition rate HHG as the starting point, the method applied, the main parameter indices and the technical difficulties of the driving source are summarized. This paper can be a reference for the future development of high-repetition rate ultrafast laser technology for driving HHG. First of all, the research involving femtosecond enhancement cavity (fsEC) using passive amplification is introduced. The repetition rate of the high-order harmonics as obtained from this method has exceeded 100 MHz, which serves as the main technical means to obtain OFC in the XUV region. However, key issues, such as dispersion control of the high-precision resonator and stabilization of femtosecond laser frequency, are still the focus for future research and the current application difficulties of fsEC technology. Secondly, the research on Ti:sapphire laser system, ytterbium (Yb) doped fiber laser system and Yb all-solid-state laser system are reviewed. The few-cycle femtosecond pulse output by the Ti:sapphire laser system has an extremely high peak power, and it is the main driving source for generation of high-order harmonics and isolated attosecond pulses. However, constrained by the average power of the Ti:sapphire laser system, it is difficult to increase the repetition rate of XUV laser pulses to hundreds kilohertz or even megahertz. The thin-disk laser oscillator and the Yb fiber amplifier can produce femtosecond pulses with high average power. By means of nonlinear spectral broadening and pulse compression, an extreme ultraviolet radiation with a repetition rate of 10 MHz has been obtained in the HHG process of gases, yet the system structure remains complex and the technical difficulty is still high. Meanwhile, the Yb all-solid-state femtosecond amplifier, which can directly produce ultrashort pulses with high peak power, serves as an ideal driving source to realize HHG with the repetition rate on the MHz level. In view of the development trends of high-repetition rate driving sources, and based on the research experience on high-power Yb femtosecond lasers of our group, we propose high repetition rate ultrashort all-solid-state Yb amplifier for driving MHz repetition rate HHG with sub -40 fs all-solid-state Yb oscillator as seed and key techniques of gain narrowing suppression, precise dispersion control and efficient thermal management. Finally, the parameters of various technical means in passive amplification and gain amplification, as well as the key problems that need to be solved, are summarized, and the development trends of high repetition rate ultrafast laser technology for driving HHG are prospected.

Generation of coherent broadband high photon flux continua in the XUV with a sub-two-cycle fiber laser.

High harmonic sources can provide ultrashort pulses of coherent radiation in the XUV and X-ray spectral region. In this paper we utilize a sub-two-cycle femtosecond fiber laser to efficiently generate a broadband continuum of high-order harmonics between 70 eV and 120 eV. The average power delivered by this source ranges from > 0.2 µW/eV at 80 eV to >0.03 µW/eV at 120 eV. At 92 eV (13.5 nm wavelength), we measured a coherent record-high average power of 0.1 µW/eV, which corresponds to 7 · 109 ph/s/eV, with a long-term stability of 0.8% rms deviation over a 20 min time period. The presented approach is average power scalable and promises up to 1011 ph/s/eV in the near future. With additional carrier-envelop phase control even isolated attosecond pulses can be expected from such sources. The combination of high flux, high photon energy and ultrashort (sub-) fs duration will enable photon-hungry time-resolved and multidimensional studies.

Reflective aperiodic multilayer filters for metrology at XUV sources.

We present a general method for designing XUV aperiodic multilayer mirrors that can mimic a given target spectrum, specifically, the spectral transmission of an XUV optical system. The method is based on minimizing a merit function and using fidelity parameters that quantify the matching of the multilayer reflectivity spectrum with that of the target spectrum. To assess the feasibility of fabricating such a system, we show how to reduce the layer-to-layer thickness variations throughout the aperiodic layer stack. We demonstrate the design method using an example of an EUV optical system composed of 12 identical Mo/Si multilayer mirrors having a reflectivity peak at 13.5 nm. We found that the target spectrum can be mimicked with high fidelity either with a single reflection at an aperiodic multilayer mirror combined with standard absorbing filters or, if required, with two subsequent reflections at a mimic mirror. These examples demonstrate the applicability for metrology at XUV sources, including spectrally proper source imaging. Because our approach is of general applicability, the process can be used to mimic any other narrowband, single-peaked target spectrum in the XUV region.

Theoretical calculations on photoelectron angular distribution of sequential two-photon double ionization for Ar atom

With the development of the intense light source, such as free electron lasers, the experiments on the nonlinear process in atomic photo absorption in the XUV and X-ray region became more and more feasible. As one of the simplest possible nonlinear processes, the sequential two-photon double ionization, in which the first photon produces an ion which is subsequently ionized by the second photon, attracts increasing attention of theorists and experimentalists. Study on the angular distributions and angular correlations of the photoelectrons in the sequential two-photon double ionization process are especially attractive, which provides valuable information about the electronic structure of atom or molecule systems and allows the obtaining of additional information about mechanism and pathway of the two-photon double ionization. In this paper, the expression for the photoelectron angular distribution in a sequential two-photon process is given based on the multi-configuration Dirac-Fock method and the density matrix theory. And then, the relativistic calculation program for photoelectron angular distribution is further developed with the help of the program packages GRASP2K and RATIP which are based on the multi-configuration Dirac-Fock method. By using this code, the sequential two-photon double ionization of the 3p shell in atomic argon is studied theoretically. The cross section, magnetic cross section, alignment of residual ions and the asymmetry parameter of the photoelectron angular distribution, each as a function of photon energy, for the first and the second step of sequential two-photon double ionization of argon are presented. The calculations predict that the alignment has a maximum value and the asymmetry parameter has a minimum value in the region of the cooper minimum. The angular distribution of the first step ionization for Ar atom and the second step ionization for Ar&lt;sup&gt;+&lt;/sup&gt; ion are given at 33.94 eV and 55.34 eV photon energy, respectively. In addition, the difference in property between the angular distributions of the first photoelectron in sequential two-photon double ionization and in conventional one-photon single ionization is discussed. The present calculated results are compared with other available results, showing that they are in good agreement with each other. The results of this paper will be helpful in studying nonlinear processes in the XUV range.

Four-wave mixing of extreme ultraviolet pulses and infrared pulses for studies of atomic dynamics

We apply a cascaded four-wave mixing process in the extreme ultraviolet (XUV) region using two collinear multiple-cycle laser pulses with incommensurate frequencies (wavelengths 1400 and 800 nm) to construct a two-dimensional cross-correlation spectrum. We show that the two-dimensional spectrum can be used to extract the amplitude and phase modifications of the atomic dipole moments of the coupled states in atomic krypton interacting with the intense pulsed laser light. The experimental configuration and a simple model for qualitative interpretation allow us to demonstrate the validity and power of the 2D spectroscopy method in the XUV region.

Self referencing attosecond interferometer with zeptosecond precision.

In this work we demonstrate the generation of two intense, ultrafast laser pulses that allow a controlled interferometric measurement of higher harmonic generation pulses with 12.8 attoseconds in resolution (half the atomic unit of time) and a precision as low as 680 zeptoseconds (10-21 seconds). We create two replicas of a driving femtosecond pulse which share the same optical path except at the focus where they converge to two foci. An attosecond pulse train emerges from each focus through the process of high harmonic generation. The two attosecond pulse trains from each focus interfere in the far field producing a clear interference pattern in the extreme ultraviolet region. By controlling the relative optical phase (carrier envelope phase for pulsed fields) between the two driving laser pulses we are able to actively influence the delay between the pulses and are able to perform very stable and precise pump-probe experiments. Because of the phase shaping operation occurs homogeneously across the entire spatial profile, we effectively create two indistinguishable intense laser pulses or a common path interferometer for attosecond pulses. Commonality across the two beams means that they are extremely stable to environmental and mechanical fluctuations up to a Rayleigh range from the focus. In our opinion this represents an ideal source for homodyne and heterodyne spectroscopic measurements with sub-attosecond precision.

Phase-matched nonlinear wave-mixing processes in XUV region with multicolor lasers.

We report here experimental results of perturbative nonlinear optical wave-mixing processes in the extreme ultraviolet region by using two-color and three-color laser fields. Besides the usual odd-harmonic spectrum of high harmonic generation, new spectral components are observed when multiple incommensurate lasers (one driving plus one or two control field) interact with neutral krypton gas. To demonstrate the wave-mixing process underlying such an observation, we first couple the driving field with either the signal or the idler field of an optical parametric amplifier in the gaseous ensemble to generate certain mixing frequencies. The two control fields are then simultaneously combined with the driving field to produce broad and distinguishable mixing peaks that clearly reveal the contribution of each control laser. Finally, the variation of the intensity of the mixing waves with the intensity of each control field, the gas density, and the relative focus position is examined for signatures of phase-matched generation of the mixing fields in this spectral region.

XUV spectra and soft X-ray laser wavelengths of 4f–4d transitions in $${\hbox{Ni}}^{+8}$$ Ni + 8

For $$3p^{6}3\hbox {d}4l$$ where $$l=s, p, d, f$$ states in $$\hbox {Ni}^{+8}$$ , we evaluated both oscillator strengths and energy levels to investigate the probability of laser wavelengths production in the soft X-ray and XUV regions. The calculations are executed using CIV3 and LANL codes. By comparing the values of our results with other published experimental and theoretical data, a good match is achieved in addition to unpublished values of oscillator strengths and energy levels have been obtained. Using calculated oscillator strengths, the gain coefficients, and reduced populations have been calculated for $$\hbox {Ni}^{+8}$$ at different plasma temperatures, such as $$T = 1/4$$ the ionization potential energy (IP) of the $$\hbox {Ni}^{+8}$$ ; and the same thing for $$T = 1/2\ IP$$ and $$T = 3/4\ IP$$ . Promised values of positive laser gain are shown to obtain laser wavelengths in XUV and soft X-ray regions from current computed atomic data. Extreme ultraviolet radiation XUV is electromagnetic radiation in the part of the electromagnetic spectrum spanning wavelengths from 124 nm down to 10 nm.

The emission spectra and hydrodynamic properties of Al plasma using Nd-YAG laser

In this work, the emission spectra and atomic structure of the aluminum target had been studied theoretically using Cowan code. Cowan code was used to calculate the transitions of electrons between atomic configuration interactions using the mathematical method called (Hartree-Fock). The aluminum target can give a good emission spectrum in the XUV region at 10 nm with oscillator strength of 1.82.The hydrodynamic properties of laser produced plasma (LPP) were investigated for the purpose of creating a light source working in the EUV region. Such a light source is very important for lithography (semiconductor manufacturing). The improved MEDUSA (Med103) code can calculate the plasma hydrodynamic properties (velocity, electron density, pressure, electron temperature, ion density, ion temperature and average ionization Z*). Aluminum target was considered in these calculations (Z=13). This work was done by using three laser power densities (1011, 1012 and 1013 W/cm2) with a 10 ns pulse width and 10 ps pulse width for laser wavelength (1064 nm). These laser intensities with 10 ns pulse width give high ionization stage of the Aluminum from 2.4-11 for electron range from 16.5-3000 eV.

Cascaded four-wave mixing in the XUV region.

We present a detailed study of the wave-mixing process in the extreme ultraviolet (XUV) region (around 30nm) by using two collinear multiple-cycle laser pulses with incommensurate frequencies (wavelengths 1400 and 800nm). The experimental data provide evidence for the coherent accumulation of wave-mixing fields and a high third-order response of the medium in this spectral range. We show that the time evolution of the mixing fields can be used to study the coherence dynamics of the free-electron wave packet with a lifetime of 200-750fs.