We describe our recent progress in the investigation of the spectral properties of collisional XUV lasers, including both
experimental measurements and numerical calculations. Using a wavefront-division, variable path-difference
interferometer, we have characterized the temporal coherence and the spectral width of an injection-seeded transient
XUV laser emitted at 18.9 nm from a Ni-like Mo plasma. Our results show that the temporal coherence of the beam is
significantly increased by the injection-seeded operation, compared to the standard ASE mode, in agreement with
detailed numerical simulations. Using the PPP code we have calculated the intrinsic linewidth of the same lasing line
over a range of electron density and at temperatures that are relevant to transient collisional pumping. We discuss the
relative contributions of homogeneous and inhomogeneous broadening to the overall profile.
The LASERIX facility provides coherent and short soft x-ray beams for scientific applications. The beams are generated through high intensity laser interaction with matter using two different schemes, plasma based soft x-ray lasers, and high order laser harmonic generation. We describe in this communication the present status
of the facility. The LASERIX beamtime has been recently opened to external users. We present two typical experiments performed in that context with the facility. The first one is dedicated to the fundamental study of the plasma based soft x-ray laser, whereas the second uses the existing beam to study irradiation induced
dammage in DNA samples. We present also the development performed on the soft x-ray laser source to improve its stability and high repetition rate operation.
Since the first seeding of an OFI soft x-ray laser in 2004, we progressed towards the full characterization of the output
beam. The final is to be able to deliver to users well-known beam. Temporal as well as spatial parameters have been
measured for different conditions of amplification. We observed a strong enhancement of the spatial coherence due to
the amplification process with a far-field pattern exhibiting an airy-like shape. The gain zone having strong discontinuity
behaves like a hard pinhole. Spatial filtering has been also observed on the wave front (δ/5 root-mean-square, rms,
before seeding and δ/20 rms after amplification). Temporal coherence has been studied thanks to the use of a Fourier-
Transform spectrometer. Spectral widths, δδ/δ, around 10<sup>-5</sup> have been measured for different plasma lengths or gas pressures. Departure from Gaussian shape has been clearly observed on the spectral line for some cases.
EUV lithography is expected to be inserted for the 32 nm node and extended for the 22 nm and below. Phase shift masks (PSM) are evaluated as a possible option to push the resolution limit of the Extreme Ultra violet lithography. This paper will focus on designs and measurements of PSM implemented by etching into the Mo/Si multilayer (ML). The design and the technological developments to elaborate PSM by etching is described. Phase shift Sample (PSS) have been carried out to calibrate in "true operating conditions", i.e. through the measurement of the phase shift they produce on a reflected wavefront, at the wavelength (λ=13.5nm). The method of calibration have been investigated with a Fresnel bimirror interferometer installed on the PSI Swiss Light Source Synchrotron to measure directly the value of interest, i.e the optical phase.
We present a detailed analysis of an experiment carried out recently in which the temporal coherence of the Ni-like silver transient X-laser at 13.9 nm was measured. Two main consequences of this measurement will be discussed and interpreted with numerical calculations. First we show that the high temporal coherence length measured corresponds to an extremely narrow spectral width of the X-ray laser line. Second we show that the high temporal coherence helps to explain the presence of small-scale structures observed in the cross-section of all transient X-ray laser beams.
We give an overview of recent advances in development and applications of deeply saturated Ne like zinc soft X-ray laser at PALS, providing strongly saturated emission at 21.2 nm. Population inversion is produced in the regime of long scale-length density plasma, which is achieved by a very large time separation between the prepulse (<10 J) and the main pump pulse (~500 J), of up to 50 ns. This pumping regime is unique in the context of current x-ray laser research. An extremely bright and narrowly collimated double-pass x-ray laser beam is obtained, providing ~10 mJ pulses and ~100 MW of peak power, which is the most powerful soft X-ray laser yet demonstrated. The programme of applications recently undertaken includes precision measurements of the soft X-ray opacity of laser irradiated metals relevant to stellar astrophysics, soft X-ray interferometric probing of optical materials for laser damage studies, soft X-ray material ablation relevant to microfabrication technologies, and pilot radiobiology studies of DNA damage in the soft X-ray region. A concomitant topic is focusing the x-ray laser beam down to a narrow spot, with the final goal of achieving ~10<sup>13</sup> Wcm<sup>-2</sup>.
We review our recent progress in the development of transient x-ray lasers and of their application to plasma diagnostic. The first observation of C-ray laser emission at the new PHELIX-GSI facility is reported. This TCE X-ray laser will be a promising tool for heavy-ion spectroscopy. We then present the main results obtained at the LULU-CPA facility with a compact high-resolution X-UV imaging device. This device was used to investigate the spatial source structure of the Ni-like silver transient X-ray laser under different pumping conditions. The key-role of the width of the background laser pulse on the shape of the emitting aperture is demonstrated. Finally the imaging device was used as an interference microscope for interferometry probing of a laser-produced plasma. We describe this experiment performed at APRC-JAERI.
We present a review of new progress performed in several laboratories (Laboratoire pour l'Utilisation des lasers Intenses, Rutherford Appleton Laboratory, Prague Asterix Laser System, Institute of Laser Engineering, Laboratoire d'Optique Appliquee). Concerning the realization of x-ray lasers sources, using different laser pumping techniques (600 ps, 100 ps, ns/ps, OFI) and the optimization of their optical properties, using curved and plane half-cavity mirrors. In parallel of these developments, we present the main results obtained with x-ray laser in interferometry applications. These studies concern on the one hand the Michelson interferometry with an x-ray laser emitting at 13.9 nm (recently realized at LULI), and on the other hand the Fresnel bi-mirror with an x-ray laser emitting at 21.2 nm (recently realized at PALS).
This paper summarizes our recent progress achieved in the characterization and understanding of the Ni-like Ag transient x-ray laser pumped under traveling wave irradiation. At the Rutherford Laboratory CPA laser facility, we measured the temporal history of the 13.9 nm laser pulse with a high-resolution streak camera. A very short, approximately 2 ps x-ray laser pulse was directly demonstrated for the first time. More recently we carried out an experiment at the LULI CPA laser facility. Several diagnostics that recorded the plasma emission at the XRL wavelength or in the keV range indicate the presence of small-scale spatial structures in the emitting XRL source. Single-shot Fresnel interferograms at 13.9 nm were successfully obtained with a good fringe visibility. Strong lasing was also observed on the Ni-like 4f-4d line at 16 nm.
We present new progress in the optimization and understanding of the transient collisional pumping scheme using an ultra-short sub-ps heating pulse. The effect of traveling-wave irradiation in enhancing the lasing output of the 4d-4p Ni-like Ag line is studied in detail. A new irradiation scheme using a frequency-doubled 600 ps pulse to preform a plasma is tested. Strong lasing is also obtained on a new line at 16.05 nm that we identify to a 4f-4d transition in Ni-like Ag. Finally we review our recent work in the development of applications of the 21.2 nm zinc laser for imaging or exciting matter. New experiments include the probing of a plasma by imaging Fresnel interferometry and a first attempts to demonstrate two-photon ionization in a xenon gas.
We use x-ray laser interferometry to probe defects induced by a strong electric field on niobium surface. Niobium has been chosen on account of its frequent use in superconductive cavities of particle accelerators. The x-ray laser emits bright, 50 ps-duration pulses at (lambda) equals 21.2 nm. The beam is reflected on the niobium surface under grazing incidence. The interferometer is of the wave-front division type. Interferograms are single shot recorded, which enables to probe `instantaneous' defect morphology. We observed appearance and evolution of defects between 14 MV/m and 35 MV/m. The vertical set amplitude is of 10 - 20 nm. The defect structure has been observed to shift by 500 micrometers along the metal surface under a constant 35 MV/m electric field, during the 20 minutes time interval between two laser shots.
Collisional X-UV lasers are now currently produced world-wide. The LSAI team has developed at LULI an efficient, high brightness laser at 21.2 nm, using neonlike zinc. Beside the effort aimed at improvement of efficiency of the neonlike X-UV lasers, the LSAI recent activity has covered scaling the collisional scheme down to shorter wavelengths, as well as development of applications. In this paper we present results of applications of the 21.2 nm laser in atomic physics, solid state physics, and X-UV interferometry of surfaces. The emphasized message is that the characteristics of the existing X-UV lasers render possible applications in many research areas nowadays.
The luminance<sup>1</sup> of third generation synchrotron sources, (ALS, Elettra) and even some older ones such as NSLS (line X1A) ar BNL, and Super ACO (line 5U7) at Orsay which we are using, is now large enough to allow the practical construction of interferometers and transfer all applications of interferometry to the soft X ray domain (λ = 2-10 nm). Our purpose with the present work is to transpose to soft X rays the concept of measuring the real part n = 1-δ of the refractive index from the fact that interference patterns are shifted by eδ/λ fringes when a sample of thickness e is inserted in one arm of the interferometer. The n values of all materials in that range are quite close to unity and determination methods used so far are generally indirect and strongly affected by absorption. While of course a large imaginary part of the refractive index, i.e. the absorption, ultimately affects the interference contrast and therefore the accuracy, it does not affect the average value, which allows to expect a significant gain in accuracy from interferometry.
In-line holography is attractive for x-ray microscopy due to its recording simplicity. A drawback of this method is the superposition of the virtual and real images, in which structures and details can be modified or lost. This superposition effectively limits the application of in-line holography to x-ray microscopy. We present in this work an iterative constrained algorithm for twin image elimination from Gabor holograms of finite support objects. It is based in the different spatial extent of both images, together with a finite support constraint. The conditions under which the algorithm is applicable are presented, together with an alternative Monte Carlo method for holograms of complex objects recorded in the shadow regions.
Gabor holographic recording is an efficient way to collect information for soft x-ray imaging with undulator synchrotron radiation sources. In addition to being well adapted to the radiative properties of these sources, the high simplicity and large field of the recording operation makes it akin to a particular kind of sample preparation. This is comparable to the conditions of contact microscopy. But, to take advantage of these properties, several difficult problems concerning hologram reconstruction have to be solved. We have investigated the theoretical performances and the practical implementation of Gabor holographic imaging with optical reconstruction, with the realization of a dedicated optical instrument in mind. Such an instrument is presently under construction; it is expected to provide low noise images, with a resolution better than 0.1 micrometers .