We report temporal coherence measurement of solid-target plasma-based soft X-ray laser (XRL) in amplified spontaneous emission (ASE) mode. By changing the XRL pumping angle, we generate lasing at two-times higher electron density than the routine condition. A relatively shorter coherence time at a higher pumping angle indicates a clear spectral signature of higher electron density in the gain region. We probe the amplification dynamics of XRL in routine, and high electron density conditions to confirm gain-duration reduction resulting from ionization gating in the latter case. We also present recent results on the seeding of a vortex beam carrying orbital angular momentum (OAM) in XRL plasma. A small part of the high topological charge extreme ultraviolet (EUV) vortex is injected in XRL. These preliminary results suggest that the vortex seed indeed can be efficiently amplified. In the end, we propose a pathway towards the seeding of the complete vortex beam and wavefront characterization of the amplified beam.
We present an experimental intensity and wavefront characterization of the infrared vortex driver as well as the extreme ultraviolet vortex obtained through high harmonic generation in an extended generation medium. In a loose focusing geometry, an intense vortex beam obtained through phase-matched absorption-limited high harmonic generation in a 15 mm long Argon filled gas-cell permits single-shot characterization of the vortex structure. Moreover, our study validates the multiplicative law of momentum conservation even for such an extended generation medium.
We present in this paper a laser-driven coherent EUV beamline resulting from the combination of a versatile
high-order laser harmonic generator with a robust plasma-based EUV laser amplifier. Both devices can be used
separetely or in synergy. Seeding of the plasma amplifier by a high-order harmonic beam leads to a strong
improvement of the EUV laser beam divergence and uniformity. Moreover the system can be turned easily into
a IR pump-XUV probe setup for plasma opacity probing. The possibility to generate two separate harmonic
sources from the same gas cell offers the opportunity to explore EUV pump-EUV probe experiments.
The potential for coherent extreme ultra-violet (EUV) light in probing laser-produced plasmas is investigated. New
results are presented to demonstrate that EUV radiation can be employed to measure heat penetration into solid targets
from electrons using the signature of a change of opacity due to heating. We examine, in particular, the effects of hot
electron heating of targets. In addition, phase variations after transmission through a laser-irradiated target change the
subsequent propagation of the radiation, suggesting a simple diagnostic measuring the far-field footprint of coherent
EUV radiation can be a useful measurement of the uniformity of target heating.
Ultra-intense X-ray sources have opened new avenues by creating new states of matter or probing and imaging living or inert matter. Free-electron lasers have a strong leadership by delivering pulses combining femtosecond duration and 10s of microJoules to milliJoule energy. However, these sources remain highly expensive limiting their number to a few worldwide. In parallel, laser-pumped soft X-ray lasers hold outstanding promises having demonstrated the most energetic monochromatic soft x-ray pulse and being intrinsically fully synchronized with any secondary source of the pump laser. Since the first successful demonstration of amplification of a high harmonic pulse in a plasma from gas in 2003 and from solid in 2008, we have developed an extensive numerical study. 2D hydrodynamic simulations showed that optimized Transient Collisional Excitation plasma amplifiers, may store up to 0.4 mJ in the population inversion. If carefully seeded, pulses of 80 fs and 20 μJ might be generated with table-top lasers (10J). As the energy extracted is far from the milliJoule requirements of most exciting applications, we studied the seminal experiment of Ditmire et al who seeded a plasma emitting milliJoules in the form of Amplified Spontaneous Emission (ASE).We retrieved and explained for the first time the experimental result (ASE 1,000 times stronger than amplified seed). We thus proposed and fully modeled the transposition of the so-called Chirped Pulse Amplification (CPA) in the soft X-ray range, showing that 6 mJ, 200 fs, fully coherent soft X-ray pulse is accessible with compact pump lasers.
An experiment was set up to measure the wavefront of an injection-seeded soft x-ray laser based on a solid-target plasma amplifier. The 43rd harmonic signal from a Ti:Sa laser was used to seed a molybdenum plasma amplifier operating in the λ=18.9 nm line of Ni-like Mo. A Hartmann wavefront senor with an accuracy of λ/32 rms at this wavelength was employed to measure the wavefront of both the high harmonics seed and the seeded soft x-ray lasers. A significant improvement in wavefront aberration from 0.51±0.04λ rms to 0.25±0.03λ rms was observed as a function of plasma column length. The variation of wavefront characteristic by the time delay between the injection of the seed and the peak of soft x-ray amplifier pump was studied in this paper.
We report recent experimental measurements of the duration of a Ni-like Mo transient XUV laser emitted at 18.9 nm and
generated under GRIP geometry at the LASERIX facility. These measurements have been performed using an ultra-fast
X-ray streak camera (AXIS Photonique). A new trigger line was implemented, yielding a shot-to-shot jitter of less than
10 ps. The KBr photocathode of the streak camera was positioned close to the plane of the magnified near-field image of
the XUV laser emitting aperture. Saturation in the streak camera was avoided by carefully adjusting the signal level of
the focused image. The sweep speed was calibrated in-situ by generating a double-pulse XUV laser. Finally the temporal
resolution of the instrument was measured directly with a femtosecond, high-order harmonic pulse. XUV laser pulse
durations as short as 2.8 ps were measured for a 20° GRIP angle and a 0.75 ps GRIP pulse duration. We present and
discuss our study of the effect of these two parameters on the measured pulse duration.
We present an experimental design to independently pump two soft X-ray laser media suitable for a seed-amplifier
configuration. Both the seed and the amplifier target are operated in the TCE scheme utilizing the DGRIP technique with
its intrinsic travelling wave excitation. Controlled injection of the seed X-ray laser into the amplifier medium is realized
via a spherical XUV mirror. The experimental design is perfectly appropriate for benchmarking combined simulations of
the ARWEN and DeepOne code. A first experiment at the PHELIX laser utilizing this scheme has been conducted,
demonstrating signs of amplification and allowing for the direct measurement of the gain life time of a Ni-like silver
SXRL.
By seeding amplifying plasmas pumped with the so-called Transient collisionnal excitation scheme, the amplified pulse
seems to be limited to an energy of several 10's of μJ. Aiming to attain several mJ, we study the seeding of plasma
pumped by long laser pulse. Thanks to our time-dependant Maxwell-Bloch code, we demonstrate that direct seeding with
femtosecond pulse is inefficient. We also study the amplification of pulse train with the drawback of re-synchronizing
the pulses. We proposed and studied the amplification of high harmonic seed stretched by a grating pair, amplified
finally compressed. We consider off-axis diffraction on the gratings for maximizing their efficiency. Considering the
phase deformation induced by the amplification and the spectral narrowing the final pulse is 230 fs in duration and 5 mJ.
Seeding plasma-based soft-x-ray lasers (PBSXR) with high order harmonics (HOH) is a promising way to obtain
fully coherent, short (hundreds of femtoseconds), tens of microJoules pulses. Nevertheless, up to date only 1
μJ, 1 ps pulses have been demonstrated seeding plasmas created from gas targets and solid targets. As the
amplification process couples plasma hydrodynamics, atomic processes and the propagation of electromagnetic
fields, a careful optimization of seed and amplifier properties is essential to reach multi-microJoule, hundreds
of fs regime. Recent papers showed that short and wide (up to 1 mm) plasmas present an optimal gain
zone and up to 20 μJ could be extracted when seeding. Nevertheless, the temporal duration and profile of the
output beam is still not optimal. Simulations show that the HOH is weakly amplified whereas most of the
energy is within a long (several picoseconds) wake induced by the HOH. In addition to this, these simulation
pointed out the presence of deleterious Amplified Spontaneous Emission (ASE). In order to obtain intense pulses
useful for practical applications is crucial to reduce the duration to hundreds of fs and obtain ASE-suppressed,
structure-free (ideally only an amplified HOH) pulses. Using the 1D Bloch-Maxwell code DeepOne we will show
that fully coherent, wake and ASE-suppressed, 15 μJ, 120 fs pulse can be obtained when optimizing at the same
time both the seed and the plasma conditions.
We present in this paper some effort and prospects in order to turn a high intensity infrared laser facility into a
installation providing external users with EUV coherent sources. Development of an harmonic beamline based
on quasiphase matching in capillary is presented. Plasma based soft x-ray laser scheme involving a plasma seeder
and an amplifier is revisited with the aim of obtaining a robust fully coherent x-ray laser.
LASERIX is a high-power laser facility leading to High-repetition-rate XUV laser pumped by Titanium:Sapphire laser.
The aim of this laser facility is to offer Soft XRLs in the 30-7 nm range and auxiliary IR beam that could also be used to
produce synchronized XUV sources. This experimental configuration highly enhances the scientific opportunities of the
facility, giving thus the opportunity to realize both X-ray laser experiments and more generally pump/probe experiments,
mixing IR and XUV sources. In this contribution, the main results concerning both the development of XUV sources(X-Ray
lasers and HHG sources) and their use for applications are presented.
We present a comprehensive theoretical analysis of the conditions that lead to absorption limited generation of
high order harmonics in the case of low energy, long pulse duration infrared pump laser beams. With these pump
laser beam parameters, tight focussing is necessary to reach the high laser intensity required for high non linear
response at the atomic level. A limitation of phase-matching is then induced through the so-called Gouy phase
shift. We explain how the positive atomic dispersion can compensate for that effect and derive the conditions for
perfect phase matching. The influence of gas pressure, harmonic order, maximum laser intensity and focussing
conditions are analysed. This work enables a precise separation between pure classical harmonic from possible
XPA effects discussed in a recent experiment. It also constitutes a benchmarking of a code under development
for quasi phase matching scheme investigation.
In this paper we report the perspectives of the development of the XUV laser sources and applications using High-power laser facilities. We focus our paper on the present status of the French LASERIX facility and more especially about its role in the development of the XUV laser sources considering the French "Institut de la Lumière Extrême " (ILE) and the potential European project Extreme Light Infrastructure (ELI).
Finally, we present the scientific perspectives of X-ray laser sources developments using these laser facilities.
Seeding plasma-based soft x-ray laser (SXRL) demonstrated diffraction-limited, fully coherent in space and in time
beam but with energy not exceeding 1 μJ per pulse. Quasi-steady-state (QSS) plasmas demonstrated to be able to store
high amount of energy and then amplify incoherent SXRL up to several mJ. Using 1D time-dependant Bloch-Maxwell
model including amplification of noise, we demonstrated that femtosecond HHG cannot be efficiently amplified in QSS
plasmas. However, using Chirped Pulse Amplification concept on HHG seed allows to extract most of the stored energy,
reaching up to 5 mJ in fully coherent 130 fs pulses. Original pump-probe experiments will be proposed thanks to the
high laser energy available in ELI facilities.
The demonstration of a 7.36 nm Ni-like Sm soft x-ray laser pumped by 36 J of a Nd:glass chirped pulse amplification laser is presented. Double-pulse single-beam non-normal incidence pumping was applied for the efficient soft x-ray laser generation. Here the applied technique included a new single optic focusing geometry for large beam diameters, a single-pass grating compressor traveling-wave tuning capability and an optimized high energy laser double-pulse. This scheme has the potential for even shorter wavelength soft x-ray laser pumping.
Stable and reliable operation of a nickel-like molybdenum transient collisional soft x-ray laser at 18.9 nm demonstrated and studied with a 10Hz Ti:sapphire laser system proves the suitability of the double-pulse non-normal incidence pumping geometry for table-top high repetition soft x-ray lasers and broadens the attractiveness of x-ray lasers as sources of coherent radiation for various applications. X-ray laser emission with pulse energies well above 1 μJ is obtained for several hours at 10Hz repetition-rate without
re-alignment under optimized double pumping pulse parameters including energy ratio, time delay, pulse duration and line focus width.
In this paper we present the perspectives of the development of the XUV laser sources using High-power laser facilities.
We focus our paper on the present statuts of the LASERIX facility and especially its role in the development of the XUV
laser sources considering the French "Institut de la Lumière Extrême" (ILE) and the potential European project Extreme
Light Infrastructure (ELI).
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.
Plasma-based seeded soft x-ray lasers have the potential to generate high-energy, highly coherent, short pulse beam. Due to their high density, plasmas created by interaction of intense laser with solid target should store the highest amount of energy density among all plasma amplifiers. However, to-date output energy from seeded
solid amplifiers remains as low as 60 nJ. We demonstrated that careful tailoring of the plasma shape is crucial for extracting energy stored in the plasma. With 1 mm wide plasma, energy as high as 22 μJ in sub-ps pulse is achievable. With such tailored plasma, gain and pumping efficiency has been increased by nearly a factor of 10 as compared to the narrower plasma amplifiers studied previously and here.
S. Liehn, C. Le Sech, E. Porcel, B. Zielbauer, J. Habib, S. Kazamias, O. Guilbaud, M. Pittman, D. Ros, M.-A. Hervé du Penhoat, A. Touati, H. Remita, S. Lacombe
Samples of plasmid DNA were irradiated with pulsed 18.9 nm radiation originating from a Mo X-ray laser (XRL)
pumped in GRIP configuration at the LASERIX facility. Up to 21 000 pulses were delivered with a repetition rate of 10
Hz and average pulse energy of 200 nJ. Radiosensitization by two different platinum compounds (platinum terpyridine
chloride (PtTC) and platinum nanoparticles) were investigated. SSB and DSB yields were measured using agarose gel
electrophoresis. The occurrence of single and double strand breaks not present in controls having undergone the same
treatment except for the XRL irradiation can be seen as a clear effect of the XRL irradiation. This confirms the role of
direct effects in DNA damages as previously seen with low energy ions and electrons (1) (2). In addition we demonstrate
a DNA breaks enhancement in the presence of platinum. No difference of enhancement was seen between these two
radiosensitizers.
The PHELIX laser at the GSI Helmholtz center for heavy-ion research is dedicated to provide high energy, ultra-intense laser pulses for experiments in combination with energetic ion beams. Development of x-ray lasers is targeting a number of applications in this context, including x-ray laser spectroscopy of highly-charged ions, and Thomson scattering diagnostics of heavy-ion driven plasmas. Recent developments centered on the application of a novel double-pulse
pumping scheme under GRIP-like, non-normal incidence geometry for both the pre- and the main pulse for transient pumped Ni-like lasers. This scheme considerably simplifies the set-up, and provides a very stable pumping situation even at low pump energies close to the lasing threshold. The technique was scaled to pulse energies above 100 J for the pumping of shorter wavelength x-ray lasers. In addition, a slightly tunable high-harmonic source using a split-off beam from the Nd:Glass pre-amplifier of PHELIX was developed as a seeding source.
Results of a novel X-ray laser application, aimed at understanding the microscopic effects involved in formation of laserinduced
damage in optical materials exposed to sub-ns laser pulses, will be presented. Specifically, we studied thin plane
beamsplitters that are presently the weakest element of the next generation of high-energy lasers (LMJ, NIF), with
permanent damage threshold below 20 J/cm2. Standard fused silica substrates and a model system, containing welldefined
micron grooves as seeding sites to trigger damage when irradiated by 438 nm laser pulses, were in situ probed by
a neon-like zinc X-ray laser delivering up to 10 mJ at 21.2 nm. The probing beamline employed a double Lloyd's mirror
interferometer, used in conjunction with an imaging mirror to provide magnification of ~8. In conjunction with an array
of in-situ optical diagnostics, one of the questions addressed was whether the damage (transient or permanent) on the
rear surface of the beamsplitter occurs during or after the laser pulse, i.e. whether it is due to local electrical fields or to
other processes. Another issue, examined by both the X-ray interferometric microscopy and the optical diagnostics, is
whether a local rear-surface modification is associated with non-linear effects (self-focusing, filamentation) of the laser
beam in the bulk.
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 10-5 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.
D. Ros, G. Jamelot, M. Pittman, F. Plé, S. Kazamias, O. Guilbaud, K. Cassou, A. Klisnick, J. Habib, J.-C. Lagron, P. Jaeglé, A. Huetz, J.-P. Chambaret, S. Sebban, P. Zeitoun, G. Mourou
LASERIX is a high power laser facility intended to realise and use for applications transient collisional excitation (TCE) X-ray lasers (XRLs) at various wavelengths, using grazing incidence pumping (GRIP) configuration with 10 Hz repetition rate. In addition new types of XRL schemes giving rise to emission at short wavelengths will be developed using the high energy LASERIX driver with 0.1 HZ rep-rate. Thus, this laser facility will both offer Soft X-ray lasers in the
40-10 nm range and synchronised auxiliary IR beam that could be also used to produce XUV sources. This experimental configuration highly enhances the scientific opportunities of the facility. Indeed it will be possible to realise both X-ray laser experiments and more generally pump/probe experiments, mixing IR and XUV sources. Then, this facility will be useful for the community, opening a large scale of investigations, including imagery and irradiation.
LASERIX is a high power laser facility intended to realise and use for applications transient collisional excitation (TCE)
X-ray lasers (XRLs) at various wavelengths, using grazing incidence pumping (GRIP) configuration with 10 Hz
repetition rate. In addition new types of XRL schemes giving rise to emission at short wavelengths will be developed
using the high energy LASERIX driver with 0.1 HZ rep-rate. Thus, this laser facility will both offer Soft X-ray lasers in
the 40-10 nm range and synchronised auxiliary IR beam that could be also used to produce XUV sources. This
experimental configuration highly enhances the scientific opportunities of the facility. Indeed it will be possible to realise
both X-ray laser experiments and more generally pump/probe experiments, mixing IR and XUV sources. Then, this
facility will be useful for the community, opening a large scale of investigations, including imagery and irradiation as
illustrated in the case of laser Interaction with matter investigations using XUV interferometry.
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 ~1013 Wcm-2.
We have developed a double Lloyd's mirror wavefront-splitting interferometer, constituting a compact device for surface probing in the XUV and soft X-ray spectral domain. The device consists of two independently adjustable superpolished flat surfaces, operated under grazing incidence angle to reflect a diverging or parallel beam. When the mirrors are appropriately inclined to each other, the structure produces interference fringes at the required distance and with tuneable fringe period. The double Lloyd's mirror may be used alone for surface topography with nanometric altitude resolution, or in conjunction with an imaging element for interferometric XUV surface microscopy. In the latter case, resolution in the plane of the probed
surface is about micron, which is given by the quality of the imaging element and/or by the detector pixel size. Here, we present results obtained using the double Lloyd's mirror in two separate X-ray laser and high harmonics generation (HHG) application projects. The first
experiment was aimed at understanding microscopic nature of the effects involved in laserinduced optical damage of thin pellicles, exposed to sub-ns laser pulses (438 nm) producing fluence of up to 10 Jcm-2. The probing source in this case was a QSS neon-like zinc soft X-ray laser, proving a few mJ at 21.2 nm in ~100-ps pulses. The second experiment was carried out using a narrowly collimated HHG beam near 30 nm, employed to topographically probe the surface of a semiconductor chip.
We present early results of an application of X-ray laser, aimed at understanding the effects involved in formation of laser-induced damage in optical materials exposed to sub-ns laser pulses. For the purpose of the experiment, a novel interferometric microscopy technique was designed and tested. The interferometric beamline employed a double Lloyd's mirror interferometer, used in conjunction with an imaging mirror to provide magnification of ~8 along a plane
inclined with respect to the propagation direction of the X-ray beam. The objects investigated were thin plane beamsplitters made of fused silica (SiO2), irradiated by damaging laser light at 438 nm and in situ probed by the developed technique of interferometric microscopy. The soft X-ray beam was emitted by neon-like zinc laser, delivering up to 10 mJ at 21.2 nm. In conjunction with an array of in-situ optical diagnostics, one of the questions addressed was whether the damage of the rear surface of the beamsplitter occurs approximately during of much after the laser pulse. Another issue examined by the X-ray interferometric microscopy technique was whether the surface perturbation seen shortly after the impact of the damaging pulse is associated or not with the pattern of permanent surface modifications.
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.
Future progress of x-ray lasers call for specific facilities intended to x-ray laser studies and development of a large variety of x-ray laser applications. This paper presents LASERIX, a future x-ray laser facility under construction for optimization of transient collisional excitation x-ray lasers, study of new x-ray laser schemes, and development of applications.
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 give an overview of recent results on optical-field-ionization collisional soft X-ray lasers developed at LOA. By focusing a 30-fs, circularly polarized Ti-sapphire laser pulse at an intensity of up to 8 x 1017 Wcm-2 into a low-density gas cell containing xenon or krypton, we produced a few mm long plasma column for soft X-ray amplifier. Saturated amplification has been achieved on the 4d95d(1S0) - 4d95p(1P1) transition at 41.8 nm in Pd-like Xe, and strong lasing at 32.8 nm on the 3d94d(1S0) - 3d94p(1P1) transition in Ni-like Kr has been demonstrated. Under optimum pumping conditions the Xe IX laser provides about 5 x 109 photons per pulse while the Kr IX laser delivers up to (2-3) x 109 photons per shot. The repetition rate of these X-ray lasers is 10 Hz. The experimental results are discussed and compared to computational simulations in which issues related to plasma formation, electron energy distribution, and atomic processes are addressed.
We report in this article the experimental and numerical tools, developed at the LSAI, for a complete characterization of an x-ray laser (XRL) beam. First, a Michelson interferometer has been used to realize a Fourrier transform spectroscopy experiment. A full comprehension of the measured linewidth requires a comparison of the XRL beam amplification in the plasma to raytrace simulation. Results of transient pumping XRL simulations are presented in this article. The last section is dedicated to a description of the XUV Shack-Hartmann wavefront sensor we have developed, and to the study of the capillary discharge XRL beam.
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 report recent investigations on collisional Optical-Field Ionization soft x-ray lasers. The amplifying medium is generated by focusing a high energy circularly polarized, 35 fs 10 Hz Ti: sapphire laser system in a few mm cell filled with gas (xenon or krypton). Using xenon, a gain of 67 cm-1 on the 4d95p-4d95d transition at 41.8 nm in Pd-like xenon and a gain-length product of 15 have been inferred at saturation. This source delivers about 5 109 photons per pulse. Using krypton, a large amplification of the 3d94d-3d94p line at 32.8 nm has been observed for the first time. The influence of the pumping energy and the laser polarization on the lasing output are also presented.
Recent experiments, performed at the C.E.A./Limeil-Valenton P102 laser facility on the Ni-like transient collisional scheme, are reported in this paper. They mainly aimed at enhancing the efficiency and improving the optical properties of the already demonstrated 4d J equals 0/4p J equals 1 Ag19+ x-ray laser at 13.9 nm. The now classical 2- stage traveling-wave irradiation of slab targets was used, the illumination sequence being constituted of a long (600 ps) low-flux (0.5 - 11 J) laser pulse followed (200 ps later) by a short (< 1 ps) high intensity (1 - 20 J) one. The work novelty was the use of frequency-doubled pulses, either for the pre-forming or the pumping one. Various combinations ((omega) -(omega) , 2(omega) -(omega) , (omega) - 2(omega) ) have been investigated in terms of lasing performances. High gains, around 34/cm, have been measured and saturation achieved for target lengths above 4 mm. A strong enhancement, up to a few (mu) J, of the x-ray laser output has been observed, due to traveling-wave irradiation method, while the emission duration was decreased to less than 10 ps, resulting in a 300 kW source. Moreover, under specific laser conditions, a second lasing line at 16 nm was detected. Finally, the possibility of cavity operating transient collisional x-ray lasers has been demonstrated.
Annie Klisnick, Antoine Carillon, Gerard Jamelot, Pierre Jaegle, David Ros, Philippe Zeitoun, F. Albert, P. Fourcade, Jaroslav Kuba, Jean-Luc Miquel, Nathalie Blanchot, J. Wyart, Pierre Agostini, P. Breger, David Garzella, Heimo Mueller-Seelich, Denis Joyeux, Daniel Phalippou, E. Bechir, S. Hubert, G. De Lacheze-Murel, Hiroyuki Daido
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.
A numerical code COLAX solving the Maxwell-Bloch equations has been developed and applied to the modeling of soft X-ray lasers in hot laser-produced plasmas. First results in the case of Ne-like Zn from solid targets are presented, including refraction, saturation, coherence properties, and the effect of a half-cavity mirror.
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.
This work has consisted in demonstrating that high gain can be achieved by pumping x-ray lasers (XRL) with a combination of a high intensity and short duration driving pulses (approximately 100 ps). Short pulses are very well suited for pumping collisional XRL since a high lasant ion density, electron density and temperature can be achieved simultaneously. We have successfully tested this pumping scheme on the 4d-4p (J equals 0 - 1) transition of Ni-like tin (lambda approximately 11.93 nm) and silver (lambda approximately 13.89 nm) as well as on the 3p-3s (J equals 0 - 1) Ne-like iron (lambda approximately 25.5 nm) at an intensity of approximately 2 X 1013 Wcm-2 (130 ps in duration). The driving laser (lambda equals 1.06 micrometer) was composed of three pulses (a prepulse and two main pulses). Large amplifications were demonstrated in tin and silver (respectively GL approximately 12 and GL approximately 16). Finally, the saturation of the 3p-3s (J equals 0 - 1) transition of Ne-like iron at 25.5 nm was achieved on both pumping pulses, using a prepulse of 109 Wcm-2. A gain coefficient of 15 plus or minus 3 cm-1 (GL approximately 26 plus or minus 5) on the first main pulse and 12 plus or minus cm-1 (GL approximately 23 plus or minus 2) on the second one was measured.
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