Gabriel Faivre

A high-intensity highly coherent soft X-ray femtosecond laser seeded by a high harmonic beam

Synchrotrons have for decades provided invaluable sources of soft X-rays, the application of which has led to significant progress in many areas of science and technology. But future applications of soft X-rays—in structural biology, for example—anticipate the need for pulses with much shorter duration (femtoseconds) and much higher energy (millijoules) than those delivered by synchrotrons. Soft X-ray free-electron lasers should fulfil these requirements but will be limited in number; the pressure on beamtime is therefore likely to be considerable. Laser-driven soft X-ray sources offer a comparatively inexpensive and widely available alternative, but have encountered practical bottlenecks in the quest for high intensities. Here we establish and characterize a soft X-ray laser chain that shows how these bottlenecks can in principle be overcome. By combining the high optical quality available from high-harmonic laser sources (as a seed beam) with a highly energetic soft X-ray laser plasma amplifier, we produce a tabletop soft X-ray femtosecond laser operating at 10 Hz and exhibiting full saturation, high energy, high coherence and full polarization. This technique should be readily applicable on all existing laser-driven soft X-ray facilities.

Progress in optical-field-ionization soft X-ray lasers at LOA

We give on overview of recent advances in collisionally pumped optical field-ionization soft X-ray lasers developed at LOA. Saturated amplification has been achieved on the 5d-5p transition in Xe^8+ at 41.8 nm, and on the 4d-4p transition in Kr^8+ at 32.8 nm. We demonstrate a significant increase of the energy output from the Xe^8+ laser driven within two types of wave-guide. Finally, we present results of a pioneering work aimed to set up and characterize the first true soft X-ray laser chain.

New techniques for the measurement of x-ray beam or x-ray optics quality

Metrology of XUV beams and more specifically X-ray laser (XRL) beam is of crucial importance for development of applications. We have then developed several new optical systems enabling to measure the x-ray laser optical properties. By use of a Michelson interferometer working as a Fourier-Transform spectrometer, the line shapes of different x-ray lasers have been measured with an unprecedented accuracy (δλ/λ~10-6). Achievement of the first XUV wavefront sensor has enable to measure the beam quality of laser-pumped as well as discharge pumped x-ray lasers. Capillary discharge XRL has demonstrated a very good wavefront allowing to achieve intensity as high 3*1014 Wcm-2 by focusing with a f = 5 cm mirror. The measured sensor accuracy is as good as λ/120 at 13 nm. Commercial developments are under way.

Status and Prospects on Soft X-Ray Lasers Seeded by a High Harmonic Beam at LOA

Thanks to the most recent works on x-ray laser and on high order harmonics (HHG), it is now possible to produce an energetic beam having at the same time the required optical properties. The solution consists in seeding the XRL amplifier medium with another beam (HHG). This experiment was successfully realized in LOA. We studied seeding of two x-ray laser transitions, 4d-4p at 32.8 nm in Kr8+ and 5d-5p 41.8 nm in Xe8+. The amplifying medium is generated by focussing a high energy circularly polarized, 35 fs 10 Hz Ti: sapphire laser system in a few mm cell filled with gas (xenon or krypton). We succeeded to increase from a factor 10 to 200 the HHG energy, without deteriorating their optical qualities. The resulting beam was polarized, coherent and we estimate the output energy to be about 0.5 eJ.

Soft X-ray laser of second generation

This paper explores the second generation soft X-ray laser both numerically and experimentally. Numerical studies have been achieved by successively using two numerical codes. The first code (hydrodynamic code) describes the spatio-temporal evolution of the plasma while the second code (ray-trace) models the amplification and propagation of the seed along the plasma amplifier. Preliminary numerical study tends to show that mJ level, fully coherent, soft X-ray laser with 100 fs in duration is achievable for wavelengths ranging from 30 to 4 nm, and with a pump laser of several tens of joules as the driver. Moreover, experimental studies have been performed using a 2 J, 20 fs Ti:sapphire laser operating at 10 Hz. About 100 mJ has been used to generate the seed i.e. high harmonics of the fundamental laser. Amplification as high as 1000 have been observed leading to 3 /spl mu/J, 500 fs, highly coherent, polarised soft X-ray laser.

Soft x-ray lasers seeded by a high harmonic beam

We studied seeding of two x-ray laser transitions, 4d-4p at 32.8 nm in Kr8+ and 5d-5p 41.8 nm in Xe8+. The amplifying medium is generated by focussing a high energy circularly polarized, 35 fs 10 Hz Ti: sapphire laser system in a few mm cell filled with gas (xenon or krypton).We succeeded to increase from a factor 10 to 200 the input HHG energy, without deteriorating their optical qualities. The resulting beam was polarized, coherent and we estimate the output energy to be about 1 μJ.