High repetition rate laser for lensless imaging in the XUV – HELLIX

The generation of high-harmonic (HHG) radiation is one of the most exciting and promising areas of research in ultrafast optics and strong field laser physics. The ability to produce coherent radiation in the extreme UltraViolet (XUV 1-100nm) as well as the possibility to produce attosecond light pulses has opened up new research areas. Besides their fundamental interest, this process carries great potential for a series of applications now coming of age. In particular, nanoscale imaging using XUV coherent light has seen tremendous progress. In this framework, lensless imaging methods such as coherent diffraction imaging (CDI) are used. These experiments have been mostly carried out using synchrotron or free-electron laser sources, with very limited overall beam time. Thanks to the advent of tabletop HHG sources, XUV microscopy experiments on a lab-scale have been realized, with resolution approaching the wavelength. Additionally, HHG sources open the fascinating possibility to follow nanoscale processes with attosecond/femtosecond temporal resolution. HHG relies mostly on extensively proven Ti:Sapphire amplifier driving laser. As a result, some major drawbacks exist for many academic and industrial applications, e.g., repetition rates limited to a few kHz and high acquisition and maintenance costs.

The central idea of this proposal is to develop new HHG sources for ultrafast nanoscale imaging applications using recent developments in diode-pumped ultrafast fiber laser technology and state-of-the-art hollow core waveguides. This will allow us to make a breakthrough in terms of repetition rate, robustness, and compactness of lasers used to drive secondary sources. Due to the low efficiency of the HHG process and the high number of XUV photons required in coherent diffractive imaging, high laser peak and average powers are required. To achieve that challenging goal, we plan to develop, characterize, and optimize a tabletop high energy (150 µJ), high repetition rate (100 kHz), carrier-envelope phase (CEP)-stabilized, and few-cycle (10 fs) laser source at 1 µm. Although several leading laboratories in the field of ultrafast lasers are currently pushing towards this goal, such a source would be unprecedented at the international level. It will be based on an industrial-grade Yb-doped ultrafast fiber laser followed by one or two stages of nonlinear compression in gas-filled guiding structures. The unique character of the HELLIX laser source will allow going beyond the state of the art in terms of imaging applications, with attosecond nanoscale imaging at sub-20 nm spatial resolution. Novel strategies for images reconstruction combining holography and iterative algorithms will be applied to solve the bandwidth blurring due to the bandwidth of attosecond pulses. Control over the CEP will allow the generation of reproducible spectra and will open perspectives in attosecond imaging.

The project, led by Laboratoire Charles Fabry (LCF), gathers specific and complementary skills from four partners whose expertise is recognized at the international level. LCF is widely acknowledged as a major actor of the research in diode-pumped ultrafast lasers. Amplitude Systemes (AS) is the world leading company providing integrated, industrial-grade ultrafast laser systems, and has a long-standing collaboration with LCF through a common laboratory. Laboratoire de l’Accélerateur Linéaire (LAL) brings its unique know-how in CEP control of laser systems, demonstrated in the frame of ambitious cavity enhancement experiments. Finally the Laboratoire Interaction, Dynamique, et Laser (LIDyL) has international recognition for major contributions to nonlinear optics in the gas phase, and applications to ultrafast nanoscale imaging.

HELLIX consortium will demonstrate a reliable high repetition rate laser source with unprecedented parameters, with scientific and industrial outcomes at the laser, secondary source, and applications levels.