Ultra-Broadband Injectors for Contrasted Ultra-Intense Lasers – UBICUIL

Femtosecond laser systems are now widely available. They are extensively used for applications ranging from material science, biology and medecine to high energy density physics (HEDP). In the particular case of HEDP, femtosecond lasers with multi-TeraWatt peak-powers are extensively used for short pulse X-ray generation, electron and ion acceleration and more recently for the production of energetic attosecond light pulses. National and European projects aim at bringing HEDP experiments with femtosecond lasers to the next level by proposing large-scale femtosecond laser systems. The more emblematic project is the European ELI proposal (Extreme Light Infrastructure). In the immediate future, the ILE project (Institut de la Lumière Extreme), promoted by the Ile de France region, proposes to build a 15fs, multi-joule class laser system within the next few years, as a stepping stone towards an ELI-type European laser infrastructure. These ambitious programs will have to rely on the transfer of state-of-the-art femtosecond laser techniques from the laboratory to a large-scale facility environment with tight operational constraints: reliable performance, easy integration and upgradability. We believe it is the role of small-scale laboratory teams to supply large-scale laser facilities with robust ultrashort pulse laser technology emerging from fundamental studies of basic nonlinear optics. Both ILE and ELI projects plan to reach the desired ultra-high output pulse energies using a combination of 'classical' Titanium:sapphire CPA amplifiers (Chirped Pulse Amplification) and OPCPA (Optical Parametric Chirped Pulse Amplification). Whichever solution is adopted, these high-energy amplifiers need to be seeded with a highly stable source of high-fidelity ultra-broadband pulses (i.e. short). Ideally, the seed laser should have the following characteristics: the pulse energy should be on the order of several milliJoules, the spectrum should be smooth, have near-Gaussian shape and extend over more than 300 nm at central wavelength of 800 nm (compressed pulse duration below 10 fs), the carrier-envelope-phase (CEP) offset should be stabilized, the pulse should exhibit a high peak-to-background contrast ration, free of any long-duration pedestal before its peak. This project is about constructing such a laser. During the past few years, we have demonstrated a novel nonlinear technique called Cross Polarized Wave Generation or XPWG, which can be used to efficiently clean up the temporal profile of amplified femtosecond pulses. We have patented this technique in the case of more 'conventional' laser systems delivering pulses with durations ranging from a few tens to a few hundred femtoseconds. We have just recently demonstrated the possibility of extending this technique to the few-optical-cycle regime (sub-10 fs). We have just developed a carrier-envelope phase stabilized, milliJoule-level few-cycle (< 5 fs) laser source in our laboratory. In a way, we have validated separately each of the characteristics required to build the ideal seed laser. Therefore, we are in perfect position to put together all those elements and develop a prototype injector for large-scale laser facilities. Finally, we have close research and development ties with laser companies providing state-of-the-art femtosecond technology (Femtolasers, Amplitude Systems, Thales Laser and Fastlite), which will help us turn our laboratory innovations into reliable, integrated solutions for a large-scale laser facility.