The SLIC group conducts R&D programs aiming at maintaining the laser platforms of the LIDYL at a high level of performances and to adapt them to the new needs of their users. To a lesser extent, SLIC is also involved in prospective R&D not motivated by the improvement of the LIDYL lasers but relying on techniques related to femtosecond lasers such as the use of CPA in XUV FELs.
The main topics of R&D studied by the SLIC group over the last ten years are:
One of the main R&D programs at SLIC is the development of high power, high recurrence (1 to 10 kHz) and CEP (Carrier Envelope Phase) stabilized high power Titanium-Sapphire lasers.
We have studied and developed with Amplitude Technologies new amplifiers corresponding to medium term needs for the ATTOLab FAB1/10 laser. This activity has been conducted in close collaboration with the Amplitude-Technologies company within the joint R&D laboratory "IMPULSE".
Our work focused on a regenerative cavity at 10kHz whose originality is to include two crystals. By distributing the thermal effects between the two crystals, the quality of the spatial profile is maintained even when high pump energies are used. This cavity has allowed us to almost triple the power delivered at equivalent beam quality (see Figure). After re-amplification in a double crystal single-pass amplifier, the power reaches 10W (1 mJ / pulse).
Spatial profile for different pump powers for 1-cristal and 2-cristal cavity
The better spatial quality of the beam also optimises the operation of the AOPDF (Mazzler) filter inserted into the regenerative cavity to mitigate the spectral gain narrowing, allowing producing 17fs pulses (110 nm spectrum in 1 /e2). We have also been able to tune the wavelength from 760 to 850nm with a spectral width of 35nm (FWHM) and a resolution of 1nm at the output of the regenerative cavity. The duration of the pulses is then about 40fs.
Finally, the CEP was stabilized with a residual noise of 200 mrad over several hours (170 mrad over 1 minute) using our analogue stabilization loop. This result is one of the best reported for this kind of laser to our best knowledge and approaches the performance of passively stabilised OPCPA systems.
This front-end is installed on the ATTOLab FAB1/10 laser where it seeds the cryogenic power amplifiers. Pulses of 17.5fs with 0.9TW power (16mJ) and CEP noise of 350mrad were obtained on the 1kHz line.
The CEP (Carrier Envelope Phase) stabilization of intense amplified Titanium-Sapphire lasers is one of our main domains of R&D. This activity has been conducted in close collaboration with the Amplitude-Technologies company since 2009 within the joint R&D laboratory "IMPULSE".
In particular, we have proposed an innovative device to control CEP fluctuations [O. Gobert et al., Opt. Express 19, 5410-5418 (2011)]. This device is simple, low-cost, and compact. Its fast response allows operation at high repetition rates. It is based on the use of the linear electro-optic (EO) effect in a bulk material (LiNbO3 or RTP by example): under the action of an electric field applied to the crystal, the phase and group velocities of the laser pulses propagating through the crystal are independently changed, allowing full electronic CEP adjustment.
Measured CEP shift as a function of applied voltage
The demonstration of the efficiency of this electro-optic shifter was carried out within IMPULSE. The measurements were in very good agreement with the simulations and led to a variation of the CEP of about 1 radian for an applied voltage of 300V to the selected crystal (4 cm long and 4 mm thick LiNbO3) [J.-F. Hergott et al., Opt. Express 19, 19935-19941 (2011)]. This method has led to a CEA - Amplitude Technologies patent [O. Gobert et al., Patent FR2969841 (2010)].
On addition, we have developed a diagnostic to monitor CEP drift that is now marketed by Amplitude Technologies. This system based on f-2f interferometry allows the use of a fast totally analog loop to measure and correct the CEP fluctuations. Using such a loop, we stabilised the CEP of a 5W, 10kHz, 23 fs TiS laser and achieved a residual noise of 200 mrad over several hours [Golinelli et al., Opt. Lett. 42, 232925 (2017)]. This result, one of the best reported for this type of laser to our knowledge, approaches the performances of passively stabilized OPCPA systems.
Since 2009, we are involved in R&D activities on the new XUV FEL "FERMI @ ELETTRA" with the Laboratory of Applied Optics (LOA), the Sincrotrone Trieste and the University of Nova Gorica. After a preparatory work on the LUCA laser at LIDYL, we (SLIC, LOA, Nova Gorica and ENEA-FRASCATI) were able to fully characterise the spatial coherence properties of the ELETTRA FEL and to study experimentally and numerically, the effects induced by the chirp of the electron beam and of the injection laser [B. Mahieu et al., Applied Physics B-lasers and Optics 108 (1), 43-49. (2012)] [E. Allaria et al., Nature Photonics 6 (10), 699-704 (2012)].
More recently, an experiment conducted at ELETTRA in collaboration with the Sincrotrone Trieste, the LOA and the Institute of Molecular Sciences of Orsay (CNRS-INP) demonstrated that the duration of pulses produced at 37, 3 nm by an FEL seeded by an external laser at 261nm was reduced from 143fs to 50fs when the chirped pulse scheme is implemented.