Terawatt femtosecond laser chain based on LED-pumped alexandrite – TERALEDx

The TERALEDx project aims to develop a new terawatt femtosecond laser suitable for laser-plasma acceleration. After a rapid research development in the last 20 years, this method of generating energetic particles is now approaching applications. One of the most promising applications is non-destructive testing (NDT) using X-rays, which can be used to detect and size defects in objects and to monitor their development. The sectors concerned by NDT are: energy (nuclear, oil, gas, hydraulic, wind, etc.); land transport (especially rail); marine; aeronautics; aerospace; defence and security, etc.
To meet the industrial needs of NDT, a paradigm shift is required in laser-plasma acceleration methods, which are traditionally associated with large high-energy laser installations, of which there are only about a hundred worldwide. This is what SourceLAB, the only company in the world developing industrial laser-plasma accelerated particle sources, is proposing. SourceLAB's strategy is to develop a particle beam line based on a femtosecond laser of much simpler design with parameters typically 10 mJ, 10 fs, 100 Hz. Today, the realization of such a source is very open because none of the traditional femtosecond laser technologies (Ti:sapphire or ytterbium) fully meet the specifications.
It is in this context that the Charles Fabry Laboratory (LCF) is proposing a totally original laser architecture, based on LED-pumped alexandrite crystals. The LCF has 10 years of experience in LED pumping of tunable lasers in the near infrared via luminescent concentrators. In an ASTRID research project (named ALEDxandrite), the LCF has demonstrated the proof of concept of this new type of pumping and has matured the pump head technology (laser medium + pump system) to a TRL3 level by developing a series of prototypes. LED pumping combines the advantages of other types of pumping, without the disadvantages: robust, simple and low cost, like flashlamps; efficient, stable and long life like laser diodes. It has all the attributes required to make an industrial laser chain because it is clear that it is the pumping that determines the parameters and quality of the laser.
SourceLAB and the LCF have therefore decided to combine their complementary skills to develop an LED-pumped femtosecond laser suitable for laser-plasma acceleration. The architecture is designed in a modular way, integrating from the start the requirements of industrial laser-plasma acceleration (temporal contrast, stability and operability of the source). The laser system is made up of several blocks: the laser chain delivering the temporally stretched pulses, then the grating compression and post-compression blocks allowing the duration to be reduced to 10 fs by phase self-modulation in a gas cell. The laser chain comprises a femtosecond oscillator, a pulse stretcher and two LED-pumped amplifiers using alexandrite as the amplifying medium. This crystal is tunable in the near infrared (700-800 nm) and has exceptional mechanical, spectroscopic and thermal properties for a laser medium. Long used in medical lasers, alexandrite has a strong potential for industrial development. To prove the relevance of the architecture, the final objective of the TERALEDx project is to install the laser chain on the SourceLAB electron beam line during a measurement campaign to evaluate the performance of the complete system.