Broadband mid-Infrared SuperCOnTinuum sources – BISCOT

We have developed unique semiconductor waveguides that combine single-mode guiding over a wide spectral range, low transmission losses, and characteristics particularly suited for parametric conversion in the mid-infrared. These structures have enabled the first realization of parametric sources emitting ultrashort pulses around 4 and 12 µm in a waveguide geometry.
We have also developed new ultrafast lasers emitting at wavelengths centered between 2 and 3.4 µm. These lasers are based on transparent fibers in the mid-infrared range and exploit the Raman effect to realize monolithic fiber sources delivering femtosecond pulses of several tens of kW peak power and widely tunable in wavelength.

From these lasers we have, in partnership with the CEA, realized secondary radiation sources through high order harmonics generation (HHG) in the extreme ultraviolet (EUV) from solid targets. Until now, this type of radiation has been produced with high energy sources emitting in the near infrared around 800 and 1030 nm. The use of ultrashort pulses at long wavelengths brings a better conversion efficiency to this process. Moreover, the exploitation of the light confinement effects in solid structures lowers the threshold required for the HHG process triggering, thus opening the way to the development of highly compact EUV sources for applications in imaging, medicine and nano-electronics.
This project also allowed us to pursue our work on a concrete application of high brightness extended supercontinuum sources, namely Fourier transform infrared spectromicroscopy (FTIR) which combines the spatial resolution of optical microscopy with the spectral selectivity of vibrational spectroscopy. Until now, this technique, essential for biological and material science studies where high spatial resolution is required, relied mainly on synchrotron sources that can provide diffraction-limited beams in the infrared. In the framework of BISCOT, we have demonstrated that extended-spectrum laser sources in the mid-infrared allow rapid spectral mapping of localized material properties with a resolution close to the diffraction limit, thus opening the way to a possible in-situ exploitation for early diagnosis in the hospital context for example.

The results obtained within BISCOT show that the studied approach is very promising for the development of broadband sources in the mid-infrared. Coupling fiber lasers with semiconductor waveguides offers a relatively compact platform that could open new paths for applications in spectroscopy and imaging. Indeed, the study carried out on the imaging of human liver samples shows that the results obtained with the laser source are comparable or superior to those obtained with a synchrotron to identify a localized chemical species related to a pathology.
Moreover, the ultrafast laser sources developed around 2.8 µm open new possibilities for applications in nano-photonics. Indeed, coupling ultra-short pulses in the mid-infrared with solid nano-structures contributes to the exacerbation of the associated electric field thus allowing to significantly lower the threshold of the strong field regime. This has been successfully exploited for the generation of high order harmonics in solids opening the way to the realization of highly compact EUV sources for imaging, medical and nanoelectronic applications.

The results concerning the development of femtosecond fibered lasers in the mid-infrared have been published in two articles in the specialized journal Optics Letters.
The results concerning spectromicroscopy have been published in Optica.
The results related to EUV radiation generation by HHG have been published in Scientific Reports and Optics Letters.
Results on parametric generation in OP-GaAs guides have been submitted to Optics Letters.
The results of BISCOT have been presented in 14 regular communications in international conferences, including 3 invitations.

Mid-infrared (mid-IR) supercontinuum generation (SCG) from 2 to 15 µm is a hot topic owing to remarkable scientific and commercial opportunities. The state-of-the-art solution makes use of complex and cumbersome pulsed pump sources associated with nonlinear infrared fibres and components. Although very promising in the long run, these nonlinear fibres have not reached the performances or maturity for large scale commercial adoption. This programme will take up this timely challenge by developing a new paradigm to achieve extended mid-IR coverage in a rugged, highly-integrated format. It relies on the fact that 3-µm femtosecond lasers exacerbate broadband generation from 2 to 15 µm via combined quadratic and cubic nonlinear effects in Orientation-Patterned GaAs components. We will thus develop optimised semiconductor waveguides with nonlinear response tailored by quasi-phase matching and fibre-based femtosecond lasers emitting at 3 µm.
The consortium is composed of two academic teams and three companies including a SME, benefitting from their unique respective positions in the fields of long wavelength ultrafast fibre lasers and OP-GaAs components. Moreover, the partners have identified valorization opportunities in both fields. In particular, a prototype of mid-IR supercontinuum source is planned for the end of year 2 in order to carry out field trials with several already identified French end-users. A second riskier approach will lead to high-power spectral density superior to 10 µW/nm over the whole mid-IR spectral range.