Generation of mid-infrared supercontinuum (see submitted ATTRACT proposal “SMIL”) requires the development of a sub-ns laser source based on thulium-doped silica fibres. In order to achieve sub-ns pulses, a novel semiconductor saturable absorber (SESAM) will be developed within this project. Unlike off-the-shelf SESAMs from a commercial supplier, the consortium will develop a custom GaSb-based saturable absorber structure that will be composed of lattice-matched layers and monolithically integrated with a crystalline heat-sink substrate, hence achieving the required lifetime stability and reproducibility of the parameters. The SESAM concept will be based on a groundbreaking substrate-transfer technology from Crystalline Mirror Solutions (CMS).
The advantages versus conventional (soldering-based) mounting methods are a lower temperature increase, reduced thermal lensing and less surface deformation. Moreover, the SESAM performance also benefits from a superior optical flatness of the crystalline heat-sink substrates that will be deployed. For the final wavelength selection between 1850 and 2100 nm, a volume Bragg grating (VBG) would be state-of-the-art but exhibits several disadvantages, such as severe bandwidth limitation. Therefore, within this project, we will also explore whether/how such a wavelength selective optical component can be realised based on crystalline coatings with their excellent optical properties, avoiding or mitigating the shortcomings of VBGs.
Apart from being an imaging and sensing enabling device in its own right, this 2 μm laser will (as mentioned at the beginning of this Public Summary) be primarily developed as the pumping stage of a mid-infrared supercontinuum laser with groundbreaking characteristics and very wide application potential for advanced sensing and imaging in the mid-infrared spectral range.