For our 4th and last episode "Mid-IR photonics for environmental sensing" Kristinn Gylfason from KTH welcomes Delphine Marris-Morini from the University of Paris Saclay and Jana Jágerská, associate professor at the Artic university of Norway, to discuss Mid-IR photonics for environmental sensing. Prof. D. Marris-Morini is specialised in silicon photonics in the near-IR and mid-IR wavelength range. Dr J. Jágerská is group leader in the field of nanophotonics and laser spectroscopy with a focus on mid-infrared on-chip sensors for trace gas detection.