The femtosecond laser, with pulse durations smaller than 100 femtoseconds, is being focused in a microscope into liquid photoresist which rests on a glass substrate or an optical fiber. Two photons of the red laser beam with a wavelength of 785 nm are being absorbed simultaneously in the focus and expose the photoresist. This crosslinks the polymer and hardens it. The laser beam is directed with a scanner or by moving the substrate over the substrate. After exposure, the unexposed photoresist is washed away with a solvent. Only the hardened transparent polymer remains and forms the optical element.
Using this method, optical free form surfaces can be created with sub-micrometer accuracy. The precision of the 3D laser writing allows not only for construction of common spherical lenses, but also the more ideal surfaces such as paraboloids or aspheres of higher order are possible. Particularly optical lens systems with two or more lenses can be realized for the first time with this method. This opens the door to aberration correction and microoptical imaging systems with unprecedented quality.
Full story and contact information can be found from University of Stuttgart website.