Current advanced femtosecond laser systems offer myriad possibilities to modify materials, from implementing new optical functionality to improving existing materials properties. Femtosecond direct laser writing exhibits enormous potential in the development of a new generation of powerful components in 3-D for micro-optics, telecommunications, optical data storage, imaging, micro-fluidics, and biophotonics at the micro- and nano-scale. To highlight breakthroughs in femtosecond laser systems, the editors of the Optical Society's (OSA) open-access journal Optical Materials Express have published a special Focus Issue on Femtosecond Direct Laser Writing and Structuring of Materials. The issue is organized and edited by Guest Editors Thierry Cardinal of France's University of Bordeaux, Bertrand Poumellec of the University of Paris-Sud XI, and Kazuyuki Hirao of Kyoto University, Japan.
"At a time when many different scientific communities are getting involved in the field of femtosecond laser writing, this focus issue aims to give readers an overview of the current, state-of-the-art research being done," said Cardinal. "The focus issue includes original papers and reviews from leading groups on fabrication processes, related mechanisms, and photo-produced structures."
Femtosecond Direct Laser Writing, which relies on non-equilibrium synthesis and processing with photon beams, opens up new ways to create materials and devices that are not currently possible with established techniques. The main advantage remains in the potential to realize 3-D multi-functional photonic devices, fabricated in a wide range of transparent materials. The papers in this issue focus on fabrication processes, related mechanisms, and photo-produced structures, taking into account physical and chemical aspects.
Key Findings & Select Papers
- Researchers from the University of Bordeaux and the University of Central Florida provide a review of recent advances in photochemistry in transparent optical materials induced by femtosecond laser pulses. This paper illustrates the importance of the temperature for material structuring using femtosecond lasers. Arnaud Royon et al. show that the temperature becomes a key parameter that determines the final state and the purpose of the material. Paper: "Femtosecond laser induced photochemistry in materials tailored with photosensitive agents," Optical Materials Express, Vol. 1, Issue 5, pp.866-882. http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-1-5-866
A group of researchers from the Optoelectronics Research Centre at Southampton present a review of recent progress in applications of femtosecond laser nano-structuring of fused silica. The paper focuses on polarization controlling devices written with self-assembled nanograting. Martynas Beresna et al. discuss how femtosecond laser direct writing can be used for fabricating complex optical devices in a single step. This research will open new opportunities for precise control of induced birefringence, which can be widely used in material processing, microscopy, and optical trapping and manipulation. Paper: "Polarization sensitive elements fabricated by femtosecond laser nanostructuring of glass," Optical Materials Express, Vol. 1, Issue 4, pp.783-795. http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-1-4-783
Research conducted in collaboration between the University of California Davis, the Missouri University of Science and Technology, and the Dipartimento di Fisica del Politecnico di Milano has investigated, in the scope of femtosecond laser writing of waveguides in phosphate glass, the relationship between the initial glass composition and the structural changes associated with laser-induced refractive index modification. Luke B. Fletcher et al. have shown that the initial glass structure plays a very important role in the resulting change to refractive index and is a fundamental parameter for predicting how the glass will respond to the absorption of tightly focused fs-laser pulses. Paper: "Femtosecond laser writing of waveguides in zinc phosphate glasses," Optical Materials Express, Vol. 1, Issue 5, pp.845-855. http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-1-5-845
A research group from the University of Laval in Canada has shown new physical insight into the 1-D optical multi-filamentation process allowing for the inscription of high-quality first-order Fiber Bragg Gratings with femtosecond pulses and a phase mask. This approach has been validated for both silica fiber and fluoride glass fibers. Results by Martin Bernier et al. show the huge potential of femtosecond pulses in the filamentation regime to write first-order Fiber Bragg Gratings in various materials. Paper: "Role of the 1D optical filamentation process in the writing of first order fiber Bragg gratings with femtosecond pulses at 800nm," Optical Materials Express, Vol. 1, Issue 5, pp.832-844. http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-1-5-832
Yves Bellouard of Eindhoven University of Technology demonstrates that femtosecond lasers can efficiently be used to produce arbitrarily shaped high-strength mechanical devices, opening new opportunities for the design of monolithically integrated optomechanical devices. The paper reports on the mechanical properties of fused silica flexures manufactured by a two-step process combining femtosecond laser exposure below the ablation threshold and chemical etching. This creative approach paves the way toward increased monolithic integration where features as diverse as gratings, waveguides, mechanical flexures, and fluidic channels can be made out of a single substrate while reducing the number of fabrication steps. Paper: "On the bending strength of fused silica flexures fabricated by ultrafast lasers," Optical Materials Express, Vol. 1, Issue 5, pp.816-831. http://www.opticsinfobase.org/ome/abstract.cfm?uri=ome-1-5-816