Volume photoinscription of glasses: three-dimensional micro- and nanostructuring with ultrashort laser pulses

Abstract

Ultrafast laser photoinscription of optical materials has seen a strong development in the recent years for a range of applications in integrated photonics. Fueled by its capability to confine energy in micro-domains of arbitrary geometries, it forecasts extensive potential in optical design. The process can locally modify the material structure and the electronic properties, changing in turn the refractive index. It thus lays down a powerful concept for three-dimensional modifications with the potential to design integrated optical functions. Using fused silica as model glass, this report discusses the physical mechanisms of photoinscription, outlining the possibility of refractive index engineering. We will review basic mechanisms of light propagation, excitation of matter, and energy relaxation concurring to material structural and photo-physical modification. A dynamic perspective will be given, indicating relevant times for relaxing different forms of energy (electronic, thermal, etc.). The possibility to structure beyond diffraction limit will be explored, as well as the subsequent optical response of hybrid micro-nano structures. Different irradiation geometries for photoinscription will be presented, pinpointing their potential to generate optical and photonic systems in 3D. Spatio-temporal pulse engineering can optimize the material response towards the achievement of accurate positive and negative index changes. An optimality concept can thus be defined for index design. A particular potential derives from the utilisation of non-diffractive beams with engineered dispersion. Finally we indicate a range of application domains, from telecom to optofluidics and astrophotonics, outlining the potential of volume micro and nanoprocessing.

Research on the Response Characteristics of Vanadium Pentoxide Film to the Irradiation of Ultrafast Pulsed Laser

“…After the sample was irradiated by ultrafast laser, most of the pulse energy was transferred to the material, which induced a series of refractive index modification-related processes, such as excitation and recombination. The natural phenomenon of laser irradiation weakens the strength of molecular bonds, which makes the material easier to expand and rarefact [ 23 ]. As the volume of the film expands, its density decreases, thus showing a negative refractive index change.…”

“…In addition, the shift of the Raman spectra revealed that strain existed in the film, which led to a vibration of bonds length. Electron excitation is associated with the weakening and breaking of molecular bonds and formation of defects of color centers [ 23 ]. Each broken bond will produce a dangling bond or trigger a structure rearrangement process.…”

Advances in ultrafast laser structuring of materials at the nanoscale

“…From the material side, additional constraints appear on matter transport due to spatial confinement. These aspects were reviewed several times [102,103] and were recently revisited in [104] in the context of laser volume nanostructuring. Whenever the energy at the impact point overcomes the material resistance, a structuring phenomenon takes place.…”

Characterization of a hybrid scanning system comprising acousto-optical deflectors and galvanometer scanners

“…Ultra-short pulse (USP) lasers emit pulses in the pico-and femtosecond range and have gained particular significance in high-precision micro-material processing due to negligible thermal load, often attributed to the so-called cold ablation [1,2]. Thus, USP lasers are typically used in electronics manufacturing [3][4][5], medical technology [6][7][8][9][10], aerospace applications [11][12][13], thin film technology [14] and material modification [15][16][17][18][19][20]. Although excellent processing qualities are possible, a broad adoption in industrial applications is constrained by low processing speeds and consequently limited productivity [21].…”