Applications of femtosecond laser induced self‐organized planar nanocracks inside fused silica glass

Abstract

We review our recent experimental efforts towards developing photonic and biophotonic applications of femtosecond laser induced self-organized planar nanocracks inside fused silica glass. Our results show that sub-diffraction limited, periodic, planar cracks can be produced, organized, erased and rewritten and basically controlled inside fused silica glass where they can be diagnosed optically using form birefringence. The high degree of control over these self-replicated periodic structures allows us to investigate applications in micro-and nanofluidics, porous capillaries for biofiltering and rewritable data storage for harsh environments.Optical birefringence measurement of a grating voxel. CCD P2 OBJ P1 0 1 2 3 4 5 0.001 0.01 0.1 1 Intensity, a. u. Distance, m I max I min O 1 m

Femtosecond laser microstructuring: an enabling tool for optofluidic lab‐on‐chips

“…). Broadly speaking, they can be classified into three categories, in order of increasing laser fluence [36][37][38]: a) for a fluence just above the permanent modification threshold, a smooth modification is achieved, resulting mainly in positive/negative refractive index changes; b) for higher fluence, sub-wavelength nanogratings [37] are formed (so far only observed in fused silica glass), oriented perpendicularly to the writing laser polarization and with period λ =2n, where λ is the laser wavelength and n the refractive index of the substrate; c) for even higher fluence, a disruptive modification is obtained, with the creation of voids and microexplosions [39,40].…”

“…However, in this regime only a very modest increase in the etching rate is obtained after irradiation. A second mechanism, active for high intensity irradiation and giving a much higher etching selectivity, is the formation of self-ordered nanocracks, perpendicular to the laser polarisation direction [37]. The physical processes underlying the formation of nanocracks have been studied in detail in [69,70] and involve the following transient nanoplasmonic model: i) in the focal volume, hot spots for multiphoton ionization occur due to the presence of defects or color centers; ii) such hot spots evolve into spherically shaped nanoplasmas over successive laser pulses due to a memory effect [71], equivalent to a reduction of the effective bandgap in the previously ionized region; iii) field enhancement at the boundaries of the nanoplasma droplets results in asymmetric growth of the initially spherical droplets, in a direction perpendicular to the laser polarization, leading to the formation of nanoellipsoids, which eventually grow into nanoplanes; iv) the nanoplanes are initially randomly spaced; when the electron plasma density inside them exceeds the critical density, they become metallic and start influencing light propagation in such a way that they assemble in parallel nanoplanes spaced by λ =n, where λ is the wavelength of the femtosecond writing laser and n the refractive index of the medium.…”

Periodic and uniform nanogratings formed on cemented carbide by femtosecond laser scanning

“…[15]. However, the variability of the nanograting period is inconsistent with the simple nanoplasmonic model [26], which only allows for structures to be formed with a fixed period of λ/2n.…”

Monolithic integration in fused silica: When fluidics, mechanics and optics meet in a single substrate

“…In fused silica, femtosecond laser pulses can, not only locally increase the refractive index [8], they can also enhance the etching rate [10], introduce sub-wavelength patterns [12], create voids [13] or change its thermal properties [14]. By scanning the laser through the specimen volume [15], one can distribute, combine and organize these material modifications to form complex patterns to be used for instance as waveguides or fluidic channels.…”