Elastic properties of self-organized nanogratings produced by femtosecond laser exposure of fused silica

Abstract

Under certain exposure conditions, a femtosecond laser beam focused in the bulk of fused silica leads to the formation of self-organized structures consisting of a series of "nanolayers," parallel to one another. Remarkably, this laser-induced nanoscale anisotropy offers the possibility to locally engineer macroscopic properties of a given substrate by selectively exposing it in arbitrarily chosen locations to a laser beam with designed polarization states. Although various physical properties are affected by the laser, this paper specifically discusses in-plane elastic properties of these nanostructures. Using a method based on monitoring resonant properties of vibrating cantilevers combined with a mechanical model of the nanostructures, the Young's moduli of individual nanolayers are calculated and used to define the stiffness matrix of the composite structure. The model shows a good agreement with measured mechanical properties of arbitrarily oriented nanostructures. This work demonstrates the predictability and controllability of laser-induced nanoscale mechanical properties and offers a framework for engineering arbitrary elastic properties through 3D laser writing.

On the abnormal temperature dependent elastic properties of fused silica irradiated by ultrafast lasers

“…The volume inside those cantilevers are exposed to ultrafast laser as depicted in Figure 2a. The fabrication of these structures, dimensions and exposure strategy are further detailed in [25].…”

“…In a-SiO 2 , the modified volume is associated with microscale material property changes, e.g. refractive index [20], chemical susceptibility [21], thermal conductivity [22], thermal expansion coefficient [23] and Young's modulus [24,25]. These laser-induced physical properties changes are particularly useful in the context of monolithic micro-devices and led to the creation of monolithic devices, e.g.…”

“…These laser-induced physical properties changes are particularly useful in the context of monolithic micro-devices and led to the creation of monolithic devices, e.g. complex integrated photonics circuits [26], tuned resonators [25,27], optomechanical devices [28] and optofluidics [29][30][31], made from a single piece of material and functionalized through laser exposure sequences were reported. Specifically, a-SiO 2 is attractive for its remarkable material properties, such as its low thermal expansion, its low optical losses over a broad spectral range as well as its low mechanical losses and high thermal stability.…”

Index Modulation Embedded in Type I Waveguide Written by Femtosecond Laser in Fused Silica

“…In particular, the period of self-organized grating structures was controlled by the pulse energy and the number of irradiated pulses [11]. The typical nanogratings reveal strong bond breakage and deficit of oxygen [12,13], with void-like morphologies (type II), and seem to be the result of regular field enhancement due to scattering and interference [14]. On the other hand, the self-organized microstructures with a period larger than laser wavelength have been demonstrated using a high-repetition-rate femtosecond laser [15,16], whose possible explanation concerns the hydrodynamics instability.…”

ABH damping of monolithic silica glass cantilever by structural and material modification using fs laser micromachining

“…While 3D microfabrication of fused silica using femtosecond laser may realize enough preciseness according to numerous optimization reports for irradiation conditions, [11][12][13][14] the effects of the laser at the atomic level are not fully understood as it is difficult to see the detailed gradation of material properties after writing complex patterns inside the material. 15 In addition, the effects on material properties, such as thermal expansion coefficient, 16 Young's modulus, 17,18 and density, 19,20 after the etching process are not revealed. Further understandings on these mechanisms will enhance its reliability and broaden application fields.…”