Femtosecond Laser-Induced Crystallization in Glasses: Growth Dynamics for Orientable Nanostructure and Nanocrystallization

Abstract

Laser-induced crystallization in glasses is of great interest because of its significant applications in optics. However, the mechanisms involved are not yet concluded and this paper is to make progress on this problem. Major aspects of the laser-induced crystallization are the nanostructure formation, textured crystallization, and growth dynamics. Herein, firstly, we review the previous works on the laser-induced crystallization in various glasses by different kinds of lasers. Then lithium niobium silicate glasses were used as a "glass model" to investigate the nanostructure formation and crystallization by fs laser irradiation at high repetition rate (100-500 kHz). Based on the deposited fs laser power inside glasses, three crystallization regimes can be classified with the increase of laser power. In addition, the boundary between neighboring regimes can be adjusted by changing the writing parameters (e.g. focus depth). Regime 1: modifications of the amorphous structure. Regime 2: phase separation into crystalline LiNbO 3 and amorphous SiO 2 . There is appearance of an organized lamellar nanostructure and textured nanocrystals, embedded in amorphous lamellas. Polar axes are perpendicular to laser polarization direction. Remarkably, this hierarchical micro/nanostructure can induce an orientation tunable second harmonic generation and form birefringence. Regime 3: crystallization morphology is sensitive to the angle between laser writing and laser polarization direction. With parallel configuration, crystal grains are at the micron scale. With perpendicular configuration, crystal morphologies resemble regime 2 but they are not textured. In this paper, a crystallization dynamic model is proposed to explain the nano/micro-crystals formation and their morphology induced by fs laser irradiation. This model allows thinking that it is very likely possible to extend conclusions to other non-congruent glasses. This provides guidelines for manufacturing a wide variety of multifunctional optical devices.

Femtosecond-laser-irradiation-induced structural organization and crystallinity of Bi2WO6

“…This control is due to the fact that lasers can deposit a large amount of energy per unit area over a temporal scale shorter than the phonon-electron relaxation time 64 . Recently, fs-laser-induced crystallization in glasses 65 , aspirin 66 and many different kinds of films such as Si [67][68][69][70] , Ti 71 , Ge 72 , and diamond 73 , among others [74][75][76][77][78][79] , has been demonstrated 80 .…”

Space-Selective Control of Functional Crystals by Femtosecond Laser: a Comparison Between SrO-TiO₂-SiO₂and Li₂O-Nb₂O₅-SiO₂ Glasses

“…This is achieved at any place of the HAV and may form a complete crystallized volume. Its size is comparable to the laser beam size as it is demonstrated in [16]. Note there is homogeneous nucleation but the growth of the nuclei is favored when their c-axis are oriented in the direction of scanning because c-axis exhibits the fastest growth rate in such a structure [38] and aligned with the largest gradient (like in the method of single crystal growth by floating zone).…”

“…a few m/s), which is our case as the effective scanning speed for crystallization is smaller than 100 m/s. So the average temperature space and time distributions can be controlled and use for space-selective crystallization, which was described in ref [16]. Considering a point in the material at some distance of the center of the T bell shape, it experiences an increase of T followed by a subsequent decrease controlled by the heat diffusion coefficient in our conditions that we call thermal treatment curve quoted TTC.…”

“…It is polar along the trigonal axis and thus shows the maximum non-linear optical property in this direction. It is a uniaxial crystal but with the largest refractive index being perpendicular to the polar axis [16]. With those properties, we showed it is possible to control the orientation of LiNbO3 nanocrystals appearing at low fs pulse energy, with the laser polarization [17].…”

Stress‐induced crystal axis spiral rotation in multiferroic β'‐Gd2(MoO4)3 observed only in glass crystallization

“…Recently, laser-induced crystallization has received much attention, in which single crystals and nanocrystals are patterned freely in spatially selected parts in glasses, being a completely different approach to the glass-crystallization compared with a usual crystallization technique in an electric furnace. 12,[20][21][22][23][24][25][26] Among glass-ceramics reported so far, an extremely unique and curious phenomenon has been observed in the crystallization of multiferroic (ferroelectric and ferroelastic) β'-Gd 2 (MoO 4 ) 3 (designated here as β'-GMO) in Gd 2 O 3 -MoO 3 -B 2 O 3 glasses (GdMoBO glasses). [27][28][29][30][31][32][33][34] That is, crystals formed in the crystallization break into small pieces spontaneously during the crystallization in the inside of an electric furnace, not during the cooling in air after the crystallization.…”