The influence of femtosecond laser wavelength on waveguide fabrication inside fused silica

Abstract

We have investigated the effect of the laser wavelength on the fabrication of optical waveguides and tracks of modified material via direct laser writing inside fused silica. The size of the laserinscribed tracks, the material modification thresholds, the structural changes, and the waveguide writing energy range show a strong dependence on laser wavelengths ranging from ultraviolet to near-infrared. We used numerical simulations that consider the laser-excited electron plasma dynamics (via multiple rate equations) along with Gaussian beams theory to calculate the size of the laser-affected volume that has been further compared with the experimental results. This study yields insight into how to predict and design the spatial features of laser-inscribed lines and also aids of understanding the underlying physical mechanisms linked to laser-glass interaction when using different laser wavelengths.

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

“…In this paper, the measured values of the local Young's modulus increase and its corresponding refractive index increase, from 2 × 10 −2 to 5 × 10 −2 [−] as measured in Ref. [25], are significantly higher than the ones found for the regime-I modification [33,34], where an increase from 10 −4 to 10 −3 [−] is reported. The mechanisms which have been accounted for the refractive index increase for laser irritated material are (i) compaction due to the increase of fictive temperature by rapid solidification [35], (ii) increase of density due to bond breaking and reorganization [36], (iii) color center formation [37], or simply (iv) mechanical compression [38,39].…”

Raman spectroscopy of femtosecond multipulse irradiation of vitreous silica: Experiment and simulation

“…The densification of v-SiO 2 due to laser irradiation seems reasonable to cause a uniform RIC [4,5]. The supporting evidence of this mechanism was provided by micro-Raman spectroscopy for both single- [6,7] and multi-pulse [8][9][10][11][12][13][14] experiments.…”

Ultrafast time-resolved spectroscopy of a fs-laser-induced plasma inside glass using a super-continuum probe beam

“…The geometry on which we base our model consists of an electron plasma layer, parallel to the z-y plane, and a SC probe that passes through it along the x-axis (see Fig.1). The Fresnel-Kirchhoff integral can be used to calculate the electric field of the focused pump beam at the z-y plane from where one can retrieve a cross-section that yields a Gaussian curve [16]. Thus, it is reasonable to assume that the electron density will follow a Gaussian distribution.…”

“…Direct laser writing is the cornerstone of laser processing in bulk dielectrics, for instance, to inscribe optical waveguides as demonstrated for the first time by Hirao and Miura more than 20 years ago [7][8][9]. This technique is based on the inscription of 3D structures inside transparent materials by locally modifying the refractive index using a train of tightly focused fs-laser pulses while translating the sample, which offers an unprecedented spatial resolution and has been demonstrated in several crystalline and amorphous dielectrics, i.e., diamond [10], sapphire [11], quartz [11], fused silica [11][12][13][14][15][16][17], borosilicate glass [18], phosphotellurite glass [19,20] and zinc phosphate glasses [21,22].…”

“…Finally, we show the processing energy dependence of the electron plasma properties retrieved using the model and experiments and link those to the imprinted final modification. Figure 1a shows an example of fs-laser inscribed lines inside fused silica using direct laser writing [16]. The images illustrate the lateral view and the cross-section of a track of damage (top) and a waveguide (below).…”