Thermally resistant waveguides fabricated in Nd:YAG ceramics by crossing femtosecond damage filaments

Abstract

We report on femtosecond laser writing of channel waveguides in Nd 3+ ion doped YAG ceramics by multiple inscriptions of damage filaments. Waveguiding between filaments was found to resist annealing temperatures as high as 1500°C. Microluminescence imaging experiments have been carried out to elucidate the potential application of the obtained waveguides as integrated laser sources as well as to elucidate the waveguiding mechanisms. © 2010 Optical Society of America OCIS codes: 230.7380, 180.2520, 160.3380. Neodymium-doped transparent YAG ceramics (hereafter Nd:cYAG) is nowadays one of the most promising laser materials with outstanding properties [1][2][3]. The future incorporation of Nd:cYAG in compact devices requires the fabrication of channel waveguides in which the 2D light confinement would lead to a much higher optical intensities. Among the different methods already used for the fabrication of channel waveguides in the Nd:cYAG system [4], direct laser writing with femtosecond pulses is of special relevance because of its reduced processing times, its simplicity, and its true 3D versatility [5]. In the case of a Nd:cYAG system, waveguides based on the so-called double-line approach have shown excellent optical and superior laser properties [6,7]. The main drawback of these waveguides is the instability of the strain-field-induced refractive index increment, i.e., of the waveguide, against thermally induced lattice relaxation [6]. This is a negative aspect in laser waveguides, where relevant pump induced thermal loadings are expected to occur [8].In this Letter we report on the fabrication of thermally resistant Nd:cYAG waveguides by an approach consisting of the consecutive inscription of two orthogonal pairs of femtosecond filaments. The ability of the obtained structure for light confinement and its thermal stability has been investigated. The potential application of the obtained waveguides as laser sources has been explored by luminescence imaging experiments.The Nd:cYAG sample used in this work was provided by Baikowskii Ltd. (Japan) and was a 1 ϫ 1 ϫ 1 cm 3 prism with a nominal Nd 3+ concentration of 2 at. %. Damage filaments were inscribed by using an amplified Ti:sapphire laser system providing 120 fs pulses linearly polarized at 796 nm and 1 kHz of repetition rate. The laser beam was focused 250 m below the surface with a 10ϫ microscope objective ͑NA= 0.3͒. The on-target pulse energy was set to 3 J, leading to ϳ40-m-long filaments. In a first step, two filaments were written separated 30 m by translating the sample in the direction perpendicular to the laser polarization and the pulse propagation, with a speed of 50 m / s. Then the sample was turned 90°and a second pair of filaments, overlapping to the first one was inscribed. The end-face of the obtained quadruple-line structure is shown in Fig. 1(a). The ability of the obtained structure as an optical waveguide was investigated by both endcoupling experiments using a He-Ne laser [ Fig. 1(b)] as well as by transmission scanning near-field m...

Low loss depressed cladding waveguide inscribed in YAG:Nd single crystal by femtosecond laser pulses

“…6, 7). Thus the initial compressive stress in the tracks is expected to be in the range of 0.25-0.75 GPa, which is consistent with the results of [16].…”

“…The magnitude of this stress was estimated then as high as 0.4 GPa. We suggest that the sign of stress in our tracks is also negative, and the magnitude of frozen stress in our case does not seem to be sufficiently higher than that described in [16] since we used slightly lower femtosecond pulse energy while the beam waist had nearly the same cross section area. This conclusion is supported by the fact that we observed a fundamental mode with a single maximum in the oscillation experiments, which is only possible for magnitude of the averaged stress σ av less than 0.75 GPa according to the numerical solution of the eigenvalue problem.…”

“…Hence the circular distortion could be rectified by inscribing the whole waveguide structure deeper under the surface while the mirror asymmetry can be eliminated by accurate placing of the waveguide symmetrically between the crystal surfaces. Another way of cardinal eliminating of the distortions is a heat treatment [16].…”

“…Earlier spectroscopic investigations [16] gave the evidence of residual compressive stress inside a track written in ceramic Nd:YAG. The magnitude of this stress was estimated then as high as 0.4 GPa.…”

Stressed waveguides with tubular depressed-cladding inscribed in phosphate glasses by femtosecond hollow laser beams

“…This suggests already techniques of waveguide writing using the collateral stress-induced positive refractive index variation for guiding light [6]. Using this concept, pair line structure consisting of two parallel tracks on each side of the unexposed central domain was successfully demonstrated to confine light [7][8][9][10]. More complicated closed-form structures such as tubular designs consisting of a number of parallel tracks have also been demonstrated to confine light and to generate laser effects in ZrF 4 -BaF 2 -LaF 3 -AlF 3 -NaF (ZBLAN) fluoride glass [11].…”