Refractive index change mechanisms in femtosecond laser written ceramic Nd:YAG waveguides: micro-spectroscopy experiments and beam propagation calculations

Fluorescence imaging of lattice re-distribution on step-index direct laser written Nd:YAG waveguide lasers

“…The intensity, bandwidth, and peak position of this particular fluorescence line have been extensively used as precise spectroscopic indicators of the local damage, disorder, and distortion of the YAG lattice, respectively. 10,20 Figure 2 shows this fluorescence line as obtained at the waveguide core (B) and at an unprocessed (A) area. The spectrum obtained from an unprocessed area agrees well with previous works as it is constituted by a narrow and symmetric band centered at around 938.9 nm.…”

“…The spectrum obtained from an unprocessed area agrees well with previous works as it is constituted by a narrow and symmetric band centered at around 938.9 nm. 10 On the contrary, the emission spectrum obtained from the WG core volume is completely different. It is constituted by the superposition of two fluorescence lines centered at around 939 and 940 nm, with an energy separation between them close to 11 cm À1 .…”

“…This is in contrast with the case of Nd:YAG stress-field based Type II WGs, in which the fluorescence generated at WG volume was composed by a single line. 10 According to Lupei et al multi-line emission in Nd:YAG ceramics denotes a multi-site distribution of Neodymium ions in the YAG lattice, i.e., the presence of Neodymium ions in different non-equivalent sites within the YAG lattice. 22,23 When all the Nd 3þ ions replace Yttrium ions in the YAG lattice (single site distribution) 4 F 3/2 !…”

“…4 DLW has been found especially appropriate for the local modification and controlled fabrication of laser waveguides in rare earth doped YAG crystals and ceramics. [5][6][7][8][9][10][11][12] In the simplest channel waveguide fabrication scheme (in which waveguides are constituted by either a single or double laser-written line tracks), waveguiding is produced at the stress affected volume (generally called Type II stress-induced waveguides) where the refractive index changes are produced through the piezo-optic effect. 10 In other cases, waveguiding is produced by a low-index cladding.…”

“…[5][6][7][8][9][10][11][12] In the simplest channel waveguide fabrication scheme (in which waveguides are constituted by either a single or double laser-written line tracks), waveguiding is produced at the stress affected volume (generally called Type II stress-induced waveguides) where the refractive index changes are produced through the piezo-optic effect. 10 In other cases, waveguiding is produced by a low-index cladding. 13,14 Both types of structures are typically fabricated using low-repetition rate lasers (1 kHz) and have been successfully used for the demonstration of efficient Nd:YAG waveguides lasers operating at 1.06 lm ( 4 F 3/2 !…”