A 2D μ-Raman analysis of low repetition rate femto-waveguides in lithium niobate by using a finite element model

We present a μ-Raman two-dimensional analysis of 1 kHz femtosecond laser written waveguides in an x-cut lithium niobate crystal. At first, the fitting between a two-dimensional elastic model and experimental micro Raman spectroscopy data (MR) were examined to validate the numerical model. In this, the Raman Potential Deformation Theory (RPDT) was employed to fit the wavenumber shift of the A1(TO)4 phonon. Then, the adequate values for geometrical parameters of the numerical model (horizontal and vertical ellipse radius) were estimated. Finally, using these parameter values, the guided modes were computed for different ellipse expansions and compared with experimental guided modes.