Micro structuring of LiNbO 3 by using nanosecond pulsed laser ablation F. Meriche a, * , E. Neiss-Clauss b , R. Kremer a , A. Boudrioua a , E. Dogheche c , E. Fogarassy d , R. Mouras e , A. Bouabellou f a LMOPS, CNRS UMR 7132, Universite ´ de Metz et Supe ´lec, 2 rue E. Belin 57070 Metz, France b Laboratoire des Syste `mes Photoniques, ENSPS, bd Se ´bastien Brant, BP 10413, 67412 Illkirch Cedex, France c Institut d’Electronique et de Microe ´lectronique du Nord, CNRS, Villeneuve d’Ascq, 59652 Lille, France d Institut d’E ´ lectronique du Solide et des Syste `mes, 23 rue du Loess, 67037 Strasbourg, France e Institute for Materials and Processes, University of Edinburgh, King’s Buildings Mayfield Road Edinburgh, EH9 3JL, Scotland, UK f Laboratoire des couches minces et interfaces, Universite ´ Mentouri de Constantine, 25000, Algeria Available online 25 September 2007 Abstract In this work, we report on the fabrication and characterization of surface microstructures in lithium niobate thin films and single crystal by using KrF excimer laser ablation technique at 248 nm with 6 ns pulse width. Ablation is carried out through a mask projection set-up. Various experimental conditions are used in order to evaluate the potential of laser direct writing for photonic waveguides fabrication in lithium niobate. The surface morphology of the processed structures was studied by optical and atomic force microscopy. Laser processing mechanism is investigated by using micro-Raman spectroscopy. # 2007 Elsevier B.V. All rights reserved. Keywords: Laser micromachining; Laser ablation; Lithium niobate; Photonic structure 1. Introduction Lithium niobate (LiNbO 3 ) is a ferroelectric material of great interest in the field of optics and telecommunications, due to its large electro-optic and non-linear optical coefficients [1]. It has been widely used as electro-optic modulator, wavelength converter and optical waveguide. Moreover, it is expected that this material might be of great interest as a photonic crystals thanks to its linear and non-linear optical properties. Recently, several techniques have been reported for lithium niobate microstructuring such as reactive ion etching (RIE) [2], electron beam lithography (EB) [3], focused ion beam (FIB) [4] and light induced frustration of etching (LIFE) [5]. Pulsed laser ablation is one of the most commonly used methods for materials machining. It offers many benefits such as wide design flexibility, relatively high speed and low cost. For instance, laser machining has been proposed as an alternative technique to create photonic elements such as gratings and microholes [6]. Deshpande et al. [7] performed a study on femtosecond laser processing of lithium niobate surface and subsurface structures by using a Ti:sapphire femtosecond laser (800 nm, 300 fs). The investigation of the modification induced in z-cut congruent LiNbO 3 bulk crystal by femtosecond laser irradiations has been reported in ref. [8]. It was found that the utilization of an amplified Ti:sapphire laser system with a repetition rate of 1 kHz and energy per pulse of 1 mJ allows a precise control of the microstructure size. Generally speaking, the utilization of amplified femto- second lasers allows athermic drilling processes which are needed for sub-micron structuring without relief modification at the periphery of the holes. However, cheaper and less complex lasers in the nanosecond regime can also be used. For instance, in ref. [9] the authors reported the fabrication of bulk- LiNbO 3 phase gratings with a 2 mm period and 110 nm depth by using a nanosecond excimer laser ablation (248 nm, 30 ns) through a phase mask. To improve the quality of the ablated patterns realized with a nanosecond KrF excimer laser on x-cut bulk lithium niobate surface, Chong et al. [10] deposited a 1 mm thick silicon dioxide overlayer on the sample prior to ablation. www.elsevier.com/locate/apsusc Available online at www.sciencedirect.com Applied Surface Science 254 (2007) 1327–1331 * Corresponding author at: LEM, De ´partement de Physique, Universite ´ de Jijel, BP 98 Ouled Aissa 18000, Algeria. Tel.: +33 66 5311865; fax: +33 38 7378559. E-mail address: faiza_meriche@yahoo.com (F. Meriche). 0169-4332/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2007.09.053