Laser ablation and waveguide fabrication using CR39 polymer W. Kam, Y.S. Ong, W.H. Lim, R. Zakaria n Photonics Research Centre, University of Malaya, 50603 Kuala Lumpur, Malaysia article info Article history: Received 20 June 2013 Received in revised form 26 September 2013 Accepted 12 October 2013 Keywords: UV-laser ablation CR39 Surface modification Refractive index modification abstract We report on the ablation and fabrication of optical waveguide using allyl-diglycol CR39 polymer. Pulse nanosecond (ns) laser (248 nm KrF) and continuous wave (CW) (244 nm argon-ion) irradiation are performed to observe surface modification on the polymer and potentially utilize it for channel waveguide. The pulsed UV laser creates craters with different depth as fluence increases to quantify threshold fluence for this material. For continuous wave UV irradiation, refractive index value on the CR39 channels varied as fluence changed, and shows the potential use of this polymer in planar waveguide applications. An upper fluence limit where laser ablation commences is also determined. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Laser and polymeric materials that induce surface modification and ablation are an interesting topic since decades ago [1]. Poly- meric materials have been used in various applications including in high-performance photonics devices such as micro/nanofluidics channel fabrication, micromachining/microdrilling [2,3], splitters, waveguide gratings and filters, and also in optical waveguide fabrication [3–5]. Few significant studies in the research field of photonics are refractive index modification of germanium doped silica glass using 244 nm UV laser irradiation as well as studies on nonlinear refractive index change of glass by femtosecond laser irradiation, [6] an all-optical switch with simple configuration realized with rare earth doped fiber with pump laser [7] and a proposal of low power switching for rare earth doped fiber [8]. Over the years, interaction of polymer materials with laser at different photoetching technique was reported using excimer laser, infrared nanosecond laser and femtosecond laser [9]. The material removing process however depends on the combination of various para- meters such as laser pulse, laser energy and material [10]. Additionally, the wide uses of polymers are due to its low cost, high accessibility and the handling during fabrication is simple. It would be the best solution for cost effective optical waveguide fabrication. Here, CR39 polymers are chosen as a target for our ablation experiment as it is an important material for wide applications in medical and optical industries. In this work, we focused on using KrF (248 nm laser) to obtain ablation threshold for this material at this wavelength. Varying the laser fluences using continuous wave laser changes the refractive index of CR39. To obtain higher fluence in respect for the changes to be made, the laser spot size is focused down to microns in diameter. For pulse laser, an aperture size of 6 Â 3 mm 2 is aligned and located before the lens to assure that the significant edge of craters can be observed on the film. The pulse crater is then investigated under microscope and the depth of each crater is determined. Relation between changes of energy fluence and etch depth is established and the fluence threshold is also obtained. For continuous wave laser, the refractive index is calculated after laser induced is based from the numerical aperture measurement of the written waveguides. Positive refractive index change is observed and relation between irradiation fluence and refractive index change is also determined. An upper fluence limit is also obtained where laser ablation commenced above this limit. 2. Experimental setup 2.1. Pulsed UV laser at 248 nm Laser ablation experiment used in this study was a KrF excimer laser (Opto Systems Ltd Excimer Laser series CL5100) operating at 248 nm wavelength. Maximum repetition rate range is up to 100 Hz with a maximum average output power of 5 W and a pulse duration range from 9–11 ns. A 50 mm focusing lens onto the CR39 focuses the light. The CR39 sample is in sheet form with a thickness of 1 mm (product from Solarlens). The sample was mounted onto a 3-axis x-y-z translational stage. Position of the sample varied through the micrometer driven sample holder, in order to place the polymer at the focus point. The minimum spot size created on the Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/optlaseng Optics and Lasers in Engineering 0143-8166/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.optlaseng.2013.10.012 n Corresponding author. Tel.: þ603 79674177; fax: þ603 79674146. E-mail addresses: rozalina@um.edu.my, drrozalina@gmail.com (R. Zakaria). Optics and Lasers in Engineering 55 (2014) 1–4