Laser-induced Bessel beams can realize fast all-optical switching in gold nanosol prepared by pulsed laser ablation Santhi Ani Joseph, 1, * Gaurav Sharma, 2 Misha Hari, 1 S. Mathew, 1,2 P. Radhakrishnan, 1,2 and V. P. N. Nampoori 1 1 International School of Photonics, Cochin University of Science and Technology, Cochin 682–022, India 2 Centre of Excellence in Lasers and Optoelectronic Sciences, CUSAT, Kochi 682022, India * Corresponding author: santhia.a@gmail.com Received December 7, 2009; revised January 22, 2010; accepted January 26, 2010; posted January 26, 2010 (Doc. ID 121135); published February 25, 2010 We demonstrate the possibility of realizing, all-optical switching in gold nanosol. Two overlapping laser beams are used for this purpose, due to which a low-power beam passing collinear to a high-power beam will undergo cross phase modulation and thereby distort the spatial profile. This is taken to advantage for performing logic operations. We have also measured the threshold pump power to obtain a NOT gate and the minimum re- sponse time of the device. Contrary to the general notion that the response time of thermal effects used in this application is of the order of milliseconds, we prove that short pump pulses can result in fast switching. Dif- ferent combinations of beam splitters and combiners will lead to the formation of other logic functions too. © 2010 Optical Society of America OCIS codes: 140.0140, 140.6810, 160.3380, 160.4236, 190.4870, 250.5403, 350.6830. 1. INTRODUCTION All-optical logic operations are necessary for optical pro- cessing systems to avoid cumbersome electro-optic con- version. Many materials, concepts, and technologies have been studied and developed to realize all-optical switch- ing such as self-electro-optic devices, laser-induced optical devices, and microelectromechanical systems (MEMS). However, the all-optical regime is still not in a position to completely replace the electronic counterparts in switch- ing. The most current “optical” devices are based on opti- cally interfaced electronics in which the electronic core does the switching. However, optical switching has a fu- ture inside digital machines if the concept is simple and not power consuming. There is a report regarding the su- perposition of light beams in semiconductors and the simple use of their intrinsic and extrinsic features such as free-carrier absorption, lifetime of excited carriers, and impurity absorption and related properties to cause an optical switch [1]. In this way, optical switching was dem- onstrated by using the infrared absorption of a pulsed Nd:YAG laser in silicon, and a hybrid bistable device was realized by superposing the emission of a green light- emitting diode (LED) and a He–Ne laser in a cadmium sulfide (CdS) crystal. There is a recent report on the real- ization of an all-optical logic AND–NOR gate based on cross-gain modulation that requires only one semiconduc- tor optical amplifier to perform the logic gate with three input signals. The switching time reported was about 650 ps for the rise time and 100 ps for the fall time [2]. There is also a report regarding all-optical logic gates con- taining a local nonlinear Mach–Zehnder interferometer waveguide structure. Here, the light-induced index changes in the Mach–Zehnder waveguide structure make the output signal beam propagate through different non- linear waveguides. Based on the output signal beam propagating property, various all-optical logic gates like XOR/NXOR, AND/NAND, and OR/NOR were obtained by using the local nonlinear Mach–Zehnder waveguide inter- ferometer structure with two straight control waveguides [3]. In this paper, we report the possibility of realizing all- optical logic functions in a lab setup by making use of self- and cross-phase modulations of light beams. For this pur- pose, we make use of two overlapping beams having Gaussian intensity distribution. As the high-power beam propagates through the absorbing medium, it experiences phase change due to various processes like photothermal effect, self-focusing, or defocusing, etc. Since the low- power beam is overlapping this, it will have an induced phase shift due to the first beam, and depending on the strength of the phase modulation the Gaussian beam will be converted to Bessel beams of various orders. This is il- lustrated in the photograph shown in Fig. 1. The novelty of the work is that, unlike in usual photothermal effects that rely on thermal diffusion, which has a slow response, we have proved that it is possible to obtain a fast all- optical switch using instantaneous thermal effects that depend on the pulse duration of the pump beam. This will ultimately make simple configurations for fast all-optical switches using two laser beams. 2. EXPERIMENTAL TECHNIQUE When a spatially Gaussian pump is used, the interaction of light with matter is stronger at the central part of the laser beam than the edges and as a result, a probe beam which spatially overlaps the pump beam is perturbed spa- tially and inhomogeneously. The spatially inhomogeneous Joseph et al. Vol. 27, No. 3/March 2010/J. Opt. Soc. Am. B 577 0740-3224/10/030577-5/$15.00 © 2010 Optical Society of America