Materials Science and Engineering B 194 (2015) 27–33 Contents lists available at ScienceDirect Materials Science and Engineering B jo ur nal ho me page: www.elsevier.com/locate/mseb Photothermal, photoconductive and nonlinear optical effects induced by nanosecond pulse irradiation in multi-wall carbon nanotubes J.A. García-Merino a , C.L. Martínez-González a , C.R. Torres-San Miguel a , M. Trejo-Valdez b , H. Martínez-Gutiérrez c , C. Torres-Torres a,∗ a Sección de Estudios de Posgrado e Investigación, Escuela Superior de Ingeniería Mecánica y Eléctrica Unidad Zacatenco, Instituto Politécnico Nacional, 07738 México Distrito Federal, Mexico b Escuela Superior de Ingeniería Química e Industrias Extractivas, Instituto Politécnico Nacional, 07738 México Distrito Federal, Mexico c Centro de Nanociencia y MicroNanotecnología del Instituto Politécnico Nacional, 07738 México Distrito Federal, Mexico a r t i c l e i n f o Article history: Received 2 July 2014 Received in revised form 8 December 2014 Accepted 20 December 2014 Available online 5 January 2015 Keywords: Nonlinear optics Thermal response Photoconductivity Carbon nanotubes a b s t r a c t The influence of the optical absorption exhibited by multi-wall carbon nanotubes on their photothermal, photoconductive and nonlinear optical properties was evaluated. The experiments were performed by using a Nd:YAG laser system at 532 nm wavelength and 1 ns pulse duration. The observations were carried out in thin film samples conformed by carbon nanotubes prepared by an aerosol pyrolysis method; Raman spectroscopy studies confirmed their multi-wall nature. Theoretical and numerical calculations based on the heat equation allow us to predict the temporal response of the induced effects associated to the optical energy transference. A two-wave mixing method was employed to explore the third order nonlinear optical response exhibited by the sample. A dominant thermal process was identified as the main physical mechanism responsible for the optical Kerr effect. Potential applications for developing a monostable multivibrator exhibiting different time-resolved characteristics were analyzed. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Due to their remarkable physical properties, carbon nanotubes (CNTs) have been considered potentially useful in a wide range of attractive applications related to materials sciences [1]. There have been explored fascinating optical characteristics associated to CNTs that can be employed for controlling mechanical [2,3], thermal [4,5] electrical [6,7] and nonlinear optical functions [8]. Particularly, all- optical operations based on the powerful and ultrafast third order nonlinear optical phenomena of CNTs have been found [9]. Besides, it has been demonstrated that carbon nanotubes could be not only related to different physical mechanisms of optical nonlinearity, but also, they can show opposite nonlinear optical processes, as it is the case of two-photon absorption (TPA) and saturated absorption (SA) [10,11]. The helicity, morphology, tube diameter, intertube distance and tube length are among the most important parameters to take into account to tailor the resulting optical features exhibited by multi-wall CNTs (MWCNTs) [12]. More to the point, other forms ∗ Corresponding author. Tel.: +52 55 57 29 60 00x54686; fax: +52 55 57 29 60 00x54587. E-mail addresses: crstorres@yahoo.com.mx, ctorrest@ipn.mx (C. Torres-Torres). of carbon nanostructures also exhibit unique properties [13]. CNTs have a band gap determined by circumferential quantum confine- ment, which depends on the tube diameter [14,15]. Then, optical and conductive properties of MWCNTs depend on their morphol- ogy; particularly on the number of their layers. On the other hand, the conductivity and the nonlinear optical properties are strongly related to the temperature; the conductance increases if the tem- perature rises [16], and the mass density, resulting in a change of refractive index, decreases in proportion to the increment of temperature. Particularly, large-diameter CNTs do not typically show gate effect, but structural deformations can modify enough their electronic structure to allow Field Effect Transistor (FET) behavior [17]. Generally, low-dimension structures based on CNTs present very weak optical reflectance and relatively high optical absorbance. Nevertheless, with a high volume fraction, MWCNTs arrays exhibit a large optical absorbance together to a strong opti- cal reflectance that can be essential for optical limiting applications [18]. It is worth noting that impurities and structural defects in CNTs samples originate noticeable modifications on their thermal response [19]. Additionally, the effect of incorporating MWCNTs on nanocomposites yields an enhancement in a resulting thermal con- ductivity that is increased several times [20]. On the contrast, it has been indicated that in the field of nanofluids, the heat transference http://dx.doi.org/10.1016/j.mseb.2014.12.022 0921-5107/© 2015 Elsevier B.V. All rights reserved.