pISSN 0374-4914 eISSN 2289-0041

## Research Paper

New Physics: Sae Mulli 2016; 66: 1260-1265

Published online October 31, 2016 https://doi.org/10.3938/NPSM.66.1260

## Nonlinear Optical Characteristics of Colloidal Carbon Nanoparticles According to their Concentration

Isae KIM, Jaeran LEE, Sok Won KIM*

Department of Physics, University of Ulsan, Ulsan 44610, Korea

Correspondence to:sokkim@ulsan.ac.kr

Received: June 14, 2016; Revised: August 11, 2016; Accepted: August 31, 2016

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

### Abstract

The nonlinear absorption coefficient and the nonlinear refractive index of 0.2 wt% carbon nano colloidal liquids were measured using a double-beam technique. The nonlinear optical coefficients were obtained by using the open- and closed-aperture methods with a $z$-scan technique that moves the sample along the $z$-axis. The Gaussian laser beam used in this experiment was focused with a lens having a focal length of 5 cm. An Nd:YVO$_4$ laser beam ($\lambda$ = 523 nm) with a 64 mW power was used as the pump light source and a He-Ne laser beam ($\lambda$ = 633 nm) with a 4.7 mW power was used as the probe light source. To find the concentration-dependent optical property, we changed the concentration level of the carbon nano colloid from 0.076 M to 0.087 M. The result showed that the linear absorption coefficient increased as the concentration was increased. Therefore, as the concentration increases, the intensity of light at the focal point becomes weak, and the nonlinear absorptance and the nonlinear refractive index decrease.

Keywords: Carbon nano tube, z-scan method, Nonlinear absorption coefficient, Nonlinear refractive index, Thermal lens effect