Optical Nonlinearity of Oxazine Dye Doped PMMA Films by Z-Scan Techniques

In this experimental work, a study (by using a high sensitive method known as Z-Scan technique) of the nonlinear optical properties for the laser dyes oxsazine in PMMA doped films with different concentrations with the solvent Chloroform.Z-scan experiment was performed using CW diode laser at 650 nm with the power output of 40 mW, in two parts. The first part was done using a closed-aperture placed in front of the detector to measure the nonlinear refractive index. In the second part; the aperture in front the detector was removed (open aperture) to measure the nonlinear absorption coefficient. The experimental results for closed aperture show that the dye doped films exhibits negative refractive index (self_defocusing) for the law concentrations (10 -6 &10 -5 M/L), while the large concentrations 10 -4 &10 -3 M/L had damaged. The results show also that the nonlinear refractive index and the third order nonlinear susceptibility increased with the increasing concentration. This is due to the increasing of the film thickness which caused an increase in the nonlinear phase shift in the samples. For open aperture z-scan the results show that the samples exhibited saturation absorption. The samples of law concentrations have a large nonlinear optical effect, which can be a promising candidate for photonic device application. Keyword: Z-scan technique, nonlinear refraction and nonlinear absorption, dye doped polymer films. Introduction Incorporating dye molecules into solid matrices have resulted in significant advances towards the development of practical tunable solid-state lasers .The use of a synthetic polymer host presents advantages as these materials show much better compatibility with organic laser dyes and are amenable to inexpensive fabrication techniques. These polymers provide an opportunity for the production of active elements that can effectively control the characteristics of laser radiation. [1]. Dye doped polymers find applications in the fields of modern photonic technology apart from its use as an alternative to solid state laser media. [2]. A nonlinear absorber of light has the unique property that its optical absorption can be altered by introducing changes in the intensity of radiation incident upon it. [3] Embedding it in third order susceptibility and nonlinear refractive index (n2). Open aperture Z-scan technique is of either two types: saturable absorption (SA) and reverse saturable absorption solid matrices can modify the nonlinear optical proprieties of the dye. The basic absorption processes in dyes can be divided into linear and nonlinear absorption. Nonlinear optics is a material phenomenon in which intense light induces a nonlinear response in the medium, and in return the medium modifies the optical fields in a nonlinear way. In fact, all media are nonlinear to a certain degree [4, 5]. The Z scan technique is a simple, sensitive and popular experimental method to measure nonlinear optical prosperities (NLO) of materials. There were two parts of the Z-scan: closed aperture and open aperture. Closed aperture Z-scan helps to measure the sign and magnitude of both real & imaginary part of (RSA) depending on the pump intensity and on the absorption cross section at the excitation wavelength [5]. Open aperture Z-scan helps to measure the nonlinear absorption coefficient ß2. Theory When the applied electric fields are sufficiently small, the electric polarization (p) is approximately linearly proportional to the applied electric field E: