Spectral, nonlinear and optical limiting studies of some organic dyes in liquid and solid media

Abstract

Dye lasers are unique sources of tunable coherent radiation, from the ultra violet to the near infrared, using hundreds of dye molecular species. Broadly tunable lasers have a tremendous impact in diverse fields of science and technology. Polymeric materials have some important advantages over other host materials because they are simple to prepare and cheap to produce. Poly Methyl metha crylate (PMMA) is one of the most commonly used polymeric host for its optical homogeneity and high transparency in the visible region of electromagnetic spectra. The present work reports about the spectral characteristics, the nonlinear characteristics and the optical limiting effect of the dyes in liquid and polymeric environment. Dyes chosen for our studies are i) Acid Red 27, ii) Sudan IV, iii) Natural Red 25, iv) Ethyl Violet, v) Safranin O and vi) LD 490. Z -s can experiment was performed for the dye in solvent for different concentration and the dye doped polymer film of thickness nearly 1 mm and concentration of 0.05 mM. The closed aperture Z- scan trace of the dyes studied showed a negative nonlinear refractive index characterized by a peak followed by a valley (i.e) self-defocusing. The-defocusing effect is attributed to the thermal nonlinearity resulting from absorption of radiation at the excitation wavelength. The limiting effects of the dyes were studied by using a 50 mW Nd:YAG laser. All the samples show similar optical limiting behavior. The limiting effect decreases with increase in the dye concentration in the polymers. That is, the optical limiting responses of the low concentration solution are generally much weaker than those of high concentrated solutions, while high concentrated solution exhibits strong optical limiting. This indicates that the number density of dye molecules in the laser beam is the main factor affecting the clamped level.