A narrow linewidth (∼8 MHz, instrument limited) CW green laser at 532 nm is demonstrated in linear orthogonally polarized modes resulting in an unidirectional travelling wave cavity using intracavity second-harmonic generation technique with >250-mW output power.
We report the optical limiting performances of a newly synthesized chromophore, 4 (2'-hydroxy- naphthyl azo ) antipyrine ( H-NAP ) and it's rare earth perchlorate complexes, La ( NAP )<sub>2</sub> ClO<sub>4</sub> and Dy ( NAP)<sub>2</sub> ClO<sub>4</sub>, in solution for 20ns pulses of wavelength 532nm. Comparing with the limiting response of C<sub>6</sub>0 in toluene (already reported optical limiter), the limiting threshold of H-NAP and it's complexes were found to be much lower. The origin of the optical limiting behavior observed for the samples are under investigation. To elucidate the various phenomena involved, z-scan experiments were performed in all the samples. From the closed aperture data, a negative refractive non-linearity (de-focusing effect) can be inferred in all the three cases. Larger magnitude of n<sub>2</sub> is expected to result in a more effective optical limiting, which implies a lower threshold for limiting and correspondingly lower output above threshold. The second hyperpolarizability of the compounds has a negative sign and is much larger than the reported values for fullerenes. The limiting in H-NAP can be attributed to the large nonlinear absorption of the material and in La (NAP)<sub>2</sub>ClO<sub>4</sub> and Dy (NAP)<sub>2</sub> ClO<sub>4</sub>, the main mechanism may be de-focusing caused by the nonlinear refractive index. H-NAP and its rare earth perchlorate complexes can hence be considered as very promising materials for optical power limiting.
We report the results of our investigations on the nonlinear optical absorption and refraction of an organic chromophore, neutral red, both in solution and in solid film forms, using z-scan technique. Z scan experiments were performed with the samples in solution form, in methanol and in solid film form in polyvinyl alcohol (PVA) matrix, using 532nm, 20ns, Nd-YAG laser pulses. The pre-focal peak and post focal valley in the closed aperture z-scan for solution sample are suggestive of a negative optical nonlinearity; where as, the open scan for the same indicates that excited state absorption (ESA) takes over saturable absorption (SA) when the input intensity is increased. For the solid film sample, on the other hand, the closed scan exhibits a sharp pre-focal valley followed by a post focal suppressed peak showing the predominance of two photon absorption (TPA) process. The open scan of the solid film has a dip, which is characteristic of ESA. As both solution and solid samples of this chromophore exhibit nonlinear absorption as well as refraction, neutral red can be a promising material for optical limiting applications.