Search

The concentrations-dependent refractive index n 2 and the nonlinear absorption coefficient β of Ethidium bromide dye-doped deoxyribonucleic acid (biological polymer DNA) solutions in the SDL regime at 532 nm are reported. The Z-scan technique was performed in two ways and two different wavelengths, 532nm and 473nm, the open aperture technique and the closed aperture technique. From open aperture Z-scan measurements it is found that the Ethidium bromide doped deoxyribonucleic acid films exhibited reverse saturable absorption. The coefficient of nonlinear refraction and nonlinear absorption coefficient at 473nm wavelength is greater than at 532nm.

We theoretically study the two- and three-photon coherence in a Ξ−Λ type four-level system for stationary as well moving atoms at the room temperature using density matrix formalism. We discuss the role of dressed states to elucidate the electromagnetically induced transparency and electromagnetically induced absorption phenomena. The presence of the third field induces absorption at the line centre. A negative dispersion slope owing to the enhanced absorption results in super-luminal light propagation and the group index variation with the coupling field is switched from sub- to super-luminal. Group index with probe detuning shows super-luminal light propagation behaviour at the dressed state positions. The three optical fields trigger four-wave mixing as a result of the third order nonlinearity. The transient evolution is also discussed for optimum strengths of the coupling and drive fields to realize the optical switching in the system.

It has been demonstrated that an initial phase mismatch in type I second-harmonic generation processes with ultrahigh intensity laser pulses can be used to compensate for third-order nonlinearity not only in temporal profiles but also in spatial distributions of fundamental and second-harmonic pulses. The spatial profile of the second-harmonic pulse shows a good reappearance of the input fundamental pulse throughout the compensation for the third-order nonlinearity.

Second- and third-order optical nonlinearity was measured by second- and third-harmonic generation of the glass, respectively. Second-order optical nonlinearity can be seen in thermally poled SiO2 glass samples. The intensity of the second-harmonic generation depends on the concentration of some additives such as OH or TiO2. On the other hand, third-order optical nonlinearity can be found all kinds of glasses. The magnitude of third-order optical nonlinearity basically depends on the linear refractive index of the glasses.

Nonresonant-type third-order nonlinearity of high refractive index PbO-TiO2-TeO2 and Nb2O5-TiO2-TeO2 glass has been evaluated by means of third-harmonic generation. The PbO-containing glass show higher χ(3) than Nb2O5-containing glass, and the largest χ(3) of 3.7×10-12 esu is obtained for 10 mol%PbO-10 mol%TiO2-80 mol%TeO2 and 25 mol%PbO-10 mol%TiO2-65 mol%TeO2 glass.

A beat signal between longitudinal modes of the laser cavity is detected, amplified and fed back to an electro-optic element inserted in the laser cavity. In this case, if the gain of the beat amplifier is large, this element should have a large equivalent third order nonlinearity. Since this nonlinearity make the modes couple, many types of mode-looking phenomena are expected. In this paper, a theoretical analysis is presented and compared with experiments using a He-Ne 6328 Å laser.