In this talk I will review our recent results in the field of optical parametric oscillation. In particular, the demonstration of Degenerate Optical Parametric Oscillation (DOPO) using a phase-coherent dual-tone pump scheme will be discussed. This work highlights the potential of photonic molecules as a platform for achieving high-quality DOPO, which could have important applications in areas such as quantum communication, quantum cryptography, and quantum computing. The phase-matching conditions are carefully controlled to achieve maximum DOPO efficiency, and the results show that the DOPO signal can be efficiently generated and optimized. This work opens new avenues for further investigation in the field of DOPO and its applications.
The hyper-Rayleigh scattering technique was used to determine the first order hyperpolarizability β of magnetic nanoparticles dispersed on colloidal solutions. Pulse trains of mode-locked pulses of 100 ps on an a Q-switcher envelope of 150 ns emitted by a Nd:YAG laser, centered on 1064 nm, were used since this method allows measurements as a function of the incident beam intensity without the need of external elements. In order to determine the procedure to measure second-order optical nonlinearities on magnetic nanoparticles and avoid cumulative effects during the measurements, that lasts between to consecutive pulse trains, the results were studied for different values of the Q-switcher repetition rate, from 5 Hz to 800 Hz. Since cumulative effects were verified for higher values of repetition rates, all measurements were performed at the rate of 30 Hz. Therefore, the first-order hyperpolarizability β was measured in the presence and absence of external magnetic field of magnitude H = 800 G. The linear attenuation spectrum was determined and didn't change with the appliance of magnetic field since large aggregates of nanoparticles were not formed. Nonlinear scattering measurements were performed in the case were the laser light polarization was parallel and perpendicular to the external field lines, employing a half-wave plate to change the light polarization state. In the absence of magnetic field, βH=0 = 8:5(1)×10-28 cm5/esu, while in their presence of magnetic field, β = 9:8(2)×10-28 cm5/esu and β⊥ = 8:1(1)×10-28 cm5/esu, showing an anisotropy β-β⊥/β of about 17%.
Nonlinear optical properties of colloids have technological appeal, since nanoparticles with nonlinear optical properties can be combined with the fluidity of liquid carriers, in the emerging area of Optofluidics. Ferrofluids, especially, can be used in magnetically-controllable applications or in optical limiting devices, where nonlinear absorption is a key characteristic. Besides two-photon absorption, some phenomena are present in experimental studies in optical nonlinearities of colloids: the particles can absorb light and heat the liquid around it, giving rise to a temperature and a subsequent refractive index gradient, what originates a thermo-optical self-focusing; also, the temperature gradient can drive the particles inward or outward the illuminated region, what changes the refractive index and the absorption coefficient of the material. In this work, the z-scan technique is performed in ferrofluids and thin films made from ferrofluids to measure the two-photon absorption coefficient of magnetite and manganese ferrite nanoparticles and to determine their two-photon absorption cross-section (σ2PA). To avoid the influence of the cited thermo-optical effects in these measurements, the frequency of the pulsed Gaussian beam (pulse width of 196 fs) is decreased with an electro-optic modulator and a shutter is used to allow the measurement of the nonlinear effects, present at the first pulse illuminating the sample, after a period of 2 seconds without illumination. The z-scan curves with and without using shutter are compared in colloids and thin films. The achieved values of σ2PA at 800 nm are 50 GM and 107 GM, for the magnetite and manganese ferrite nanoparticles, respectively.
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