Optical Nonlinearity and Bistability in Artificial Colloidal Materials

There is a growing interest in developing low dimensional nonlinear materials in recent years. Some dielectric, metal and semiconductor microparticles doped into the transparent liquid or the glass to form a kind of zero dimensional material, so-called colloidal media, have very large nonlinearity. There are different nonlinear optical mechanisms for the different size of colloidal particles. It can be divided into three types: First, the particle diameter is comparable with or larger than the wavelength of the incident light about 0.1 μm-100 μm, the nonlinear mechanism is due to laser radiation pressure and thermal effect. For example, the liquid suspension of dielectric spheres [1], in which the third-order nonlinear optical susceptibility X(3), is about 10-4-10-5 (esu) with response time (grating formation time ) of 100-200 ms. Second, the particle diameter is less than the wavelength of the incident light about 100-1000Å, the nonlinear mechanism comes from the resonance of surface plasmon. For example, the metal colloid[2] and the semiconductor-doped glass[3], for them the third-order nonlinear susceptibility X(3) is about 10-8-10-9 (esu) with the response time of 1-10 ns. Third, the particle diameter is comparable with or less than the carrier's de Boroglic wavelength, namely with the quantum size about 50-100Å. For example, the glass doped with semiconductor microcrystallites[4] or the metal colloid with above size[5], for them the third-order nonlinear susceptibility X(3) is about 10-9-10-10 (esu) with response time 10-100 ps.