Optical bistable interaction of laser radiation with micro-particles

Intrinsic optical bistability in the scattering and absorption of laser radiation from microparticles having an intensity-dependent refractive index is investigated.1 We work only with particles whose radius is small compared with the wavelength of the incident radiation. Our calculation is based on the assumption that the electric field inside the particle is in fact uniform (as is the case in the linear regime). For particles with fairly sharp surface piasmon resonances, optical bistability can occur if the frequency detuning is above a certain critical value. The threshold intensity is found to be reduced by several orders of magnitude compared with the non-resonant case. Optical switching can also occur at fixed intensity above the threshold by sweeping the frequency across the resonant frequency. Right at the critical detuning frequency, the particle can act as an optical transistor with a very sizable differential gain. Spherical1 as well as elongated microparticles2 are studied. In the latter case, optical tristability can also be achieved, and there are, in addition, interesting shape dependence and orientational effects.