Terahertz wave generation in coupled quantum dots

Based on coupled quantum dots,we present an interesting optical effect in a four-level loop coupled system.Both the two upper levels and the two lower levels are designed to be almost degenerate,which induces a considerable dipole moment.The terahertz wave is obtained from the low-frequency component of the photon emission spectrum.The frequency of the terahertz wave can be controlled by tuning the energy levels via designing the nanostructure appropriately or tuning the driving laser field.A terahertz wave with adjustable frequency and considerable intensity(100 times higher than that of the Rayleigh line) can be obtained.It provides an effective scheme for a terahertz source.     

Z-scan analysis of high-order nonlinear refraction effect induced by using elliptic Gaussian beam

The irradiance of an elliptic Gaussian beam that is high enough to excite high-order nonlinear refraction effect is used to calculate the normalized on-axis transmittance function in the z-scan technique by introducing complex beam parameters which make the calculation simpler. The transmittance formula is applied to the first-, first two-, and first three-order nonlinearities. Numerical evaluation shows that the symmetry no longer holds when using an elliptic Gaussian beam instead of a circular Gaussian beam. A distortion is observed in the central part of the curve, which decreases as ellipticity increases. Moreover, the variation of the normalized peak-valley difference decreases as ellipticity decreases.