Abstract
In the thesis, we used a Mode-locked Ti：Sapphire Laser and a ZnTe crystal to generate Tera-Hertz radiation. By purged with nitrogen in a Teflon box, the absorption of water vapor can be reduce (in 1.1THz、1.4THz、1.7THz and 2.2THz). We have measure the transmission THz time domain spectroscopy of silicon nano-particles size of 7nm、20nm and 30nm.The effective medium theory and the calculation of thin film be used to estimate the sample. The doped of wafers for the samples will affect the accuracy of data. The oxidation of sample could influence the dielectric constant and absorption. From the data, we found the absorption of 20nm and 7nm particles size samples is larger than 30nm particles size sample.