Ultrafast terahertz spectroscopy of solid state materials

Abstract

Terahertz (THz) frequency band has got increasing interest and is useful spec troscopic tool being used in every aspect of science, including material charac terization, imaging and sensing. However, at this frequency there is a lack of manipulation devices that require precise control as well as fine tuning of optical, dielectric, and conductive properties. Among many materials, titanium dioxide and polymers are of particular importance as their properties can be tuned. Ac curate characterization of these parameters demands for reliable and reproducible measurements with minimum uncertainty. This thesis contributes to upgrading the THz-TDS setup by reducing the uncertainty to a minimum level by con trolling the laser beam pointing fluctuations and making it feasible to monitor small changes in optical, dielectric, and conductive parameters as well as for time resolved analysis. Moreover, we have tuned and measured these parameters of materials with the help of upgraded THz-TDS system to develop the data base for designing of THz optics and devices. The properties of titanium dioxide have been tuned by doping and co-doping the impurities from group-V of periodic ta ble. A prominent tuning of these properties have been observed. Plasma frequency and carriers scattering time have been extracted by fitting THz conductivity with Drude Smith model. However, these properties of polymers have been tuned with temperature and their temperature-dependent optical properties have been reported. The temperature- dependent Sellmeier coefficients and thermo-optic coefficients of these polymers have been investigated which will be beneficial for device designing in THz technology.