The electrical and magnetic properties of perovskite structures have great scientific interest. In this report we present a
spectroscopy study of LaCa<sub>0.7</sub>Mn<sub>0.3</sub>O<sub>3</sub>/MgO thin film to determine its optical properties. Terahertz time-domain
measurements were performed to obtain THz transmission and emission spectra. The LaCa<sub>0.7</sub>Mn<sub>0.3</sub>O<sub>3</sub>/MgO thin film used in
this work was grow on single crystal substrate MgO (100) by pulsed laser deposition (PLD) technique and the transport
measurement has shown that the thin is a colossal magnetoresistance (CMR) material. The insulator to metal transition
temperature, <i>T</i><sub>IM</sub> is about 150K according to the temperature dependence of the resistivity measurement. On the THz
transmission measurement, the spectra of the MgO and the thin film were taken in both air and N<sub>2</sub> to determine the effect
of water absorption. In the emission measurement, the femto-second laser is incident on either the LaCa<sub>0.7</sub>Mn<sub>0.3</sub>O<sub>3</sub>/MgO thin
film or on the InAs wafer. The emitted THz signals in both cases were obtained and compared.
The optical properties of Cesium Iodide (CsI) in the frequency range from 0.1 to 2.0 THz were studied by employing
THz time-domain spectroscopy. The CsI samples were synthesized using CsI powder that was pressed into 2 mm thick
pellets. The obtained time-domain data were transformed into the frequency domain using Fourier Transforms, and then
analyzing the respective phase and amplitude spectra, the refractive index (RI) and the absorption constant of CsI were
deduced. The RI of CsI is seen to increase from 2.55 to 3.15 as the frequency increases from 0.15 to 1.4 THz. For
frequencies above 1.4 THz, the data was unusable due to the increased absorption. The empirical Sellmeier equation was
used to fit the frequency-dependent RI and to determine the absorption wavelength λ<sub>1</sub>.