The book describes: 1) Theoretical concepts of nonlinear optics for generation and detection of terahertz radiation; 2) Pulsed photoacoustic spectroscopy of energetic materials. In brief the following points describes the main tasks achieved the presented work.- The physical and chemical properties such as thermal stability, decomposition and efficiency as a rocket fules of several new energetic materials are studied using pulsed photoacoustic pyrolysis technique coupled with thermo gravimetric-differential thermal analysis (TG-DTA) analysis.- Investigated the role of position of principal functional groups on thermal stability of energetic materials.- Proposed graphite is a sensor for identification of TNT and other energetic materials using picoseconds 532 nm and 1064 nm wavelengths.- Generation of THz radiation from non linear optical crystals like DAST, Zn GeP2 and measured the power of THz radiation using pyroelectric detector. - Also, recorded the time resolved photoacoustic spectra of gas molecules like N2O, nitromethane and methanol using terahertz radiation.