In this study, we investigate THz pulses generated from optical rectification with tilted-pulse-front pumping scheme in which the laser beam is focused to a line in a stoichiometric lithium niobate (sLN) crystal. A cylindrical lens and a common lens are used to focus the pump laser beam to a line. The power law of THz pulse generation and the redshift induced from the sLN crystal are measured. The spectral shapes of the laser pulse are changed by inserting a filter into the pump laser beam, causing the THz radiation to change. The filter is a metal wire with 2 mm diameter. Experimental results show that this method can change the generated THz time waveforms but not their spectra. Such method offers a simple means to change and manipulate THz field generated from optical rectification with tiled-pulse-front pumping scheme.
Using the high penetrability of the terahertz waves and the characteristic absorption spectra in this frequency range, we
built a non-invasive mail inspection system targeting drugs and explosives. The system is composed of two stages; in
the first stage, the scattering of a continuous terahertz wave is used for selecting mail that contains concealed powder; in
the second stage, the absorption spectrum of the suspicious mail is measured and the material is identified using a
terahertz spectrum database. We evaluated the performance and the limits of the inspection system.