Terahertz time-domain spectroscopy for non-destructive testing

We present terahertz (THz) time-domain spectroscopy (TDS) as a versatile tool for applications in non-destructive testing. Due to fiber-coupled THz systems, which exploit the advantages of mature telecommunication technology, THz- TDS is a promising tool for industrial process control. As an example, we demonstrate thickness measurements on multilayered plastic pipes by combining THz reflection measurements with a transfer matrix method for data evaluation. Furthermore, we show the potential of THz-TDS for time resolved 2D imaging. For this, we combine a photoconductive near-field probe with a commercially available fiber-coupled THz TDS system. Due to the coherent measurement scheme, which provides amplitude and phase information at each sampling point, in combination with an acquisition rate of 40 pulse traces per second, dynamic processes on the picosecond timescale can be monitored with unprecedented resolution. Exemplarily, we visualize the propagation of a THz-wave on the surface a of photoconductive THz emitter with a lateral resolution of 20 mm and sub-picosecond temporal resolution.