CW Terahertz Wave Generation with Laser Diode Pumping and Its Applications for High-Resolution Terahertz Spectroscopy

We have developed a high-resolution and continuous-wave (CW) terahertz spectroscopic system based on difference frequency generation (DFG) with an excitation of phonon-polariton in Gallium phosphide (GaP). The pump and signal near-infrared (NIR) lasers used in this system are an external cavity laser diode (ECLD) and a distributed feedback laser diode (DFB), respectively. Each line width of the NIR laser is less than 4 MHz, thus the quality factor Q of generated THz waves is more than 106. The terahertz wave frequency can be tuned automatically by changing wavelength of the DFB laser. As an example for the THz spectroscopic application for non-destructive inspection of ultra high molecular weight polyethylene (UHMWPE), we have shown terahertz spectra of UHMWPE with some degrees of deformation.