We report the experimental results of generation and coherent detection of narrow linewidth tunable terahertz radiation at room temperature utilizing a difference frequency generation as a result of stimulated scattering in the nonlinear crystal of MgO:LiNbO3. The terahertz radiation was generated from an all-solid-state tunable injection-seeded THz-wave parametric generator (is-TPG), which emits the monochromatic THz-wave over a wide tunable frequency range from 0.6 THz to 2.4 THz with the linewidth of narrower than 100 MHz. Mixing of terahertz radiation (frequency ωT ) with a near-infrared intense pump pulse (frequency ωP ) results in the excitation and amplification of the difference frequency component with frequency ωi =ωP -ωT, which is detected with a InGaAsbased photodiode. We demonstrate this method a fast response and very sensitive THz-wave detection running at room temperature, which is at least three of magnitude faster and two of magnitude more sensitive than a typical Liquid-He cooling Si bolometer for detecting the quasi-cw THz-wave beam. This detection technique is possible for coherent detection, it can measure the THz electric field, not only the intensity. As a result, the phase information is preserved, the real and imaginary parts of a sample's dielectric function may be determined simultaneously with this detection.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.