We propose an integrated high power single frequency terahertz source. This source will include a double wavelength solid-state infrared laser developed specifically for this application with two different intra-cavity laser materials that will emit at close but distinct infrared wavelengths.The combination of the two emitted wavelengths in organic materials OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile) and DSTMS (4-N,N-dimethylamino-4'-N'-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate) will produce high power monochromatic THz radiation at a frequency determined by the difference of the infrared wavelengths. We propose the realization of two different terahertz sources one operating at 4.27 THz, the other one at 9.31 THz. For these two THz sources we will develop two different double-frequency lasers TWIN-1 and TWIN-2. The first one will be based on Nd:YAG and Nd:YLF as laser hosts, with emission wavelengths at 1.33 µm and 1.31 µm. TWIN-2 uses Nd:YAG and Yb:YAG as laser hosts, with emission wavelengths at 1.03 µm and 1.06 µm. Both TWIN-1 and TWIN-2 will operate within a common and compact laser cavity.The high THz power which can be generated in a compact device is due to the very high nonlinear optical susceptibility, the low THz absorption and the relatively high optical damage threshold and phase matchability of the OH1 and DSTMS crystals. A fully integrated, compact, all solid state system operating at room temperature will result from this research. This high power single terahertz frequency source will be used to investigate non-destructively high molecular weight polyethylene materials for biomedical applications.