New THz sources for bio-medical imaging

We present an evaluation of new terahertz sources for biomedical imaging based upon quantum cascade lasers (QCL) and orientation patterned gallium arsenide (OP-GaAs) optical parametric oscillator (OPO). The recently developed terahertz quantum cascade laser emits a peak output power of up to 40mW at 3.7 THz (&lgr;=81&mgr;m). Utilizing coherent terahertz radiation greatly improves the signal to noise ratio of the detection, where it provides a relatively large dynamic range and high spatial resolution. We demonstrated biomedical imaging of malignant tissue contrast in an image of a mouse liver with developed tumors with a THz imaging system based on a QCL. In addition, images of various tissues, such as lung, liver, and brain sections from the laboratory mouse were also obtained. We also explored distinct images from fat, muscle and tendon and measured the absorption coefficient and compared this with FTIR measurements. Another recent technological advance in THz source is based on cascaded optical down-conversion in an OP-GaAs OPO, which provides a tunable THz source over a broad wavelength range with an average power of 1mW at room temperature (RT). The tunability of the OPO source provides additional imaging modes through the ability to excite molecular vibrations and obtain biochemical and structural information in addition to normal absorption or reflectivity contrast.