Search

We report on a scattering-type scanning near-field optical microscope (s-SNOM) based on a terahertz quantum cascade laser (QCL) and a fast terahertz quantum-well photodetector (QWP). The natural polarization of terahertz QWP and terahertz QCL can improve the coupling efficiency. A resolution of about 60 nm is obtained.

The fast detection of terahertz radiation is recognized as a key technology of terahertz imaging systems. We realize a terahertz imaging system employing a terahertz quantum-well photodetector (QWP) and a terahertz quantum cascade laser (QCL). The detector can rapidly detect the 4.3THz light generated from a pulsed electrically-pump terahertz QCL, which is used as the terahertz source of the imaging system. The object is placed on a rotary scanning platform to realize fast scanning. A practical detection method of the terahertz pulse signal is employed to extract the amplitude information from the terahertz signal and improve the signal-to-noise ratio (SNR) of the system. The electrical and optical performances of the fast terahertz QWP are characterized, and the results show that the terahertz QWP can completely meet the fast detection requirement of the terahertz imaging system. The terahertz images of some invisible objects are obtained with a high contrast within 5 s. The imaging system owns a resolution of 0.3 mm and a circular imaging region with a diameter of 100 mm. An image processing algorithm is applied in this system to solve the noise problem and improve the quality of the images. The imaging results indicate that terahertz QWP has a good application prospect in nondestructive inspection applications and the research of the fast physical or chemistry process.

For the terahertz imaging systems, the fast detection of terahertz light is deemed as a key technology. We present a fast terahertz reflective confocal scanning imaging system employing a fast terahertz quantum-well photodetector (QWP) and a fast rotating translational platform. The excellent performance of the terahertz QWP indicates that the device can rapidly detect the 4.3 THz radiation generated from a pulsed electrically pumped terahertz quantum cascade laser, which is used as the terahertz source of the imaging system. Two 200 μm pinholes are placed in the two focuses to filter out the scattered light and improve the resolution of the imaging system, we achieve a lateral resolution better than 110 μm and an axial resolution of about 320 μm. The terahertz two-dimension images of some objects are obtained within 5 s with a high contrast. The three-dimensional sections of the object demonstrate the great axial selectivity of the terahertz imaging system.