Improved image quality of terahertz transmission microscope: Example of graphene film observation

This paper describes non-uniformity reduction in terahertz (THz) imaging system, using a coherent THz source and a THz camera. The beam wobbling technique reduces the interference pattern, but illumination distribution often remains. In order to reduce the illumination distribution, post-image process is applied. In this method, the raw image is divided by the reference image without the sample, which is found effective for improving image quality. The graphene sample is used for validation of this method. The phase shifter is also developed to obtain a high signal-to-noise ratio (SNR) and short image acquisition time in the lock-in imaging.