Development of real-time near-field THz microscope

Near-field terahertz (THz) imaging is expected to have a broad impact for biological applications, such as cellular imaging and molecular imaging (water distribution, status in the living cells, the conformational dynamics of the large biomolecules and so on). A lot of work has been done to develop THz microscopes with high spatial resolution beyond the diffraction limit. However, even if a spatial resolution below 10 μm was successfully achieved at THz frequency, the traditional schemes remain all based on raster scanning techniques, and typical measurement time takes more than 10 minutes to obtain a full image. Since samples are changing its conditions with time for biological applications, real-time acquisition is needed in addition to the high resolution. For this purpose, we have developed a real-time near-field THz microscope using a traditional camera. In our microscope system, a high intensity THz pulse (>;100 kV/cm) is focused onto a sample directly placed on a thin electro-optic (EO) crystal in a region before diffraction of light occurs. In order to get real-time THz images of a micron-size sample, a probe beam is magnified by 11 times and retrieved the images to either a CMOS or an EMCCD camera operating at 1 kHz and 32 Hz, respectively. Notice that the top and bottom surfaces of the EO crystal have a high-reflection and anti-reflection coating for the probe light at 800 nm, respectively.