Near-field THz imaging of free induction decay from a tyrosine crystal

We demonstrate images of free induction decay (FID) signals from a grain of tyrosine in the near-field of the THz frequency region. By combining electro-optic sampling with a charge-coupled-device (CCD) camera, our near-field THz microscope allows us to visualize the electric field blinking with the FID signal with spatial resolution of better than 70 microm. The oscillating frequency of the FID signal centered at approximately 1 THz corresponds to the vibrational mode of the tyrosine crystal. These results confirm that the THz near-field microscope can take spectroscopic images with subwavelength spatial resolution (approximately lambda/4).