Terahertz radiation imaging of vortices penetrated into YBCO thin films

A Terahertz (THz) radiation and detection system with a scanning femtosecond (fs) laser is employed to visualize the supercurrent distribution in vortex-penetrated YBCO thin films. This free-space, non contact, and nondestructive imaging system utilizes the principle that the fs optical pulses excite THz radiation into free-space and that the radiation amplitude is proportional to the local supercurrent density at the excited area. The remanent states after removal of the supercurrent biased to the thin film strips with and without ordered arrays of small antidots are examined and compared to the theoretical distributions. The THz radiation images are successfully transferred into the quantitative supercurrent density distributions, which agrees with the theoretical predictions. The antidot effect is also discussed.