Ghost spintronic THz-emitter-array microscope

Microscopy: imaging 'ghosts' more clearly with terahertz waves A modification of the technology called terahertz near-field microscopy brings improvements in resolution and speed for biological and medical imaging and nondestructive materials testing. Terahertz waves lie between the microwave and infra-red regions of the electromagnetic spectrum. The improved 'ghost-imaging' procedure was developed by researchers in China, Singapore and the USA, led by Li-Guo Zhu at the China Academy of Engineering Physics. In ghost imaging the illuminating radiation is split into one beam that interacts with the object being studied and another beam that does not. The so-called ghost image of the object is then constructed by computational comparison of the different behaviour of the two beams. The innovation depends on gaining enhanced control of the structure of the terahertz radiation using a system called a spintronic terahertz emitter array. Terahertz (THz) waves show great potential in nondestructive testing, biodetection and cancer imaging. Despite recent progress in THz wave near-field probes/apertures enabling raster scanning of an object's surface, an efficient, nonscanning, noninvasive, deep subdiffraction imaging technique remains challenging. Here, we demonstrate THz near-field microscopy using a reconfigurable spintronic THz emitter array (STEA) based on the computational ghost imaging principle. By illuminating an object with the reconfigurable STEA followed by computing the correlation, we can reconstruct an image of the object with deep subdiffraction resolution. By applying an external magnetic field, in-line polarization rotation of the THz wave is realized, making the fused image contrast polarization-free. Time-of-flight (TOF) measurements of coherent THz pulses further enable objects at different distances or depths to be resolved. The demonstrated ghost spintronic THz-emitter-array microscope (GHOSTEAM) is a radically novel imaging tool for THz near-field imaging, opening paradigm-shifting opportunities for nonintrusive label-free bioimaging in a broadband frequency range from 0.1 to 30 THz (namely, 3.3-1000 cm(-1)).