Ghost spintronic THz-emitter-array microscope

Si-Chao Chen,Kang He,Zheng Feng,Ze-Ren Li,Jiang Li,Li-Guo Zhu,Zhao-Hui Zhai,Xi-Cheng Zhang,Yuncan Ma,Jianwang Cai,Liang-Hui Du,Wei Tan,Haifeng Ding,Cheng-Wei Qiu

doi:10.1038/s41377-020-0338-4

Abstract

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).

Highlights

The unique properties of terahertz waves (0.1–10 THz)[1,2], such as the nonionizing photon energy, spectral fingerprint, and transparency for most nonpolar materials, have attracted much research interest and enabled many applications, such as nondestructive testing[3], biodetection[4,5,6], and cancer imaging[7]
The spintronic THz emitter array (STEA) is capped with a 150-nm SiO2 layer (n = 1.97) to protect it from being damaged by the fs laser
On the exit surface of the STEA, the profile of the output THz pulse is as accurate as that of the excitation fs laser because the 150 nm propagation distance in the SiO2 protective layer is too thin for the THz wave to be diffracted (150 nm ≈ 5 × 10−4λ0/n, where λ0 = 600 μm and n = 1.97; see Supplementary Fig. S1 for the theoretical calculation of the near-field evanescent wave)

Summary

Introduction

The unique properties of terahertz waves (0.1–10 THz)[1,2], such as the nonionizing photon energy, spectral fingerprint, and transparency for most nonpolar materials, have attracted much research interest and enabled many applications, such as nondestructive testing[3], biodetection[4,5,6], and cancer imaging[7]. The total intensities (or electric field amplitudes) of encoded THz images are collected and detected with a single-pixel detector in the far field. After postprocessing via computational algorithms to correlate the detected THz intensities (or electric field amplitudes) with the deterministic patterns[18,19], near-field images can be reconstructed. In this scheme, the subwavelength spatial information “hidden” in the diffracted far-field distribution can be recovered from the intensities (or amplitude fields) recorded by a mere single-pixel detector

Methods

Results

Conclusion