Hiding a Realistic Object Using a Broadband Terahertz Invisibility Cloak

TL;DR

This paper presents the first experimental broadband terahertz invisibility cloak for realistic 3D objects, demonstrating concealment of both shape and spectroscopic features over a broad frequency range.

Contribution

It introduces a scalable fabrication method for a 3D THz cloak that operates over 0.3-0.6 THz, enabling concealment of realistic objects in the terahertz domain.

Findings

Successfully concealed the shape and spectroscopic signatures of an object

Operates effectively over a broad frequency range (0.3-0.6 THz)

Demonstrated using angular-resolved THz spectroscopy

Abstract

The invisibility cloak has been a long-standing dream for many researchers over the decades. The introduction of transformational optics has revitalized this field by providing a general method to design material distributions to hide the subject from detection. By transforming space and light propagation, a three-dimensional (3D) object is perceived as having a reduced number of dimensions, in the form of points, lines, and thin sheets, making it "undetectable" judging from the scattered field. Although a variety of cloaking devices have been reported at microwave and optical frequencies, the spectroscopically important Terahertz (THz) domain remains unexplored. Moreover, due to the difficulties in fabricating cloaking devices that are optically large in all three dimensions, hiding realistic 3D objects has yet to be demonstrated. Here, we report the first experimental demonstration of a 3D THz cloaking device fabricated using a scalable Projection Microstereolithography process. The cloak operates at a broad frequency range between 0.3 and 0.6 THz, and is placed over an {\alpha}- lactose monohydrate absorber with rectangular shape. Characterized using angularresolved reflection THz time-domain spectroscopy (THz-TDS), the results indicate that the THz invisibility cloak has successfully concealed both the geometrical and spectroscopic signatures of the absorber, making it undetectable to the observer.