Recording the angular dispersion of a terahertz beam into its frequency spectrum for fast measurements

Abstract

The frequency-dependent divergence angle of terahertz (THz) beams is a crucial aspect in understanding the generation and transmission of broadband THz waves. However, traditional beam profiling methods, such as 1D or 2D translation/rotation scanning detection, are time-consuming and wasteful of THz energy, making them unsuitable for fast measurement applications, such as single-shot THz generation and detection. Here, we proposed a simple solution that involves passing the THz beam through a core-anti-resonant reflective (CARR) cavity (e.g., a paper tube). The spatial information of the beam is then recorded into its frequency spectrum, which can be easily detected by a following traditional THz time-domain spectroscopy (TDS) system or a single-shot sampling setup. Our method enables the acquisition of the angular dispersion without repetitive measurements, and represents a significant step forward in fast and efficient achievement of spatial properties of broadband THz beams.

Core-antiresonance-based terahertz cavities and applications [Invited]

“…Additionally, the F-P equation [i.e., Eq. ( 1)] indeed offers a sound explanation for the observed phenomena in our studies [15][16][17] . However, in the end, we decided to name our scheme the core antiresonant reflection (core-ARR or CARR), drawing parallels to traditional antiresonance (also known as ARROW), [5] , a hexagonal cage [6,7] , a quadrilateral multilayer channel [8][9][10] , and a ring-nested fiber [1] .…”

“…In order to examine the experimental CARR effect, numerical simulations can be performed by the commercial software RSoft [15][16][17] . Our experimental parameters of D = 8-16 mm, t = 0.08 mm, and n 0 = 1.6, as well as L = 15 cm and θ = 85 deg were all taken into consideration while building the numerical model.…”

“…In this work, we provide an overview of our recent investigations into a new antiresonant phenomenon termed core antiresonant reflection (Core-ARR or CARR) [15][16][17] , which yields a broadband THz spectrum with periodic dips at resonant frequencies when THz waves traverse a hollow core tubular structure, such as a single-layer paper tube. Unlike existing principles, e.g., the traditional antiresonant reflection inside hollow optical waveguides (ARROWs) [1][2][3][4][5] , our CARR theory relies solely on characteristics of the tube core (e.g., the inner diameter) instead of the cladding thickness or refractive index, making it fundamentally distinct from established approaches.…”