The Terahertz Gap: Understanding 0.3 to 30 THz Frequencies

Introduction

The term “Tera” signifies $10^{12}$, and Terahertz refers to the region in the electromagnetic (EM) spectrum spanning approximately 0.1 to 10 THz frequencies. THz wavelengths range from 1 mm to 0.1 mm.

This terahertz radiation resides between microwave radiation and infrared radiation on the electromagnetic spectrum. It’s often viewed as an extension of the microwave and millimeter-wave frequency bands, offering potentially greater communication bandwidth than these.

You might hear it called by other names like the submillimeter band, T-rays, T-waves, T-lux, or T-light. Terahertz frequencies share characteristics of both microwave and infrared (IR) radiation.

THz waves propagate via Line of Sight (LOS) and are non-ionizing, similar to IR and microwave waves. Moreover, like microwaves, THz waves can penetrate various non-conducting materials like clothes, wood, paper, plastic, cardboard, and ceramics. However, metals highly reflect terahertz radiation.

What is the Terahertz Gap?

The “Terahertz Gap” refers to a specific challenge in generating and manipulating electromagnetic waves within the terahertz frequency range. Here’s a breakdown:

• Low Microwave Frequencies: At lower microwave frequencies, generating effective radiation is relatively straightforward using oscillating circuits built from high-speed transistors.
• High Frequencies (Visible Spectrum): At the higher frequencies of the visible spectrum, semiconductor lasers excel at efficiently producing radiation.
• The Problem: Transistors and other electronic devices have a practical upper limit of around 50 GHz (though some reach 300 GHz), while semiconductor lasers have a lower limit of around 30 THz. This leaves a “gap” in the EM spectrum where neither technology performs optimally.

In essence, the Terahertz Gap represents the frequency range from approximately 0.3 to 30 THz, where traditional electronic and photonic technologies struggle to meet each other.

The terahertz frequencies have found applications in spectroscopy, pulsed imaging, impulse ranging, communication, sensing, security, mine detection, and bio-chemical agent detection. Ongoing research into developing viable THz radiation sources, detectors, and modulators is accelerating the potential use of terahertz frequencies in wireless communications.