Terahertz is one of the mysterious bands of the wide electromagnetic spectrum. It is an interesting spectral band which is flanked on both sides by infrared and microwave bands which have revolutionized our lives. The infrared region has been exploited for high speed gigabit internet communications through optical fibres. On the other hand, the microwaves are powering our cellular phone communications. So, what does this band have to offer to mankind ? This is a tough question because some research puzzles don’t quite solve the technological problems bothering mankind. This spectrum ranges from 0.1 to 10 THz( some say it is 30 and some debate it as 100 ). So, the secret is that this band can pass through many materials unhindered just like X-rays except for metal and water. Besides, they are not as harmful as X-rays. This makes these rays holy grail of the security scanners at airport trying to search for metal weapons without harming the individual using ionising X-rays.
Terahertz spectrum is dubbed as a band which can bridge the gap existing between the optics and electronics. The electronics so far have been able to reach upto 100 GHz only. For spectrum upto near infrared, the optics is well-understood and sources and detectors are available, But the moment you enter the mid-IR and far-IR ranges, things get difficult, as sources are weak and the detectors are not so sensitive or highly prone to noise. Interestingly,a black body at room temperature(300K) emits 6 THz radiation. That means that we are constantly submerged in THz waves without even knowing it.
With all these silver linings, however there is a huge dark cloud which we ignored till now. THz waves are absorbed by water vapour causing heavy attenuation when propagated in air. This rules out any possibility of using these waves for communicating through air. Nevertheless, these challenges can hardly limit the researchers who are burning the midnight oil to make newer advancements in this growing field. Some of these achievements include using THz for explosive detection, handheld THz detectors, THz microprobes, adhesion tape induced THz, artwork examination using THz and so on. Non-destructive testing is very useful in preserving the integrity of the sample while determining its identity. Technology Review (MIT) 2004 selected THz as one of “10 emerging technologies that will change your world”.
Some interesting references !
- Wikipedia article: Terahertz Spectroscopy
- Excellent review on Cutting-edge terahertz technology by Prof Tonouchi from Osaka University
- The truth about terahertz: A very realistic account by Carter M. Armstrong in IEEE Spectrum about current progress in terahertz field. Although it is a bit negative but still holds true.
Light Physics 