Frequency Comb Makes Terahertz Spectroscopy Smaller and Faster

gain medium

An artist’s embellishment of an image of the “gain medium” used to produce terahertz frequency combs. The different colors indicate that different wavelengths of oscillating terahertz radiation travel different distances through the medium, which has a different refractive index for each of them.

Explosives could soon be detected with a handheld device that uses terahertz spectroscopy to identify chemicals. A team of researchers developed a chip scale device that could replace traditional bulky and slow terahertz spectroscopy systems. Colleagues from MIT, two institutions in The Netherlands, and Sandia National Laboratories described their new and improved spectroscopy system in the journal Optica.

The new version uses a quantum cascade laser (QCL)—a tiny radiation source that enables the system to extract a material’s spectroscopic signature in just 100 microseconds. The device uses a frequency comb setup with a range of frequencies that are evenly spaced. It has a unique gain medium with regular, symmetrical indentations in its sides that alter the refractive index and uniformly emit the frequencies.

With this work, we answer the question, ‘What is the real application of quantum-cascade laser frequency combs?’ Terahertz is such a unique region that spectroscopy is probably the best application. And QCL-based frequency combs are a great candidate for spectroscopy.

Yang Yang, MIT
Source: MIT | Image by Yan Liang/

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