“Frequency combs” are optimally suited for chemical sensors. A revolutionary technology developed at TU Wien (Vienna) now produces these laser frequencies in a much easier and more robust way.
Most lasers have only one color. All the photons it emits have exactly the same wavelength. However, there are also lasers whose light is more complicated. If it consists of many different frequencies, with equal intervals in between, just like the teeth of a comb, it is referred to as a “frequency comb”. Frequency combs are perfect for detecting a variety of chemical substances. At TU Wien (Vienna), this special type of laser light is now used to enable chemical analysis on tiny spaces – it is a millimeter-format chemistry lab. With this new patent-pending technology, frequency combs can be created on a single chip in a very simple and robust manner. This work has now been presented in the journal “Nature Photonics”.
A comb with a Nobel Prize
Frequency combs have been around for years. In 2005, the Nobel Prize for Physics was awarded for this. “The exciting thing about them is that it is relatively easy to build a spectrometer with two frequency combs,” explains Benedikt Schwarz, who heads the research project. “It is possible to make use of beats between different frequencies, similar to those that occur in acoustics, if you listen to two different tones with similar frequency. We use this new method, because it does not require any moving parts and allows us to develop a miniature chemistry lab on a millimetre scale.”
At the Vienna University of Technology, frequency combs are produced with quantum cascade lasers. These special lasers are semiconductor structures that consist of many different layers. When electrical current is sent through the structure, the laser emits light in the infrared range. The properties of the light can be controlled by tuning the geometry of the layer structure.