TECHNOLOGY LASERS
TECHNOLOGY LASERS
Accessing the
mid-infrared and beyond
Merging the quantum cascade laser and transistor promises new applications involving mid-infrared wavelengths through to terahertz frequencies
BY JOHN DALLESASSE AND KANUO CHEN FROM THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN
IT IS FAR FROM EASY to create a coherent source of emission between mid-infrared wavelengths and terahertz frequencies. But if success is possible, great rewards may follow − if these new devices could be commercially viable, they could serve new applications and open the door to new markets.
Many of the opportunities for frequency- tuneable sources in the mid-infrared and beyond are associated with identification of chemical species. Numerous substances have distinct molecular resonances in this spectral range, so frequency- tuneable sources could be used for chemical process monitoring, automotive
applications, biomedical imaging and histopathology, chemical and explosive detection, greenhouse gas monitoring, ground and waste water monitoring, homeland security, and a host of other applications that rely on detecting the presence and quantity of a given chemical.
A frequency-tuneable source can be used to detect chemical species by sweeping its frequency so that it excites a molecular vibration. Hitting a frequency that causes molecules to resonate leads to the absorption of light, and this can be picked up by the dip in the response of a detector. To detect with the best signal- to-noise ratios, high-intensity, spectrally
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www.compoundsemiconductor.net October 2014 Copyright Compound Semiconductor narrow, tuneable source are required.
Such sources are also preferred for imaging, with power changes in a detector array enabling spatial localization of compounds in various samples, including biological specimens. When imaging techniques with mid- infrared lasers identify cancerous cells, this approach can realise greater speed, accuracy, and resolution than conventional methods.
Another application for optical sources emitting from the mid-infrared to terahertz frequencies is point-to- point communication links. To serve
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