Head of the Group
Marcin Motyka
office: 259, A-1
phone: +48 71 320 29 86
Fourier-transform Infrared Spectroscopy
The mid-infrared spectral region between 3 and 5 μm is of great importance for medical diagnostics, free space communication, and high-sensitivity hydrocarbon detection, among other applications. In particular, tunable laser absorption spectroscopy allows sensitive monitoring of gaseous hydrocarbons such as methane, ethane, and formaldehyde. Because these gases have strong absorption lines in the mid-infrared, this region offers higher sensitivity than more accessible parts of the spectrum. The Interband Cascade Laser provides single-mode continuous-wave uncooled mid-infrared emission that should be particularly useful for sensing gaseous hydrocarbons.
Also the terahertz frequency range, loosely defined as the frequencies 300 GHz to 10 THz, or the wavelengths from 30 μm to 1,000 μm, has its potential for applications including but not limited to: astrophysics and atmospheric science, biological and medical sciences, security screening and illicit material detection, non-destructive evaluation, communications technology, and ultrafast spectroscopy. The terahertz region historically has been characterized by a relative lack of convenient radiation sources, detectors and transmission technology and still remains one of the least developed spectral regions, although a surge of activity in the past decade. Greatly desired for many applications is a compact, coherent, continuous-wave (c.w.) solid-state source, analogous to the semiconductor laser diode in the visible and infrared, or to transistor oscillators and amplifiers in the microwave. However, at high frequencies the power generated by solid-state electronic devices, such as transistors, Gunn oscillators and Schottky diode multipliers, rolls off owing to both transit-time and resistance–capacitance effects, and even for the best devices, the available power generated above 1 THz is generally well below the milliwatt level.
It was in October of 2001 that the first Quantum Cascade Laser with a photon energy less than the semiconductor optical phonon energy was demonstrated at 4.4 THz (equivalent to a wavelength of 67 μm) by Köhler et al. at the Scuola Normale Superiore in Pisa, Italy, in a collaboration with Cambridge University. Although the first device lased only in pulsed mode with peak powers of a few milliwatts and ceased lasing above temperatures of several tens of kelvin, intensive research over the past few years has produced rapid improvements. At present, spectral coverage has been demonstrated from 0.84–5.0 THz, at maximum temperatures up to 199 K in pulsed mode.