Real-time spectroscopy enabled by external cavity QCLs with MOEMS diffraction gratings
In this contribution, we report on real-time mid-IR spectroscopy enabled by rapidly tunable External Cavity Quantum Cascade Lasers (EC-QCLs). High speed spectral scanning in a Littrow-type resonator is realized by employing a resonantly driven micro-opto-electro-mechanical-systems (MOEMS) grating as wavelength selective element. Oscillating at a frequency of 1 kHz with mechanical amplitudes of up to 10°, the MOEMS grating is able to cover the whole spectral range provided even by broad-gain QCL chips in just 500 ms. In addition to the high spectral scanning frequency, the MOEMS approach also allows for a miniaturized and rugged design of the EC-QCL. An evaluation of this laser source with regard to spectral reproducibility of consecutive scans, pulse intensity noise, and spectral resolution will be given. Furthermore, we present spectroscopic measurements in backscattering as well as in transmission geometry, demonstrating the real-time capability in different scenarios.