Mid-infrared laser spectroscopy using a tunable gain-switched Cr2+: ZnSe laser

Absorption spectroscopy in the mid-infrared (mid-IR) is mostly done by Fourier transform infrared (FT-IR) spectroscopy using wide bandwidth light sources [1]. To reduce artifacts and to have the advantage of spatial resolution we built a narrow bandwidth high resolution mid-infrared laser spectroscope using a tunable laser. The broad gain band of the chromium-doped zinc selenide/sulfide laser allows a spectral coverage from 2200nm to 2850nm, wide enough to see typical vibration bands of biological macro-molecules. This provides a unique opportunity to investigate wavelength dependent absorptions of numerous chemical and biological materials.
Since the laser should be used for spectroscopic applications, an accurate wavelength calibration was performed. It was also ensured that the optical elements meet the requirements for the use in the mid-IR spectrum and that the results are not distorted by absorption of other substances or by interference.