Infrared Molecular Gas Lasers

Laser emission in the infrared spectral region can be generated with molecular gas lasers by exploiting transitions between vibrational and rotational energy levels. Purely rotational transitions without changing the vibrational state of the molecule involves the emission of photons with low energy, corresponding to long-wavelength radiation in the spectral range from 25 µm to 1 mm. This leads to the far-infrared lasers (Sect. 6.1). The energy differences between vibrational-rotational levels of the same electronic state are larger, hence shorter wavelengths ranging from 5 to 30 µm are emitted from lasers based on such transitions. The CO2 laser operating at wavelengths around 10 µm represents the most important member of this group of lasers and will be comprehensively discussed in Sect. 6.2. Electronic transitions in molecules result in visible and ultraviolet emission. Here, the nitrogen (Sect. 7.1) and excimer lasers (Sect. 7.2) are of particular relevance.