Tunable far-infrared spectrometer

Figure 10.32. Tunable far-infrared spectrometer of Evenson [66], the so-called Tufir spectrometer. 

Other groups have built tunable far-infrared spectrometers which do not involve high-frequency backward-wave oscillators. Verhoeve, Zwart, Versluis, Eirabbels, ter Meulen, Meerts, Dymanus and McLay [61] have described a system in which fixed frequency far-infrared radiation is mixed with tunable microwave radiation in Schottky barrier diodes. This instrument has been operated up to 2.7 THz, and used to study OD and N2H+. A similar system, combined with a continuous supersonic jet, has been described by Cohen, Busaiow, Laughlin, Blake, Havenith, Lee and Saykally [62]. This instrument was used to study rare gas/water clusters. 

Figure 1 The Second Order Tunable Far Infrared Spectrometer FIR i ...

Fig. 1.62 Section of the pure rotational spectrum of 03 recorded with a high-resolution Fourier spectrometer (left spectrum) and a small section of it, measured with a tunable far-infrared laser spectrometer (right spectrum with expanded frequency scale), demonstrating the superior resolution of the laser spectrometer [201]...

Now several thousands of laser lines are known which span the whole spectral range from the vacuum-ultraviolet to the far-infrared region. Of particular inters are the continuously tunable lasers which may in many cases replace wavelength-selecting elements, such as spectrometers or interferometers. In combination with optical frequency-mixing techniques such continuously tunable monochromatic coherent light sources are available at nearly any desired wavelength above 100 nm. 

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