Precision frequency measurements of far-infrared (FIR) emission lines are traditionally based on heterodyne detection by comparison with a microwave source. In this article, we discuss in more detail two of these techniques, one based on the nth harmonics of a MW oscillator and a new one based on the frequency comb generated by a femtosecond laser. We describe the experimental apparatus, and we present our experimental results. We discuss also in detail the nonlinear devices available in the FIR region that play a crucial role in all the frequency measurement techniques. The accuracy in the frequency measurement of molecular laser lines is limited by the perturbation on the emission frequency due to the cavity pulling and cannot exceed 10(-8). More accurate frequency measurements could be performed by absorption spectroscopy. This requires, however, the availability of cw tunable source with a convenient level of power and spectral purity. We will discuss the solutions that have become available as technology progresses.
|Autori:||Beverini N; Carelli G; De Michele A; Maccioni E; Moretti A; Nyushkov B; Sorrentino F|
|Titolo:||High-accuracy frequency measurements in the far infrared|
|Anno del prodotto:||2005|
|Appare nelle tipologie:||1.1 Articolo in rivista|