The Air-Spaced FPI

The pressure-tunable FPI is used for high-resolution spectroscopy of line profiles. The transmitted intensity Ix(p) as a function of pressure is given by the convolution 

For Doppler-free resolution of fluorescence lines (Chap.9) the laser-induced fluorescence of molecules in a collimated molecular beam can be imaged through a FPI onto the entrance slit of the monochromator (Fig. 4.47). In this case the crossing point the laser and molecular beams, indded, represents a point source. 

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