What is the relationship between the single frequency line width measurement and wave numbers described typically in spectroscopy applications?
When measuring and understanding single frequency line width at values in the range less than 1MHz, one has to link the issue with a characteristic exposure time in a set-up where a single frequency laser is to be used. For instance, if such a laser is used for recording a hologram of a large scale object requiring exposure time up to minutes, the spectral width of the laser emission would appear as comprising of two parts; the first being a short-time (momentum) spectrum of the emission and the second being a broadening of this momentum spectrum due to physical and technical instabilities always present to a certain extent in any set-up. Two major types of instabilities that potentially affect the result of the spectral width measurement are the characteristic transient processes inside the laser active medium and laser cavity, and the external influences on the laser set-up. While the internal transient processes are rather fast and would be averaged at a time scale in the sec-msec r
