Modulation intracavity laser spectroscopy, polarimetry, and interferometry

A review is given of the history of the method of modulation intracavity measurements in which use is made of amplification of a signal in a laser at the frequency of its relaxation oscillations. An analysis is made of the advantages and ultimate potentialities of the method in spectroscopy, polarimetry, and interferometry. The results are reported of an investigation of the laser noise as the principal factor which limits the sensitivity of such measurements. A description is given of the method for stabilization of a cw YAG:Nd³⁺ laser in which the amplitude noise at frequencies 10–100 kHz is reduced to the natural noise level. It is described how this laser can be used in measurements of the Kerr constants of gases with a birefringence sensitivity at a level of 10^–9 rad; the results are given of such measurements carried out on N₂, O₂, CO₂, and H₂ at the wavelength of 1.06 μ.