Higher Order Calculation of the Lamb Dip in the Output of an Optical Maser

Abstract

A higher order calculation of the theory of an optical maser is carried out for the purpose of obtaining more accurate theoretical expressions of the Lamb dip. The amplitude of maser oscillation is calculated in the approximations up to the fifth order and the calculated power vs. frequency characteristics by the third and the fifth order approximations are compared. The Lamb dip becomes considerably shallower if the fifth order term is included. The fifth order calculation should therefore be employed for a more accurate determination of the linewidth parameters of the active atoms from observed shapes of the Lamb dip. It is shown, however, that the correction due to the fifth order calculation is small when the relative excitation is very close to the threshold. The fifth order calculation in the case when the “Doppler limit” does not apply is also discussed as well as in the case of the “Doppler limit”.