Systematic errors in laser gain, saturation irradiance, and cavity loss measurements and comparison with a HCN laser

A pair of laser parameters of considerable practical interest are the small signal gain and saturation irradiance of the gain medium. These are common ly measured by observing the dependence of the output power on some adjusta ble cavity loss parameter and comparing the measured data with the predicti ons of a suitable laser model. Because of the inevitable approximations in this model the resulting estimates of gain and saturation irradiance are al ways affected to some extent by systematic errors. The small-gain, plane-wa ve, mean-field, and pure homogeneous or inhomogeneous line-broadening appro ximations are considered, with estimates of the magnitudes of these errors being presented for the case in which the gain, the saturation irradiance, and the cavity loss are fitted to the data. It is shown that these errors c an be quite substantial, and therefore accurate absolute measurements of th e three laser parameters can be quite difficult to obtain using the variabl e loss method As an illustration of these errors, a comparison between the measured output power from a HCN laser and the power predicted, using exper imentally measured gain and saturation irradiance values is shown. The poor quality of these predictions illustrates the serious effects that the syst ematic errors can have, although an alternative analysis in which the cavit y loss is supplied and only the gain and saturation irradiance fitted is al so shown and gives good predictions despite inaccuracies in the model. (C) 1999 Optical Society of America.