Abstract

Intracavity absorption (ICA) combines extreme sensitivity with ease of operation. Realistic theoretical models have predicted simple linear spectra.¹ In fact, clear-cut ICA spectra have been observed, e.g., in time-resolved studies of the rotational kinetics of molecules in the afterglow of a discharge.² The occasional observation of complicated nonsymmetric line shapes have, however, raised some questions about the practical applicability of ICA. Moreover, frequency locking of narrowband oscillators, related to ICA, has not been given a satisfactory quantitative explanation. We propose an analytical two-parameter model which takes into account the interplay of resonator loss and line dispersion. It gives rise either to absorption or dispersion profiles or to complex multipeaked line shapes. In corresponding experiments, Cs vapor has been used as line absorber (6s²S_1/2 - 6p²P⁰_1/2 inside the cavity of a ${\text{LiF}}_2^{+}$ color center laser. On variation of the resonator parameters and the vapor density, a broad variety of line shapes has been generated which are satisfactorily matched by predicted profiles. These observations confirm the applicability of the model. As a consequence, the line shapes unwanted in practical applications are avoided when selecting the resonator geometry close to the condition of minimum loss. For efficient locking, the opposite condition is favorable.

© 1985 Optical Society of America