Effective transmittance of Fabry–Perot cavity under non-parallel beam incidence

Abstract

The Fabry-Perot (F-P) resonant cavity is widely used in laser and spectroscopic measurements due to its unique Interference Transfer Function (ITF). In the ideal case of parallel incident light, the ITF of the F-P resonant cavity can be expressed by the Airy function. However, in reality, it is difficult to achieve perfect parallelism with collimated beams. In this article, a theoretical model is established for non-parallel light incidence, which assumes that the non-parallel incident light is a cone-shaped beam, and the cone angle is used to quantify the non-parallelism of the beam. The transmittance function of the F-P resonant cavity under non-parallel light incidence is derived. The accuracy of the model is experimentally verified. Based on this model, the effects of divergence angle, tilt angle, and F-P cavity parameters (reflectivity, cavity length) on the ITF are studied. The reasons for the decrease in peak value, broadening, and asymmetry of the interference peak under non-parallel light incidence are explained. It is suggested that a fine balance between the interference peak and the collimation effect of the incident light should be considered in the design and application of F-P resonant cavities, especially for tilted applications such as angle-scanned spectroscopy. The research results of this article have certain significance for the design and application of F-P resonant cavities.