Filtering characteristics of external cavity diode laser based on angular spectrum theory

A physical model of the Littman configuration external cavity diode laser is established based on the angular spectrum theory, and the external cavity transfer function is derived. The wavelength-dependent coupling efficiency is calculated, obtaining the external cavity filtering envelope. Based on this model, we numerically simulate the filtering envelope with different parameters. The simulation shows that the filtering bandwidth of the external cavity narrows with the decrease of the collimator focal length. The wave aberrations of the collimator lens seriously degrade the peak reflectivity and filtering bandwidth of the external cavity. The impact of the external cavity length and the beam misalignment on the filtering function is studied, providing a theoretical basis for the error analysis of the optical path design.