Three-dimensional angular deviation and diffraction efficiency of a grating in Littrow-configuration ECDL

We consider in this paper the angular deviation and diffraction efficiency of the reflection gratings in Littrow-configuration for applications of external cavity diode laser using the rigorous coupled-wave analysis method. We consider the three-dimensional diffraction case in general, where the incidence plane is un-parallel with the grating vector, i.e. conical diffraction. The angular tolerance of arbitrary gratings under plane and conical diffraction are thus derived and presented. A typical blazed grating is chosen as an example to calculate its diffraction efficiency using the rigorous coupled-wave analysis method. Furthermore, we point out that the angular tolerance and reflection efficiency can be improved if the appropriate parameter settings are selected for Littrow-configuration devices, including incidence angle, diffraction order, grating period and blazed angle. Otherwise, a tiny slanting angle of the grating vector deviated from the incidence plane will deviate the feedback light away from entering the laser-diode-chip and halt laser oscillation in the external cavity. Finally, a general rule for the parameter settings in Littrow-configuration is provided as a benchmark.

Automated summary

In this paper, we study the angular deviation and diffraction efficiency of reflection gratings in the Littrow-configuration for external cavity diode laser applications using the rigorous coupled-wave analysis method. We consider the general three-dimensional diffraction case, where the incidence plane is un-parallel with the grating vector, i.e., conical diffraction. The angular tolerance for arbitrary gratings under plane and conical diffraction is derived and presented. Furthermore, we find that selecting appropriate parameter settings can improve the angular tolerance and reflection efficiency, including the incidence angle, diffraction order, grating period, and blazed angle. We also highlight the importance of avoiding slight deviations in the grating vector from the incidence plane, as it can disrupt laser oscillation in the external cavity.