Analysis of spectrum narrowing of diode laser bar

Abstract

Laser diode bar (LDB) are used increasingly often for many applications, but spectral bandwidth of LDB are generally approximately 2-4nm, far too wide for many demanding applications, e.g. spin-exchange optical pumping, terahertz generation, and lidar. External-cavity feedback can improve the spectral properties of LD or LDB. However, spectrum narrowing of LDB is more difficult than that of LD. Bar curvature (i.e. "smile") produced in the manufacturing process affects the spectrum narrowing greatly. By geometrical optics approach and ORIGIN software, smile which can be corrected by plano-convex cylindrical lens is simulated and the result is in good agreement with experiment. The selection of grating which is also a critical factor of spectrum narrowing will be stated. Finally, an external cavity consisting of fast axis collimator, two plano-convex cylindrical lens and a diffraction grating is used. The scheme is implemented on a 19-element LDB and yields 3-fold reduction in spectral linewidth under the situation that all optical elements in the system which are not optimized. Further, we use a slit in the experiment and analyze the spectrum narrowing of each element in LDB. Show more