Alignment method and arrangement for external optical feedback for semiconductor diode lasers

A semiconductor diode laser has at least one output beam emitted from an emission aperture from a facet of the laser. An external optical feedback resonator redirects the output beam back into the laser emission aperture. The resonator comprises a reflective surface mirror on the facet laterally adjacent to the laser emission aperture and a spherical mirror spatial positioned from the laser facet to receive the output beam and image the same onto the facet mirror and, then, reimage the beam reflected from the facet mirror back into the laser emission aperture. The improvement comprises the spherical mirror being spaced from the center of the facet a distance substantially equal to the radius of curvature of the mirror so that the reimaging of the beam provides a spot size substantially equal to the spot size of the emission aperture or the beam waist, W0, at the laser facet. The alignment of the spherical mirror relative to the laser facet in directions laterally of and rotationally about the radius of curvature of the spherical mirror is insensitive to limited relative movement between the spherical mirror and the laser in those directions.