Hänsch introduced intracavity telescopic beam expansion to grating tuned laser oscillators thus producing the first narrow-linewidth tunable laser.  This development has been credited with having had a major influence in the development of further narrow-linewidth multiple-prism grating laser oscillators. In turn, tunable narrow-linewidth organic lasers, and solid-state lasers, using total illumination of the grating, have had a major impact in laser spectroscopy.