``Double Michelson'' mode selector and pressure scanning of a cw single-mode dye laser

A single-mode dye laser is described in which a “double Michelson” mode selector is used instead of intracavity Fabry-Perot systems. This simple device gives a lower threshold, a high single-mode power (≳250 mW), and a good geometrical quality of the laser beam. Synchronous pressure scanning of the cavity and the mode selector frequencies makes it possible to continuously sweep the optical frequency over 40 GHz without any difficulty. Another version, in which one mirror of the “double Michelson” has been replaced by a retroreflecting optical grating, is also reported. In this case, no selective element (Lyot filter, wedge, ...) has to be inserted in the laser cavity.