Very low threshold microchip lasers with stable microcavities

Abstract

Microchip lasers are very compact and very simple diode-pumped solid-state lasers with a monolithic cavity where mirrors are directly deposited on the laser material. Their batch collective fabrication process leads to excellent reliability and low-cost mass production well suited for industrial applications. Basic microchip lasers consist of plane-parallel Fabry-Perot cavities that are stabilized by thermal effects due to the heating of the pump beam, which also defines the laser mode and the beam waist. Optically stable microcavities can be fabricated using micro-optics technologies to reduce the laser threshold and to control the laser mode without needing the thermal effects. We have developed a collective fabrication process of such stable plano-concave microchip laser cavities. A curved face for acting as a concave micromirror is obtained by a two-step microlens array fabrication technique based on photolithography and melting of a photoresist followed by a selectively controlled dry etching process. When the radius of curvature of the concave mirror is a few millimeters for a cavity length <1 mm, the microcavity is optically stable and the laser mode is well defined. Micromirrors in the range of 100-200 /spl mu/m diameter and 1 /spl mu/m thickness have been successfully fabricated on 1-inch-diameter wafers of various laser materials and for different laser wavelengths.