In an apparatus and method for generating high power laser radiation, the geometry of the resonant laser cavity defines a fundamental spatial or transverse cavity mode. A gain medium is disposed within the resonant cavity and an energy source energizes the gain medium within a first volume. This causes spontaneous and stimulated energy emission to propagate in the gain medium in a direction transverse to the fundamental cavity mode. The transverse emission in turn optically pumps a second volume of the gain medium about the first volume. When the intensity of the transverse emission is sufficiently high, inversion and gain are produced in the second volume. By optimizing the geometry of the cavity such that the fundamental cavity mode is coupled to both the first and the second volumes encompassing the first pumped volume, the transversely-directed energy of the first volume which would otherwise be wasted is instead captured by the fundamental beam, improving the overall power efficiently of the laser. When configured in an appropriate cavity, the high-power laser of the present invention is especially amenable to frequency conversion of the output beam, as it provides beam intensities suitable for efficient nonlinear frequency conversion. The vertical external cavity laser may employ an optical element configured on one side as a resonator mirror and on the other side as a focusing device for coupling the laser beam to an optical fiber. The resonator mirror side is concave while the focusing side is convex with the optical element being disposed relative to the body of the laser so as to optimize power output and to provide optimal focusing of the beam into the aperture of the optical fiber. The optical element may have an electrode attached on each side with the electrodes measuring light output from the laser via an ohmmeter connected in series with the electrodes.