Unstable Resonator Semiconductor Lasers
Abstract
We describe high-brightness, broad-area mid-IR semiconductor lasers. The optically pumped devices achieved higher brightness operation as unstable resonators. Each unstable resonator was realized by polishing or etching a diverging cylindrical mirror at one of the facets. In general. for facet separation Land diverging facet mirror radius R, the geometry generates two virtual mode source points located at distances V = +/- sqrt(L**2 + LR) from the flat facet Radiation from a virtual source point is characterized by reimaging onto itself after a round trip through the resonator. If we refer to the figure, the left virtual source, V(+), is at an object distance (V+L) from the diverging mirror with focal length (-R/2). Upon reflection from the curved facet, the radiation forms a virtual image, V(-), at a distance (V-L) to the right of the curved facet. These distances satisfy the imaging equation 1/(V + L) - 1(/V - L) = -2/R. This regenerative reimaging of the circulating radiation is the critical mechanism leading to high brightness from the virtual source locations. In actual operation, we outcouple the radiation from the flat facet side of the device. so that the virtual waist of the lateral mode is located behind the output facet at a refractively reduced distance, D = V/n, in which the index of refraction is given by n=3.82. For a typical device geometry with L = 2500 mm and R 10000 mm, this reduced distance is inside the device at approximately 1460 mm from the flat facet In addition to the high brightness generated by the regenerative reimaging of the virtual source points, the natural divergence of the propagating mode tends to mitigate self-focusing filamentation, leading to further brightness improvements. For several mid-IR unstable resonator devices, we will show experimental near- and far-fields near threshold, as well as at many times threshold.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 25, 2005
- Accession Number
- ADA444843
Entities
People
- Andrew P. Ongstad
- Donald Gianardi Jr.
- Gregory Dente
- Joseph Chavez
- Michael Tilton
- R. Kaspi
Organizations
- Air Force Research Laboratory