John G. Endriz

Advances in high average power long life laser diode pump array architectures

Sophisticated packaging architectures have been developed that enable low cost, very high average power, long lived pumping of solid state lasers. Single water cooled manifolds now provide slab pumping of up to 2.5 kW of average optical power, while low cost yet flexible bar mounting techniques allow burn-in that enables very long lifetimes. Architecture modification allows for high peak power of up to 80 kW per water cooled pump manifold. Specialized high brightness packaging now allows approximately 20 watt cw bars to be lensed into less than 200 micrometers diameter spot sizes (approximately 54 kW/cm2).

Highly reliable high-power cw AlGaAs (808 nm) 1-cm bar laser diodes for Nd:YAG pump application

The reliability of high power continuous-wave (CW) 1 cm monolithic AlGaAs (808 nm) laser diodes is extensively investigated. Lasers with two total aperture sizes, 1800 micrometers and 3000 micrometers , are life tested at power levels of 10 W and 20 W, respectively for 1500 hours to 4000 hours at 30 degree(s)C heatsink temperature. These lasers exhibit no failures during the lifetests (total device hours of 45,000 hours for the 10 W lasers and 42,000 hours for the 20 W lasers). We demonstrate a mean time between failures (MTBF) exceeding 50,000 hours and a median life (ML) of 40,000 hours for the 10 W laser diode and a MTBF over 48,000 hours and a ML of 13,000 hours for the 20 W laser diode.

Ultrahigh-average-brightness semiconductor laser arrays

Methods of reformatting the output of laser diodes and maintaining much of their intrinsic brightness are discussed. A commercial, fiber-coupled package is shown with a symmetric etendue and a brightness of 15 kW/(cm2 sr). A symmeterized beam with a brightness of 200 kW/(cm2 sr) is demonstrated by using a combination of a micro-lensed diode array and a lens array.

Efficient, lightweight, broadbeam laser transmitter for space communications

A compact, broad beam diode based laser transmitter has been developed for moderate range and data rate free space laser communications. The laser transmitter spatially combines high average power AlGaAs laser diodes in the near field and overlaps several beams into a uniform beam in the far field. Individual high brightness laser diodes are lensed with a cylindrical lens along the length of the emitting aperture and projected with a short focal length lens into a broad beam of several milliradian divergence in the far field. The engineering prototype laser transmitter consists of six precision aligned diode assemblies, two fold mirrors and a six lenslet macrooptic assembly all mounted on a beryllium baseplate. Data will be presented showing that the laser transmitter is highly efficient by reserving the inherent high brightness of the individual diodes in the optical design, by the development of a pulsed switcher electrical circuit based on recent lightweight dc power converter designs for spacecraft applications and the removal of excess diode heat via the beryllium baseplate.