Edmund L. Wolak

110 W fiber laser

We demonstrate a Yb-doped double-clad fiber laser with record average power output of >110 W cw in a single spatial mode beam. The conversion efficiency was /spl sim/58% with respect to the incident pump power.

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).

Reliability of high-power multi-mode pump modules

Developers building high-power fiber lasers and diode pumped solid state lasers can receive significant benefits in thermal management and reliability by using single emitter multi-mode diodes in distributed pump architectures. This proposed distributed architecture relies on independent single emitter pump lasers and a modest level of pump redundancy. Driving the remaining diodes slightly harder componensates individual diode failures. A model of the ensemble lifetime based on module failure rates and power-scaling factors demonstrates that the distributed pump architecture requires random failure rates corresponding to better than 200,000h mean time between failure (MTBF), which meets typical industrial requirements. A high power, pigtailed, multi-mode pump module suitable for commercial applications is created through this model. Critical elements are based on telecom architectures, including the optical train and the fiber alignment. The module has a low thermal resistance of 4°C/W from the chip-on-sub-mount to the external heat sink, coupling efficiency of over 80% into 0.2 NA, and demonstrated reliable output power of over 5W cw with peak wavelengths near 915 nm. Individual pump modules are predicted to produce 5W cw output power with an MTBF of more than 400,000h. The relationship between anticipated MTBF requirements, test duration and test population is shown.

High-power high-reliability cw and qcw operation of single AlGaAs laser diode array design

A single laser diode bar design, based on the AlGaAs material system, has been developed for high power, high reliability operation at a variety of CW and QCW operating conditions. The bar has a cavity length of 750 micrometer and a fill factor of 40%. Typical CW operation has a threshold current of approximately 10A and a conversion efficiency of greater than 45% at 40W. A variety of lifetests have been conducted at both CW and QCW operating conditions from the same bar design. On- going 3000 hr CW operation at 45C and 40W shows an extrapolated median lifetime (20% current increase) of 16,500 hrs at 45C or approximately 50,000 hrs at 25C (with 0.45eV activation energy). On-going 3000 hr QCW operation at 60C/60W and 35C/100W, with a pulse width of 200 microseconds and a duty factor of 2%, shows a median lifetime of approximately 10 billion shots and approximately 5 billion shots, respectively. In addition to single bar operation, this bar design can be stacked in various 2-D configurations. A 4 bar linear stack operating at 160W CW and a 6 bar vertical stack operating at 240W CW have been developed with superior performance. Results for high duty and low duty QCW stacks will also be presented.

Low-cost environmentally proven high-brightness fiber-coupled laser diode

A low cost and highly reliable fiber coupled laser diode is demonstrated with up to 1.0 W output power in 0.14 NA out of a 60 micrometer core fiber. Package reliability with extended operation at 600 mW is shown for over 600 hours at 85 degrees Celsius, and with stringent environmental tests, including thermal cycling, high temperature storage, and two sec. on two sec. off power cycling.

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.