Existing thermal management technologies for diode laser pumps place a significant load on the size, weight and power consumption of High Power Solid State and Fiber Laser systems, thus making current laser systems very large, heavy, and inefficient in many important practical applications. To mitigate this thermal management burden, it is desirable for diode pumps to operate efficiently at high heat sink temperatures. In this work, we have developed a scalable cooling architecture, based on jet-impingement technology with industrial coolant, for efficient cooling of diode laser bars. We have demonstrated 60% electrical-to-optical efficiency from a 9xx nm two-bar laser stack operating with propylene-glycolwater coolant, at 50 °C coolant temperature. To our knowledge, this is the highest efficiency achieved from a diode stack using 50 °C industrial fluid coolant. The output power is greater than 100 W per bar. Stacks with additional laser bars are currently in development, as this cooler architecture is scalable to a 1 kW system. This work will enable compact and robust fiber-coupled diode pump modules for high energy laser applications.
The scalability of semiconductor diode lasers to multi-kilowatt power levels has increasing importance in direct diode material processing applications. These applications require hard-pulse on-off cycling capability and high brightness achieved using low fill-factor (FF) bars with a tight vertical pitch. Coherent uses 20%FF bars operated at <60W/bar packaged on water-cooled packages with a 1.65mm vertical pitch in the Highlight D-series, which achieves <8kW of power in a < 1mm x 8mm beam line at a working distance of ~ 280mm. We compare thermal measurement results to thermal fluid flow simulations to show the emitters are cooled to low junction temperatures with minimal thermal crosstalk, similar to single emitter packaging. Good thermal performance allows for scaling to operation at higher power and brightness. We present accelerated life-testing results in both CW and hard-pulse on-off cycling conditions.
A W-band unamplified direct detection radiometer module is described that provides a wideband response and is
scalable to large arrays. The radiometer design is intended to provide sufficient sensitivity for millimeter wave imaging
applications with a goal of 2K noise equivalent temperature difference (NETD) at a 30 Hz frame rate.
This effort leverages previously reported device scaling to increase sensitivity. We present a radiometer module
designed for 60 GHz RF bandwidth that utilizes HRL's antimonide-based backward tunnel diode. An impedance
matching circuit with on- and off-chip elements, as well as ridged waveguide, provides a wideband match to the
detectors. Modules were designed with two different microwave substrates: 125 micron thick quartz and 100 micron
thick alumina. flip-chip bonding of the detectors is amenable to automated pick-and-place for high volume
manufacturing. The modular nature of the array approach allows large arrays to be manufactured in a straightforward
manner. We present the design approach along with both electromagnetic simulations and measured performance of the
modules. This work was supported by phase II of DARPA's MIATA program.