Robust High-Power Diodes for Next Generation Laser Systems

Project Overview

Semiconductor laser diode devices are and will be a key component of present and future laser systems for scientific, inertial confinement fusion, high energy density, and national security lasers. We addressed two key technology limitations of laser diodes: 1) uncovering material aging mechanisms leading to performance loss and 2) developing advanced thermal management architectures for increased brightness. A combination of device design, diagnostic development, and modeling showed that the formation of localized absorbing defects within the solid-state laser cavity is the primary mode of slow power loss in the devices we studied. We used new capabilities to disambiguate catastrophic failure from slow performance loss and for the first time directly imaged defects non-destructively on packaged devices. We also developed a radically new thermal management architecture based on direct immersion of the devices in a refrigerant. We demonstrated devices with >2× brightness with superior heat extraction compared to the current state of the art. The key physics are captured in a fluid-thermal model and pave the way for designing even brighter devices in the future. These science and technology developments will be key to future laser systems that are more powerful, efficient, economical, and reliable.

Mission Impact

Laser diodes are a core technology for Lawrence Livermore National Laboratory (LLNL) laser systems and will be used for future scientific lasers, inertial confinement fusion/stockpile stewardship, and directed energy applications. Understanding and overcoming present limitations to their brightness and lifetime will allow future LLNL laser systems to operate more reliably and economically while improving size, weight, power, and efficiency.

Enduring new capabilities include novel diode laser diagnostics, RSoft and thermal models, diode submount fabrication and assembly processes, and a fully instrumented immersion test stand. Combined, the science and technology outcomes will allow LLNL to meet future national security challenges.

Publications, Presentations, and Patents

Kotovsky, J, et. al. "System and method for laser diode array having integrated microchannel cooling." US Patent 20220329048A1 (2021), WO Patent 2022216910A1 (2022)

Swertfeger, RB, et. al. "Operation of broad area high power diode lasers immersed in coolant." Proc. SPIE 11982 (2022)

Fenwick, WE, et. al. "Facet effects on generation-recombination currents in semiconductor laser diodes." Semiconductor Science and Technology 37 (2022)

McVay, E, et. al. "Determination of nonradiative carrier lifetimes in quantum well laser diodes from subthreshold characteristics." Semiconductor Science and Technology 38 (2023)

Cassada, N, et. al. "SiC microchannel heat sinks for high heat flux dissipation of 1 kW/cm2." IEEE Transactions on Component, Packaging, and Manufacturing Technology 13 (2023)

Wang, L, et. al. "High-resolution thermal profiling of a high-power diode laser facet during aging." IEEE Journal of Quantum Electronics, in press, (2023).

N. Cassada, et. al., "Immersion cooling of laser diodes for high brightness applications" (Presentation, 24th Annual Directed Energy Science & Technology Symposium 2022, Mobile, AL, April 2022).

D. Funaro, et. al., "Immersion-cooled CW laser diode with 2.1 kW/cm2 output on 0.39 mm bar pitch" (Presentation, 25th Annual Directed Energy Science & Technology Symposium, San Antonio, TX, April 2023).