Maximizing the brightness of semiconductor laser diodes is important for increasing the delivery of their optical output to gain media, in order to enhance the output power and efficiency of diode pumped lasers. Devices such as fiber lasers, diode-pumped solid-state lasers, and diode-pumped gas lasers all benefit from improved laser diode brightness. A particular challenge for laser diodes is a significant increase in their slow-axis divergence when operated at high power output. The increased divergence results in a (proportional) decrease in diode brightness. It is believed to be caused by thermal lensing, which in turn is induced by waste heat in the semiconductor laser that spreads along the slow axis to create a thermal profile. The change in semiconductor temperature causes a change in refractive index which forms a thermal lens.
Laser diode lensing effect can be substantially reduced by creating a pattern interface such that the substrate is only attached at the diode mesa. This is achieved by either creating a pattern solder joint and/or pattern substrate.
In a standard diode attach process, planar substrate surface is attached to the laser diode for heatsinking purpose. However, for high power diode with large emitter array, this can cause a thermal lensing issue due to large temperature difference within each emitter. Changing emitter pitch and or changing emitter width have minimal effect on thermal lensing problem for the planar interface.
This effect can be substantially reduced by creating a pattern interface such that the substrate is only attached at the diode mesa. This is achieved by either creating a pattern solder joint and/or pattern substrate.
Current stage of technology development: TRL 2-3
LLNL has filed for patent protection on this invention.
U.S. Patent Application No. 2023/0106189 Patterning of Diode/Substrate Interface to Reduce Thermal Lensing published 4/6/2023
- Minimizes detrimental thermal lensing effects.
- Limits slow axis divergence in laser diodes at high output power levels.
- Improves overall laser diode brightness at high output power levels.
- High average power laser materials processing
- High average power solid-state laser and fiber laser pumping
