High-brightness spectral beam combining of diode laser array stack in an external cavity

Area of Science:

• Optics and Photonics
• Laser Technology
• Semiconductor Lasers

Background:

• Diode laser stacks are crucial for high-power laser applications.
• Spectral beam combining (SBC) is a technique to increase the output power of laser systems.
• Efficient coupling of high-power diode lasers into optical fibers remains a challenge.

Purpose of the Study:

• To demonstrate spectral beam combining of a diode laser stack.
• To achieve high output power and good beam quality from the combined laser system.
• To assess the fiber coupling capability of the spectrally combined beam.

Main Methods:

• Utilized an external cavity for spectral beam combining of a three-bar 970nm diode laser stack.
• Operated the laser stack at pump currents of 60A and 75A.
• Measured output power, spectral bandwidth, electro-optical conversion efficiency, and beam quality (M²).

Main Results:

• Achieved 127W output power at 60A pump current with a 12nm spectral bandwidth.
• Attained an electro-optical conversion efficiency of 48.35%.
• Measured beam qualities of M² ≈10.2 (slow axis) and M² ≈11.5 (fast axis).
• Exceeded 159W output power at 75A injection current.
• Demonstrated sufficient beam quality for coupling into a 50µm core / 0.22NA fiber.

Conclusions:

• Spectral beam combining in an external cavity is an effective method for high-power diode laser stacks.
• The achieved power and beam quality are suitable for practical fiber coupling applications.
• This technique offers a pathway to scalable high-power laser sources.