Multiwatt-power highly-coherent compact single-frequency tunable...

Area of Science:

• Semiconductor lasers
• Photonics
• Laser physics

Background:

• Vertical-External-Cavity Surface-Emitting Lasers (VECSELs) are crucial for high-power laser applications.
• Achieving stable, single-frequency operation with high beam quality remains a challenge.

Purpose of the Study:

• To demonstrate high power, low noise, single-frequency operation of a tunable VECSEL.
• To investigate the use of a compact external cavity for improved laser performance.
• To analyze the key parameters influencing laser power and coherence.

Main Methods:

• Utilized a short (3-10 mm) plano-plano external cavity without an intracavity filter for thermal lens-based stability.
• Optically pumped a GaAs-based VECSEL membrane (emitting at 1 µm) with an 8W, 808 nm diode laser at a large incidence angle.
• Bonded the VECSEL membrane on a SiC substrate for efficient heat management.
• Simulated laser beam dynamics using Fresnel diffraction.

Main Results:

• Achieved 2.1W output power with a low-divergence, quasi-circular TEM00 beam (M² = 1.2).
• Demonstrated linear light polarization (>30 dB) and a side-mode suppression ratio > 45 dB.
• Observed a free-running linewidth of 37 kHz, relaxation-oscillation-free dynamics, and low intensity noise (< 0.1%).

Conclusions:

• The compact, tunable VECSEL design enables high-power, low-noise, single-frequency operation with high beam quality.
• Thermal lens stabilization and a high-Q external cavity are key to achieving superior coherence and low noise.
• The demonstrated design principles can be extended to other wavelengths for diverse applications.