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175 GHz, 400-fs-pulse harmonically mode-locked surface emitting semiconductor laser.
Keith G Wilcox1, Adrian H Quarterman, Vasilis Apostolopoulos
1School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, UK. K.G.Wilcox@soton.ac.uk
Optics Express
|March 29, 2012
Summary
We achieved stable harmonic mode-locking in a vertical external cavity surface emitting laser (VECSEL) at 175 GHz using a diamond heat spreader. Stable operation requires exceeding a threshold pulse energy for high-frequency VECSELs.
Area of Science:
- Optics and Photonics
- Laser Physics
- Materials Science
Background:
- Vertical external cavity surface emitting lasers (VECSELs) are crucial for high-power, high-brightness laser applications.
- Achieving high repetition rates (100s of GHz) in VECSELs is challenging due to thermal management and mode-locking stability.
- Harmonic mode-locking offers a pathway to increase repetition frequencies beyond the fundamental cavity modes.
Purpose of the Study:
- To investigate stable harmonic mode-locking in a VECSEL at a 175 GHz repetition frequency.
- To explore the role of intracavity components, specifically a diamond heat spreader, in achieving high-frequency operation.
- To determine the conditions necessary for stable harmonic mode-locking versus pulse grouping in VECSELs.
Main Methods:
- Utilized a single crystal diamond heat spreader in thermal contact with the gain sample via liquid capillary bonding.
- Established harmonic mode-locking by tuning the laser cavity length to the 117th harmonic of the fundamental cavity.
- Introduced an intracavity etalon (not in thermal contact) to observe the effects on pulse behavior.
Main Results:
- Achieved 400 fs pulses at a 175 GHz repetition frequency with 300 mW average output power using the diamond heat spreader.
- Observed pulse groups (300 fs pulses with 5.9 ps spacing) when an intracavity etalon without thermal contact was used.
- Demonstrated that stable harmonic mode-locking is dependent on exceeding a critical pulse energy threshold.
Conclusions:
- Stable harmonic mode-locking in VECSELs at high repetition frequencies (100s of GHz) is achievable with effective thermal management, such as using a diamond heat spreader.
- A threshold pulse energy exists, above which stable harmonic mode-locking is favored, and below which pulse grouping occurs.
- The thermal contact and microcavity design, influenced by the diamond heat spreader, are critical parameters for stable high-frequency VECSEL operation.
