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Dynamics of actively mode-locked Quantum Cascade Lasers.
V-M Gkortsas1, C Wang, L Kuznetsova
1Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Optics Express
|July 1, 2010
Summary
An extended upper state lifetime is crucial for stable pulse formation in actively mode-locked quantum cascade lasers (QCLs). Spatial hole burning reduces pulse duration but causes instabilities and degrades performance at higher pumping levels.
Area of Science:
- Quantum optics
- Semiconductor lasers
- Laser physics
Background:
- Actively mode-locked quantum cascade lasers (QCLs) are vital for generating ultrashort pulses.
- Understanding factors influencing pulse shape and stability is critical for optimizing QCL performance.
Purpose of the Study:
- To investigate the effects of upper state lifetime and spatial hole burning on pulse dynamics in actively mode-locked QCLs.
- To determine the conditions for stable, isolated pulse formation and identify factors leading to instabilities.
Main Methods:
- Numerical simulations were employed to model the behavior of actively mode-locked QCLs.
- The study systematically varied parameters such as upper state lifetime and spatial hole burning effects.
Main Results:
- An extended upper state lifetime is essential for achieving stable, roundtrip-per-pulse operation.
- Spatial hole burning shortens pulse duration by enabling broadband multimode lasing but introduces instabilities.
- Increased pumping exacerbates instabilities, leading to structured pulses and eventual suppression of mode locking due to gain saturation and recovery.
Conclusions:
- Stable pulse formation in actively mode-locked QCLs requires a sufficient upper state lifetime.
- Spatial hole burning offers benefits for pulse duration but compromises stability, particularly at high pump levels.
- The interplay between spatial hole burning, pumping, and gain dynamics dictates the laser's steady-state behavior, with spatial hole burning preventing stable mode locking.
