Active mode locking of quantum cascade lasers in an external ring cavity.

D G Revin,J W Cockburn,M Hemingway,Y Wang,A Belyanin

doi:10.1038/ncomms11440

D G Revin, J W Cockburn + Show 3 more

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https://doi.org/10.1038/ncomms11440

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Abstract

Stable ultrashort light pulses and frequency combs generated by mode-locked lasers have many important applications including high-resolution spectroscopy, fast chemical detection and identification, studies of ultrafast processes, and laser metrology. While compact mode-locked lasers emitting in the visible and near infrared range have revolutionized photonic technologies, the systems operating in the mid-infrared range where most gases have their strong absorption lines, are bulky and expensive and rely on nonlinear frequency down-conversion. Quantum cascade lasers are the most powerful and versatile compact light sources in the mid-infrared range, yet achieving their mode-locked operation remains a challenge, despite dedicated effort. Here we report the demonstration of active mode locking of an external-cavity quantum cascade laser. The laser operates in the mode-locked regime at room temperature and over the full dynamic range of injection currents.

Highlights

Stable ultrashort light pulses and frequency combs generated by mode-locked lasers have many important applications including high-resolution spectroscopy, fast chemical detection and identification, studies of ultrafast processes, and laser metrology
Active mode locking (AML) by gain modulation at the period equal to the round-trip time was identified as the only viable route to Quantum cascade lasers (QCLs) mode locking[6,7,8,9]
In the following we demonstrate the AML of a QCL operating in an external ring cavity at room temperature

Summary

Introduction

Stable ultrashort light pulses and frequency combs generated by mode-locked lasers have many important applications including high-resolution spectroscopy, fast chemical detection and identification, studies of ultrafast processes, and laser metrology. A more robust and potentially more practical approach to AML of QCLs has been proposed (but not achieved until the present publication) for lasers operating in free-space external cavities[9,11] In this case, one can utilize a high-performance QCL, electrically modulate the whole laser chip, achieving deep gain modulation, while at the same time maintaining a very short gain window when compared with the round-trip time of the light along the external cavity. One can utilize a high-performance QCL, electrically modulate the whole laser chip, achieving deep gain modulation, while at the same time maintaining a very short gain window when compared with the round-trip time of the light along the external cavity This extends the dynamic range of currents where the AML can be observed far above threshold. Contrary to widespread belief, MCT CW BS

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