Gapless tuning of quantum cascade laser frequency combs with external cavity optical feedback

Area of Science:

• Quantum optics
• Laser physics
• Spectroscopy

Background:

• Quantum cascade lasers (QCLs) are semiconductor devices emitting in the mid-infrared.
• QCL frequency combs offer potential for high-resolution spectroscopy.
• Optimizing QCL frequency comb performance remains an active research area.

Purpose of the Study:

• To investigate the effect of an external cavity on QCL frequency comb operation.
• To enhance the stability and tunability of QCL frequency combs.
• To assess the suitability of this configuration for spectroscopic applications.

Main Methods:

• Implementing a quantum cascade laser frequency comb in an external cavity setup.
• Conducting experimental observations of comb repetition rate and optical spectrum.
• Performing dual-comb measurements to evaluate comb stability.

Main Results:

• Comb repetition rate and optical spectrum were found to depend on external cavity length.
• A broader range of bias currents allowed for low phase-noise operation and gapless frequency tuning.
• Dual-comb measurements demonstrated improved comb stability against optical feedback.

Conclusions:

• A simple external cavity configuration significantly enhances QCL frequency comb performance.
• This approach improves comb stability and enables gapless frequency tuning.
• The enhanced QCL frequency combs are well-suited for spectroscopic applications.