Active linewidth-narrowing of a mid-infrared quantum cascade laser without optical reference

Area of Science:

• Quantum optics
• Laser physics
• Mid-infrared technology

Background:

• Quantum cascade lasers (QCLs) are crucial for mid-infrared applications.
• Achieving narrow linewidth and low frequency noise in QCLs is essential for high-resolution spectroscopy and sensing.
• Existing methods often require complex optical frequency references.

Purpose of the Study:

• To demonstrate a new method for frequency noise reduction and linewidth narrowing of mid-IR QCLs.
• To achieve significant performance improvements without relying on external optical references.
• To enhance the stability and precision of QCLs for advanced applications.

Main Methods:

• Sensing voltage fluctuations across the QCL.
• Amplifying these fluctuations and feeding them back to the QCL's temperature control.
• Utilizing a near-infrared laser for fast feedback control.
• Implementing a closed-loop system with a 300 kHz locking bandwidth.

Main Results:

• Achieved a factor of 10 reduction in frequency noise power spectral density.
• Narrowed the laser linewidth from 2 MHz to below 700 kHz (at 10 ms observation time).
• Demonstrated effective frequency stabilization without optical frequency references.

Conclusions:

• The developed technique offers a practical and effective way to stabilize mid-IR QCLs.
• This method significantly enhances laser performance, enabling new possibilities in mid-infrared spectroscopy and sensing.
• The absence of optical references simplifies the system, making it more accessible.