Engineering the spectral bandwidth of quantum cascade laser frequency combs

Area of Science:

• Quantum optics
• Laser physics
• Spectroscopy

Background:

• Quantum cascade lasers (QCLs) are compact sources for mid-infrared and terahertz frequencies.
• These spectral regions are vital for molecular spectroscopy due to fundamental absorption lines.
• Broadening the optical bandwidth of QCLs is essential for high-precision spectroscopy.

Purpose of the Study:

• To numerically and experimentally investigate QCL comb spectral width.
• To optimize QCLs for maximum spectral width, limited by gain bandwidth.
• To identify optimal dispersion compensation strategies.

Main Methods:

• Numerical simulations of comb spectral width.
• Experimental investigation of QCLs.
• Analysis of Kerr nonlinearity and cavity dispersion effects.
• Implementation of high mirror losses.
• Injection locking techniques for QCLs.

Main Results:

• Nonoptimal Kerr nonlinearity and dispersion narrow the comb spectrum.
• High mirror losses promote comb sidemode proliferation.
• Injection locking offers external control over comb state.
• Maximum spectral width is recoverable using optimized parameters.

Conclusions:

• Optimizing QCLs requires careful management of Kerr nonlinearity and dispersion.
• High mirror losses and injection locking are key techniques for bandwidth enhancement.
• This work provides a pathway to wider spectral comb sources for advanced spectroscopy.