Ultra-broadband room-temperature terahertz quantum cascade laser sources based on difference frequency generation

Area of Science:

• Quantum Optics
• Solid-State Physics
• Terahertz Technology

Background:

• Terahertz (THz) quantum cascade lasers (QCLs) are crucial for various applications, but achieving broadband emission remains a challenge.
• Existing THz sources often suffer from narrow bandwidths or require cryogenic cooling.
• Intra-cavity difference frequency generation (DFG) offers a promising route to broadband THz generation.

Purpose of the Study:

• To demonstrate ultra-broadband room-temperature monolithic terahertz quantum cascade laser (QCL) sources.
• To achieve continuous emission over more than one octave in the terahertz frequency range.
• To investigate the performance of these QCLs at different temperatures.

Main Methods:

• Utilizing intra-cavity difference frequency generation (DFG) in a monolithic QCL structure.
• Designing a mid-infrared QCL with a dual-upper-state active region.
• Incorporating a distributed feedback grating and a Fabry-Perot cavity to achieve broadband emission through nonlinear mixing of single-mode and multi-mode spectra.

Main Results:

• Achieved ultra-broadband terahertz emission from 1.6 to 3.8 THz at room temperature, covering more than an octave.
• Obtained a peak output power of approximately 200 μW at room temperature.
• At 150 K, the device produced a peak power of ~1.0 mW with broadband THz emission centered at 2.5 THz (1.5–3.7 THz).

Conclusions:

• The developed monolithic QCLs represent a significant advancement in broadband terahertz sources.
• The room-temperature operation and wide bandwidth make these devices highly attractive for various spectroscopic and imaging applications.
• Further optimization could lead to even higher power and broader bandwidth terahertz generation.