Frequency and phase-lock control of a 3 THz quantum cascade laser

Area of Science:

• Terahertz (THz) science and technology
• Laser physics and engineering
• Spectroscopy and remote sensing

Background:

• Quantum cascade lasers (QCLs) are crucial for generating THz radiation.
• Precise frequency control of THz sources is essential for high-resolution spectroscopy.
• Existing THz QCLs require stabilization for demanding applications.

Purpose of the Study:

• To demonstrate precise frequency locking of a 3 THz QCL.
• To achieve frequency control accuracy exceeding requirements for heterodyne receivers.
• To enable stable, long-term operation of a locked THz QCL.

Main Methods:

• Frequency locking a 3 THz QCL to a far-infrared gas laser.
• Utilizing a tunable microwave offset frequency for precise control.
• Characterizing the locked QCL line shape and stability.

Main Results:

• Achieved indefinite lock condition without extensive temperature or bias current regulation.
• Observed a Gaussian line shape with -3 dB linewidth of 65 kHz and -10 dB of 141 kHz.
• Demonstrated frequency control accuracy of 1 part in 10^8.

Conclusions:

• A THz QCL can be reliably frequency-locked to an external reference.
• The achieved accuracy surpasses requirements for local oscillators in astronomical and atmospheric spectroscopy.
• This technique paves the way for more sensitive THz heterodyne receivers.