8-beam local oscillator array at 4.7 THz generated by a phase grating and a quantum cascade laser

Area of Science:

• Astrophysics and Instrumentation
• Quantum Electronics
• Terahertz Science

Background:

• The [OI] line at 4.7 THz is crucial for astronomical studies.
• Generating multiple local oscillator (LO) beams at terahertz frequencies is challenging for array receivers.
• Quantum cascade lasers (QCLs) offer potential for compact THz sources.

Purpose of the Study:

• To present an 8-beam LO system for the 4.7 THz [OI] line.
• To characterize a Fourier phase grating for THz beam generation.
• To validate the system's performance at high frequencies.

Main Methods:

• Utilizing a quantum cascade laser (QCL) and a Fourier phase grating to generate 8 beams.
• Characterizing the grating with a distributed feedback (DFB) QCL at 4.7 THz.
• Validating grating bandwidth using a 5.3 THz far-infrared (FIR) gas laser.
• Coupling a 4.7 THz beam into a superconducting hot electron bolometer (HEB) mixer.

Main Results:

• Achieved a measured diffraction efficiency of 74.3% for the phase grating at 4.7 THz.
• Demonstrated uniform power distribution among the eight diffracted beams.
• Confirmed consistent performance at 5.3 THz, showing broad operational bandwidth.
• Verified coupled power into an HEB mixer aligns with QCL output.

Conclusions:

• The developed 8-beam LO system is suitable for pumping array receivers at 4.7 THz.
• This work reports the highest operating frequencies for THz phase gratings to date.
• The system represents a significant advancement in THz instrumentation for astronomy.