A diffraction-compensating 0-25 ns free space terahertz delay line for coherent quantum control.

Area of Science:

• Optics and Photonics
• Terahertz (THz) Spectroscopy
• Quantum Control

Background:

• Free space delay lines are crucial for optical experiments requiring variable pulse timing.
• Diffraction-induced beam divergence limits the effectiveness of traditional delay lines in the THz region.

Purpose of the Study:

• To develop a novel double-folded variable delay line for terahertz (THz) frequencies (0.24-1.2 THz).
• To overcome diffraction limitations inherent in traditional free space delay lines.
• To provide controllable pulse spacing for advanced optical and quantum experiments.

Main Methods:

• A symmetric lens arrangement compensates for diffraction at each delay stage.
• Variable spacing silicon etalon beam splitters control relative pulse amplitudes.
• The system is enclosed in a desiccated volume (<0.5 m3) for optimal performance.

Main Results:

• The delay line achieves up to 25 ns (approximately 8 m) of total delay.
• Experimental profiles at 0.24 THz align well with theoretical calculations, even at long delays.
• Insertion loss per delay stage is approximately 3 dB.

Conclusions:

• The novel double-folded delay line effectively compensates for diffraction in the THz range.
• The design is scalable to other wavelength regimes and offers precise control over pulse characteristics.
• This advancement facilitates sophisticated experiments in THz spectroscopy and quantum control.