double-pass-breadboard

The goal of this project is to realize stable, modular, and compact double pass acousto-optic modulator (AOM) systems for controlling the frequency and amplitude of laser light. This project was directly inspired by Ike Chuang's group.

Breadboard versions are organized in directories labeled by the date (YY-MM) when the machined parts were initially ordered. Each directory includes a README with a link to the corresponding STEP files (GitHub doesn't support the STEP file format) for the parts to be machined.

2026-07-version is the most recent.

Schematic

Polarizing Beam Splitter Handling

We use Pattex Repair Extreme to secure the polarizing beam splitter (PBS) cubes to their mounts.

• Note: use only a little dab of epoxy for a single corner and avoid the joint between the two halves of the cube. If epoxy contacts this joint, it will seep in over time, eventually ruining the PBS.

Maximizing Double Pass Efficiency

• Adjust the beam path until it is level over the length of the breadboard and passes through the AOM aperture.
• Use a beam profiler to measure the beam far away (100cm) from the input fiber port, and minimize beam divergence using the three Zθ adjusters of the Thorlabs PAF2 Series Collimators.
• Set the rough angle of the AOM with the rotating base mount so that it is orthogonal to the beam.
• Adjust the AOM's position using the kinematic mount to maximize diffraction efficiency at the desired AOM center drive frequency.
• Measure the single pass efficiency and bandwidth.
• Place a plano-convex lens a focal length (f = 50 mm) away from the AOM with the convex side facing the AOM. Adjust the position of the plano-convex lens so the 0th order beam passes through the center of the lens.
• Put a flat mirror at the smallest beam width position, and adjust mirror to retro-reflect the beam.
• Adjust the quarter wave plate and the flat mirror to maximize the light transmitted through the PBS.
• Check the double pass efficiency and bandwidth before fiber coupling.
• If the bandwidth is significantly smaller for the double pass than the single pass, adjust the distance between the AOM and lens to improve the bandwidth.
• Couple the light into the output fiber using the two mirrors before the output port. For detailed instructions on how to fiber couple with Thorlabs PAF2 Series collimators, see Thorlabs manual chapter 6.

To-do

• Measure temperature stability.
• Test different mirror mounts.