3 - Building the Optical Setup
A. Ashkin, J. M. Dziedzic, J. E. Bjorkholm, and Steven Chu
TL;DR Summary
Learn how to build a trap from scratch, starting with fundamental laser alignment, Gaussian beam opticals, and the balance of gradient and scattering forces.
Chapter 3: Building the Optical Setup
To trap a nanoparticle, you need more than just a laser. You need to amplify it, control its polarization, route it through the vacuum chamber, and finally detect the scattered light. Now that you understand the theory behind optical tweezers and the thermodynamics of the trap, it is time to build the experimental table yourself.
The Challenge
Use the interactive optical table below to construct a functional trapping and detection setup.
- Source: Start by placing your Laser on the table.
- Routing: Use Mirrors to steer the beam around the table.
- Trapping: Route the laser directly into the Vacuum Chamber to trap a particle.
- Detection: Direct the output beam from the chamber into the Photodetector to capture the scattered light.
- Control: Experiment with the PBS, Beam Block, and other components to see how they affect the beam path.
Hint: Click on a component in the palette, then click on the grid to place it. Click on a component already on the table to rotate it 90 degrees!
Components
* Click a placed component to rotate it 90°.
Understanding the Signal
Once you successfully route the beam through the vacuum chamber and into the photodetector, you should see both the “Particle Trapped” and “Signal Detected” indicators light up. In a real laboratory, this photodetector would be connected to an oscilloscope or a spectrum analyzer. The voltage changes caused by the particle scattering the light as it moves in the trap is exactly how we generate the time traces and PSD plots we analyzed in Chapter 2.
If your beam hits a block, or if you misalign a mirror and route the laser off the table, the signal drops to zero. In levitated optomechanics, alignment is everything!
Equation testing: