Optical Limiting With Colloids

Department of Defense funded research on a laser that traps nanoparticles to block intense light, reversibly.

Aim

Limit the light that gets through by pulling nanoparticles into a dense phase with a focused laser, then find the mixture that does it most efficiently and reverses cleanly.

Tools

Continuous-wave optical trap
Fluorescence microscopy
Phase diagram mapping

Skills

Optical trapping
Fluorescence calibration
Statistical mechanics of colloids
Phase behavior of colloid-polymer mixtures
Presenting research

Outcome

Released as a SPIE proceedings paper and a poster. Mixtures at the phase boundary recover almost fully when the laser eases off.

The simulation is an illustration of the method. The fluorescence scan and the final potential are from the experiment.

Method

Fluorescence was calibrated to particle concentration. The trap potential was then reconstructed from the density profile through the Boltzmann distribution.

Paper

Xia, Li, Perez, Biaggio, Ou-Yang. Optical manipulation and osmotic compressibility of depletion-interacting colloids. Proc. SPIE 14194, 141940A (2026).

Read the paper

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