Conclusion

We have described and demonstrated a method for measuring colloidal pair interactions based on particles' equilibrium statistics in an extended optical trap. This method is self-calibrating in the sense that no a priori information regarding the trap's effective potential energy landscape is required to measure trapped particles' interactions. We furthermore demonstrated that this method can make good use of the flexible reconfigurability of holographic trap projection through shape-phase holography. The same analytical technique also can be applied to line tweezers created with cylindrical lenses, or through rapid scanning.

Combining optical micromanipulation, digital video microscopy and optimal statistical analysis offers an exceptionally rapid and accurate method to probe colloidal interactions. The method described here is easily generalized for dissimilar pairs of particles. Even more appealing is the possibility of performing multiple simultaneous measurements by projecting multiple holographic line traps. This opens up the possibility of using colloidal interaction measurements for process control and quality assurance testing.

This work was supported by the National Science Foundation through Grant Number DMR-0451589.