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Computational Trapping - Casey Cannon
Sphere aerosol being trapped by a continuous-wave laser.
Experimental setup: In the left panel, an aerosol of spheres are sprayed in the vicinity of a continuous-wave trapping laser. At least one of these spheres is caught. The chamber is brought to vacuum. Then, in the right panel, a high-intensity pulse is fired at the trapped sphere in order to study stochastic heating. Not to scale.
Macroscopic view of collagen gel (left) and microscopic view of collagen matrix (right)
A reflective sphere is trapped in a so called "Donut" mode laser. It is called this because it has a low intensity on the central vertical axis, a higher intensity slightly to the side of this, and a low intensity at large distances away from the central vertical axis. The trajectory of the sphere shown is taken directly from my code. The sphere has been dropped from below with a slight radial offset. Not to scale.
When we study stochastic heating, the interaction between the spherical target and the laser pulse must happen in vacuum and the sphere cannot be in contact with any support structure. If there were a support structure, the electrons involved in stochastic heating could escape into this object.
One strategy is to use an optical trap to hold the target sphere in place. I am developing and using a computational model that can be used to track the trajectory of a sphere in the vicinity of a laser. A laser can be used to levitate a spherical ablation target. In the past, the model has been used only for transparent spheres, but I'm working on modifying it to study reflective spheres and spherical shells.
Current Progress
Our group is collaborating with Prof. Roland Smith's research group in Imperial College London. They have become interested in what it is like to launch the spherical targets from below the optical trap in order to load them into the optical trap. In this way, if no spheres are successfully loaded, the spheres will fall back onto the loading mechanism and the attempt can be repeated.