Physics and Astronomy Colloquium Series
The Physics and Astronomy Colloquium Series is open to all members of the university. Unless otherwise noted, talks are held on Thursday afternoons at 4:00-5:15 in Mendocino 1015. Schedule is regularly updated as dates, titles, and abstracts are received. Please check back often. To receive updates about the Colloquium Series, please join our Events Mailing List. For past semesters' series, see our archive.
Spring Semester ScheduleFebruary 2, 2012 February 16, 2012 March 1, 2012 March 29, 2012 April 12, 2012 April 26, 2012
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February 16, 2012Jay Sharping In the 1970s, Alan Ashkin first demonstrated optical trapping of suspended dielectric particles manipulated by radiation pressure forces. Subsequently, a simple fiber-based dual-beam system with two unfocused, counter-propagating beams from single-mode standard fibers has become popular. In the dual-beam scheme, a micron-sized particle is trapped by a combination of optical scattering and gradient forces due to interactions with the incident electromagnetic radiation on the dielectric particle. The dual-beam configuration provides a non-contact technique that permits stretching of the bulk volume of a trapped cell or vesicle. The membrane of a trapped biological cell experiences stress forces that are normal to a given surface element and dual-beam traps, it turns out, can produce deforming stresses up to 400 times greater than optical tweezers, with significantly lower light intensity due to unfocused beams. |
