Physics & Astronomy Seminar Series continues today
Physics & Astronomy Seminar Series Present:
Coherent Raman Standoff Detection with Shaped Femtosecond Pulses
By: Marshall Bremer
Applied Physicist
Appareo Systems
Friday, November 13 | 3:30 pm | HA 325
Standoff detection of explosives in order to protect public spaces is very challenging.
Explosives generally have very low vapor pressures, limiting the effectiveness of air
sampling and promoting research into optical methods to detect thin residues or microparticles
on surfaces as indicators of concealed danger. With excellent chemical
specificity, Raman spectroscopy is capable of detecting particular compounds within the
chemically complex background manifest in everyday surfaces, but the weak signal of the
spontaneous process prohibits quickly detecting such small quantities.
I will discuss my graduate work at Michigan State University in which stimulated
Raman scattering was used to quickly detect and image trace quantities of explosives in a
standoff configuration.* Stimulated Raman microscopy techniques generally employ two
synchronized laser pulses and wavelength scanning to tune to the appropriate vibrational
frequency. Our approach uses a single femtosecond laser and pulse shaper to selectively
excite a particular transition with the broad bandwidth. I will present images showing
detection of single microcrystals of ammonium nitrate on a variety of real world surfaces
using a few laser shots and collecting the strong signal at ten meters.
I will also briefly discuss my new position at Appareo Systems in Fargo and the
skills acquired during school that I have found the most useful.
* Bremer, M. T. & Dantus, M. Standoff explosives trace detection and imaging by selective stimulated
Raman scattering. Appl. Phys. Lett. 103, 061119–061119–5 (2013)