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Ultrafast shock wave spectroscopy |
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Dana D. Dlott (Curriculum Vitae) Dana D. Dlott (personal home page) David M. Dlott (personal home page) |
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Shock waves are produced in condensed matter as a result of a violent impact. A shock front, running through a material, produces a very fast uniaxial compression, resulting in an increase in density, pressure and temperature. Most interesting chemical processes involve large amplitude displacements from equilibrium, for example breaking chemical bonds. Shock waves directly produce large amplitude displacements which can be studied using ultrafast spectroscopy. In our nanoshock experiments, a typical displacement is 0.1-0.2. For example a protein with a mean radius of gyration of 40Å will experience a displacement from equilibrium on the order of 4-8Å. Typical values for pressure and temperature in our experiments are 0-4 GPa (1 GPa = 10,000 atm) and 50-400 deg. The name "nanoshock" derives from the fact that the amount of material shocked is about one nanogram. Also the duration of the nanoshock pulse is about one nanosecond. Ordinarily, shock wave experiments are performed using large facilities at national laboratories, where shock waves are generated using guns, bombs or high-energy pulsed lasers. With the nanoshock technique, a tabletop picosecond or femtosecond laser is used to generate powerful but microscopic shock waves in thin film samples, which can be studied with ultrafast spectroscopy. Highly reproducible shock waves are generated at repetition rates of 100-1000 per second. Nanoshocks are used in the Dlott group to study high explosives, polymers, lubricants, high strain-rate surface phenomena and biological molecules. A brief tutorial on the nanoshock technique, produced by Drew Stout, is available by clicking here. An animation by Drew Stout of how nanoshock spectroscopy works is available by clicking here. Go to Nanoshocks in Materials Go to Nanoshocks and surfaces: fracture and lubrication Go to Nanoshocks in biological chemistry and medicine
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Ultrafast microscopy of a nanoshock Coherent Raman spectra of 700 molecule thick anthracene layer while a shock passes through it. The shock front is <100 molecules wide
Prof. H. Kim, visiting from Chungnam University in Korea |
