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Radiometric Particle Levitation In A Laser Beam At High Ambient Gas Pressure

Student Name: Petersen, Robert
Advisor Name: Peatross, Justin B.
Approval Date: 8/1/2008
Report Type: Senior Thesis
Title: Radiometric Particle Levitation In A Laser Beam At High Ambient Gas Pressure
Abstract: We observe the stability of ne graphite particles (diameter 1-10 microns) sus- pended radiometrically in a laser beam, as the ambient gas pressure increases from 1 atm to 10 atm. Particles are self-selectively captured near the focus of a 2.5 W CW 532 nm beam, by sprinkling graphite powder above the beam. After a particle becomes trapped in the beam, the ambient pressure of nitro- gen gas is gradually increased until the particle is observed to `fall out' of the laser. Results show that 90% of the graphite particles do not remain trapped in the beam past an ambient pressure of 4 atm. The mean `fall-out' pressure is about 2 atm. Only 2% of the particles remained trapped in the laser above 8 atm. No particle in our 40-particle sample group remained trapped at 10 atm. Qualitatively, we observed that smaller particles (i.e., particles that scatter less light) tend to survive to higher pressures.
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