TEMPERATURE-MEASUREMENT OF SINGLE LEVITATED MICROPARTICLES USING STOKES ANTI-STOKES-RAMAN INTENSITY RATIOS

A method has been developed to determine the temperature of single mic roparticles levitated in an electrodynamic balance. Particle temperatu res were ascertained from the measured intensities of the Stokes and a nti-Stokes Raman spectra. Temperatures near ambient were obtained for titanium dioxide and calcium nitrate microparticles with the use of a Raman-based calibration of the optical system to correct for wavelengt h-dependent effects. Higher temperatures were also measured with the u se of a carbon dioxide infrared laser to electromagnetically heat the particle. In an effort to minimize particle instabilities caused by th e heating beam, the Gaussian intensity profile of the beam was modifie d with an axicon beam expander to produce a doughnut-like intensity di stribution. The temperature measurement technique and quantitative Ram an composition analysis were applied to study dehydration of a calcium nitrate tetrahydrate particle.