Time-resolved temperature determinations from Raman scattering of TiO2 coatings during pulsed laser irradiation

Simultaneous measurement of Stokes/anti-Stokes Raman intensities for a particular vibrational mode allows instantaneous surface temperatures to be determined. Time-resolved Raman spectra were measured on a specially constructed spectrometer using pulsed laser excitation and gated detection techniques. Measurements on equilibrated coatings and uncoated substrates at several temperatures served to confirm the utility of the technique for temperature determination as well as calibrate the intensity response of the instrument. Pulsed irradiated SiO2 and Y(PO3)3 glass substrates yield no temperature increase at laser energies where surface damage is not apparent. At higher pulse energies, an increase in anti-Stokes scattered radiation is observed, signifying a temperature rise. Analogous results are seen in Raman spectra of low energy pulse-irradiated TiO2 coatings recorded at delays of 0 and 72 ns from the excitation pulse. At higher energies, increased coating temperatures are observed at these times as well as at short times preceding the peak maximum of the excitation pulse. Raman results are used to model the thermal response of pulsed laser-irradiated dielectric coatings.