Ultra high temperature Raman spectroscopic technique enhanced by intensified charge coupled device

A newly constructed ultra high temperature Raman spectrometer based on JY LabRAM HR and enhanced by ICCD detector was used to record in-situ Raman spectra of various inorganic materials and their melts under ultra high temperature. It proved that the influence of thermal radiation background as well as intense fluorescence can be effectively eliminated. Raman spectroscopy exhibits its advantage of sensitivity to hyperfine structure of materials, especially to that in molten states compared with other methods, such as high temperature NMR and X-ray scattering techniques. In order to eliminate the influence of intense thermal background of blackbody radiation, several high temperature Raman spectroscopic (HTRS) techniques have been developed, which greatly enhanced the intensity ratio of signal to background thermal radiation by using pulsed laser source[1], confocal microscopic Raman[2] and using ultraviolet laser[3]. These techniques above mentioned demonstrate independently effective in that the key applications of the accumulated time resolution, spatial resolution methods and the use of short wavelength excited laser, individually. Shanghai Enhanced Laboratory of Ferrometallurgy (SELF) have modified its JY U1000 Raman spectrometer to meet this need based on accumulated time resolution method. Such constructed Raman spectroscopic assembly coupled with the pulsed semiconductor laser was used to study the temperature dependent Raman spectra (up to 2023 K) of various inorganic materials including silicates, borates, phosphates, carbonates and zirconia even in their molten states[4, 5]. Intensified Charge Coupled Device (ICCD) was designed for multichannel solution for time resolved optical spectroscopy and capable of single photon sensitivity. It can be gated on and off in nanoseconds, which intensifier acts as a very fast electronic shutter, controlling the exact instant and duration when light is incident on the CCD sensor. The ultrafast electronic gating capabilities makes it perfect for measurements requiring the isolation of weak signals of interest from a strong noise background. So it is fit for the application of HTRS and allows the detector gate out the thermal background or fluorescence when the laser is off. JY LabRAM HR confocal micro-Raman spectrometer was modified by using the pulsed semiconductor laser (Coherent Compass 501QM-VD). The laser emits 532 nm (excited line) and 1064 nm light simultaneously. An external dichroic mirror is needed to separate green and infrared light. The laser pulse during time, τ = 10 ns, is much shorter than the period between two contiguous pulses, T = 2×10 ns, while the pulse frequency is fixed at 5 kHz. Andor iStar ICCD (DH720i-25F-03) detector based on Marconi 30-11 sensor was coupled with the spectrometer and can be precisely synchronized to collect signal for a few nanoseconds when the laser is on. This newly constructed instrumentation combined with the advantage of both time and spatial resolution, which was predominant step to distinguish the signal from the overwhelming background radiation under high temperature. Such detection mechanism was also effective under the circumstances of recording Raman spectrum interfered by fluorescence. Figure 1.A. demonstrated that the sample of pure zirconia poly-crystal powder transformed from monoclinic to tetragonal phase while was being heated, and the temperature of the phase transition is around 1440 K. Spectrum obtain under high temperature was in accordance with that of previously reported[5]. The average laser power is 180 mW with 100 s of the accumulated acquisition time. No smoothing and background correction was made which revealed good quality