We have a Renishaw inVia™ confocal Raman microscope at Swinburne University of Technology. We usually operate the equipment to obtain room temperature Raman spectra of the samples. However, we are aiming at getting the Raman signal of molten glass samples at about 1500C. We have Linkam hot stage to heat the sample. However, was wondering if we need any specific accessories to retrofit the current system, such as filter to get rid of any radiation etc.
Would appreciate expert opinion on this.
If you are interested in examining a molten glass, the high temperature material emits strong infrared radiation. This would disturb infrared analysis. However, Raman spectroscopy examines the vibration energies from the difference in visible frequencies. The Stokes spectrum you usually observe is the difference between the original radiation and the inelastically scattered radiation (Stokes lines). Both are in the visible frequencies. The difference corresponds to infrared frequency, but the actual frequency you observe is in the visible region, if you use a visible laser excitation. Thus, the infrared radiation emitted from the molten glass is far from the Raman signals and will not interfere with your spectrum, especially you further purify the radiation using monochromator. I do not believe, therefore, you need a special filter. Usual microRaman analysis uses a single monochromator which does not have as discriminating power as the double or triple monochromator. However, even the single monochromator will allow you to obtain spectrum above 150 cm-1 Raman lines.
If you are interested in examining a molten glass, the high temperature material emits strong infrared radiation. This would disturb infrared analysis. However, Raman spectroscopy examines the vibration energies from the difference in visible frequencies. The Stokes spectrum you usually observe is the difference between the original radiation and the inelastically scattered radiation (Stokes lines). Both are in the visible frequencies. The difference corresponds to infrared frequency, but the actual frequency you observe is in the visible region, if you use a visible laser excitation. Thus, the infrared radiation emitted from the molten glass is far from the Raman signals and will not interfere with your spectrum, especially you further purify the radiation using monochromator. I do not believe, therefore, you need a special filter. Usual microRaman analysis uses a single monochromator which does not have as discriminating power as the double or triple monochromator. However, even the single monochromator will allow you to obtain spectrum above 150 cm-1 Raman lines.
Dear Prof. Hatsuo Ishida,
Thank you very much for sharing your opinion.
I'm worried about putting anything at 1500 C near the microscope objective. I would want to get a fiber optic probe to move the sample away from the system. For what you are doing do you need a microprobe anyway (inclusions of interest?) - conventional Raman system would work fine and give you more sampling distance to keep the heat away from the optics. There would be plenty o room for a "hot" filter as well. The stage looks like it is designed for microscope work and you are at the top of its range in temperature. As Mohammad Hasan above says the Raman effect shouldn't have a problem with the infrared.
I agree with Nicholas Edward Schlotter , 1500 °C may cause problems with objective (btw, how far it from a limit for Linkam stage you have?), and increasing distance from stage to the optic is necessary.
But fiber optic may require special setup and testing, for your experiment I'd look into using long range 5x or lower magnification objective - so you can still see the sample from a distance of ~1 cm, and in worse case scenario these objectives are cheap.
Hello Prof Nicholas Edward Schlotter,
I don't need a microprobe for my regular study. I would check without a probe with a long range 5x mag objective first as suggested by Yury Igorevich Klyukin Yury Igorevich Klyukin The stage has a working depth of about 1cm including the quartz window. I believe it will work with the 5x obj.
You cannot rally escape the problem of infra red radiation with filters. If the radiation is within your spectrum, there is not much you can do. However, if it is in the spectrum depends on what laser wavelength you use and what wavenumber range you are interested in. Using a red or infrared laser will almost certainly be problematic. With a blue laser (e.g. 488nm), you may still have problems at high wavenumbers (molekular vibrations, OH bands...), but the low ones (structural vibrations) should be OK. That all assumes that you are looking at Stokes bands. If you use Anti-Stokes, blue or green lasers should be no problem for any wavelength but you may potentially run into limitations with the UV transparency of your optics (depending mostly on the specs of the objective). You will probably need to try and see what works best for the particular setup and samples.
I would also recommend having a little fan that cools the objective. Depending on the working distance it may not be strictly necessary but it is a very minor investment compared to having to replace an objective that got too hot.
Best regards,
Anselm
If i were you, I would like to check a sample holder without any molten samples on the hot stage at ~1500deg first, to see the background spec and compare with it at RT. This will practically give you an idea about the baseline of spec of the molten samples, i.e. infrared noise impact. This will also avoid or minimize the risk of damaging your system.
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