Hello,
For spectral analysis, I need to collect collimated light rays transmitted from a sample. The entire experimental set up is heated up to 800°C.
I got a Sapphire optical fibre to transfer the light rays to the spectrometer for further analysis. Also, I got a Sapphire optical lens to focus collimated light rays into the Sapphire optical fibre.
But the problem is the tolerance for the error is very minute and it will be very difficult to maintain the system at very high temperatures due to thermal expansions. (The focal point shifts due to thermal expansions)
I would gladly appreciate your advice on this problem.
I have attached a PPT for a visual description of my problem.
Thanks in advance.
Best regards,
Vayalthota Gopikishore
I agreed that the best way is to move the fiber and Sapphire ball lens outside of the heating drum.
Another way is integrating a cooling system to the optical fiber and sapphire lens. High pressure gas is a good choice.
If light is indeed collimated, then your best chance is to place your fiber coupler outside of the hot area. A collimated beam will pass some distance easily without any change.
On the other hand, you also say that the beam is focused on the sample. In this case, you are limited in where you can put your coupler. 800°C is suitable for quite many materials, e.g. ceramics, NiCr alloys, special types of steel. You can even use different materials to compensate thermal expansion. This might not work well if you need measurements in whole temperature range from room to 800°C, but for some shorter range it should do. There exist special solid lubricants up to 1500°C.
My experience with adjustable optic mechanics at high temperature is limited by something like 500°C. Even there, adjustments were always rough and hard to use. I wish you good luck in fighting your challenging problem!
I agreed that the best way is to move the fiber and Sapphire ball lens outside of the heating drum.
Another way is integrating a cooling system to the optical fiber and sapphire lens. High pressure gas is a good choice.
Dear Gopikishore Vayalthota , I agree Vladimir I Chukharev and Michael Yao , your best option would be to place all your optics outside the heating drum. The sample is the only part that must be heated in your experiment. Apparently you are only interested on the transmitted light so we can assume the sample is not hot enough to emit light... at least visible light. The sample should be transparent at some extension and some structural or/and chemical changes should happen at 800ºC that modifies the spectrum of the transmitted light. The condenser lens can be outside the heating drum and focusing light on the optical fibre. Even if these changes on the sample cause scattering the lens should collect some light from it. If the heating chamber is open to the air, specially on the optical path, aberrations caused by air fluctuations due to temperature gradients and flows could cause light fluctuations.
Hope it helps, good luck.
I suggest fixing the optical fiber out of the setup( 800°C ) and using a coupling lens to matching the beam with the fiber
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