Dear Gopikishore Vayalthota ,

you may have a look at:

https://www.lasercomponents.com/de-en/product/sapphire-fibers-1/

Gerhard Martens

Thanks for the suggestion

Dear Gopikishore Vayalthota

but why do you intend to use a single mode fiber. You should know that their core diameters are in the low µm regime. Thus the efficiency of light pick up is very, very poor, even when you use some kind of focussing optics. You should go for a multimode fiber or even a fiber bundle for your purpose and focussing optics (preferably outside your furnace).

Good luck

I can give a link to the work where such high-temperature optical fibers were studied "high-temperature optical FIBERS WITH a COPPER coating" Approximate characteristics of the Type of optical fibers: Single-mode (G. 652), multimode.(G. 651), “quartz-quartz”

Type of coating: copper, aluminum and alloys based on Them

Operating temperature: 500 °C (aluminum coating),

800 °C (copper-based coating)

Length: up to 5 km (continuous)

Optical losses: minimal (depends on the design of the light guide and operating conditions) 1-4 dB/km (at 20 °C) at λ=1310, 1550 nm

2-4 dB/km (at 700 °C) at λ=1310, 1550 nm

Strength: 8-10 GPa

Diameter of the light guide: 125-1000 microns.

Conference Paper High temperature metal coated optical fiber with copper coat...

Typically, high-TEMPERATURE optical FIBERS coated with COPPER are used in the oil and gas industry. I think you can find commercial samples at reasonable prices.

Dear Gerhard Martens

Regarding mode of the optical fibre, we came to the same conclusion that it would be better to use a multi-mode fibre than a single-mode fibre because of its better range.

We can not go outside of the furnace because of the technical constraints. One end of the sapphire optical fibre will be connected to the spectrometer. But on the collecting end of the optical fibre, we are working to install a suitable collimating lens to pick more light. But we are facing problems to find a suitable lens at these temperatures.

On other hand, we are working to use optical fibre for the light source instead of light coming from the LED lamp with a 3cm diameter hole opening.

If there is no diffuse radiation, the light coming from an optical fibre will have less span compared to the one with the LED lamp with a 3cm dia hole opening.

I would gladly appreciate your feedback

Dear Gopikishore Vayalthota ,

according to the link below there are for example lenses made of sapphire available:

https://www.edmundoptics.de/f/sapphire-and-ruby-ball-lenses/12451/

So your set up should have

a) a lens for picking up part of the light passed through the sample and

b) a lens for setting up a quasi-parallel beam.

Both the pick up fiber as well as the LED or light providing fiber being in the focus (at distance f) of the lenses.

c) The distance of the quasi-parallel beam section has to be a small as possible.

Please see the attached sketch.

From the spectroscopic point of view I think your

DT-MINI-2-GS light emitter system is the best,

but from the light transfer aspect the LED source is the best because of its inherent small light emitting area.

Best regards

G.M.