Dear Arkadiy,

I recommend you to measure the background spectrum using suitable reference (either barium sulfate or spectralon® reference sample) and then make the measurement in the whole region using the same settings with those references in place. Ideally, you should have 100 % reflectance with the information about the noise of your device. This should give you a hint if your PbS detector is working well.

Best regards

Tomas

I used spectralon@ as reference for calibration when measurement began.

In the next time I try to measure the reflectance of spectralon@ itself with calibration that is made with the same reference.

Regards

Dear Arkadiy Mastin ,

you are operating at quite low % of reflectivity.

There might be an automatic gain switching active when crossing the 880nm.

Please check your system with respect to such an isssue...

Please see for example page 47 of:

https://www.s4science.at/wordpress/wp-content/uploads/2019/04/L6050007_Getting-Started-Guide_en-US.pdf

There is a hint on enabling/disabling of automatic 'attenuators'...

Model 950 is explicitely mentioned there.

Best regards

G.M.

My samples have very low reflectivity. Less then 3% of diffusive reflectivity. They intended to use inside of optic devices to absorb scattered light.

Dear Arkadiy Mastin ,

thanks for feedback with respect to the sample reflectivity.

Please see the link (page 47) which have I provided above, just as that time when you have written your answer...

Good luck

Dear Gerhard Martens,

You suppose that I have high noises becouse I have attenuators enabled ?

Enabled attenuators decreased reference beam intensity level ?

and I almost havent get signal from sample.

No, to make measurents of higly absorbing materials I have to enable attenuators.

I try to do this at next measuremet.

Dear Arkadiy Mastin ,

that is always the crux with high dynamic range in a) the measurement and b) with respect to the reference.

So you should enable*) the attenuator over the whole measurement range; and not only above 800nm. The noise issue can be reduced by adding up a lot of scans and/or using much lower scan speed (if it is possible)...

*) block automatic 'gain'/attenuator action

Best regards

G.M.

Here is results of comparison of Diffuse reflection spectrums of light absorbing paints. The measurents was done with 1% Reference beam attenuation and 100 % Reference beam attenuation

Dear Arkadiy Mastin ,

thanks for sharing the 'new' results; they 'look' a bit 'better'.

But still, at about 800nm there is a step, which might be a result of

a) changing the lamp or applying/remove additional filter (for the use of longer wavelengths) having quite different spectral output there.

combined with

b) insufficient linearity of the detector there.

Best regards

G.M.