Dear Emmanuel,

this is a typical behaviour of a normalized transmission spectra It/Io when one or both of the following two conditions come into play:

a) primary light intensity Io in that spectral range is poor and so noise comes up and enters Io and It; the noise is further enhanced in the It/Io ratio.

a) high sample attenuation, so that the transmitted light intensity It is very poor and thus gets noisy; so the transmission T= It/Io does.

If conditions a) and b) are valid the noise is further enhanced in T= It/Io due to the strong noise in It.

Countermeasures:

a) please increase measurement time (= decreasing scan speed),

b) increase primary photon flux,

c) decrease spectral resolution (e.g. by enlarging slit widths of monochromator)

Good luck

Dear Emmanuel,

this is a typical behaviour of a normalized transmission spectra It/Io when one or both of the following two conditions come into play:

a) primary light intensity Io in that spectral range is poor and so noise comes up and enters Io and It; the noise is further enhanced in the It/Io ratio.

a) high sample attenuation, so that the transmitted light intensity It is very poor and thus gets noisy; so the transmission T= It/Io does.

If conditions a) and b) are valid the noise is further enhanced in T= It/Io due to the strong noise in It.

Countermeasures:

a) please increase measurement time (= decreasing scan speed),

b) increase primary photon flux,

c) decrease spectral resolution (e.g. by enlarging slit widths of monochromator)

Good luck

What is the instrument? Many instruments have a change in detectors at ~800nm and this can produce discontinuities in the spectra, such as you are observing. Check the manual!

Dear Mr. Gerhard Martens!

I think that increasing the width of the slit of monochromator is the worst way to carry out measurements, if the experimenter has enough time for measurements.

With best wishes to You.

20180217Д\д

Dear Ivan,

you are completely right; if there is time enough to do the scan or even multiple scans one should not touch a running system.

Thank Gerhard,

I changed scan speed, especially for baseline correction, increase slit size and managed to minimize the noise (image attached ). I want to remain noiseless, more advise please. Again how do i increase photon flux? Thanks again Gerhard

Dear Emmanuel, thanks for feedback.

a) Increasing slit size(s) is one option to increase photon flux. You just did it.

b) Operating the light source at higher power conditions is another one; but please be careful. The manual of your system will give advice with respect to the power conditions of your light source. Operate according to the manual, otherwise you may destroy your light source.

c) As far as you operate in the transmission mode you may decrease sample thickness. But with respect to your sample transmission of about 80% (at around 500 to 1500nm) for your present sample you would not gain that much.

d) Please perform multiple scans and add the appropriate spectra. This is like increasing primary photon flux.

Final remark: experimental spectra without any noise are a dream of all of us. Spectroscopists fight their whole working life against noise. You cannot completely remove the noise; you have to live with.

Thanks Gerhard for your advices, they helped a lot. Your options are useful, am going to consider them carefully, thanks again