I am interested in measuring the recombination times in TiO2 dye sensitized thin films. I study this by measuring the transient absorption (either the recovery of the dye bleach or the decay of the oxidized state). It seems that there is a lot of scattering from the film during the measurement which interferes with the real signal. How can I reduce the scattering?
Hi,
what is the wavelength of your pump? Did you try some kind of filter?
Actually, you may try some noise reduction (SVD filter) after the measurement.
Andras
Hi, the pump is 580 nm and the probe is 880 nm. There is a monochromator before the photodiodes detector set at 880 nm, so I quite don´t understand why the scattering signal should be sooo huge. I have tried also putting a filter and reducing power from the OPO but I still get an ugly response. Please look at the attachment if you have time. Thanks for your answer. Valeria
Well, it looks bad indeed. My recollection is, that TiO2 makes the solution quite turbid, and that is always a problem. You can try a filter right after the sample to reduce the scattering, maybe an RG610 or RG630, that will cut the scattered 580 nm quite well.
Same time it seems to me that you have a quite regular noise. Are you using a sample mover here? This noise (if it is so regular) can be removed by SVD filtering.
Andras
Hi,
The film sits on a holder which is fixed to the table. There is no solvent present for this specific measurement. This regular noise that you see seems very strange to me because it is a really big signal (around 0.003 delta absorption), but other times is smaller, around 10e-5 units of delta A. The most strange is that sometimes when I measure a very similar sample (prepared by exactly the same procedure) I get a nice decay response, and other times, unexpectedly, I get this very strange signal. Do you thing that the position angle of the film plays a big role? Or the concentration of dye molecules in the film? Once I measured without any filter and the signal was really nice...
Valeria
I am not sure of your system, but we had to do pump probe spectroscopy on a vapour cell and the background scattering was causing huge problems. We were doing a phase detection, which makes the signal much more sensitive to tiny changes. We noticed such a pattern depending on the of the vapour cell with the beam direction. It is some sort of a spurious interference effect as far as I can understand. The way we overcame was putting the detection photodiode very away from the cell. The spurious scattering will diverge differently than the laser and hence the spatial density will reduce and finally we put a iris in front of the diode. Also we adjusted the cell along an angle such that these spurious interference is minimized.
Hope this helps.
Hi, thanks for all your comments! Yesterday we found out that we had a problem with a cable!! :X so, after fixing this cable the signal looks perfectly normal, what we thought was scattering was just electronic signals... Anyway I appreciate a lot your time, it will be helpful in the future for sure ;D
At least you know what to do in the case you have real scattering. :-))
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