dye laser part 3

 Dye Death

 Regarding the experiment described in the last post. We tested 5 power levels : 0.1W, 0.2W, 0.4W, 0.8W and 1.6W with the same power * time product of 30 sW. All samples degraded the same, which suggests that it is a photochemical reaction and not a thermal decomposition. It's much better to see this in real life than on the photos, but for those that are curious I'll attach it below. Looking up in the appropriate literature the most probable explanation is an oxidation of molecules excited to triplet state by the oxygen dissolved in to the solution. This also explains why sample in basement held in such a good state. It was enclosed in flask with air tight, ground seal.

extreme left and right are without the laser exposure, different power levels in between

What's interesting though, is that the dye died above, as well as at the level of laser beam but not below. This means that the amount of heat generated is enough for the convection in order to mix the fluid around.

Green thing

The scientific paper about possible realization of the chlorophyll laser describes pumping it with green DPSS laser. We tried it, but we obtained almost zero output fluorescence. Either this paper is wrong (there's more evidence pointing to the paper being done in a very sloppy way) or there's some organic magic that makes the radish chlorophyll extract not sensitive to green where as plants used in paper are.

Proper plots

All of this lead us to visit proper optical lab to measure properties of the chlorophyll. At first, we measured transmittance of a sample for 2 different concentrations (for all further plots I have the raw data. If anyone wants to process it by himself feel free to contact me).


 

 Then we measured the emitted spectrum for 420nm excitation to find all interesting fluorescing wavelengths. Once we did that, we tuned our detector to these frequencies and swept the pumping light to find possible pump wavelengths. At last, we swept the entire emission spectrum for all our possible pump wavelengths to make sure there's no "hidden" emission.


ignore sharp spikes, they're diffraction grating artifacts


A few interesting things showed up. Red emission peak moves a bit depending if we pump it with 420 or 468nm. What's much more interesting is that both blue and orange lines are crossing near 690nm in first plot. This means there's an intermediate level somewhere which populates one of light emitting level indirectly. Most probably there's a triplet state somewhere between 420nm and 460nm that populates 790nm triplet state, but not 650nm singlet state. However until we measure lifetimes it's just a hypothesis.


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