A waste of time

While it was “fun” to destroy a quartz cuvette and bring it back to life, it was also a complete waste time.

The point of the whole operation was to bring the focal point of the microscope objective inside the sample volume by reducing the wall thickness of the cuvette from 1.25 mm to 0.75 mm.

The microscope objective has a working distance (WD) of 1.0 mm in air, which means that the WD is >1.0 mm in any medium with a refractive index >1.

I’ve tried to photograph the focal point:

The images show fluorescein’s emission by excitation with a 532 nm laser. The spectroscopic cell has a wall thickness of 1.25 mm. The difference in the illumination angle is due to a difference in the diameter of the collimated laser light entering the microscope objective.

If you really want you can sort of persuade yourself to see that the light is focused just inside the spectroscopic cell. If you’re more of a sceptical kind of person you’ll need more pictures:

This is tetraphenylporphyrin’s emission by excitation with the same laser. The image on the right is just a crop. Here it’s clear that the light is focused somewhere inside the sample liquid.


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