new box, new setup, new alignment

It’s winter vacation, so I’m out of the classroom for a little while. I’ve looking forward to it for some time and like a good little squirrel, I’ve been stocking up on parts and stuff to do.

I bought new boxes for the Raman spectrometer – the old ones were slim and sexy but I was getting tired of the constraints on my lebensraum:


Initial alignment of the optics in the Raman box. The new box is so spacious.

I’ve already presented the new beamsplitter in a previous post and here you see it in action. It made alignment 1000% easier and for the first time the laser beam is actually along the optical axis and not parallel to it.

Of course it doesn’t quite reflect 100% so the beam dump will have a place in the Raman spectrometer after all. The reason you see three laser spots is that the JDS Uniphase µgreen lasers always have two off-axis spots – and because they’re off-axis they are more readily transmitted rather than reflected.


The beam splitter is a rather tight fit in the 3D-printed structure and it actually broke when I tried to remove it – one corner is sort of chipped off. Luckily the back-scattered light hits the beam-splitter in an ellipse that stays nicely within the intact part.

The last bit of alignment to be done was to make sure that the scattered light actually hit the fiber. Here you see the difference:


We’re once again looking at the fluorescence of tetraphenylporphyrin (because that’s what I had at hand). The lens-and-fiber-assembly (the black tube to the left of the dichroic mirror) was tilted slighty in the picture to the right.

After checking everything twice, I finally took a look at the vertical alignment of the dichroic mirror. It was slightly off, but with the help of my girlfriend’s hair-drier I gently heated the plastic holder and fixed it.

This was a terrible experience, so in my next Raman spectrometer (don’t laugh!) the beam splitter will be in some sort of kinematic mount.


This is not HAL 9000, it’s what the fiber-port looks like without a fiber.

Anyway the conclusion is that with the new box and the new Raman setup, the fiber port is now located on the box. This should lower the fiber coupling losses significantly.


3 thoughts on “new box, new setup, new alignment

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