- #1
pfollansbee
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I'm currently updating an old raman spectrometer that had fallen out of alignment requiring some modifications to its design.
I have attached an image of what it currently looks like. I am using a HeNe laser which is directed into a bifurcated fiberoptic. The combined end is pointed at my sample to hit it with the laser and collect its emission. The other end is pointed at a lens which then enters a double monochromater before hitting a PMT. The PMT is hooked into a
This setup was optically aligned using an LED on a fluorescent compound. Fluorescent peaks were observed, so the machine is working fine. I am also getting plenty of excitation from the laser.
So here is my dilemma, why am I not seeing raman peaks? I am just seeing a flat line, no structure at all, when I should see... http://www.chem.uAlberta.ca/~mccreery/images/Photo raman intensity standard/polystyrene.jpg
Things that have been tried
1. Slits are WIDE open
2. Moved fiber optic away from sample to avoid reflections
3. Angled sample to omit direct reflections
4. Checked and rechecked wavenumbers for correct range
Ideas
1. Filter to remove laser light.
-I am hesitant to use this though because I don't want to block out my raman signal.
or
2. Focusing optics at the joined end of the fiber optic between it and the sample.
-This may be the issue because the fiber optic is acting like a point source rather than a beam.
So what do you guys think? Are fiber optics a bad idea for transmitting laser light? Would focusing optics do the trick? Just needs a filter?
Thanks! :D
I have attached an image of what it currently looks like. I am using a HeNe laser which is directed into a bifurcated fiberoptic. The combined end is pointed at my sample to hit it with the laser and collect its emission. The other end is pointed at a lens which then enters a double monochromater before hitting a PMT. The PMT is hooked into a
This setup was optically aligned using an LED on a fluorescent compound. Fluorescent peaks were observed, so the machine is working fine. I am also getting plenty of excitation from the laser.
So here is my dilemma, why am I not seeing raman peaks? I am just seeing a flat line, no structure at all, when I should see... http://www.chem.uAlberta.ca/~mccreery/images/Photo raman intensity standard/polystyrene.jpg
Things that have been tried
1. Slits are WIDE open
2. Moved fiber optic away from sample to avoid reflections
3. Angled sample to omit direct reflections
4. Checked and rechecked wavenumbers for correct range
Ideas
1. Filter to remove laser light.
-I am hesitant to use this though because I don't want to block out my raman signal.
or
2. Focusing optics at the joined end of the fiber optic between it and the sample.
-This may be the issue because the fiber optic is acting like a point source rather than a beam.
So what do you guys think? Are fiber optics a bad idea for transmitting laser light? Would focusing optics do the trick? Just needs a filter?
Thanks! :D