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Raman spectroscopy

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After some internal debate, I ditched the gun scope accessories and instead got digital camera alignment accessories. I got a 4 way macro focus rail, a 360 tripod ball (laser will go on these to have up/down, left/right, and rotation control). For the optical tube I got a flexible arm and clamp. All this for $69.

Don't know how well it will work though.
 
I just ordered two Newport Optics stands, one with a Newport lens holder, the other with Thorlabs lens holder.. roughly $100. The fiber optic probe arrived yesterday, that was ~$220. So did the 532nm bandpass filters. Hopefully the green laser arrives monday. Also ordered a focusing lens and SMA-905 adapters (the latter arrived yesterday).
I just need to figure out what I'm going to do about a beamsplitter, if it's even necessary. I still need to get a longpass/notch filter *edit* just ordered one.

anywho, here's some relevant reading... The Alkaloids-Chemistry and Biology Vol. 67, Ch. 4: Determination of Alkaloids through Infrared and Raman Spectroscopy
 

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Observing the schematic, the filters and lenses will be mounted on the stands, with the SMA-905 adapters. I have the stainless steel fiber optic cable, it is 600um dia. for each fiber, 6x1 configuration (six collection fibers, around one excitation). I also ordered BP and BR filters for the 780nm laser, and a beamsplitter.
 

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That last book looks great, thanks for all the resources benzyme.

I started building the optical tube. Turns out I need a special wrench to screw everything in (oops), so I oreded that and need to wait moar now. On the plus side, the laser and optical tube fit well on the cheap parts I ordered from the consumer electronics world.

I've also ordered 50nm Ag nanoparticles from eBay (only $30 for 10g). Hoping to try SERS with them, kind of like the attached paper did (for example).
 

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This is very cool stuff that you guys are doing here!

Don't call me the party pooper again but I am struggling a bit how you will use this.

Usually one uses Raman to complement infrared spectroscopy. Especially for small and symmetric molecules (smaller than what you are agree) they go hand in hand.

To identify compounds one would rely on infrared (especially the fingerprint region of the spectrum).

One thing I could see is to look at mixtures of alkaloids to see if there is anything. I would guess that would work qualitatively but not quantitatively.

Am I missing something here?
 
you don’t need an IR spec (although as I’ve mentioned, I have one, and an LCMS) to compare the spectra, as raman scattering is directly inverse to IR transmission.
Quantitative analysis can absolutely be employed, and this is discussed in Ch. 10 (McCreary, 2000), which also discusses calibration/validation procedures, further emphasizing that an IR spec wouldn’t be necessary.


the only major issue with this mode of analysis, particularly with the analytes we commonly consider here, is fluorescense..
which is why I coughed up some coin to get a 780nm laser, to compare against the 532nm. The only adjustment I foresee I’d need to make, is getting a 600L/mm grating.
 
To avoid fluorescence (which is lower than the laser energy) the anti-stokes Raman radiation (the molecular oscillations that boost the laser energy) can be looked at, right? This involves switching the edge-pass filter from longpass to shortpass and maybe adjusting the spectrometer's optimal wavelength range. Downside is that anti-stokes emmisiom is not as strong, but maybe SERS can help.

Unfortunately I got AR coating in the optics I ordered (400-700nm range) before I read about the dual laser approach from benzyme, so switching lasers would not be straightforward for me.

DrSeltsman, incase you have not seen it yet, we crudely overlayed DMT spectrums from FTIR absorption and Raman emmision here. Like benzyme said they sure look complimentary.
 
I just got that 532nm.. wow, that is bright. Apparently, the peak wavelength of human optical detection is 555nm, and the far end is 780, so that explains why this green laser appears very bright, while the 780nm which has 4x the power, is not particularly bright.

I noticed the absorbance shift, of lysergol in 50:50 methanol:water, using a 405nm (appears as 445 on the detector) laser pointer, and this 532nm laser module (I still need to measure this one). The former fluoresces the solution as mint green, maybe 480-ish nm. The 532nm laser fluoresces the solution as a reddish-orange, maybe 650+
 
benzyme said:
I have not, and I think this spec supports lasers up to 650-680nm with the stock 1800L/mm grating
I did a test with the green laser, but for some reason, the peak shows as 1327 pixels. any ideas on how to troubleshoot?
Click to expand...

I think we may need to adjust the optics to center the wavelength of interest. There is a procedure for this on the spectrometer vendor site you may have seen already. I will start by slowly rotating the grating hoping to not have to adjust the mirrors (since the peak looks narrow and well focused). I believe this can be done while shining two lasers (green and red) at the optical fiber and watching the spectra.

I'm in a similar situation, want to move the green laser line to a lower pixel index. Seems like the spectrometer comes optimized for shorter wavelengths.

Edit: Here something similar was observed: the spectrometer comes optimized for the blue-green region and an adjustment was needed to cover the green-red region:

The Pulsar said:
The unit I got was pre-aligned but the 200 nm span was not the one I was looking for (it recorded the blue-green region while my experiments require me to study the green-red region).
Click to expand...
 
benzyme said:
tale of four lasers: 405, 532, 680, and 780nm
power: 100, 200, 5, and 800mW, respectively.
the analyte: lysergol (λmax = ~308nm) , ~2mg/mL in 50:50 MeOH:H2O
Click to expand...

That's just beautiful. Have you collected any Raman emmision from the sample and sent it to the spectrometer yet? You were going to use a fiber probe, right?
 
Update: I've ordered a new lens and laser filter to update the lens tube design.

Now I'll have 3 lenses in the tube (first design had two lenses). Two will be short focal length condenser lenses and one will be a longer focal length lens to couple to the optical fiber and match the numerical aperture that the spectrometer seems to have (~0.2).

The nice thing about this set-up is that 4x Raman signals are picked up, since the filters are dichroic they should reflect the rejected light. Also, the mirrored laser beam can be used to focus and align the optics in front of the edge filter. The outgoing laser beam should match the incoming beam when the tube is aligned and in focus. The last part to adjust is the optical fiber and it's coupling lens behind the edge filter which can be done using the spectrometer signal I think.

Diagram and light Ray simulation is below.
 

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