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RAMAN-spectroscopy

paul1598419

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The problem with using mirrored gratings is you may not see the lines as three separate peaks. I have a clear sheet grating that at a distance, these lines show up as individual dots. Close in, they will likely look like one line.
 

diber

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So... took a while before I found the time to further investigate this... So far I did not manage to observe the spurious lines with the standalone laser and the spectrometer, probably due to the big intensity difference between the 532nm light and the 537 - 543nm light, which makes them difficult to observe without attenuation of only the 532nm beam.

The easiest way to confirm this is with a diffraction grating. You will see a group of three peaks next to one another.
Pauls approach, using a transmission grating is probably indeed better than trying to observe directly with the spectrometer.

cant you background sub the lines?
Kecked: it is almost impossible to subtract these spectral lines with the background since their intensity is continuously varying. For my laser they are not stable modes in the current condition.

The green lines are reflection sensitive I put a rotator in front and all but the fundamental and pump vanish. The lines are pretty weak but way above the signal from raman so they are significant. A line filter on the green 2-3nm wide will fix it. Try angling the laser a little or putting a microscope slide in front of the laser to act as a window and reflect light off at an angle. It takes very little light to make the problem.

However, the good news is that, thanks to the suggestion from kecked, it seems indeed that placing a microscopy slide under angle between the laser and the fiber input is an easy way to get rid of those peaks without loosing a lot of signal, at least for the time being in my setup. I do not really understand why... could be due to the limited beam intensity loss in the system caused by the reflections from the slide, could be that the slide affects the back-reflection into the laser, could be that the temperature is now different then last week, making the conditions for the spurious peaks more marginal, something else... in any case, so far it seems to work in my setup and it is much cheaper than a laser line filter or buying a single mode laser . And since I still have some TECs lying around, modifying the laser temperature by a few degrees will be my next try in case the peaks would still reappear.

Note: I do realize that a single mode laser gives probably much better resolution in the raman lines due to the narrower laser line (narrower in the spectrum), but I first would like to find a setup that works well before investing a lot more in equipment (... the trying to make it work is anyway my main objective, more than the use of the setup afterwards...).
 

kecked

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I did use the grating from inside one of the bw units and I could separate the three lines BUT it took 15 feet of distance to make them only an inch apart. I vote line filter or a sharp edge high pass filter. The best way to prevent reflection is a rotator but that is expensive. Glad the microscope slide worked. Last idea. I didnot try this. Are those two other lines differently polarized? Try it might work.
It might also give a different raman spectrum not sure.
 

kecked

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I found the mystery 543/6 line. YAG makes 1064 and 1084. So doubled is 543. Variance in pump boom. You got your lines. The power ratio is just about right. I barely noticed the bump in the spectra.

The only way to stop that would be a line/ lowpass filter before the doubling. Amazing how messy the dpsslaser system is once you start looking.
 

paul1598419

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@ kecked

You should use the edit icon at the lower right of your last post. It helps to keep this thread from getting cluttered with multiple posts by one member. ;)
 

paul1598419

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You needn't add information to a previous post if anyone has posted since your last post. For me, I let 24 hours go by before posting again if no one has posted since my last post. It is mainly seeing post after post after post, only a few minutes apart that gets people's ire up here. That is what we call double, triple, quadruple posting here.
 
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leo2018

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In post #322 of the B&W Tech spectrometer thread, I posted a few raman spectra I managed to obtain with the 473nm laser and unmodified beam splitter (and if I am not mistaken, some other successful results were posted as well, but I could not find them back yet). Check also posts #468 and #478 discussing the setup/method used to acquire these spectra. For me it worked best by putting a small bottle of transparent fluid with a strong raman scatterer (aceton and isopropanol worked best for the liquids I had at hand) almost against the input lens of the beamsplitter. Recently, following the example of chloderic, I found that using a diamond instead of the liquids gave by far the strongest signal I have seen, but I did not try this with the 473nm laser yet.

In general, it was quite simple: (1) specify spectrometer acquisition settings (for instance, longer integration time of 300 ms or higher and nr of averages 20), empty bottle (or no sample) in front of beamsplitter (almost touching the lens) (2) acquire spectrum and set it as background (3) put acetone/isopropanol (or any other strong raman scatterer) in bottle (sample (f.i. diamond)), (4) acquire raman spectrum.
Hi, Diber

I'm new here. Just wondering did you remove the filter (block wavelength under 480nm) and baffle in the spectrometer when you got those raman spectra? Or everything is in original condition ( machine from ebay) ?

Thanks a lot!
 

kecked

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I removed the filter and the baffles but those spectra are on an ocean optics hr2000 I believe. I did it both ways. The bw uni5 works fine.
 

leo2018

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I removed the filter and the baffles but those spectra are on an ocean optics hr2000 I believe. I did it both ways. The bw uni5 works fine.
Hi, Kecked

Thanks for the reply, I don't have any ocean optics HR2000, i thought the raman spectra Diber got was using a B&W Tek spectrometer.

So you mean you got raman spectra with B&W Unit? can you provide more details?
 

kecked

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Doesn’t matter the spec you use. If you want to go bw tek. Open then unit and remove the baffles. In the entrance slit there is a lowpass filter. Remove that too. All I did was unscrew the fiber to the bw tek unit and screw it into my ocean unit. Same spectra. The free software for the bw tek doesn’t do Raman shift. You can try the original bw tek software but it will hose you even though it will run in win10. The driver toasts your mouse driver. Make sure to run in win7 machine.

The unit as designed does a reasonable job with the given 473nm laser. You are better off changing to 532 or 660 or 785. 473 makes poor resolution spectrum. 532 is good for inorganic like rock. 660 and down for organics.

If your going lower to 532 you can and should leave the lowpass filter in there. Will block second order spectrum overlap and anti stokes lines above 470nm. The unit as bought does work once the baffles are removed.
 
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leo2018

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Thanks for all those details. One more question: where can i get 'original bw software' ?

For now, i'm using termite - serial communication tool to get the readings from linear CCD.
 

chloderic

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To keep this project running i ordered today some new filters for a new assembly at BJOMEJAG ebay that should be a little bit more effective.
Because this parts have a litte bit of delivery time i first selected them and ordered , bevore go on with the other projects.

1. Optical Interference Filter 532SC0.9 24.5mm Ulta-narrow 2nd Harmonic YAG High T%
cleaning up filter, is for isolating, resolving emission from a 2nd Harmonic YAG laser, occuring at 532 nm.
Intended application would be to "clean up" a laser output, or to detect ouput energy of the laser.
Individual filter specifications : CWL 532.0+-0.2nm,
HBW 0.9+- 0.1nm,
Size 24.5mm,
Free Spectral range from 0.8 to 1.2 times the CWL. to.
Unmounted 1.3mm thickness.

2. Optical Filter 535EFLP Laser Block 25mm Green Em Omega
longpassfilter is NOS of OEM, for detecting Green emission of Dyes such as FITC, Spectrum Green, GFP, and many other green dyes.
It could be used with any blue exciter.
Specification : Cut on wavelength 535 +- 3 nm,
Transmission band from 540 nm to 1500 nm,
Blocking band X-ray to 515nm avg >> OD 6,
Size 25+-0.2mm,Thickness 3.0mm, Unmounted.

3. Optical Filter 538AELP 25 mm dia, Laser Block 532 & 535mm Green/Orange Sputtered
longpassfilter is NOS of OEM too, for detecting Green/Orange emission of Dyes such as TRITC, YFP, and many other green dyes. It could be used with any blue or Green exciter. Designed to achieve OD 5+ at 534 nm. Also ideal for Raman signal when excited with 530 to 535nm laser.
This filter is a monolithic Schott Glass substrate with a refractory oxide surface coating.
Specification : Cut on wavelength 535 +- 2 nm,
Transmission band from 540 nm to 1500 nm,
Avg T 540 to 950 > 95%,
Blocking 400 to 535nm avg >> OD 6,
Size 25+-0.2mm,
Thickness 2.0 mm, Unmounted.

4. Optical Filter Barrier 535EFLP 25mm X 1.5mm LED Blocking Window
longpassfilter with slightly other transmission, also for detecting Green/Orange emission of Dyes such as TRITC, YFP, and many other green dyes.
It could also be used with any blue or Green exciter. Designed to achieve OD 5+ at 534 nm.
Also ideal for Raman signal when excited with 530 to 535nm laser.
This filter is a monolithic Schott Glass substrate with a refractory oxide surface coating.
Specification : Cut on wavelength 535 +- 2 nm,
Transmission band from 540 nm to 1500 nm,
Avg T 540 to 950 > 95%,
Blocking 400 to 535nm avg >> OD 6,
Size 25+-0.2mm,
Thickness 2.0 mm, Unmounted.

5. Optical Filter Dichroic 540DRLP 25mm dia X 1mm Beamsplitter @45 R95% @532nm
dichro-beamsplitter from Omega OEMogram. The filter is idea as a Greenier Filter, attenuating the tail of a Cyan or Green LED, while transmitting 95% of the emission from Fluorescence, excited by the LED or Diode Laser.
Filter specs : Cut-on wavelength 535+-2nm,
Attenuating region deep UV to 530 nm to O.D. 6.0,
Transmitting range min 538 to 2000nm,
size 25mm dia x 1.5mm thick, unmounted.
 

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