Raman-spectroscopy

[paul1598419]

Much of this was collected over years of buying and trading. I have a room full of laser related parts.

 

[kecked]

Any reason to not just use a beamsplitter and add the line filter just before the detector Ie skip the dichro in the beam path.

 

[Singlemode Laser]

Any reason to not just use a beamsplitter and add the line filter just before the detector Ie skip the dichro in the beam path.

You lose 50% of the pump laser light and 50% of your signal. In addition you will have more straylight. I don't see any real advantages besides this.

Singlemode

 

[paul1598419]

@ Singlemode Laser. I have a 575nm DPSS laser scheduled for delivery to me tomorrow. I am very excited about seeing what I can do to improve this laser's output. It's almost like Christmas morning and I am 5 years old again. :yh:

 

[Singlemode Laser]

@ Singlemode Laser. I have a 575nm DPSS laser scheduled for delivery to me tomorrow. I am very excited about seeing what I can do to improve this laser's output. It's almost like Christmas morning and I am 5 years old again. :yh:

This is awesome Paul. Such a great wavelength and I am am afraid we won't see it as a direct diode for some time. Can't wait to see your beam shots!

Regarding beam improvement: you can try a pinhole to do spatial filtering or even better, an optical single mode fibre.


Singlemode

 

[paul1598419]

I'm very familiar with spatial filters. Used them a lot in holography. I've been wanting a 577nm laser since the first time I saw one. This is close enough. I will be experimenting with this thing for days. I could use a fiber optic as I have plenty of them. Will just have to see what works best. YEEEE!!! I am so excited!

 

[kecked]

So I was thinking collectively we can design up a Raman unit from the eBay unit and post the full build plans. Anyone game? I think we should try it first with the 473 since the spec already has the anti stokes filter fitted and the line filter. We also benefit by already having the sma fiber connectors in place and aligned. Next change out the filter in the Raman head to 532 and use the pbs cube shown earlier. Next the microscope objective setup for Raman microscopy. By then I should have my confocal running and will be hopefully able to add Raman to that unit. Yes that’s a lot but I think it can be done and documented for others to do it. Who’s in?

I’m also thinking we use the 462nm diodes as the Raman laser and see if we can shift them up to use the existing line filter. They are 9w. Or 2w not remembering but if we heat them and only run them at 1w we still have a huge excess of photons to work with and line filters can clean up the beam or we can even use a grating to select the beamfollowed by a slit or pinhole. We can do the same for 520nm diodes but just clean the beam up with a 520 filter and hole.

The advantage. Of 473 is the stronger Raman signal and the disadVANTAGE fluorescence. But. Maybe we also set this up to do fluorescence just change filter to low pass ie longpass

Last is there a reason you must use the path for the laser and signal? What if you used two different fibers and put a collection lens on the signal fiber. Now you need no filter until the detector and no beam split loss. Is the Raman return only scattering in a narrow cone? I think it’s non coeherent and in all directions.

 

[kecked]

So looking for filters. How narrow do I need to make the filters? For example I see a 520nm band pass filter for the 520nm laser diodes but the filter is about 50nm wide. They say 15nm but the graph looks more like 50nm to me. I could heat tune the laser diode so it falls at say 525nm and cut off one side. Not sure how wide band the diodes are. The dpss yellow is 6nm wide my so called 532 is really 534nm. Looks like you need to really control the laser line to make this clean up work. I’m not convinced the 473 lasers are always 473 yet either. Hence...maybe not cleanup the laser and use a better low pass/longpass filter. Seems you can get much sharper edges for those. Issue at 532 is your right in the middle of the spectrum so you must use a band pass and if it’s wide you lose spectrum. Thinking of both stokes and anti at the same time. Speaking of which which is best....so many questions. Absorption is much easier with specs than this.

Last has anyone hooked this up to a spec library yet?

 

[Agastar]

So I was thinking collectively we can design up a Raman unit from the eBay unit and post the full build plans. Anyone game? I think we should try it first with the 473 since the spec already has the anti stokes filter fitted and the line filter. We also benefit by already having the sma fiber connectors in place and aligned. Next change out the filter in the Raman head to 532 and use the pbs cube shown earlier. Next the microscope objective setup for Raman microscopy. By then I should have my confocal running and will be hopefully able to add Raman to that unit. Yes that’s a lot but I think it can be done and documented for others to do it. Who’s in?

I’m also thinking we use the 462nm diodes as the Raman laser and see if we can shift them up to use the existing line filter. They are 9w. Or 2w not remembering but if we heat them and only run them at 1w we still have a huge excess of photons to work with and line filters can clean up the beam or we can even use a grating to select the beamfollowed by a slit or pinhole. We can do the same for 520nm diodes but just clean the beam up with a 520 filter and hole.

The advantage. Of 473 is the stronger Raman signal and the disadVANTAGE fluorescence. But. Maybe we also set this up to do fluorescence just change filter to low pass ie longpass

Last is there a reason you must use the path for the laser and signal? What if you used two different fibers and put a collection lens on the signal fiber. Now you need no filter until the detector and no beam split loss. Is the Raman return only scattering in a narrow cone? I think it’s non coeherent and in all directions.

Sounds good to me!

 

[chloderic]

So I was thinking collectively we can design up a Raman unit from the eBay unit and post the full build plans. Anyone game? I think we should try it first with the 473 since the spec already has the anti stokes filter fitted and the line filter. We also benefit by already having the sma fiber connectors in place and aligned. Next change out the filter in the Raman head to 532 and use the pbs cube shown earlier. Next the microscope objective setup for Raman microscopy. By then I should have my confocal running and will be hopefully able to add Raman to that unit. Yes that’s a lot but I think it can be done and documented for others to do it. Who’s in?

I’m also thinking we use the 462nm diodes as the Raman laser and see if we can shift them up to use the existing line filter. They are 9w. Or 2w not remembering but if we heat them and only run them at 1w we still have a huge excess of photons to work with and line filters can clean up the beam or we can even use a grating to select the beamfollowed by a slit or pinhole. We can do the same for 520nm diodes but just clean the beam up with a 520 filter and hole.

The advantage. Of 473 is the stronger Raman signal and the disadVANTAGE fluorescence. But. Maybe we also set this up to do fluorescence just change filter to low pass ie longpass

Last is there a reason you must use the path for the laser and signal? What if you used two different fibers and put a collection lens on the signal fiber. Now you need no filter until the detector and no beam split loss. Is the Raman return only scattering in a narrow cone? I think it’s non coeherent and in all directions.

Hi kecked,

in ther "B&W-tech Spectrometer & 473 module: Setup+Mods+Info" #495 i posted a raman-shift from me with the original assembly with the 473 nm .... you can use it .... with some postprocessors i created in excel.

 

[chloderic]

Last is there a reason you must use the path for the laser and signal? What if you used two different fibers and put a collection lens on the signal fiber. Now you need no filter until the detector and no beam split loss. Is the Raman return only scattering in a narrow cone? I think it’s non coeherent and in all directions.

If i understand this here, you can see such an assembly in the picture of my functioning device at page 1 . The 2 beams in and out will run 2 separate ways. I have attached a picture of the beampath of my device #1. The blue path is the laser and the red path ist the backscattering. That meens i have attached a 532nm laser left at the binoculartube , the filterassambly (i posted it) at the middle with connected spectro at the sma.
Additionally there is a 5 M-pix camera installed at the right to adjust the position in the target. AND ... it is working.

Source-webside of the picture : MBS-10

 

[kecked]

That’s interesting but I was thinking literally two fibers side by side. One laser and the second with a collection lens on it to collect the scattered Raman light. Eliminates all the optics except the lens and a single line filter. I guess you could send the laser through the collection lens to intensify the spot on the subject but I wasn’t thinking that. The stereo microscope idea is great. You can focus on a small area and then replace the eyepiece with the laser for a measurement. I like that for safety sake rather than removing the detector. Do you see peaks from the glue and glasses in the optics path?

 

[chloderic]

That’s interesting but I was thinking literally two fibers side by side. One laser and the second with a collection lens on it to collect the scattered Raman light. Eliminates all the optics except the lens and a single line filter. I guess you could send the laser through the collection lens to intensify the spot on the subject but I wasn’t thinking that. The stereo microscope idea is great. You can focus on a small area and then replace the eyepiece with the laser for a measurement. I like that for safety sake rather than removing the detector. Do you see peaks from the glue and glasses in the optics path?

I would like to repeat it in an other way; the first tubus (of the 3) at the right side ... there is connected a 5 meg-pix camera and i can see everything what goes on an the screen of the laptop where the spectrometersoftware is running. If i want, i can swap out the two beamsplitters-cubes you see, these are only to lead temporary the picture to the cam , also i can swap out the 2 central gallileo-lenses or swap in others for other enlargements.
Than i have only the beam :
laser->objectiv->material to detect->objectiv (the same)->longpassfilter->colimator->fiber->spectroscope.

 

[Civitus]

So I was thinking collectively we can design up a Raman unit from the eBay unit and post the full build plans. Anyone game? I think we should try it first with the 473 since the spec already has the anti stokes filter fitted and the line filter. We also benefit by already having the sma fiber connectors in place and aligned. Next change out the filter in the Raman head to 532 and use the pbs cube shown earlier. Next the microscope objective setup for Raman microscopy. By then I should have my confocal running and will be hopefully able to add Raman to that unit. Yes that’s a lot but I think it can be done and documented for others to do it. Who’s in?

I’m also thinking we use the 462nm diodes as the Raman laser and see if we can shift them up to use the existing line filter. They are 9w. Or 2w not remembering but if we heat them and only run them at 1w we still have a huge excess of photons to work with and line filters can clean up the beam or we can even use a grating to select the beamfollowed by a slit or pinhole. We can do the same for 520nm diodes but just clean the beam up with a 520 filter and hole.

The advantage. Of 473 is the stronger Raman signal and the disadVANTAGE fluorescence. But. Maybe we also set this up to do fluorescence just change filter to low pass ie longpass

Last is there a reason you must use the path for the laser and signal? What if you used two different fibers and put a collection lens on the signal fiber. Now you need no filter until the detector and no beam split loss. Is the Raman return only scattering in a narrow cone? I think it’s non coeherent and in all directions.

I like the idea, this can be very pedagogic.
for the laser power, by experience , we need sometimes only few mW, lower we go in wavelength, more raman we get. also, if there is fluorescence, higher is the power of the laser, higher will be thge fluorescence signal.

C

 

[kecked]

I’ll give it a try and see what happens. Must be a reason it’s done the traditional way and not side by side fibers. Guess I shall learn.

 

[Civitus]

The existing system Raman head has a filter you need to remove that blocks some spectrum and you already know about the internal spec baffles. I was hoping to move to 780nm for Raman The detector is pretty deaf down there and I might not even need a filter since it’s unlikely to even hit a pixel ...2400 or better I’m guessing so unless a different order wraps might work.

I have an Olympus scope I want to use. I think the optics will transmit 780nm. Can only try and see what I get. I’m looking for a toxin produced by toxic algae. The laser is to be a fiber telecom laser. Eventually I want to try a confocal and see if I can focus in on cell parts specifically for id.

So my point with a scope is you can select a very small area of an object to excite Raman and determine that portion and not the broad response. Is this correct. If not I’m in a dry hole.

Hi,
This is a good idea to go to 785nm for organic molecules, but keep om minde that the Raman signal will be much lower that the 473nm laser excitation.
Also, there will be much heating of the sample (now we are in the range of vibrational energy of molecules, so the energy transfer is much easier)

Finally, i f you select a very small part of the cell, the raman signal cllected will be a very small again. in this case, you wil need for sure a TEC for your spectrometer.

My advice is to try the 473nm or even 532nm and try to go to 785nm

C