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Since this seems to be the place to post information on Raman spectroscopy, I thought I'd post some of the things I've found so far as a sort of brain dump, in case it might be useful for others. Some of this info I originally posted on the XRF forum.

[originally posted on XRF group:]

In the meantime, here are a few things I've found:

• Typically Raman and cheap do not go together - much to my chagrin
• I got started by looking at this project:?
• I have also followed this project quite a bit:?
  • He has a blog that gives more detail, especially on his attempts to get a working CCD:?
• I originally wanted to try to build the whole thing from scratch - then I got impatient and realized I was going to need a metal mill and/or drill press if I was going to fabricate everything including the kinematic mounts - so instead I decided to modify an existing microscope and hack together a makeshift spectrometer from Ocean Optics surplus parts
• Ocean Optics seem to be the Amptek of the UV-VIS-NIR world and their products are widely supported by 3rd party software, such as Spectagryph, which is appealing:?
• Probably the best implementation out there is the Open Raman Project
• The key (read: expensive) parts are:
  • Good dichroic mirror and band-block filter - There used to be an Ebay store that sold a ton of surplus filters (production overruns) from Omega Filters () but it looks like Omega was just acquired and the eBay store doesn't have the thousands of filters that were there just a few months ago
  • Powerful, Monochromatic Laser - I use a lower end JDS Uniphase laser, but it's a bit weak. Their higher end Coherent Compass laser are more powerful with a more monochromatic beam - but not cheap
    • Osram seems to be producing green LEDs that are single mode and display a very monochromatic beam and they are cheap. But, they typically come in at 510 or 520nm, whereas the traditional lasers were 532nm because they were frequency doubled 1064nm IR lasers. A lot of surplus optics out there are catered to the 532nm laser - e.g. 540nm cut off, which you wouldn't want for a 510nm laser
• The problems I have had are:
  • properly launching the Raman output from the microscope into a fiber - I just got some fiber collimators that I'll experiment with
  • too much noise in the spectrometer at long integration times - this means that I either need a more powerful laser or TEC cooling of the CCD sensor or both
• Thunder Optics is one of the cheaper turnkey solutions but they are still not cheap
• My favorite YouTube channel "Applied Science" did an episode on a quick down and dirty Raman system that shows cheap proof of concept:?

[A reply from Dud:]

Soren,

Thanks for the links The Open Raman is the best technical DIY one I’ve been following but he uses rather expensive open beam Thorlabs parts ($3,000) where I want to use fiber. ?http://www.thepulsar.be/article/openraman-starter-edition/

I have a B&W 473nm Raman laser and spectrometer but no software and for mineral work it’ll have a lot of fluorescence.

I run Ocean Optics and Stellarnet spectrometers with both their factory software and Spectragryph for optical reflectance and LIBS and Spectragryph for XRF and gamma spec. I was planning on using one of those for the Raman but finding a single mode laser cheap enough is a problem not to mention the dichroic and edge filter. However it is in the bucket list.

Dud

Some notes on Cheap Lasers for Raman

Raman and cheap typically don't go together, but one of the most expensive parts is easily the laser which much be very stable and very monochromatic. I have used a low power JDS Uniphase, which is a nice little laser available reasonably cheaply, but is underpowered for Raman. Often one sees mention of the Coherent Compass 315M, which can have high powers but is anyt hing but affordable.

The very interest "new kid on the block" is the PL530 by Osram. From what I can tell, it is often used in laser based video projectors. It seems to be hard to come by, but there is at least one seller on email who sells them (when he has them). He sells a PL530 with a power driver for around $85. He also sells the PL530 as part of a small package that also includes a red and blue laser, which inclines me to thing that it came from a projector, and which sells for $55 without any driver.?

What makes this laser pretty amazing is that it is not simply a diode, but contains a lot of optical components in a tiny package less than a dime. It is, in principle, a single mode laser spec'd with a FWHM of 0.2nm which is pretty amazing. Furthermore, it is spec'd at 50mw output, but experimenters have been able to get 75-100mw output power.

It has been popular in the diy holography community, which depends upon high quality lasers for making effective holograms and must of the info on this device can be found there. There are several users who have designed driver board, which include: a controller for the heater within the model, a controller for the TEC cooling unit to which the module should be attached and a laser driver itself which controls the power doing to the laser diode. One user has posted schematics and a thorough rightup of the spectral qualities of the module. He has done some pretty comprehensive testing to determine the temperatures and current levels at which the module puts out stable peak power in single mode operation and prevents mode hopping. Although laser are not my area of expertise, this leads me to believe that with the right driver, these things could be quite usable for Raman and they seem to have been pretty successful in the diy holography community.

Here are some useful links:

• Best Resource:??
  • If you want to cut to the chase, his page is the best I've found in terms of spectral characteristics of the laser and building a driver board - the quality of the post suggest that this guy seems to know what he is doing in terms of driving lasers in a stable way and the design is recent (Nov 2020)
  • ?- His whole page/blog has a lot of information on laser diodes, circuits, PID controllers, temperature control, etc. Please don't click the link if there is something in your life that needs to get done in the next few hours, such as gainful employment, communication with spouse, or providing food for small children.
• Article from LaserWorld about the laser:?
• Great Thread from HoloWiki:?
  • page 1 has good pictures of internals
  • page 4 has a good schematic by "soda" posted?Feb 24, 2019 4:13 pm
• Thread from Laser Pointer Forums discussion the laser in detail, with picture of internals:?
• A brief discussion of Peltier cooling of the PL530:?

I have one of these modules but have been a bit hesitant to use it until I have a proper cooling setup. I'll let you now who it goes. Since Kwaoo has posted all the schematics on his site, I will mock them up in KiCad and produce a PBC/gerber file to send to OSHpark so I can try this out. Although I need to take a closer look at the site to see what kind of license he has for these designs. If it's open source, I'll post the KiCAD files.

All the best,

Soren

Link to newly reorganized and uploaded general radiation detection, XRF etc. papers and references.



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