The purpose of this project is to expand upon my previous project, since my knowledge has expanded as well, this Raman probe will provide a spectral resolution of approximately 15 cm-1.This project will also be utilizing a radical new design concept inspired by the work of Eduardo H. Montoya R, Aurello Arbildo L. and Oscar R. altuano E. in a scientific journal available here at; http://article.sapub.org/10.5923.j.jlce.20150304.02.html I will be utilizing a DSLR Nikon D3400 24.2MP Bluetooth camera as my detector, a reflecting mirror and 1800 mm/gr diffraction grating (holographic) as the spectrometer and two fiber optic cables.
Update: 02/17/2018: 2:04:AM
This is my Nikon D3400 DSLR camera that I will be using as my Raman detector:
Specifications for the Nikon D3400:
Effective Pixels (Megapixels) 24.2 million.
Sensor Size. 23.5 mm. x 15.6 mm.
Image Sensor Format. DX.
Storage Media. SD. SDHC. ...
Top Continuous Shooting Speed at full resolution. 5 frames per second.
ISO Sensitivity. ISO 100 - 25,600.
Movie. Full HD 1,920x1,080 / 60 fps. ...
Monitor Size. 3.0 in.
After some careful research, I have changed the fiber optic cable package kit to the one you see above because it is clear from documentation that 200um fiber core is certainly the right size for Raman spectroscopy, which was brought to my attention from another user's comment on my page...Thanks :)
The figure below is the collimation kit for the exit point to the spectrometer, this is pricey @ around $200.00 US but there is NO work around on this, even for a low resolution Raman probe @ 15 cm -1, this and the 2nd figure must be incorporated!
This is the low-insertion loss cable that attaches to my laser collimation tube assembly that fit to the front face of the probe.
Below is the blueprint drawing, which is also in the build instructions.
I will present far greater details about this project soon...
*note, the 88mm length of the probe is not coincidental, this is the focal length of my laser line coming from the laser collimation tube assembly.
This update includes a re-designed Raman Probe (needed because I had to widen the slot for the Raman filter,) and redesigned the re-focusing lens to accomodate the 13mm doublet lens.
Tessallation - Netgen/very fine.
I had to tweak my probe design once again after some research, and readjusted the distances from the front fiber port to the cuvette holder and the Raman edge filter (or optional Notch filter,) this also forced me to modify section 1C of the laser collimator tube assembly which I will be uploading those specs soon.
I have verified my measurements and focal distances using my mock prototype enclosure assembly and laser collimation tube assembly. I am presenting my data as my 1st official recorded test (DSLR0012[1a]). Below is the plot data and spectral image of the laser scan ( Aries 532nm green laser/150mW/DPSS/CW) and the FWHM data.
Also I am including the measurement drawings showing the exact placement and focal distances for the mirror and diffraction grating since these where not stated in the original quoted paper.
Excerpt from: “A Homemade Cost Effective Raman Spectrometer with High Performance”
Journal of Laboratory Chemical Education
2015; 3(4): 67-75
Author’s: Eduardo H. Montoya R.1, 2, Aurelio Arbildo L.3, Oscar R. Baltuano E.2, 4
“Beside this, it has to be noted that spectral resolution is not constant along the entire spectrum, being progressively worse towards the left and right sides of the focusing point. This undesired effect is connected with the fact of that it was not possible to keep the whole spectrum well focused.”
“The light travels through a 1.5 meters fused silica fiber optic with 200 micron working diameter, which illuminates a flat mirror. The light is reflected onto a 50 mm by 50 mm reflective holographic grating (1200 grooves/mm).”
“The sample is illuminated with the doubly filtered light of a bright inexpensive green laser pointer, with a nominal power indicated as “< 100 mW”.
In this presentation I want to focus on the 4 most prominent mistakes in this research paper that prevented the authors from resolving several Raman peaks and why. They are highlighted in Italics.
The first is their spectral focusing problem, in figure 1 I show two spectral images of my CFL lamp (6500K,) the red plot shows sharp focused peaks and higher detail, while the blue plot is lacking in detail and has more subdued peaks. This was something either not covered in their presentation or just not bothered with.
Two, they used a “flat mirror” as their reflective medium, big mistake, why? Because there is no way to collimate and focus the incoming light, using the flat mirror causes the image to spread in a linear fashion (un-focused and blurred.) So, when it gets to the diffraction grating half of the spectral image is lost and 40% is lost again because of the grating itself!
Three, according to my research and experience, an 1800 mm/gr holographic grating works best for Raman spectroscopy under these circumstances and for the most part others as well. A 1200 mm/gr grating mainly resides in the UV/VIS range of the spectrum as far as spectral peak resolving is concerned.
Four, and a very important factor I might add, is the type of laser used. Yes, one can use a laser pointer and it will work, the problem is, noise, yes lasers exhibit noise. So, the state they used a laser pointer of <100mW, but didn’t really state the exact value, I use an Aries 532nm 150mW Portable laser (DPSS/CW,) so it is of excellent quality.
Now, in figure 2, I have three plots, using my Aries 150mW laser, 2 are focused and 1 is not. The focal lens I am using is the same one that I will be using in the rear fiber optic port (13mmachromatic coated doublet, F=50mm.) You can clearly see from looking at the blue plot (un-focused,) a very blurred and dirty image. The red, test1C is, focused, test 1A I had to re-align the diffraction grating.
This was all done with the proto type enclosure set up I constructed to simulate the actual Raman set up. I did this to ensure that I have all my focal distances correct and angles exact.
Another important point is the Focal distance of the entrance fiber port, which is 7.5mm, it is 47mm from the rear fiber port to the 1st mirror (centerline,) so, we calculate 7.5mm travel to the 13mm doublet lens, from the lens to the 1st mirror is 34mm, well within our focal range. the 1st mirror is our 50 x 6 x 50mm concave silver coated, with an F=100mm distance, so we are good there also, because distance between 1st mirror and diffraction grating centerline is 94mm.
I am presenting figure 3 because it represents all 3 laser scans as they appear without zooming in, its just an interesting note because often you cannot distinguish important details in spectra until you zoom in on their peaks or base.
*Update* This is for those who have asked what type of fiber optical core I am using:
Thorlabs' SM300 fiber consists of an undoped, pure silica core surrounded by a depressed, fluorine-doped cladding. Since these fibers do not contain germania (GeO2), which causes electronic defects and color centers associated with the Ge-O bond, the primary cause of photodarkening is greatly reduced. As a result, power handling in the blue region is increased from several milliwats to several watts. The transmission-limiting effects caused by other nonlinearities (e.g., stimulated scattering) or even thermal damage are also increased over those of a conventional silica fiber doped with germanium. In the UV region, the SM300 will still exhibit some photodarkening, but will have superior performance compared to conventional fibers. http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=949
This is a very crude set-up but it simulates the concept and my design.
Right next to the camera U can see my laser tube collimation prototype, I used this to shoot through the slit to the 1st mirror (concave focusing mirror,) @ 45 deg. and 88 mm length to the diffraction grating, which I readjusted to about 27 deg. (I used a plastic protracting ruler). The DSLR camera settings are annotated on the plot below.
Success! The plot above illustrates the laser collimated beam (with just a little noise, I didn't do a thorough cleanup,) processed using RSpec, the peak is very sharp and FWHM is @ 2.1nm. My calculations predicted a resolution factor of 2.216nm for a 200um slit width and a 1200 mm/gr.
Below is the FWHM data from Spectragrpyh with the actual accurate data.
Below are the camera's settings at the time of spectral capture.
Close up view of collimation mirror as it relates to the diffraction grating.
Close up of camera focal lens sitting in the cut-out of enclosure. I used my Roto-Zip tool cutter to cut the section out properly.
I’m breaking a little protocol today and talking about my research over the past two years. I started this venture around the beginning of January of 2015, sounds benign enough but I had a very close friend, who had recently lost a relative to which they thought was under suspicious circumstances.
A situation that for all intents and purposes, might rise to a dime store mystery novel. (no joke!) if I was inclined with the skill to write such things, I probably really would, anyway, without getting into the personal of it all, there was a “white powdery” substance in a bottle that should not have been in there…yeah, getting it now? This friend asked me if there was any way to find out what it was and I said yeah you can take it and get it analyzed, it’ll cost some money but it can be done.
For whatever reason, that route was unacceptable and I wasn’t going to push it so, I said give some time and I’ll see what I can do. Having an engineering and chemistry background helps in matters of the scientific persuasion so, I figured I could maybe buy a spectrometer and do the job myself, ha ha ha, yeah right! I’m retired, not rich, turns out though, I came across a website called Public Lab where you can learn how to investigate environmental concerns and use inexpensive DIY spectrometer’s and techniques. So that’s where I bought my first spectrometer kit. Only problem was that, I didn’t realize the scope and magnitude that was about to unfold before me.
The adventure was on though and I was hook-line and sinkered in! Even with all my research, upgrades and intense experimentation, I could only at best (and only with 60 percent probability,) determine what the original “white powdery” substance was, which for privacy’s sake I will not disclose here, my friend though, was so very grateful that I did try, and I was glad I did also. What a grand learning experience that was and still is, and from that, is where the inspiration for the DAV5 V2.01 Raman spectrometer has come from.
Even as I’m writing this, I think of the times of frustration and disappointment, mainly at myself, wanting to just give it up, “man why am I doing all this?” 12 – 15-hour days, and for what? I keep forgetting procedures, the order of things, etc., why? well having a stroke several years earlier didn’t do me any favors. So, I developed a system of log books and these logs corresponded to files saved on my computer as a backup. I had to literally annotate just about every little thing I was doing, I have a short-term memory problem, but if I have a log of my previous actions I can recall it well.
In a lot of ways, my recovery was like an athlete sustaining a major injury rehabbing for 3 years to get back to a sense of normalcy. Still not all the way there yet!
I have now over 1000 pages of notes and research, each page has its own tab with a short description of that page, and it’s worked out very well, (this way I can refresh my memory on the details of each day,) So this is the adversity I must battle with daily, and I do it because I believe what I’m doing is significant on many levels, one being, the story I started at the beginning. I started to come to the realization just how expensive and far out of reach this technology really is, not just to your average citizen scientist or serious hobbyist, but to people I was encountering everyday over on Hackaday.com
I was interacting with brilliant individuals from Columbia, Slovakia, Chezania, and many others, all building incredible devices, with specific purposes in mind. Most of them out of sheer necessity, hey, when you are unable to afford a top of the line up to date piece of technology, your only choice is…to make it!
This is the “hook” the inner beauty of all this, yeah, I...
This is the complete bill of materials for the Raman probe, hardware included. The 3D material used for my project is Nylon PA12, since I do not have a 3d printer myself, I have to source my parts out to Sculpteo, but you can use any material you want, just keep in mind that I use Netgen tessellation (very fine,) which gives me a tolerance of 0.1mm.
My 2nd attempt using Blender, this time I was able to integrate Luxrender 1.6.0 as an addon, so now I can render images using a lot more fancy materials and controls :) This is draft V 01.0C for the 3D printed Raman Probe assembly, and I also included a platform I built custom made just for this probe.
A little "dirty" in some spots but that's only because I'm still learning how to use the program :)
This is the laser collimation tube assembly guide alignment block.
Spectrometer enclosure assembly
This is the complete enclosure assembly with the draft drawings.
Platform for Raman Probe Assembly V 01.0b
This is the draft drawing for the V 01.0b Platform with M4 setscrew which secures the Raman probe to the base of the platform. The holes on the platform are there on purpose for 2 reasons, 1 for cost savings on material when 3d printing and 2 they are 13mm in dia. which are standard for test tubes.