• Intro to DIY Raman Spectroscopy----make money online

I've been working on a Raman spectroscopy setup in my shop for a while, and was finally able to collect some real, verifiable data this evening. Raman Spectroscopy is a technique where light is directed toward a target, and the

reflected light is color-shifted by the size and type of the molecular bonds in the target. This is a non-destructive way to determine an object's molecular structure. The problem is that the color-shifted light is many, many times weaker than the non-color-shifted light. A Raman spectroscopy setup compensates for this, and allows meaningful data to be collected.

hey everyone I've been trying to get my

Raman spectroscopy setup to work for

months and finally tonight I was able to

collect some real data so let me tell

you about it first off what is Raman

spectroscopy this is a technique where

you shine a light onto an object and

then determine things about the

molecular structure of that object by

the way that the light is reflected so

specifically if you shine a light of one

color onto an object you actually get

light of different color coming back

this seems counterintuitive if you shine

a a green light on something it's not

like you get red light back but actually

you do it just happens to be like a

billion times less intense so this this

color shift is called a Raman shift has

nothing to do with noodles and the the

reason that you can't observe is because

the normal reflection called the

Rayleigh scattering is just so much more

intense so you need a special set up to

extract this color shift from the

overpowering not color shifted light the

neat thing is that the exact way that

the color is shifted for example shining

a red light on something might actually

return a small amount of green light

will indicate the type of molecular

bonds in the structure that's being

observed so depending on the vibrational

modes and the rotational modes of the

molecular bonds you can actually get a

different color shift you actually get

sort of a fingerprint for that specific

molecule this this technique is really

useful because you don't have to destroy

the object all you're doing is shining

light on it and you can actually figure

quite a lot out about the molecular

structure so here's my set up I've got a

helium neon laser tube and this is a

small amount of optics here which I'll

talk about in a minute the sample is

here it's a polystyrene cup styrofoam

and the light travels through here into

a diffraction grating and I'm observing

it with this camera this is a DSLR

camera that I've modified by removing

its infrared filter so there's actually

nothing between the sensor surface and

the front of the camera body although I

am using the stock lens in this case

here's a schematic of my optical setup

is the helium neon laser and the beam

comes out and goes through a beam

splitter some of it goes off to this

side which is just lost we don't get to

use that part of the beam the beam

splitter is about a 50-50 beam splitter

in my case so half the beam goes through

the beam splitter into a microscope

objective and the microscope objective

focuses that beam which is basically

colonnaded down to a point and that

point is on the surface of the object

that we want to investigate so when you

focus all this down a lot of it returns

from the object and it goes back through

the microscope objective becomes

collimated again because that's the same

path the same distance in everything and

that return path hits this beam splitter

and we lose half of it again goes

straight back into the laser but half of

it comes out this way so the whole trick

with Raman spectroscopy is that you have

to get rid of the sort of activation

light like if we're shining red light

from a helium neon laser onto an object

and we're looking for this this weird

sort of color shift that's you know a

billion times less intense what we need

to do is get rid of the red light from

the laser so that we can see all the

shifted light so what we do is use a

notch filter and this is a special

optical filter that only blocks light

from the laser and hopefully lets

everything else pass the trick is that

these notch filters are very difficult

to manufacture so the one that I bought

was kind of what I considered expensive

enough already and it's not a

particularly narrow notch filter this is

about 30 nanometers wide I'll get into

it later but we lose a bit of signal

right around the laser beam because this

notch filter is it also takes out some

of our signal light we ideally like it

to just get rid of the laser itself but

this will also get rid of colors that

are not in the laser after passing

through the knotch filter we send the

light through a very very narrow slit

probably about 50 micron or something on

that order and the very narrow shaft of

light comes through here gets collimated

by a

here and then hits the diffraction

grading so the diffraction grading is

actually what separates out the

different colors into different spatial

locations and it sends those spatial

locations in a cone like this and I'm

just using this DSLR camera to to

actually generate an image so the light

comes out of here in theory focused at

infinity because it's it's been

collimated by this lens and then the

camera lens focuses that infinity down

to the image sensor here so here's my

setup here I just got a black piece of

Delrin plastic that I machined and it

slips over the end of the laser tube

like this and there's the beam splitter

that I carefully lined and then hot

glued in place that's the waste beam

that we don't get to use because it's

just shooting out the side here and if

we look in the port here if I put an

object in front of this hopefully you

can see the intensity change because

we're actually getting signal back so

what's happening is is there's light

coming out the end of this but if I put

an object here especially a reflective

one then light goes back through the

system and we get it out the port here

however what we add is this laser line

filter which blocks the laser light but

hopefully lets through that color

shifted Raman signature through here and

then we plug all that light into the

spectrometer so the way I set this up

was just to clamp it here like this and

the light goes from here this is where

the slit is located sorry about that

there we go this is where the slit is

located and the light travels into the

spectrometer here hits the diffraction

grating here and then goes into the

camera I calibrated the system by

putting the knotch filter into the front

of the spectrometer and then just

shining a tungsten light bulb through

there so what this did was give me a

full spectrum but with the knotch taken

out so I that the width of the notch

agreed with the angles that were coming

out of the diffraction grating by

actually using the protractor on the

spectrometer and this seemed to agree

pretty well with the Edmond spec sheet

of having

bandwidth of around 30 nanometers so

then having that image of the notch

allowed me to calibrate the images that

I was getting out of my camera because I

knew that notch was always going to be

about 30 nanometers wide and I made the

assumption that the entire scale was

going to be linear so something that was

the width of that knotch far away in the

image would also be 30 nanometer

separation so after a bit of fiddling I

set the whole thing up with a

polystyrene cup you know styrofoam

sitting in front of the sensor head and

collected this image so there it is you

can actually see it in fact you can even

see the colors in the lines

what's weird here is that Raman

spectroscopy works on both sides of the

excitation frequency so it you should

get infrared lines as well as lines in

the color spectrum so I took the

infrared filter off the front of this

camera so that I could see the longer

wavelength lines which are supposed to

be higher in intensity but I don't see

those for some reason nonetheless it's

pretty cool to see orange and green

light coming back from a subject that

I've illuminated only with red light so

I was pretty happy to see that I used

Photoshop to combine my calibration

image and the data image that I got from

polystyrene and did a couple of quick

calculations to figure out how many

pixels per nanometer I had my image and

then I loaded it up into octave which is

sort of a MATLAB open source sort of

copy of MATLAB and combines the image

just using averaging for now into a

graph and lo and behold after

compensating for wave number which I'll

talk about in a minute it actually looks

just like the signature that I got off

the web for polystyrene clearly I've got

sort of an offset here there's there's a

lot of noise and ghosting in the image

but the signature is very clear I mean

there's there's no doubt about it this

matches the industry accepted

polystyrene signature so I'm pretty

psyched about that and in fact going

even further

one of the biggest peaks in this spectra

is for ch2 and so taking a look at the

polystyrene molecule you can see that

there's quite a lot of CH

to going on this molecule gets repeated

over and over and over again and there's

lots of ch2 bonds which explains why

this peak is so high so what's all this

wave number stuff for Raman spectroscopy

you can use different wavelengths to

excite the source so right now I'm using

a helium neon laser which is six hundred

thirty two point eight animators but you

can use any wavelength you want in fact

a lot of Raman spectroscopy is done with

longer wavelength light because you want

to avoid fluorescence so if I use the

ultraviolet light yeah you still get the

Raman phenomenon but you also get

fluorescence which is actually a pain in

the butt because that washes out your

signal again so most as far as I know

most Raman spectroscopy is done with

longer wavelength laser diodes but I

just happen to have a helium neon laser

so that's what I'm using in any case the

wave number is a generalized format so

you don't have to tell someone oh well I

use the six hundred and thirty two point

eight and ammeter laser and you'll have

to convert my numbers if you're using a

you know 850 nanometer laser so the wave

number is just a way of comparing

results without trying to be tied to a

specific source light okay well I'm

pretty stoked about this so I think I'm

going to build this into a better system

kind of with fewer light leaks and

better optics and then try to actually

use this to collect real data you can do

quite a bit with Raman spectroscopy so

I'm going to see how far I can push this

in my home shop here okay see you next

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