Re: Looking for cheap insturments to do simple Raman Spectroscopy

[EMAIL PROTECTED] wrote:
> Greetings All
>
> I'm a newbie and I would like to experiment with Raman Spectrocopy techniques.  
> Are there cheap insturments I can use just to learn and experiment with.  (Just taking readings from different
> solids and liquids)  If so where can I find them? Can i make one like he did and if so what materials would I need
>
> Example: If I need a laser why not use one from a CD player or a Laser Pointer...

Raman is fascinating, but not cheap.

First of all you need a lot of spectral resolution. For serious work I 
would ask at least 8 cm-1 (~0.5 nm with visible excitation), for playing 
around with visible excitation, 1 nm should be enough.
The Raman efficiency goes with the 4th power of the *reciprocal* of the 
excitation wavelength. Sir Raman used a filtered mercury lamp to observe 
the scattering. Giving the prices around, maybe it would be better to 
look to visible lasers. Now, you could play with the power and 
deterction system to save on mW: if you modulate the light and use 
lock-in type amplifier than you can use even a 1 mW laser. Remember that 
laser will fluctuate in power, so you have to monitor the power and 
normalise the detected output. So visible light is great, but there is a 
drawback: you will excite a lot of fluorescence (to give you an idea: if 
you shine a green laser through a sample of Coca Cola you will se a lot 
of orange light around) and fluorescence is 10^4 more efficient than 
Raman. So you better use notch filters to kill the laser light and/or 
double monochromators.

I set up a Raman spectrometer with a 50 mW laser (~$3-4000), a double 
monochromator from LOT ORIEL (here you quickly reach the order of tens 
of K$), a couple of notch filters from Barr Associates ($1000 ea.) plus 
2 lock ins ($10000) and 2 PMTs ($1-2000) plus lenses, beamsplitters, etc 
that were laying around in the lab.

For contrast an Ocean Optics Raman spectrometer as advertised for $9999. 
I am afraid that this will be the cheapest option. Alternatively, you 
could look for some used instrument. Actually you learn much more with 
the old stuff than with the new one (and it's also a lot of fun)

Cheers,
Alessandro

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