Raman Gas Analyzer - One Decked Out HeNe with Way Fancy Stuff

[madmacmo]

Raman Gas Analyzer - One Decked Out HeNe with Way Fancy Stuff
________________________________________
Edit: Title Changed from "HeNe, Power Supply & Un-Identified Complex Control Stuff"

HENE LASER ASSEMBLY UNTESTED 12 VOLT LASER POWER SUPPLY - BIN US $60.00 + $20.00 Shipping
[And I am in no way associated with this eBay listing - I just found it to be of interest]

This is a truly special purpose HeNe with over the top controls, REO mirrors, optics [possibly having a Brewster prism], heat sinks, gas sample delivery vinyl tubing, filters and desiccant containers (clear plastic cartridges with pellets), etc.




Edit: This is from Sam's Laser Faqs - The Ohmeda Raman Gas Analyzer REO One-Brewster Laser
Quote:
This unit is somewhat similar to a particle counter in that there is a very high-Q 1-B HeNe laser tube with a second HR mirror some distance away. In between is a space for an absolute filtered unknown gas to pass through with 8 "viewing ports" - 4 on each side. Sensitive photon counting detectors would normally go behind individual narrow band filters, each with a different center wavelength.
Raman spectroscopy is used to identify gases by passing a laser beam through the unknown sample. Raman scattering results in a shift toward longer wavelengths depending on the atomic/molecular composition of the gas. By measuring the intensity of the Raman scatter at several longer wavelengths, the gas composition can be determined. For these units, the relevant gases were apparently N2, O2, and N2O based on "linearization constants" printed on a label on the lasers.

To get any sort of sensitivity, the beam must be high power since a very small percentage of photons actually undergo the Raman shift. For the Ohmeda unit, this is achieved by utilizing the intracavity power between 2 super polished HR mirrors and super-polished Brewster window. While I don't know for sure what the intracavity power should be, based on tests of the mirror reflectivities and output power with an external OC mirror with known reflectivity, it is at least several watts and could be over 100 W when using the original external HR mirror!
Quote:
The 632.8 nm intracavity power would no doubt be greater without the prism but that's where it gets interesting. With the [Brewster] prism in place, the wavelength is tunable with both orange wavelengths being easily selectable for 2 of the lasers. (The 604.6 nm orange line is not present in Laser 3 for unknown reasons, but probably due to mirror reflectivities.)

Here are the stats for three similar laser assemblies with different dates of manufacture:

Laser 1 (Ohmeda PN 6090-2000-513, 15-Jul-04, Tube #IB826-5, S=0.35, T=0.57, Laser Power=3.91. REO tube MN SB/1M/BW, S/N 2856-2204-1063):

Power from <------- External Mirror -------> Intracavity
Wavelength Internal HR Type Reflectivity Power Power
--------------------------------------------------------------------------
632.8 nm 5 uW 60 cm OC 98.0% 5,400 uW 0.25 W
" " 32 uW SP-084 HR 99.966% 500 uW 1.5 W
" " 122 uW REO HR 99.9984% 186 uW 6.0 W !!
611.9 nm 166 uW " " --- 1,140 uW ---
604.6 nm 14 uW " " --- 0.280 uW ---

Laser 2 (Ohmeda PN 6090-2000-513, 20-Feb-03, Tube #I2348-8, S=1.37, T=0.53, Laser Power=3.45. REO tube MN SB/1M/BW, S/N 1151-0603-911):

Power from <------- External Mirror -------> Intracavity
Wavelength Internal HR Type Reflectivity Power Power
--------------------------------------------------------------------------
632.8 nm 381 uW REO HR ??? 141 uW ???
611.9 nm 1,120 uW " " --- 93 uW ---
604.6 nm 710 uW " " --- 32 uW ---

Laser 3 (Ohmeda PN 6090-0803-507, 9-Aug-02, Tube #2890-3, S=2.57, T=0.37, Laser Power=2.0. REO tube MN SB/1M/BW(HS), S/N 6093-0501-607):

Power from <------- External Mirror -------> Intracavity
Wavelength Internal HR Type Reflectivity Power Power
--------------------------------------------------------------------------
632.8 nm 864 uW REO HR ??? 147 uW ???
611.9 nm 2,080 uW " " --- 29 uW ---
604.6 nm 0 uW " " --- 0 uW ---
Attached Thumbnails

 

[Meatball]

What Sam says about those systems is true. I saw a RAMAN system in our lab on which the HeNe say's 50W max on the label.

 

[ped]

Any chance you could do hi res pics of this and upload?

 

[LSRFAQ]

IF a LPFer buys it, I will buy the included avalanche photodiode array from you.

These are a prism tuned hene. The brewster window is soft sealed, so they often are low power or dying.

Both ends have high reflector mirrors, so you need a output coupler or need to be happy with the leakage off the brewster window as your output.

The intracavity power is huge, but the second you mount a output coupler on it, its a normal 1-2 mW hene.

I know where he buys them from. Its a local surplus company. Every one I have seen there, and they get many of them, is low power or dying.

What you will get for your money is a nice hene supply, a hene grade littrow prism, and a 7mm hene mirror that will support 640 nm

Steve

 

[Meatball]

^^And apparently a useful photodiode array

 

[Dr_Evil]

I was just looking a couple couple of these on Sam's sales page. It seems like they are nice gas lasers if you get a working one.

Sam's Classified Page

 

[LSRFAQ]

^^And apparently a useful photodiode array

Only if you like tiny photodiodes that need biased at 90V to do any useful work. They are very fast, but the active area is very, very small. So you need a whopping optical signal to get any work done. They have a serious set of light collection telescopes in the HENE Raman gas analyzer. Might make nice collimators for laser diodes.

I need to one to replace a diode at work, and there are six or eight of them in the above mentioned array, on a TE cooler. I gave mine away to other laser folks, thinking I'd never need a cooled 100 Mhz avalanche photodiode, because I'd never do fast work. Now I work on ultra fast systems and need one piece.

The photodiode was made by RCA in the 70s and 80s and is no longer made. Its a pretty much useless orphan part when you DON'T need one. There is not much in the way of commercial stuff, made now, in the same package. One piece frees up a very expensive Newport module for other things.

What happened to the old diode you may ask? A former colleague, hoping to get more signal, focused a sharp pulse into the diode, by adding a lens. It fried a cool looking diffraction pattern into the glass lid of the photodiode. So now I have almost no signal to work with. This laser dumps out 800 nanometer, 120 femtosecond pulses, 300 mW average power, which is ironically the same laser used to make those tourist shop laser carved sculptures in the crystal blocks.

So I'm just looking for the correct replacement part to fit in the holder. I'd just buy the &^*$ thing, but no one makes the correct metal can package any more.

Steve