Monochromator 101

[NobleGas]

I just got a great deal on a Bentham M300 monochromator and am trying to learn how to set it up.
I'm pretty sure I found a table showing wavelength against counter readings for a given grating ruling, but I'm struggling to find it again. I've run the dial through its range with a white light source and I can see the full visible spectrum, so I do at least know I have the correct grating for visible light work.
Does anyone have the data I need to conver dial readings to wavelength?

[mixedgas]

You need to know the grating lines per inch, the length of the sine bar, the grating order, and the TPI on the drive screw, among other things.
May I suggest using a gas discharge lamp with a line spectrum such as a neon lamp to get started? I use neon lamps, multiline argon lasers, hene lasers, mercury, argon and helium lamps, for example.
!
If you do a search for "Penray" or Pencil lamps, you can find line charts for various gas discharges. Otherwise search for "Grating Mount" to find the math. Different gratings have different constants, so there is no universal chart, it is instrument specific.
!
http://support.bentham.co.uk/support...74-m300-manual
!

Steve

[NobleGas]

I should probably have been a bit more specific! I've seen a formula for the M300 somewhere that gives the wavelength from the grating ruling and turn counter value; I don't know what grating I have, but I can eyeball the colours from a whitelight source well enough to figure out which I have as they are something like 1200, 1800, or 2400, once I find the formula of course.
Going to trawl through Bentham's site again. Thanks for the link to the manual Steve, although I had already located it.

[mixedgas]

Call them... Email them... It Never Hurts..
If you have a neon indicator lamp at home, you have 585 as the brightest line...
I cant find the table on-line. Only table in the book is the cheat sheet for "virtual" calibration with mercury lamp. If you use Google, try your search history.
Steve

[NobleGas]

I located the formula, they'd very helpfully printed it on the model identification plate! I knew I'd seen it somehwere
For reference:
wavelength = dial reading x N, where N = 1800 / ruling density of grating (lpmm); so for the 1800lpmm grating, the dial reads directly in nm.

[NobleGas]

So, looking at my value, I have an 1800lpmm grating, but the zero value is well off. This is the counter reading vs wavelength (determined by Mk1 eyeball, so probably no better than 10nm accuracy)

799 630nm red
758 580nm yellow
694 530nm green
637 490nm lilac
633 470nm blue
566 400nm violet

So from that, I would estimate that there's an offset of around 150 on the dial reading. What I will do next is find out at what reading I get white light transmission as that should be my reference point.
There are a couple of things still to fix, the main being that one of the adjustable slits is jammed because the micrometer barrel has seized.

[kecked]

Penetration oil is a miracle worker but be careful if you have painted dial as it's also great paint remover

[NobleGas]

Penetration oil is a miracle worker but be careful if you have painted dial as it's also great paint remover

I did free it off, slightly, after a lengthy soak, but it's too stiff to use; luckily I located an identical micrometer head in my collection, so I've swapped it over now.

[NobleGas]

OK, so having figured out that the dial reads in 0.1nm steps (resolution is quoted as 0.02nm which fits as there are 5 minor divisions between the major divisions), I've figured out that I have a 1200lpmm grating. My guesses as to wavelengths proved to be remarkably close, within a couple of nm except for the reds where I was a mile out (reasonable considering I have red deficient vision, AKA RG colourblindness)