Re: "Colorimeter"

On 23/05/2025 10:04, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:
 

On 5/21/2025 6:19 AM, Liz Tuddenham wrote:

Don Y <blockedofcourse@foo.invalid> wrote:
>

Sampling jitter within a window corresponds to spectral resolution;
the more jitter, the wider the range of wavelengths potentially
involved in the sample (over time).  As sampling the detector
is a discrete time event (the interval between samples being the
width of the window), how frequently you do this further defines
the spectral resolution.

>
I was assuming very fast sampling so that the presentation of each line
was captured by many samples, that way the software could sort it out
over a large number of repeated passes.  Keep the hardware simple and
let the software deal with the errors if it can be given enough data to
start with.

>
Are you expecting to frequently sample the entire spectrum in each
"pass" ("revolution")?  Or, walk the sampling window up/down the spectrum
in stages?

 I was expecting to sweep the whole spectrum at high speed many times,
then analyse the captured data.  Television-type technology could easily
cope with that data rate from a single photocell.

That was how the early Hardy spectrophotometers did it back in the day when photomultiplier tubes were large rare expensive beasts surrounded by insanely high voltages and lots of precision megohm resistors.
I still have a few small mirror bits from taking one apart long ago.
Today with ultra cheap LCDs and some with piezo shift facility the trend is towards making a 2D spectrum on a standard rectangular CCD sensor with high dispersion on one axis from a grating and low dispersion in the other from a prism. Mapping the entire spectrum into a 2D pattern.
Echelle spectrograph is the keyword you want.  Oxford instruments make rather high end ones but you don't need anything so fancy for this.
https://andor.oxinst.com/learning/view/article/echelle-spectrographs-a-flexible-tool-for-spectroscopy
Solar spectrum measured conventionaly but displayed in that style because it allows it to fit more easily on a page here:
https://noirlab.edu/public/images/noao-sun/

A small gas-filled discharge tube, pulsed by an ignition transformer,
would suffice for non-critical calibration.

A neon lamp or a mercury vapour one will do for a wavelength reference.
It's hard to get a sodium lamp small enough and at a good price.
--
Martin Brown