Reference visual wavelength to measure accuracy on spectrometers.? - Page 1
Forum section: electronics / projects

author: DaneLaw
author_rank: Frequent Contributor
timestamp: December 06, 2023, 09:24:54 pm
content: An aspect of a reference wavelength in the visual spectrum (375nm to 790nm) to measure accuracy on spectrometers.Got some different spectrometers, all based around CCD slit-sensor, so looking for a source in the visual spectrum that can be graded down to 1 angstrøm (0.1nm) and have something tangible to compare the meters against.Have tried with some of the laser diodes I got and coherent light, but they will vary up to many nanometers, depending on current and temperature, and even on the spec sheet there is usually a +/- tolerance.

author: Someone
author_rank: Super Contributor
timestamp: December 06, 2023, 09:41:34 pm
content: https://resources.perkinelmer.com/lab-solutions/resources/docs/tch_validating_uv_visible.pdfMercury lamps are a cheap solution, available surplus too.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 06, 2023, 10:14:13 pm
content: With a little guesswork in the lines and skipping some one can use a fluorecent lamp.

author: TimFox
author_rank: Super Contributor
timestamp: December 06, 2023, 10:38:51 pm
content: A sodium-vapor bulb should show the yellow "doublet" at 588.9950 and 589.5924 nm, useful for measuring theresolutionof the spectrometer as well as calibration accuracy.

author: jmelson
author_rank: Super Contributor
timestamp: December 06, 2023, 10:41:21 pm
content: Quote from: Kleinstein on December 06, 2023, 10:14:13 pmYes, typical fluorescent lamps put out very distinct Mercury lines. There are two closely-spaced lines in the blue-green, and two in the red region.Also, the 405.6 nm line is a bit beyond the visual sensitivity, but should be fine for calibrating a sensor.Jon

author: zrq
author_rank: Frequent Contributor
timestamp: December 06, 2023, 11:07:51 pm
content: The mercury UV lamps, in combination with neon bulbs are the perfect wavelength calibration sources. One can find wavelength numbers with many digits on NIST's website (https://physics.nist.gov/PhysRefData/Handbook/element_name.htm, look at the strong/persistent lines list).The only issue is the UV disinfection lamps may not be available to European consumers as they are not safe, although I can get them in Switzerland from French amazon as aquarium disinfection lamps. Also note that ordinary household glass is capable of filtering out the most harmful 254 nm UVC light from mercury lamps(do at your own risk).

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: December 06, 2023, 11:46:51 pm
content: Quote from: DaneLaw on December 06, 2023, 09:24:54 pmYou could try the ruby R1 and R2 lines, at 692.9 nm and 694.3 nm (at room temperature and pressure).In the past I've bought small quantities of ruby spheres, various sizes (1 to 3 mm dia.) from Sandoz:https://sandoz.ch/

author: DaneLaw
author_rank: Frequent Contributor
timestamp: December 07, 2023, 01:33:22 am
content: Thx guys for the examples.Yes, a good mercury or deuterium bulb would be nice to have, but most of these short-arc mercury HBO bulbs seem persona non grata here in Europe/EU, likely regulation, so a surplus lamp shop is likely the best bet.Got some of the older fluorescent spiral lamps from brands like Phillips (Tornado ESaver 15W bulb posted from one of the spectrometers) it got two main peaks at around 546.5nm and 612nmAlso tried with some of these YAG doped DPSSL (lasers) as they do seem to have a narrow span, around 532nm, and don't seem to drift a lot even though they are highly temperature dependent, but unsure what tolerances cheap 532nm DPSS lasers got..Even vendors selling YAG doped DPSSL 532nm lasers for Raman spectroscopy, don't seem to specify nm-tolerances.https://hubner-photonics.com/product-category/laser-wavelength-guide/532-nm-laser/This vendor does state tolerances 531.9 to 532.3 (0.4nm) though on a +4000US DPSS 532nm/200mW casette-systemhttps://integratedoptics.com/cw-lasers/532-nm-lasers/532-nm-laser-dpss%3B-free-space-matchbox-2Though, have no idea what tolerances cheap 532nm DPSS laser from the far east can vary, but for coherent light. these doped crystal-based DPSS lasers centered around infrared diodes as kicker. does seem to operate with a smaller span than native single & multimode diodes.Thorlabs, rates their single 532nm low wattage DPSS laser diodes (diodes that cost around 160 to 200euro each) with a tolerance between 531 to 533nm (2nm) so there seems to be a bigger tolerance, than what I took for granted on infrared diode-pumped solid states diodes.https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=5597A lot of good informative articles posted above, thx..will see if there are is any examples I can follow suit with the remedies I already have, and to what extent holmium oxide glass can be used.Would a standard old-school haze blue/purple Plasma ball have prominent peaks from the noble gasses used.?

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: December 07, 2023, 03:34:38 am
content: You might find a DIY integrating sphere useful for your needs: fit your spectral line source (e.g lamp) to the source port, detect the lines at the output port.That way you can test your sources and spectrometers in a repeatable way. I've seen some hobbyists use cookware (dishes) and white paint (TiO2) for the construction.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 07, 2023, 03:40:58 am
content: I'd think a HeNe tube would do the trick.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 07, 2023, 08:55:37 am
content: Quote from: DaneLaw on December 07, 2023, 01:33:22 amThe plasma ball should also have pure spectral lines from a gas - just have to check which gas (e.g. He, Ne, Ar, N, H, ..).The spectrom shown for the fluorecent lamp looks rather broadend, e.g. from a not so well resolving spectrometer (e.g. slit too wide open). Normally there is a mix of very sharp line from mercury and still sharp lines from a mix of phosphores. For the phospores there is some guesswork on which ones are which, but there are lists of the common and efficient ones. Using a lower RA lamp may give a simpler spectrum.With the limited resolution one may want a source with fewer lines at a time.

author: LaserSteve
author_rank: Super Contributor
timestamp: December 07, 2023, 05:17:32 pm
content: Nd:Yag or Nd:Yvo4 in a dpss laser has a gain bandwidth of 1.4 nanometers. It has a peak in the gain curve on its shorter wavelength side and a tiny but noticeable spike off to the right. Nd:glass is worse, 20 nm wide when excited by a flashlamp, that 20 nm is great for amplifying ultrashort pulses, which is why it is still made.A slight bonus in a older green DPSS pointer or green DPSS may be a stray laser emission at 543.5 that is narrow, but will be faint.NaCl tossed in a gas stove flame or in an alcohol solution can be used in a pinch. Strontium Chloride also works well.Best bet is an ordinary ne2 Neon lamp.I can tune blue and green laser diodes 4 to 7 nm with the proper reflective optics, red ones tune around 2 nanometers.That leaves HeNe, HeCad, and Argon or Krypton Ion Lasers as the stable wavelength references of choice.Steve

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: December 07, 2023, 07:34:30 pm
content: What's the reference in a Bristol 671B wavelength meter? A HeNe tube. The upper models add stabilization to the HeNe, so you can see what sort of accuracy can be obtained-https://www.bristol-inst.com/bristol-instruments-products/wavelength-meters-scientific/671-series-cw-lasers/

author: thermistor-guy
author_rank: Frequent Contributor
timestamp: December 07, 2023, 11:23:18 pm
content: Quote from: DaneLaw on December 07, 2023, 01:33:22 amInteresting. Holmium oxide glass has proven to be so stable that NIST stopped recommending recertification:https://www.nist.gov/publications/holmium-oxide-glass-wavelengths-standardshttps://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=841100

author: richnormand
author_rank: Unknown
timestamp: December 08, 2023, 03:05:19 am
content: I typically use a HeNe laser for alignment and initial calibration.Then a NE-2 neon bulb for the mid red and a mirror pointing at my ceiling fluorescent tube for the discharge lines to the UV.Between these three methods I usually get within 0.1nm and can the check linearity for the SPEX 1680B dual grating with photon counting and also the ISA with cooled intensified ccd detectors.You can buy isotopically pure neon bulbs for a reasonable price if needed.