hydrogen gas spectral lamp question

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We picked up an outrageously expensive supposedly monochromatic light  
source that was intended to light up a 12 inch optical flat.

It lights up ok, but I sort of expected to see a "pure orange" color.
Instead it is white with a strong orange tint.

Is this normal or did some helium leak out of the bulbs?

What happens after their normal hundred hour lifetime?

Replacement bulbs are likely to cost $1000 each.



--  
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
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Re: hydrogen gas spectral lamp question
They are broadband. Usually a high pressure sodium lamp or a low
pressure mercury or helium lamp.  Sounds like your missing a filter.

Steve

Re: hydrogen gas spectral lamp question
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one: (928)428-4073
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Hi Don,  I don't know about Hydrogen lamps.  But we make a Rb lamp
with Xenon as a 'starter' gas.  I've been getting new quotes for the
interference filter (IF), so I was just looking at the spectrum
again.

For Rb there are the two D lines at 795 and 780nm., and then a whole
bunch of other peaks, mostly at longer wavelength.  The IF has to pick
off one of the D lines, and then the rest of the 'crud'.

I've used the lamp with IF to look at 2" optical flats.  (I had to use
a CCD camera to see the 795 line... PITA.)

George H.


Re: hydrogen gas spectral lamp question
On 16/10/2012 9:29 AM, Don Lancaster wrote:
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What was the spectral line supposed to be?

IIRR the main users of monochromatic light sources are people who do  
atomic absorption analysis

http://en.wikipedia.org/wiki/Atomic_absorption_spectroscopy

who rely on hollow cathode lamps (cheaper) and electrode-less discharge  
  lamps (more expensive, and need more expensive excitation, but produce  
a narrower emission line).

What sort of lamp do you think you have got?

Bill Sloman, Sydney

Re: hydrogen gas spectral lamp question
On 10/15/2012 7:30 PM, Bill Sloman wrote:
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Its a lapmaster CP-1 intended for use with optical flats up to twelve inches
.
LAP5-0010-004-0161


--  
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
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Re: hydrogen gas spectral lamp question
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uce
hes

http://lapmaster.thomasnet.com/item/accessories-flatness-instruments-1198/m
onochromatic-lights-1132/lap5-0010-004-0161-3261

which tells you absolutely nothing about the lamp.

I could have asked for more information

http://lapmaster.thomasnet.com/request/accessories-flatness-instruments-119
8/monochromatic-lights-1132/lap5-0010-004-0161-3261?&plpver10%&categid=
1198&prodid30%01132&itemid32%61

but only at the expense of filling in a very long form.

I suspect that they are charging the earth for a not-very-expensive
lamp, and hope to be able to keep on ripping off the gullible by
hiding the exact nature of wahtever it is they are selling.

--
Bill Sloman, Sydney


Re: hydrogen gas spectral lamp question



On 10/15/2012 7:30 PM, Bill Sloman wrote:
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Its a lapmaster CP-1 intended for use with optical flats up to twelve inches
.
LAP5-0010-004-0161


--  
Many thanks,

Don Lancaster                          voice phone: (928)428-4073
We've slightly trimmed the long signature. Click to see the full one.
Re: hydrogen gas spectral lamp question
On Mon, 15 Oct 2012 21:38:42 -0700, Don Lancaster wrote:

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Unfortunately this is normal.

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Same as any similar design low pressure gas discharge tube, evaporated  
electrode material traps gas on the tube walls and output gradually  
declines, but 100 hours is a ridiculously short lifetime.  The lamp is  
essentially a neon sign folded into a regular grid instead of a sign and  
filled with an alternate gas mix, powered by an ordinary neon sign  
transformer,  The far superior mercury lamp monochromatic illuminators  
are made the same way, and I know of some of them that ran almost 40  
hours per week for nearly a decade without any problematic loss of  
output; about what you would expect from a good neon sign.

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I have one of those that I got at an auction, only to recall after  
getting it home that a former employer once described it as a nearly  
unusable POS, speculating that a competitor sold it to their customers to  
prevent them from inspecting their parts, while lamenting the loss of the  
company which manufactured his large yellow-green mercury sources, which  
were large enough for his 14" flats and filtered to a single mercury  
line.  I forget the exact wavelength, but when viewed from a practical  
~20 degrees from perpendicular you saw 10 microinches per band to as  
close as you could read it (~1/20 band).  It produced far more distinct  
bands than you will ever see with the lapmaster due to the the very low  
contrast you get from it's unfiltered output.  Also, if you use the base  
of the lapmaster to support your work (as it is designed to be used) the  
heat from the transformer can cause significant workpiece and flat  
distortion.  You can remove the lamp from the base to avoid this problem.

Last time I looked Edmund was selling smaller filtered mercury line  
inspection illuminators, in a proper stand leaning ~20 degrees forward of  
vertical, for less than $1000 IIRC.

For those not familiar with this method of inspection, you are looking at  
the reflection of a diffuse source from the entire surface of a polished  
work surface under the flat interfering with the reflection from the  
flat, so the source needs to be significantly larger than the flat and  
coherent over the length of the gap between flat and work (<.001") but  
preferably not coherent between the work and the top of the flat (~ 1" or  
more).  After gently setting one side of the flat on the work and then  
lowering the other side onto the air film you can let go of the flat and  
wait for the air film to squeeze down to around a 10 band wedge, where  
band curvature (flatness) is most easily read.

If I knew where to get the large mercury line filters I would get one and  
have a neon sign maker refill the tube in my lapmaster with mercury.  But
I wonder if you could do as well today by illuminating a sheet of ground  
glass or an LCD backlight diffuser with laser diodes at lower cost.

Re: hydrogen gas spectral lamp question
On 16/10/2012 17:10, Glen Walpert wrote:

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Presumably it just has to be good enough to isolate the wanted green  
line. One of the Schott colour glasses might do eg

http://www.schott.com/advanced_optics/english/our_products/filters/overview/filteroverviewdetail_bandpass_vg.html?so=uk&lang=english

Or maybe Lee stage filters which are much cheaper. Jade #323 isn't far  
off. Hard part is removing 578 & trace sodium D-line output.



--  
Regards,
Martin Brown

Re: hydrogen gas spectral lamp question
On 15/10/2012 23:29, Don Lancaster wrote:
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Why would you expect orange?  That would be a helium or sodium lamp.

A hydrogen lamp typically looks pale pink like the red 656nm and blue  
486 lines with a hint of violet 434/410 some continuum and whatever  
other weak lines Penning mixture contributes - a CD spectrograph should  
easily show you what you have unambiguously.  eg

http://www.chemistryland.com/CHM151S/07-Atomic%20Structure/Spectra/HydrogenLampAndSpectrum.jpg

If it doesn't show the hydrogen Balmer lines then it isn't hydrogen!

Amateur astronomy filters are available that will isolate the cyan  
H-beta and red H-alpha lines pretty well. In fact for the latter  
colloidally coloured low pass glass will probably do the job.

A helium plasma does look pinker shade orange.

http://www.sciencephoto.com/image/1962/530wm/A1500391-Helium_spectra-SPL.jpg

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Why are you using Hydrogen as opposed to a much cheaper Sodium lamp?

--  
Regards,
Martin Brown

Re: hydrogen gas spectral lamp question
Oh, I just looked at the web site.  I've seen those. HP sodium lamp,
no filter. Na lamps for that cost 35-100$ at McMaster Carr.

Steve

Re: hydrogen gas spectral lamp question
On 16/10/2012 12:17, Owen Roberts wrote:
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It should be a low pressure SOX sodium lamp. The doublet line isn't  
ideal but is plenty good enough for most optical engineering purposes. A  
12W lamp ought to be more than enough light they are incredibly  
efficient the big ones still hold the record in lumens/watt.

These days I'd have thought a semiconductor laser and beamspreader or  
diffuser was more convenient and a better monochromatic light source.

--  
Regards,
Martin Brown

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