# hydrogen gas spectral lamp question

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#### Don Lancaster

Jan 1, 1970
0
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 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss: http://www.tinaja.com/whtnu.xml email: [email protected] Please visit my GURU's LAIR web site at http://www.tinaja.com O #### Owen Roberts Jan 1, 1970 0 They are broadband. Usually a high pressure sodium lamp or a low pressure mercury or helium lamp. Sounds like your missing a filter. Steve G #### George Herold Jan 1, 1970 0 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
Synergetics   3860 West First Street   Box 809 Thatcher, AZ 85552

Please visit my GURU's LAIR web site athttp://www.tinaja.com

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.

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#### Don Lancaster

Jan 1, 1970
0
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

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
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552

Please visit my GURU's LAIR web site at http://www.tinaja.com

B

#### Bill Sloman

Jan 1, 1970
0
Its a lapmaster CP-1 intended for use with optical flats up to twelve inches
.
LAP5-0010-004-0161

http://lapmaster.thomasnet.com/item...chromatic-lights-1132/lap5-0010-004-0161-3261

which tells you absolutely nothing about the lamp.

http://lapmaster.thomasnet.com/requ...er=10&categid=1198&prodid=3001132&itemid=3261

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.

B

#### Bret Cannon

Jan 1, 1970
0
"Don Lancaster" wrote in message
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

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
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552

Please visit my GURU's LAIR web site at http://www.tinaja.com

I have no direct experience with these lamps, but the visible lines of
atomic hydrogen are the Balmer series with wavelength of 656 nm, 486 nm, 434
nm, etc.., but I don't know if the relative intensities of these lines are
such that they would appear to be orange. I would guess that there should a
small amount of H2 that is efficiently dissociated by the helium metastables
produced by the discharge.

Is there enough light to look for line structure by diffraction from a CD?

Bret Cannon

M

#### Martin Brown

Jan 1, 1970
0
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.

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

What happens after their normal hundred hour lifetime?

Steve

M

#### Martin Brown

Jan 1, 1970
0
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. 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. G #### Glen Walpert Jan 1, 1970 0 Unfortunately this is normal. 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. Its a lapmaster CP-1 intended for use with optical flats up to twelve inches . LAP5-0010-004-0161 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.

M

#### Martin Brown

Jan 1, 1970
0
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.

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

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.

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