hydrogen gas spectral lamp question

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.

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Many thanks, 

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

Steve

Reply to
Owen Roberts

one: (928)428-4073

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.

Reply to
George Herold

What was the spectral line supposed to be?

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

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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

Reply to
Bill Sloman

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

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Many thanks, 

Don Lancaster                          voice phone: (928)428-4073 
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Don Lancaster

uce

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which tells you absolutely nothing about the lamp.

I could have asked for more information

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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.

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Bill Sloman, Sydney
Reply to
Bill Sloman

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

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Many thanks, 

Don Lancaster                          voice phone: (928)428-4073 
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Reply to
Bret Cannon

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

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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.

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

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Regards, 
Martin Brown
Reply to
Martin Brown

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

Reply to
Owen Roberts

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.

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Regards, 
Martin Brown
Reply to
Martin Brown

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.

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 (

Reply to
Glen Walpert

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

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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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Regards, 
Martin Brown
Reply to
Martin Brown

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