Spectra Physics 120 HeNe / 256 Exciter problem.

[Mike Tomlinson]

En el artículo <ede84062-bdd6-486e-a8f5-6bcd27eb81f0@googlegroups.com>,
Andrew Back <arback@gmail.com> escribió:

> http://designspark.com/eng/blog/breathing-life-into-a-vintage-gas-laser

Thanks for posting that, I'd been wondering what it looked like.

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[Jon Elson]

Mike Tomlinson wrote:

En el artĂ­culo <ede84062-bdd6-486e-a8f5-6bcd27eb81f0@googlegroups.com>,
Andrew Back <arback@gmail.com> escribiĂł:

http://designspark.com/eng/blog/breathing-life-into-a-vintage-gas-laser

Thanks for posting that, I'd been wondering what it looked like.

Looking at the photos, this MAY be an external cavity laser. The
typical HeNe has the mirrors cemented right on the end of the
central glass tube. External cavity lasers have one (or rarely
both) mirrors separate from the laser tube, and generally have
Brewster windows (thin glass plates mounted at about 56 degrees
on the end(s) of the tube.) The external mirror will have
some form of adjusting screws to align the mirror.

I used to be the master mirror aligner at our lab. My technique
was to shoot a working laser through the dead laser's two
mirrors, and observer the spot on a card at the far end. Generally
you could see a 2nd reflection on the card, and try to steer them
together. if the dead laser was being excited, you would occasionally
see short flashes of lasing when you passed through the proper
alignment. As you get closer, you had to make extremely small
adjustments and then take you hands away to let everything stablize
thermally. It is a very frustrating process, but if your laser
is, indeed external cavity, then you may need to do this.

Jon

 

[Phil Hobbs]

On 3/8/2014 1:45 PM, Jon Elson wrote:

Mike Tomlinson wrote:

En el artĂ­culo <ede84062-bdd6-486e-a8f5-6bcd27eb81f0@googlegroups.com>,
Andrew Back <arback@gmail.com> escribiĂł:

http://designspark.com/eng/blog/breathing-life-into-a-vintage-gas-laser

Thanks for posting that, I'd been wondering what it looked like.

Looking at the photos, this MAY be an external cavity laser. The
typical HeNe has the mirrors cemented right on the end of the
central glass tube. External cavity lasers have one (or rarely
both) mirrors separate from the laser tube, and generally have
Brewster windows (thin glass plates mounted at about 56 degrees
on the end(s) of the tube.) The external mirror will have
some form of adjusting screws to align the mirror.

I used to be the master mirror aligner at our lab. My technique
was to shoot a working laser through the dead laser's two
mirrors, and observer the spot on a card at the far end. Generally
you could see a 2nd reflection on the card, and try to steer them
together. if the dead laser was being excited, you would occasionally
see short flashes of lasing when you passed through the proper
alignment. As you get closer, you had to make extremely small
adjustments and then take you hands away to let everything stablize
thermally. It is a very frustrating process, but if your laser
is, indeed external cavity, then you may need to do this.

Jon

The other approach is to slack one adjusting screw off all the way, jam
a screwdriver in to let you rock that axis back and forth rapidly while
slowly turning the other knob. Once you start seeing flashes, you're
close enough to switch to using both knobs.

The auxiliary laser approach is certainly needed if you're aligning the
laser for the first time after a tube change, or if somebody's been
monkeying with both of the mirrors.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Samuel M. Goldwasser]

Phil Hobbs <hobbs@electrooptical.net> writes:

On 3/8/2014 1:45 PM, Jon Elson wrote:
Mike Tomlinson wrote:

En el artículo <ede84062-bdd6-486e-a8f5-6bcd27eb81f0@googlegroups.com>,
Andrew Back <arback@gmail.com> escribió:

http://designspark.com/eng/blog/breathing-life-into-a-vintage-gas-laser

Thanks for posting that, I'd been wondering what it looked like.

Looking at the photos, this MAY be an external cavity laser. The
typical HeNe has the mirrors cemented right on the end of the
central glass tube. External cavity lasers have one (or rarely
both) mirrors separate from the laser tube, and generally have
Brewster windows (thin glass plates mounted at about 56 degrees
on the end(s) of the tube.) The external mirror will have
some form of adjusting screws to align the mirror.

I used to be the master mirror aligner at our lab. My technique
was to shoot a working laser through the dead laser's two
mirrors, and observer the spot on a card at the far end. Generally
you could see a 2nd reflection on the card, and try to steer them
together. if the dead laser was being excited, you would occasionally
see short flashes of lasing when you passed through the proper
alignment. As you get closer, you had to make extremely small
adjustments and then take you hands away to let everything stablize
thermally. It is a very frustrating process, but if your laser
is, indeed external cavity, then you may need to do this.

Jon


The other approach is to slack one adjusting screw off all the way,
jam a screwdriver in to let you rock that axis back and forth rapidly
while slowly turning the other knob. Once you start seeing flashes,
you're close enough to switch to using both knobs.

The auxiliary laser approach is certainly needed if you're aligning
the laser for the first time after a tube change, or if somebody's
been monkeying with both of the mirrors.

Cheers

Phil Hobbs

I should note that if the color of the discharge truly looks correct,
it should lase despite the problems with keeping it lit.

However, it's hard to tell from digital photos whether this is the
case. The proper color is bright unsaturated red-orange, sometimes
refered to as "salmon" color. short of spectral analysis of the
discharge glow, comparing it with a known healthy red HeNe laser
tube would be best. IF it's too pink or weak, then it's probably
leaked.

If the SP specs are to be believed, the tube voltage is way low, which
is another symptom. That really is the only way the tube voltage can
be low with the proper current. It's not a power supply fault.

I'm probably not quite motivated enough yet to measure the voltage
on the one I have here that was in a stasis field for 30-40 years and
works like new.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
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| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

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[Andrew Back]

On Saturday, 8 March 2014 21:04:52 UTC, Samuel M. Goldwasser wrote:

I should note that if the color of the discharge truly looks correct,

it should lase despite the problems with keeping it lit.



However, it's hard to tell from digital photos whether this is the

case. The proper color is bright unsaturated red-orange, sometimes

refered to as "salmon" color. short of spectral analysis of the

discharge glow, comparing it with a known healthy red HeNe laser

tube would be best. IF it's too pink or weak, then it's probably

leaked.

I've been looking at a low cost spectrometer solution:

http://www.science-surplus.com/products/spectrometers

Do you know which grating might be best for this sort of task, and perhaps also using with Ar lasers?

If the SP specs are to be believed, the tube voltage is way low, which

is another symptom. That really is the only way the tube voltage can

be low with the proper current. It's not a power supply fault.

This I don't quite get -- how can the tube drag the voltage down if the current is correct? My guess was that the current would need to be too high.

Regards,

Andrew

 

[Samuel M. Goldwasser]

Andrew Back <arback@gmail.com> writes:

On Saturday, 8 March 2014 21:04:52 UTC, Samuel M. Goldwasser wrote:

I should note that if the color of the discharge truly looks correct,

it should lase despite the problems with keeping it lit.



However, it's hard to tell from digital photos whether this is the

case. The proper color is bright unsaturated red-orange, sometimes

refered to as "salmon" color. short of spectral analysis of the

discharge glow, comparing it with a known healthy red HeNe laser

tube would be best. IF it's too pink or weak, then it's probably

leaked.

I've been looking at a low cost spectrometer solution:

http://www.science-surplus.com/products/spectrometers

Do you know which grating might be best for this sort of task, and
perhaps also using with Ar lasers?

If the SP specs are to be believed, the tube voltage is way low, which

is another symptom. That really is the only way the tube voltage can

be low with the proper current. It's not a power supply fault.

This I don't quite get -- how can the tube drag the voltage down if
the current is correct? My guess was that the current would need to be
too high.

The VI relationship of a gas tube is highly non-linear and also depends
critically on the gases present. Add in low-excitation energy gases
like N2 and O2, and the voltage is lower at the same current. This
isn't a fixed resistor!

As far as the spectrometer, I've heard that they work well but the
resolution isn't that great. I use a Verity monochromator. It's more
of a pain to use being manual with a micrometer. But with a set of
narrow slits, it can easily small fraction of a nm.

--
sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. Or, you can contact me via the Feedback Form in the FAQs.