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Hewlett-Packard 5500A Helium-Neon Laser (Gallery)
HP (now Agilent) manufactures what is called a "Two-Frequency HeNe Laser"
for use in their interferometry based measurement and calibration systems.
There are several versions of these lasers including the 5500C, 5501A,
5501B, 5517, 5518A, and 5519A (shown below).
The 5500A was the first such laser and the only one to ever include
interferometer optics and an optical receiver inside the laser head.
It's generally similar to the 5500C in construction and is in the
same case but the laser tube is subtly different being the only one
where the waste beam out the rear is used for locking.
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View 01 - Left front view.
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View 02 - Front closeup view. The laser beam exits the top hole
while the return beam enters the bottom hole. The front ring may be
rotated 90 degrees to use the small "alignment spertures". The
back ring may be rotated 90 degrees in insert a polarizing beam-splitter
into the receiver aperture to entirely block the unwanted F1 frequency
component (I think!).
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View 03 - Right back view.
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View 04 - Back closeup view. The connector is for the 5515A
Measurement Display.
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View 05 - Left front interior view. The aluminum box is a shield
(and protection) for the photodiodes and preamps associated with the
REF and MEAS signals. Buried inside are the interferometer optics
which include a pair of beamsplitters and cube-corner.
The small green PCB has the drive transistors for either the HeNe laser
power supply or PZT inverters (not sure which). The other set is
buried under the tube. The inverter transformers and high voltage
components are in metal-enclosed assemblies (possibly potted) under
the HeNe laser tube. The fat red wire comes from the smaller metal
can and goes to the PZT terminal at the back of the tube.
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View 06 - Right back interior view. The HeNe laser tube can be seen
with its output beam expander pointing through the hole in the aluminum
optics/electronics enclosure. In this very early implementation, the
waveplates are mounted separately external to the tube assembly. The
fat red wire going to the tube assembly is for the anode via
the vertially mounted ballast resistor. The brown wire is
the cathode.
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View 07 - Left side interior view.
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View 08 - Right side interior view.
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View 09 - Closeup view of run time (hour meter).
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Hewlett-Packard 5500C Helium-Neon Laser (Gallery)
The 5500C was the second earliest of HP's interferometry lasers. There was
a 5500A before it which is physically similar but had built-in interferometer
optics. (For more on the tube, see the next section on the 5501A.)
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View 01 - Left front view.
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View 02 - Front closeup view. The center hole is the laser out
aperture. The "A" and "B" refer to the optical receiver channels so
that a pair of measurement axes may be handled by the 5500C.
Rotating the aperture wheel by 90 degrees enables the holes
above or below to be used for the return beam.
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View 03 - Right back view.
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View 04 - Back closeup view. The wiring of the two connectors
is not quite identical. When a single 5505A is used (single axis), it
should be plugged into the right-hand (A) connector.
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View 05 - Left front interior view. The aluminum box is a shield
(and protection) for the three electronics boards for the beam sampler
photodiodes and optical receivers. The large green PCB has the drive
circuitry for the HeNe laser power supply and PZT inverters in this early
sample of the 5500C. The inverter transformers and high voltage
components are in metal-enclosed assemblies (possibly potted) under
the HeNe laser tube. Later versions have this circuitry inside fully potted
under the HeNe laser tube with the large green PCB in those lasers only being
used for interconnects.
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View 06 - Right back interior view. The HeNe laser tube can be seen
with its output beam expander pointing through the hole in the aluminum
optics/electronics enclosure. The fat red wire going to the tube assembly
from the larger metal-cased HeNe laser power supply module is the anode
with a ballast resistor in-line hidden underneath. The purple wire is
the cathode. The shorter fat red wire from the smaller metal-cased PZT
module goes to the PZT terminal at the back of the laser tube (hidden).
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View 07 - Closeup of tube output and electronics. The PCB closest
to the beam expander is the preamp for the beam sampler photodiodes.
The PCB on the side is for the optical receivers. There is a similar PCB is
on the other side of the laser.
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View 08 - Closeup of two (of three) electronics PCBs.
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View 09 - Closeup of the four optical receiver photodiodes (behind
lenses).
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Hewlett-Packard 5501A Helium-Neon Laser (Gallery)
The tube below was used in the HP 5501A laser head, part of the HP 5501A
Interferometry Measurement System. (A physically and functionally identical
tube, though with a different part number, was used in the earlier 5500A
and 5500C lasers.)
Position/distance resolution down to better than 10 nm (that's nanometer as
in 0.000000001 meter!) were possible with this equipment. Additional
information may be found in the Laser FAQ section:
Hewlett-Packard HeNe Lasers.
I acquired this tube for its curiosity value way before I knew anything
about metrology lasers. Here are some observations of its characteristics:
- This is a red HeNe laser with a power output of about 0.25 mW
There is no model number on the tube itself.
- The cylindrical central area contains some powerful toroidal magnets.
Their field is oriented N-S along the axis as expected with poles
at each end. These are for Zeeman splitting to generate the two
frequencies needed for the interferometer application.
- The beam output is from the left side (in the photo) via a beam expander
and collimator. The exit diameter is about 6 mm.
In disassembling and already partially disassembled collimator from a 5517
laser, I found a couple of thin pieces of what look like mica, which
are 1/4 and 1/2 waveplates to generate linear polarization and orient
the polarization axes horizontally and vertically.
- The external optics are adjustable both via the knurled barrel that is
visible as well as via internal knurled rings accessible behind the cover
(attached by the single Philips head screw). By adjusting just the knurled
barrel, a very well collimated beam could be obtained. With a 6 mm diameter,
this would be quite low divergence - about 0.27 mR total. (The blue dots
line up when collimation is optimal.) By continuing to turn the barrel,
I could focus the beam to a really small dot (a singularity as far as
appearance is concerned) at 20 feet.
- With the optics assembly removed, the beam looks like the beam from any
other HeNe laser, but with a relatively high divergence.
- Both the OC and HR mirrors are totally inside the glass envelope of the
tube and are about 7 mm thick and 15 mm in diameter. They appear to be
mounted solely by springs against the ground faces of the central bore. No
mirror adjustment seems possible. I wonder if this is a case of simply
manufacturing the raw tube to such precision that no adjustment is needed.
Perfection by design!
- The beam is moderately polarized - maybe 10:1. The axis is oriented as
though there was a Brewster window angled horizontally.
I didn't know for a long time if this was by design just an artifact of
this particular tube - or the defect that caused it to be rejected (which
is apparently why I was able to get it in apparently good condition).
(I am almost certain that the defect was a bad PZT.)
- The optical window for the beam (which is separate from the OC) is fused
to the rest of the glass envelope at a slight angle - perhaps 5 degrees. It
is not AR coated (though the outside surface of the OC itself IS AR coated
as expected) and thus there is a not-so-weak ghost beam a few degrees off
of the main beam. However, this does not affect anything being totally
blocked by the optics assembly.
- Unlike most ordinary HeNe lasers, even from initial power-up, there is
minimal or no mode cycling or beam intensity fluctuations (monitoring with
a simple photodiode based laser power meter). That fat bore is Zerodur.
- Power supply connections are via an anode terminal on the far
side near the output-end and a cathode terminal on the far side of the big
glass bulb on the right. (Neither terminal is visible in this photo.)
Most HeNe laser power supplies designed for 1 mW tubes should work. It
requires a 75K ballast resistor. Optimal current is about 3.5 to 4 mA
(based on maximizing beam intensity).
- There is a third terminal which attaches to a PZT behind the rear
mirror for precise control of the cavity length to adjust the longitudinal
mode position relative to the gain curve. It's not very sensitive
requiring up to 1 kV or more during normal operation.
- A warning on the tube reads: "Do not disconnect power supply as damage to
laser may result". I don't know whether this refers to the tube, the power
supply, or the third electrode (whatever it is) specifically. I did attempt
to accidentally power it initially via the third electrode which resulted in
some zapping but no apparent damage. Though maybe that's what killed
the PZT, and it WAS some other defect that caused the tube to be rejected.
I rather doubt this but is possible.
- The total length of the tube including optics is about 250 mm and it
weighs about 3 pounds (mostly due to the magnet assembly). The distance
between the mirrors is about 125 mm.
I later discovered that the high polarization ratio was due to the
particular cavity length that just happened to be present with no
voltage on the PZT. And the defect is apparently that the PZT
somehow doesn't work - there is no change in the modes regardless
of PZT voltage from 0 V to 1.5 kV. That is, unless, my incorrect
connections somehow ruined the PZT. (But everything else about the tube
seems normal so a dud PZT makes the most sense for the defect.)
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View 01 - Overall view of strange HeNe tube.
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View 02 - End-view showing piezo electrode terminal.
Here are some views of a HP-5501A laser head with the skins off (not
the same one from which the tube, above, was removed):
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Hewlett-Packard 5501B Helium-Neon Laser (Gallery)
The HP-5501B is a functional replacement for the 5501A but uses a different
HeNe laser tube with thermal instead of PZT tuning, and thus different
electronics. The tube is physiclaly similar to the one in the HP-5517A
(below) and other later model HP/Agilent lasers.
(These 4 photos provided courtesy of:
John Cincotta (johncincotta@comcast.net).)
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View 01 - View of tube.
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View 02 - View of PCB.
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View 03 - End view showing connectors and indicators.
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View 04 - End view showing output optics.
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Hewlett-Packard 5517 Helium-Neon Laser Head and Accessories (Gallery)
The first group of photos are of the laser head and a beam splitter from a
Hewlett-Packard Interferometric Measurement System.
See the Laser FAQ section: Hewlett-Packard
HeNe Lasers for more information and links describing this technology.
(The following 7 photos provided courtesy of: Alvin Lim
(alvin100@singnet.com.sg).)
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View 01 - Interior view of right side of HP 5517A.
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View 02 - Closeup of power supply, ballast resistor, and tube label.
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View 03 - Interior view of left side of HP 5517A showing electronics PCB.
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View 04 - Beam splitter used in the interferometer to direct the beam
to/from the target or reference.
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View 05 - Beam splitter with lenses removed.
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View 06 - Another view.
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View 07 - And another.
Next, we have the bare HeNe laser tube removed from a similar HP-5517A
laserhead. Essentially the same bare tube is used in the HP-5501B, HP-5517A,
B, C, and D, and other HP/Agilent metrology lasers other than the earliest
ones like the 5501A and 5500C.
(The following description and photos provided courtesy of: Mike Harrison
(mike@whitewing.co.uk).)
The description of the HP-5517A laser head exactly matches the unit I have
down to the color of the wires and PSU part number! I think the small vent
mentioned is simply used for filling with the silicone encapsulating goop to
avoid air bubbles.
The tube initially looks fairly conventional in overall layout, but is
made of much thicker glass than normal. The capillary, with the
mirrors on each end, is mechanically separate from the outer glass
envelope, and has a translucent appearance (like silica) and is about
9 mm O.D, with a 1.5 mm bore. It's supported at each end by two springs
(presumably the spring pressure demands the thick glass envelope). The
mysterious second cathode connection goes to a coil of wire, wound in a
helical groove on the capillary, with a turn pitch of about 3 mm. This is
the heater used to fine-tune the cavity length by thermal expansion. It
is bifilar wound to minimize magnetic fields. By placing the heater inside
the tube, the time from power-on to a locked condition is reduced from
10 or 20 minutes, to under 5 minutes.
The beam output is much more divergent than conventional tubes - about
1/4 inch a foot away, hence the external optics in the laser head.
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View 08 - Overall plasma tube after being cut away from aluminum
shroud.
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View 09 - HR-end.
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View 10 - OC-end.
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View 11 - HR-end showing discharge path.
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Hewlett-Packard 5518A Helium-Neon Laser Head (Gallery)
The HP/Agilent 5518A laser is very similar to the 5517A in terms
of case style, but include an optical receiver for the return beam from an
interferometer. This allows the 5518A to be used stand-alone without any
other optical receiver, only the measurement electronics and DC power
supply. A 5517A can be converted into a 5518A by adding the optical
receiver PCB and replacing the turret/aperture wheel.
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View 01 - Front view.
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View 02 - Back view.
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View 03 - Front view with cover removed.
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View 04 - Back view with cover removed.
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View 05 - Right side view showing main PCB.
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View 06 - Left side view showing DC and HeNe laser power supplies.
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Hewlett-Packard 5519 Helium-Neon Laser Head (Gallery)
The HP/Agilent 5519A and 5519B lasers are very similar to the 5517A in terms
of case style, but like the 5518A, include an optical receiver for the return
beam from an interferometer. This allows the 5519A/B to be used stand-alone
without any other optical receiver, only the measurement electronics. In
fact, the 5519A/B are the only of these lasers to include a DC power supply
internal to the laser head so they plug into a normal AC outlet instead of
requiring a separate DC power supply.
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View 01 - Front view.
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View 02 - Back view.
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View 03 - Front view with cover removed.
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View 04 - Back view with cover removed.
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View 05 - Right side view showing main PCB.
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View 06 - Closeup of left half of PCB.
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View 07 - Closeup of right half of PCB.
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View 08 - Left side view showing DC and HeNe laser power supplies.
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View 09 - Left side view showing DC power supply.
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View 10 - Closeup of HeNe laser power supply and connectors.
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View 11 - Top view.
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View 12 - Closeip view showing beam sampler and optical receiver PCB.
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View 13 - Closeip view showing rear PCB.
