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This Standard Reference Material (SRM)
is intended for use in calibrating the photometric scale of
specular reflectometers. SRM 2011 is a gold mirror 5.1 cm
in diameter and 1.2 in thickness. The mirror was produced
by electrodepositing gold on an optically polished nickel
surface. The nickel was electrodeposited on a hard aluminum
substrate. The finished gold mirror flatness is approximately
1 to 2 fringes when tested with the Krypton yellow line at
587.1 nm. The uniformity of reflectance within a central 25
mm diameter area of the mirror is approximately +/-0.001 for
the wavelength range 600 to 1200 nm and less than this for
longer wavelengths. The mirrors were aged for one year before
calibration.
The specular reflectance of each mirror
was measured on a high-precision reflectometer for 6°
incidence at 50-nm intervals from 600 to 1000 nm 100-nm intervals
from 1000 to 1300nm, and 250-nm intervals from 1500 to 2500
nm In addition to these wavelengths, the reflectance was measured
at the laser wavelengths of 632.8 and 1060 nm.
The high-precision reflectometer was calibrated
with a master mirror which had previously been measured with
a highly accurate spectrophotometer with a specular reflectometer
attachment. The reflectance of the master mirror was measured
at the above wavelengths and at angles of incidence of 6°,
30°, and 45°. These measurements were made for both
vertically and horizontally polarized incident beams. The
overall uncertainty in these measurements is +/-0.002.
The specular reflectance of the SRM 2011
was measured relative to the master mirror at 6° incidence
only. The certified values of specular reflectance for the
SRM mirrors are based on the average value of the vertical
and horizontal polarizations for the master mirror at 6°
incidence. The certified values listed in Table 1 are for
the indicated serially numbered mirror only, and have an uncertainty
of +/-0.005.
Table 2 lists the reflectance data for the
master mirror. These data are not certified, but are provided
to show the variation in specular reflectance of a typical
first surface mirror as a function of angle of incidence and
plane of polarization.
SRM 2011 can be cleaned by bathing in isopropyl
alcohol and rinsing with distilled water. Although the gold
surface is harder than an evaporated gold surface, it should
not be cleaned by rubbing techniques. The mirrors must be
handled carefully so as not to touch the gold surface and
should be stored in its container when not in use.
This SRM was calibrated in the Radiometric
Physics Division of the Center for Radiation Research.
The technical and support aspects involved
in the certification and issuance of the SRM were coordinated
through the Office of Standard Materials by R. W. Seward.
Stanley D. Rasberry, Chief
Office of Standard Reference Materials
Washington, D.C. 20234
March 19, 1984
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Epner's Laser Gold
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How Did a Small Company in
Brooklyn Become a Supplier to NIST of The Infrared Reflectance
Standard?
Strangely, it is another story that
involves Xerox.. We were shipping reflectors for fusing
the toner on one of the best selling copiers that Xerox
had ever built. Thousands a week. Remember, this was
in the 70's when Xerox owned the copier business.
Their QC department rejected a shipment
for low reflectivity which we knew met the spec. After
all, we were calibrating our Beckman Spectrophotometer
with an NBS (National Bureau of Standards) as NIST was
then known, and they were using a standard that their
optics lab manager had produced. Our NBS Standard was
a quartz flat with a vapor deposited gold on one surface.
I flew to Xerox in Rochester NY with
my NBS standard in hand for the “shoot out.”
Frank Winski, the manager of the optics lab, no trivial
position at Xerox, measured the NBS mirror on his Beckman,
the identical instrument to ours incidentally, and actually
told me, “The NBS standard is 2% off”. I said,
“Frank, that’s like saying there is no God.
Your calibration must be off.” To my great annoyance,
he refused to back down. The reject would stand.
I called the NBS Metrology group in
Gaithersburg, MD., and made an appointment for the next
day. They remeasured their mirror and to their dismay
(and mine), indeed agreed that the vapor deposited gold
had degraded with time.
It was not a pleasant scene. I assumed
a recall of all the outstanding IR Standards was being
discussed, but as “the messenger” I was not
eager to hang around. When I thought a sufficient amount
of time had passed, I send a Laser Gold coated mirror
for their consideration as an IR Standard. It was measured
and put aside.
When it was remeasured a year later
and exhibited the theoretically high reflectivity of
gold and the ability to be physically cleaned, they
ordered 50 mirrors. These were aged for five years and
finally offered to the optics industry, unchanged from
the day we shipped them. Proud of our achievement, Cohan
Epner, as the company was then called, ordered the first
Laser Gold coated IR Standard.
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