GENERAL CLEANING AND HANDLING INSTRUCTIONS FOR ELEMENTS COATED WITH HIGH EFFICIENCY ANTIREFLECTION COATINGS

• Document Type: CREST
• Collection: NGA Records (Formerly NIMA)
• Document Number (FOIA) /ESDN (CREST): CIA-RDP79B00873A001600020004-2
• Release Decision: RIPPUB
• Original Classification: K
• Document Page Count: 9
• Document Creation Date: December 28, 2016
• Document Release Date: August 21, 2012
• Sequence Number: 4
• Publication Date: July 11, 1967
• Content Type: MISC

Declassified in Part - Sanitized Copy Approved for Release 2012/08/21 : CIA-RDP79B00873A001600020004-2
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GENERAL CLEANING AND HANDLING INSTRUCTIONS
FOR
ELEMENTS COATED WITH
HIGH EFFICIENCY ANTIREFLECTION COATINGS (HEA)
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1 . 0 Purpose
The purpose of this outline is to define certain handling and
cleaning techniques which, if properly followed, will result
in greater satisfaction in the application and use of HEA
coatings.
2.0 Scope
This outline pertains to coated glass elements only. Materials
other than glass require special considerations. Consult
Sales Engineering on these specific occasions.
3.0 General
HEA coatings generally do not deteriorate when exposed to
varying environmental or climatic conditions, and they are quite
durable (abrasion-resistant). However, to insure maximum
useful life of elements coated with HEA it is wise to employ
certain precautionary measures -within practical and economical
limits.
Also, because of the extreme efficiency of HEA, certain contam-
inants superimposed on the coating will appear more objectionable
than they would on any other type of reflection-reducing coating.
To minimize adverse effects, the following instructions should be
followed,as applicable, during assembly of equipment utilizing
elements coated with HEA.
4.0 Handling Optical Elements
Generally, it is good practice to handle optical elements, whether
coated or not, only as frequently as is positively necessary. Each
time an element is picked up, transported, and set down, it is
vulnerable to being damaged.
When handling an optical element, it is advisable to wear gloves,
(preferably light-weight nylon or cotton gloves which are relatively
lint-free) and/or rubber finger cots. Whenever possible, grasp the
part at its edges - not across the polished surfaces. This will
reduce the amount of contamination of the surfaces which would
otherwise result in a more difficult cleaning operation later. Also,
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certain types of glasses will become permanently etched by
perspiration being in contact with their surfaces.
All handling of optics should be done over a work area which
Is adequately covered with a soft, clean cloth. (Baby diapers
have been found to be quite satisfactory.) This will allow a
person to set a part down on a work surface without damaging
the optical surfaces.
During transportation or in storage , the elements should be
contained within a material-handling device which will
provide adequate protection against damage. The elements
should generally:
A. Rest on a clean, soft surface.
B. Be positioned to rest on a surface which is not a critical
optical surface.
C. Be separated so they cannot come into physical contact.
D. Be adequately covered to protect against contamination
from the surrounding environment and from physical
damage.
It is advisable that optical elements be stored in a restricted-
access area, and that only those individuals who have been
properly instructed in the handling of optical elements have
access to this storage area.
5.0 Cleaning Elements Coated With HEA
5.1 General
Imperfections resulting from fingerprints, dust, and dirt
will greatly reduce the reflection-reducing effectiveness
of an HEA coating. Removal of these imperfections will
restore the coated surface to normal high performance
characteristics.
A series of recommended procedures have been developed
to effect proper cleaning of HEA-coated surfaces. Two
different cleaning methods are discussed, each suited
for particular applications. These procedures are designed
for removal of imperfections without damaging the coated
surfaces.
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5.2 Surface Pre-cleaning Preparation
Prior to cleaning, all surfaces should be blown off with
clean, dry air. The removal of large dust and dirt
particles will reduce the abrasive action which could
damage the coating.
The air can be supplied from a small hand device,
(such as a syringe), or from a compressed air system,
whichever is convenient. In either case, the air must
be free of all oil, and the water content should be
below 30% relative humidity.
5.3 Choosing a Solvent
The choice of solvent shall be governed mainly by the
particular contaminant which is being removed from
the coated surface. For example, benzine is a good
solvent for removing oil; warm acetone can be used for
some adhesives and for paint removal; trichloroethane
can be used for paraffin removal, etc. Do not use
strong acid or bases or abrasive products to clean
coated glasses.
HEA performance is not adversely affected by any of
the common solvents such as detergent and water,
alcohol, trichloroethane, benzine, xylene, and methyl
ethyl ketone.
5.4 Procedure I - Cleaning With a Liquid Detergent and Water
This method may be used for glass elements, regardless
of size or shape, provided the element substrate material
is not water-soluble. (Certain materials will etch when
immersed in hot water.) This method should not be used
in those instances where elements are mounted in
assemblies which will be damaged by the hot water
rinse.
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Liquid detergents which have been used and have yielded
satisfactory results are "joy" and "Glim"; both types are
available at most grocery stores and supermarkets.
The liquid detergent is mixed with hot tap water, using
the proportions as recommended by the manufacturer.
The element is then washed with this solution, rinsed
with clean hot tap water and immediately wiped dry.
Clean, soft cloths must be used for the cleaning and
for the drying. Should the HEA coating not be satis-
factorily cleaned, either repeat the above procedure or
try Procedure II, (if applicable).
Precautionary Note:
If the parts are not wiped dry but are allowed to
dry in air, a stain may result which will permanently
damage the coating.
5.5 Procedure II - Cleaning With a Volatile Solvent, i.e. ,
Isopropyl Alcohol or Acetone
This method is very universal. Most people usually have
these solvents available and are familiar with their use.
There are two limitations to the application of this
method:
1. It should not be used when the element is
mounted in any assembly, the finish of which
may be soluble in the solvent.
2. Relatively inexperienced personnel will find it
difficult to satisfactorily clean large surface
areas.
It is very desirable to use this method on those elements
which have a substrate material which is water soluble.
To clean small parts, it is necessary merely to immerse
them in the solvent, rubbing the surfaces during
immersion with a clean, soft cloth, and then remove the
parts and immediately wipe dry with a clean, soft towel.
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To clean parts with a large surface area requires
that relatively small areas be cleaned and that one
progresses from area to area until the entire surface
has been cleaned. Each small area is cleaned with a
soft, clean cloth moistened with the solvent and then
immediately wiped dry with another soft, clean cloth.
Should the HEA coating not be satisfactorily cleaned,
either repeat the above procedure or try Procedure I,
(if applicable).
Precautionary Note
If the solvent is allowed to evaporate from the
surface, a stain may result.
6.0 Comments on HEA
HEA has been specifically designed and optimized. to reduce the
reflection of glass surfaces through the visible portion of the
spectrum; reflectance is generally less than 0.5% from 400m?. to
700m?. However, in the ultravioletand infrared regions adjacent
to the visible, reflectance is quite high--as high as 12 percent per
surface at certain wavelengths. In many applications (generally
multi-element lens systems), this is a very desirable feature
because unwanted energy is attenuated. However, a precaution
must be mentioned. Although permanent ocular damage is unlikely,
continuous viewing of extremely bright sources (such as the sun)
by reflection from an HEA coated surface should be avoided.
7.0 Conclusion
All of the previous information has been an outline of methods
and techniques which should be employed when handling and
cleaning glass optical elements, whether coated with HEA or
not and generally applies to conditions encountered within a
production facility. It is certainly recognized that these same
elements will ultimately be exposed to field operation and that
different circumstances will exist. However, wherever possible,
the above instructions should be followed.
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