Optical mirror coated with organic superconducting material

An optical mirror has enhanced reflectivity and reduced thermal distortions when it is composed of a substrate coated with a reflective coating made of an organic superconducting material. The substrate is best constructed of materials which have the most favorable thermal expansion and thermal conduction characteristics at temperatures near 0.degree. K. such as: silicon, diamond, copper and sapphire. The reflective coating is only a few microns thick and composed of organometallic compounds and is cooled to superconducting or cryogenic temperatures of less than 100.degree. K.

BACKGROUND OF THE INVENTION 
The present invention relates generally to optical systems, and more 
particularly to a design for optical mirrors. 
Optical systems, including modern lasers, commonly include mirrors among 
their optical components. Unfortunately, these mirrors are subject to 
thermal distortions and have reflectivities which are less than 100%. The 
task of reducing these thermal distortions and improving the 
reflectivities of optical mirrors is alleviated, to some extent, by the 
systems of the following U.S. Patents, the disclosures of which are 
incorporated by reference: 
U.S. Pat. No. 3,609,589 issued to Hufnagel; 
U.S. Pat. No. 3,703,813 issued to Olevitch et al; 
U.S. Pat. No. 4,343,533 issued to Currin et al; 
U.S. Pat. No. 4,415,234 issued to Meyers; and 
U.S. Pat. No. 4,431,269 issued to Barnes, Jr. 
Olevitch et al disclose an electrically conductive laser beam reflector 
that is cooled by a high voltage electrostatic field. The cooling effect 
of the electrostatic field has essentially the same distribution as the 
heating effect of the laser beam impinging on the reflector. The result is 
a reduction of different and varying temperature gradients in the 
reflector and the resulting distortions in the beam. 
Barnes, Jr. is directed to a cooled laser mirror constructed with a 
substrate formed of a material having a thermal conductivity peak in a 
cryogenic temperature operating range. During operation the temperature of 
the substrate is maintained at cryogenic temperatures to insure peak 
thermal conductivity. 
In Currin et al a solar radiation reflector is made using a laminate 
including cellulosic material and a curred polymer. In Hufnagel the 
coefficients of thermal expansion of bonded layers in a mirror 
construction are selected to balance out the tendency of the mirror to 
warp due to thermal gradients. Meyers uses heat-absorbing phase-change 
materials to provide passive cooling in a mirror. 
All of the systems cited above are exemplary in the art, and indicate that 
there remains a need to reduce the thermal distortions in optical mirrors. 
The present invention is intended to help satisfy that need. 
SUMMARY OF THE INVENTION 
The present invention is an optical mirror whose design and materials of 
construction provide it with improved heat dissipation. This is 
accomplished by initially coating an appropriate optical mirror substrate 
material with a suitable organic superconducting material that will 
increase mirror reflectivity, and simultaneously decrease thermal 
distortions. 
One embodiment of this optical mirror is produced when an adhering organic 
superconducting material having a material thickness in microns is placed 
over a substrate material having a thickness in centimeters. The invention 
increases the damage thresholds of optical mirrors and is directly 
applicable to weapons systems. 
It is one object of the present invention to provide an optical mirror 
which has optical characteristics which are subject to a reduced amount of 
thermal distortions. 
It is another object of the present invention to provide an optical mirror 
with increased mirror reflectivity. 
It is another object of the present invention to increase the damage 
thresholds of optical systems by providing optical mirrors which have 
improved heat dissipation characteristics. 
These objects together with other objects, features and advantages of the 
invention will become more readily apparent from the following detailed 
description when taken in conjunction with the accompanying drawings 
wherein like elements are given like reference numerals throughout.

DETAILED DESCRIPION OF THE PREFERRED EMBODIMENT 
The present invention is an optical mirror which has a reflecting surface 
composed of an organic superconducting material for increased reflectivity 
and reduced thermal distortions. 
The reader's attention is now directed towards FIG. 1 which depicts the low 
distortion cooled mirror systems of the Barnes, Jr. reference. This prior 
art system relies on the cooling of an optical mirror 14 to cryogenic 
temperatures (less than 100.degree. K.) to reduce distortions using a 
cryogenic refrigeration system 20. 
Barnes, Jr. is a milestone in the art in that he also identifies the 
selection of mirror substrate materials which exhibit a thermal 
conductivity peak at the cryogenic temperature range. More particularly, 
copper, diamond, sapphire and silicon are suitable substrate materials, 
with sapphire appearing to have the most favorable thermal conductivity 
and coefficient of thermal expansion characteristics in a cryogenic 
temperature operating range. 
FIG. 2 is an illustration of an embodiment of the present invention. The 
optical mirror of FIG. 2 is composed of a substrate material 100 upon 
which an adhering organic superconducting material 110 is deposited to 
form a reflecting surface. The term "superconducting" is used herein to 
denote that the mirror is intended to be used while refrigerated to 
temperatures near absolute zero or 0.degree. K. Like the Barnes, Jr. 
reference, such superconductivity is approached by cooling to cryogenic 
temperatures and below (less than 100.degree. K.). 
The optical mirror of FIG. 2 uses a superconductive organometallic 
substance as the reflective coating of the mirror. Broadly speaking, 
organometallic compounds are compounds which have a direct union of carbon 
with a metal. There is no agreement in the art on the definition of a 
metal. To some, most of the elements are very largely metallic to such an 
extent that, of the known elements, 68, or 74 percent of the total, are 
metals; 11 of the remainder or 12 percent of all the elements have some of 
the properties of metals (B, C, Si, P, As, Sb, Se, Te, Po, I, and element 
85); and only 13 elements are non-metals (H, N, O, S, F, Cl, Br, He, Ne, 
A, Kr, Xe, Rn). The organic chemist would prefer to delimit the "somewhat 
metallic" elements to exclude at least phosphorus, selenium, and iodine; 
and he would wisely elect to consider carbon in organic compounds as a 
non-metal, if only to avoid classifying practically all organic compounds 
as organometallic compounds. 
There are numerous types of organometallic compounds. Those having but one 
metal may contain one or more R groups and one or more X groups, depending 
on the valance of the metal and the stabilities of the organometallic 
compounds: C.sub.2 H.sub.5 Na, (CH.sub.3).sub.3 Al, CH.sub.3,HgC.sub.6 
H.sub.5, C.sub.6 H.sub.5 BeCl, (C.sub.6 H.sub.11).sub.2 PbBr.sub.2, 
CH.sub.3 SnCl.sub.3. The R group can be aliphatic, alicyclic, or aromatic, 
and although it may have a wide variety of substituents obviously cannot 
contain a substituent which can react with the selected organometallic 
linkage. 
Returning to the embodiment of FIG. 2, the substrate material 100 has a 
thickness measured in centimeters. This substrate is best composed of: 
silicon, copper, diamond or sapphire, as suggested by Barnes, Jr. 
The reflective coating 110 has a thickness of only a few microns, and is 
composed of an organic superconducting material. The organometallic 
compounds all tend to be good conductors at room temperatures and make 
suitable super conductive reflective coatings when applied to substrates 
which have favorable thermal conductivities and coefficients of thermal 
expansion. Together, the reflective coating 110 and substrate 100 has 
increased mirror reflectivity and decreased thermal distortions when 
maintained at superconductive or cryogenic temperatures. 
Superconductive and cryogenic refrigeration systems are deemed to be known 
in the art, and need not be described in detail here. The Barnes, Jr. 
reference includes an excellent summary of satisfactory coolant candidates 
as well as a description of refrigeration systems which would be suitable 
for use with the present invention. In operation, the mirror substrate and 
especially the reflective coating should be cooled below 100.degree. K. 
The present invention specifies that the reflective coating is an organic 
superconducting material. These can include halides of Group VIII metals, 
including hydrides, carbides, and carbonyls. Other suitable candidates 
would be iron halides and organoaluminum. Similarly organozinc compounds 
such as alkylzinc and diarylzinc compounds are suitable reflectors when 
cooled to superconductive temperatures. 
While the invention has been described in its presently preferred 
embodiment it is understood that the words which have been used are words 
of description rather than words of limitation and that changes within the 
purview of the appended claims may be made without departing from the 
scope and spirit of the invention in its broader aspects.