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Nov. 26, 1946. 2,411,715 G. L. DIMMICK APPARATUS FOR THE PRODUCTION OF REFLECTION REDUCING COATINGS Filed Dec. 14, 1942 'i ßm‘entor o @Nomen Patented Nov. 26, 1946 - #2,411,115 UNlTsDsTA'rss PAT ENTÍOFFICBÈ V 2,411,115 ' ` APPARATUS Foa THE PRODUCTION-0F . -REFLEo'rroN REDUCING coA'rrNGs Glenn L. Dimmick, Indianapolis, 1nd., assigner to” Radio Corporation of America, a corporation yof Delaware , Application December 14, 1342, serai-"No.sissßis 3 claims. l (orsi-12.2) '1 tion'would result in an evaporated’ñlm of uni This invention relates to an apparatus for pro form thickness upon a spherical surface with the ' ducing evaporated coatings such,l for example, as! boat or coil at its center. In practice rit is very desirable to .arrange thel evaporating `>system so 'that a coating vof' uniform thickness can `be de reflection reducing coatings or coatings of evap orated meta-1 on optical elements. The production ` of evaporated reñectionreducing coatings is de-` scribed, for example, in Cartwright et al. Patent No. 2,207,656. In the actual production of such4 coatings many dimculties are encountered. One of the difficulties is due to the fact that the coat ing material when evaporatedy in vacuum either from a coiled filament or from an evaporating posited on a flat surface. In his book “Proce dures in Experimental Physics” (page 179), Dr. "'John Strong shows how to obtain this condition by >Placing fa large number of evaporators in -a circle whose radius is equal to the distance from the evaporators to the fiat object being. coated. This has many practical objections. First it as boat travels uniformly in alldirectîons like radi sumes a large number >of evaporators with identi ant energy. As a consequence, the quantity of coating material reaching a given area ofsurface varies approximately inversely as the square of cal characteristics and which will vaporize exactly the same amount of material when heated with the same current. This is diilicult to' realize in the distance of the surface from the evaporator. The present invention provides an apparatus for practice. l . l _ y In a lens coating equipment, Iit; is desirable to rendering the coating thickness approximately coat several lenses at one time and these are often One object of the invention is to provide `an 20 in tubular mountings so that they can receive the vaporized material from only a limited angle. improved evaporating apparatus for the evapora Fig. »1 shows why those lenses which are in deep tion of thin films. , mountings could not receive the same quantity of Another object of the-invention is to providey 1 the evaporating‘apparatus which will compensate l » evaporated material on all portions of the lens for the normal irregularity in distribution of 26 surface. It will be apparent from this figure that the material from the evaporating coil-I2 will be evaporated material. obstructed by the mountings of the lenses Il so Other and incidental objects of the invention that a uniform coating will not be produced. will be apparent to those skilled in the> art from The improved apparatus according to the pres a reading of the following specification and an inspection of the accompanying drawing in 31 ent invention as shown in Fig. 2 produces much uniform over a plane surface of considerable area. more unifrom coatings on flat'surfaces and on which: . A» . , Figure 1 shows one way in which it has here tofore been attempted to secure- uniform coatings on optical surfaces. Figure 2 is a perspective view of my improved 35 lenses in deep mountings. In thearrangement illustrated, three evaporating boats are placed in a> triangular arrangement and a triangular wire screen is placed `at the proper distance above the boats. This screen obstructs` a portion of the evaporated material and permits the rest to reach ’ Figure 3 is a top view of the evaporators and the lens plate or »holder L carrying the lenses Il screen from the center of the lens holder.` in the -upper end of the `bell jar. lli.v vThe evap Figure 4 is a view of thel evaporators and screen taken from the outside edge of the lens holder 40 orating boats I3 are made of platinum or other appropriate material and are heated by electric ` on a radius _whose vertical .projection passes , currents passed through them. The-‘bell jar I0 ’ through an apex of the screen i4. , Figures is a diagram inustreting the relation ' is of course air .tightA and is evacuated to an evaporating apparatus. between lens distance and coating thicknesses, and ` . « v Figure 6 is a curve showing the corrected re appropriate degree before thecommencement of 45 evaporation. , „ . „ z As viewed from the center of >the lens fplate, Figure 7 is a view of the evaporators and'screeny ' that is, »from the'plane of the‘lenses at a point v on the common axis passing through the `centers when viewed from the edge of the lens holder on of the evaporatorassembly, the screen and the the center of any side of screen I4. When a. material is evaporated from a small boat or coil placed in a vacuum, the evaporated appear as shown in Fig. 3. It will be apparent that at this point, which is the nearest to the sults secured by the use of my improved apparatus. Y ' a. radius whose vertical projection passes through 60 lens plate, the' screen I4 and the evaporators I3 particles travel in straight lines very much like light rays‘ from a luminous source. 'I'his condi evaporators, all of the evaporators are shielded - bythe screenl and only such evaporated material can reach the surface as passes through the 2,411,715 3 4 screen. As the viewpoint recedes from the c'en ter of the lens plate, the area of the evaporating boats to which the surface is directly exposed increases until, at the edge of the circular lens holder the equivalent of two evaporating boats are completely exposed. Figure 4 showsthe rela tion between the boats and screen as‘vievved from appropriately shaped piece of magnetic material I6 counterbalanced by a membe;- Il, preferably of non-magnetic material. After the optical ele ments Il have been appropriately coated on one side, the lensl plate L is rotated with the shaft I5 by manipulation of a magnet outside of the bell jar so as to attract'the member I6 which is fas tened to the shaft' I5 and causes rotation of the lens plate L through 180 degrees to expose the the'edge of the lens holder on a radius whose ver tical projection intersects any one oi’ the apices of opposite side of the lens to the evaporators. the screen. In this case one boat is completely uncovered and two boats are each half uncovered. Ijclaim as my invention: 1‘.VV In a vacuum evaporating device for produc the edge of the lens holder on a radius whose ver ing thin ñlms on the surface oi’ an object, in tical projection passes through the center of any 1 combination, a holder for said object, three elon side of the screen. In`this case, vone boat is corn v15 gated evaporating elements equidistant from and pletely covered, and the other two-are each fully in opposed relation to said holder and arranged exposed, producing, as before, the same totalex- ' symmetrically along the sides of an equilateral Figure 7 is a similar illustration of the viewfrom f , i , posed area. At any other point on the edge of triangle, a foraminous screen in theIorm o1' an the circular lens holder, the equivalent of two equilateral triangle `placed between the evaporat 20 ing elements and said holder for procuring uni .boats are uncovered. Furthermore, the compen sation is constant for all points on any circle with ì its center on the common axisv passing vthrough the center of the lens holder, screen and -b‘oat as sembly,` an'dfproportional to the radius of the j `circle from which the view is taken. Conse 25' quently, the evaporation is substantially constant over the- whole area within the limits of the lens'v holder. ` ~ y ao ` r2 lwhere To is the corresponding thickness at ' point Po. - Fig. 6 shows how the ñlm thickness decreases as the distance b (from the center of the plate) is increased. « 40 As an example, if we make h=6" and R‘=21/2" ' ' . » mounted-between said evaporating elements and said holding means ‘and positioned in such a man - ’ ner- that said evaporating elements are at an TheA method of compensation described A‘above is linear with b (Fig.` 5) but the attenuation in . iilm thickness is not linear. ` » alternately expose opposite sides of said objects ' to said evaporating means, and a foraminous screen in the lform ofl an equilateral triangle then the ñlm thickness at the edge of the plate would be 72.6 percent of the Lthickness at the centerf' 2. In a vacuum vevaporating apparatus for pro ducing thin viilms on the surface of an object, a ’ elongated evaporating means arranged symmetri cally along the sides oi' an equilateral triangle, means for holding objects to ‘be coated with one side exposed to and substantially equidistant from said'evapora‘ting means, 'means pivotally mount ing said holding means, magnetic means con nected to said holding means whereby the position of said holding means may be changed to thereby thickness of the evaporated film at thispoint is h2 .cos2 just covered by said screen when viewed from the center of said- holder on the common axis of said container adapted to be evacuated, a plurality of _ Vis the radius of a'point P1 on the lens plate, the u elements being at an angle to the sides of said screen', the position and'size oi' said screen kbeing so selected that said -evaporating elements are holder, screen and evaporator assembly. ` n In Fig.v 5 there is diagrammatically illustrated an evaporating source S placed at a distance h ` below the lens plate'L having a radius R. If b form thickness of the'evaporated material over the whole surface of said object, said evaporating _angle to the sides of said screen and so’thatsaid screen just covers said elements when' viewed from the center of said holding means. 3. >In a vacuum evaporating‘apparatus for de ‘ curvek (a) (Fig. 6)` shows the actuai attenua - tion- While line (c) shows a close approximation 50 positing a thin film on the surface of one or more to this. Since only two of the boats areuncovered when viewed from the edge ofthe plate as vshown objects, a container adapted to be evacuated, three elongated evaporating boats-lying in a plane inFigs. 4 or '7, the transmission of the compensat- , and arranged symmetrically along the vsides of an ing screen would have to be 72.6‘X 66.6:481/2 per equilateral triangle, a holdery for said objects cent. A triangular piece of '-'No. 40 mesh brass 55. adapted to expose the surfaces to be treated to screen may be usedvfor this purpose. Its size was said evaporators and hold them ina plane par determined from the arrangement shown in Fig. allel to the plane of said boatsl and spaced there 2, the size of the screen being determined from from; ‘a foraminous screen having the form'of an lthe diameter of the lens plateand the position Aoi' the boats'in'dicatedin-Fig. 2. - " ’ equilateral triangle', positioned between said boats Y It will be apparent to those skilled in the art . 60 and said holder, parallel to the plane’of said boats, oriented> so that ' said _ boats lie symmetrically 'that my invention is not limited to the use of f evaporating boats but that the'same general ar- Y rangement may be used with other types of evap-` " .orators such as wire helices, straight wire fila ments or the like. » ‘- » from said holder that said screen just covers said 65 boats when viewed from the point of intersection In Fig. 2, the’lenses Ill are vsupported on an ap ' propriate lens plate L which is mounted on a shaft l5. across the corners of the projection of said screen on the plane of said boats’ and at such a distance shaft carries onl its 'opposite end an " ` of the plane of said objects and an axis perpen dicular to the plane of said boats andpassing through the center of said screen. v ` GLENN L. DIMMICK.