US2463280A - Spectroscope grating having spaced zones of diffraction lines - Google Patents

Description

March 1949.

- F. J. KAEHNI El AL sPEcTRoscoPE -GRATING HAVING SPAGED ZONES OF DIFFRACTION LINES s sheets-#sheet 2j Filed Feb. 16'. 1943v FIEL? FI E. E

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March 1, 1949. F.' J. KAEHNI ETAL 2,463,280

SPECTROSCOPE GRATING HAVING SPACED ZONES OF DIFFRACTION LINES Filled Feb. 16,1945 s sheets-sheet s nl l '22 F1517' 20d 27 26 42 gnll d @6 M4 n JU. 26 J2 1 l z2 l 3 l l a l J L. A 'jj' l l NVENTOR -A BY Z/rLLLf/MZ /fffEH/nrf Patented Mar. 1, 1949 SPECTROSCOPE GRATING HAVING SPACED ZONES OF DIFFRACTION LINES Frank J. Kaehni and William L. Kaehni, Cleveland, Ohio Application February 16, 1943, Serial No. 476,082

4 Claims.

This invention relates to a new form of spectrum gratings commonly called diffraction gratings, and the essential objects include producing such a grating upon surfaces .of transparent bodies. An advantage of our invention is its adaptability for use on plain or plate glass without the necessity of tedious time-consuming preparatory grinding operations. An object is to provide a method for so treating such surfaces as to produce thereon a minutely, nely, even spaced series of lines of uniform character, with comparative cheapness and within a remarkably short time.

More specilc objects are to trace essentially circular gratings, forming such lines in almost perfect circular bands .or AZones with uniformity and accuracy and by the most simple method, and of any desired spacing from a few say, 100 to an inch up to as many as is practicable for the intended use. It is entirely possible to make, and in fact we have made, gratings by our method with line divisions ranging from 20,000 to 40,000, or even more, uniformly spaced lines per inch.

A more specific object is to provide a method or means for tracing such lines by a relatively rotary motion between the tracing stylus forming the diffusion and diffraction edges or opaque lines, and the surface upon which the line is being traced, while advancing the stylus relative to each preceding line and in one continuous operation for any given diffraction band or zone. An important characteristic of the process is the maintaining of the line forming point in constant contact, avoiding lifting of it, intermittent on opposite sides of a transparent body such as a plate or block of glass.

In addition to simplicity, cheapness of manufacture and ease of obtaining unusual accuracy in the making of diffraction gratings, which will meet the requirements of a wide variety of oommercial laboratory and scientific uses, this cir-' cular band arrangement opens new fields of uses of accurate grating spectroscopes, as well as lending accuracy to cheaper, more quickly produced forms ordinarily chosen for widespread everyday uses.

Some of the examples of useful applications of our invention include night-sights; use in optical instruments in place of or in combination with cross-hairs; eye testing instruments for comparison of the two eyes for the differences in color response; and range finders and direction instruments of remarkable accuracy; blackout warning signals having a definite operational effect giving distance by color readings; as indicators of direction and color of a source of light.

Aside from the foregoing uses, innumerable decorative effects on flat glass Wear, hollow glass and opaque table Ware, mirrors, and numerous other uses may be effected. The tracingV of the spacing movements and other troublesome steps in previous processes.

Other objects include the mounting of a stylus such as a diamond point so that it may firmly hold against movement which would permit variation of line spacing and yet which permits a resilient, almost perfectly uniform contact pressure against varying surfaces or undulations, such as occur on common glass or commercial plate glass.

Still other objects are to provide series of concentric circular zones of continuous spiral diffraction lines on the same surface and the lines of each zone being of predetermined spacing having such relationships to the neighboring zone, as may be desired for many purposes, some of which are hereinafter mentioned.

Still another object is to provide diffraction gratings in substantially circular co-axial bands spirals on a common axis may be modified by advancing the circular movement of the stylus acrossvthe surface being treated and modifications of the circular movement into angular, polygon or fanciful designs have been found to give rainbow effects of a variety of patterns in striking beauty.

Reproductions upon plastics may be made by dies formed by the same method, then with the die gratings so formed on them they are used to impress the lines on the surface of the plastic transparent bodies.

The foregoing various other objects will become apparent in the following specifications and we desire that it be understood that the uses herein mentioned are indeed but a few of the possibilities for both scientific and pleasure giving purposes for which our invention may be adapted.

A number of embodiments of our invention are described in connection with the accompanying drawings in which are indicated various types of diffraction grating formations and groupings.

In the drawings we also show an illustrative form of mechanism for carrying out our process.

Fig. 1 is a face view of a transparent plate bearing grating lines formed according to 4our invention.

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Fig. 2 is a transverse section of same.'

Fig. 3 is a face view of a similar transparent plate having a wide zone of grating lines.

Fig'. 4 is a similar plate showing the grating lines formed into separated zones.

vFig. 5 is a section through a'gratlng such as Fig. 3, showing light lines from a source through the grating, to the eye.

Fig. 6 is a modified form showing a narrow band of grating lines on a circular transparent plate with an opaque center piece.

Fig. 7 is a transverse section through the same.

Figs. 8 and 9 are face and section views showing an arrangement of three narrow zones of grating lines.

Figs. 10, 11 and 12 are sectional views showing in greatly enlarged scale in conventional form the approximate nature of the opaque or diffusion lines formed on or in the plate surfaces.

Fig. 13 is a diagrammatic sectional view showing two grating plates mounted in a sight tube with a lens and illustrating passage of light from a source of light to the eye.

Fig. 14 is a similar view showing a grating such as Fig. 6 mounted in a different form of tube.

Fig. 15 is a sectional view showing gratings on opposite faces of the transparent block.

Fig 16 illustrates a disc-like grating in half circular form with a spectrum band thereon showing diffraction sighting.

Fig. 17 is a conventional plan view illustrating a mechanism for forming the grating lines.

Referring for convenience toFigs. 1, 2 and 17 we will rst describe our preferred method of forming the spaced diffraction lines upon a plane surface. A block I, shown as rectangular, having been cut from suitable plate glass, with both surfaces of the usual approximate accuracy and without preliminary grinding treatment, is selected of a size suitable for the contemplated use of the intended grating. A thickness such as shown in Fig. 5 is suitable for many purposes,

although as shown in Fig. 2, for other uses greater thickness is preferred.

The plate or block I is first mounted against the flat surface of the face-plate carrier I2 and held rmly as by spring clamps I4. The face plate is preferably rigid with a shaft I5 mounted in bearings I6 and I1 and arranged to be driven at a uniform speed by any suitable driving mechanism. 'Keyed to the shaft I5 is shown a gear 20 meshing with a pinion 22 on a shaft 25, mounted in bearings conventionally indicated at 2B and 21, and driving screw or worm 28 in turn meshing with its worm gear 30 on a shaft 32.

The shaft 32 is provided with a screw worm 35 driving the worm gear 36 to rotate a master feed screw 40 to which it is firmly fixed. The feed screw 40 is preferably provided with accurately tted bearings 42 and 44, the latter being provided with a thrust bearing collar 45, fixed on the screw shaft and at the outer side of the bearing may be provided a micrometer-like adjustment indicated at 48 which may be operated to tighten the screw by knurled nut 49. As shown, v

beneath the feed or lead screw 40 is provided a cross slide 50 having a common form of dove-tail guide 52 rising therefrom andengaging a guiding tool carrier slide 54, having a master feed nut engagement withthe screw as indicated at 56.

Transversely slidabie on the carrier 54 is tool carrier proper, 60, having a manually operated micrometer adjustment designated 62. Suitably mounted on the tool carrier as br.' screws 63 is a tool holder 65, in turn carrying a resilient cutthat at which it may heat to any such degree as,

ting tool arm 68 having at its free end a marking or cutting part such as a diamond point indicated at 10.

In operation the spacing of the grating lines having been predetermined, the ratio of the gears as at 20 and 22 having been selected as those shown in solid lines, the alternate gearing, comprising different sizes of gears and pinions as in a change-speed back gears being indicated at 23 and 24, it will be seen that as the work piece or grating plate I is rotated'wlth the carrier face plate that the worm and gear transmission 28 and 30 and 35 and 36 will rotate'the master feed screw 40 relatively slowly, that is, perhaps one revolution of the screw for each or 200 revolutions of the work plate. thus the tracing point moving radially of the carrier axis, spiral lines such as indicated at 2 and 3 on a plate in Fig. l with a spacing of 2,000 to 4,000 per inch will be formed.

As a specific example, if it be desired to make grating lines on the plate surface spaced 2,500 lines per inch, assuming that the lead screw 40 had 20 threads per inch and is rotated by the first worm and gear couple at 20 to 1 ratio and by the second worm and gear couple at 25 to 1 ratio and the ratio between the plnion'and gear 22 and 2J is 1 to 4, we have 20 X 20 25, i. e. 10,000 divided by 4-the worm and pinion ratio resulting in 2,500 revolutions of the work piece for 1 Inch advance of the diamond point. If the ratio of the back gears between the shafts I5 and 25 be approximately 1 to 1, and the two worm and gear Icouples are each 100 to 1, the threads on the lead screw 40 at 20 per inch will give y20,000 lines and at 40 per inch, pitch of the lead screw will give 40,000 lines cut'or traced spirally on the surface as indicated at 1, 2 and 3 for each inch width measured on the radius from the axis of the plate. Y

The resilient arm 68 is preferably wider tha its thickness to resist lateral movement, but its thinness permits considerable resilient action or movement of the diamond point over any undulations which may be present on the plate surface without altering the pressure upon the diamond cutting stylus. Thus the depth of the cut in the surface is not large and yet the relative position of the cutter may be accurately maintained and a smoothness and regularity of the resultant grating likewise is accomplished, even though the surface vhas not been prepared by processes such as optical grinding.

The comparative accuracy of width and depth of `grating line without change in its uniformity, is likewise much more readily attained. than were the tool Jto be lifted and caused to re-engage the work as has been the practice in parallel line gratings. This comparision is* made because the speed with which reciprocating motion cutting has been done in the past is extremely slow. In contrast, we have cut spiral lines such as indicated in zones 1 to 2 inches wide as appears at 4 in Fig. 3 and on separated zones as at 6 and 1 in Fig. 4, in but a few minutes to an hour, depending @upon various conditions and essentially upon the required number of lines per Inch.

The cutting or tracing speed of the diamond point or stylus on the surface is maintained below will affect the surface or point. Also comparatively low speeds are used to avoid relative vibration, however, it will be seen that 3,600 lines may be traced on a band or zone 1 inch wide, measured radially at the rate of one revolution per second. That is, within one hour i. e. 3,600 seconds, the cutting tool would move across the surface l inch radially traveling, producing in effect 2 inches of grating on the diameter. If the outer circle is relatively small, speeds of several revolutions per second may be used, thus within practicable limits forming one to several inches of grating zone in a matter of minutes or part of an hour. Likewise, by rotating the work piece at one or two hundred revolutions per minute good results in grating line spacings from 8,000 to 15,000 or even 20,000 lines per inch may be attained, and such grating still requires only an hour or two, depending somewhat upon its size and the hardness of the surface being worked upon.

Fig. 5 illustrates a simple use of a single zone `diffraction grating and in this view a diffraction zone 4 corresponds to the arrangement shown in Fig. 3. Light passing from a source indicated at 8 as by lines 9 leads to the eye at the left. When the center line or normal axis of the grating is slightly out of line, as for example, as when passing through a point indicated by a cross or X in Fig. 3, the spectrum or spectra, as there may be several, depending on the distance between the grating and the eye and the source of light, will be seen' in narrow radial zones designated 5 in Fig. 3 and shown by the heavier lines in the grating. The narrow spectral radial zone will appear very much as the heavy shaded portion. This' serves as a guide line along which the grating or eye may relatively move to bring the source light through the center of the circular diffraction zone, at which time the spectrum will appear entirely around the circle. 'I'his circular spectrum is not attempted to be shown in the line drawings but with any arrangement of lines of suitable spacings in a zone such as shown in Fig, 3, primary and secondary, and even third and fourth spectrum may be seen, and each in full circular form.

The angle Y in Fig. 5-for the outer light line 9 is the same for a given color as is this angle measured in the same way as a light beam passing through parallel gratings. The advantage is, however, that instead of the grating being in a comparatively narrow band from a small slit for the light source, a pin hole opening or distant single light shows the entire spectrum in a circular band. In using gratings with straight parallel bands, the light source is usually arranged to show in a narrow line or extremely narrow slit through which the light passes and suitable readings may be taken only when the lines are parallel with the band of slit at the light source. In contrast a point light or distantsource or even a larger circular light may afford effects with our gratings, not possible with the parallel straight line grating.

We have not found in the prior art a mathematical expression for computing the angle for given colors at certain angular relationships. However, we have discovered that the angle Y, Fig. 5, has a simple relationship to the rst order spectrum. Assuming 8Z as light rays arriving parallel to the axis and normal to the plane of the grating:

Then the diffraction angle or angle of bending due to light diffraction arriving at the eye for any particular color or wave length may be expressed by the formulawhere 1 is tne wave length of the particular color; d is the grating spacing or distance between adjacent lines of grating and X is the angle as shown.

The spaced zones of Fig. 4 may ,correspond to the width of a given color or to several colors of the spectra and each producing its own spectra. The spectra will appear in uniform circles in any pair of zones or within the broad Zone of Fig. 3 very much as the zones 6 and 1 of Fig. 4. If two such plates or discs with the zones like Fig. 3 are spaced apart in true alignment and brought into axial alignment with the light source or target, before the full spectrum appears, visibility through the plate is only slightly less than through a cl'ear glass with cross hair line arrangement as the center lines are there shown. Obviously, very quick and accurate sighting may be made because the target is visible and it may be brought down the narrow band or beam of the spectrum from either sight to the center as described in connection with the band 5 in Fig. 3, and one, two, or more zones of complete spectra appear, as in Fig. 4, the plane of the grating will be controlled normally to the line of sight t0- ward the source of light. For certain purposes an opaque center may be formed and it is found useful for a narrow band of wave lengths formed by a narrow band grating, as at 4a in Fig. 6, the opaque center being formed of any suitable material as opaque cutting or a disc as indicated at small d, Figs. 6 and 7. Several bands, suchas 4b, 4c and 4e in Figs. 8 and 9,*may be used for various effects, for example, by properly spacing the lines for each band according to the above formula, the same color, for example, red, can be obtained over the entire field of each narrow band at a predetermined distance from the light source 8.

Incidentally, this produces very striking ornamental effects when the grating is viewed at different angles with relation to point source of light.

In tracing the lines on ordinary plate glass, we have found that diamond point producing diffraction lines indicated conventionally in very much larger scale in Figs. 10, 11 and 12, as indicated by L, L and L", are formed about as follows: A spring tension holder, or a spring arm support, indicated at 68 in Fig. 17, carrying a diamond point 10, is brought into contact with the glassA surface and a movement of a few thousandths of an inch of the carrierl toward the glass to give a slight fraction of an ounce of pressure will produce lines of the approximate contours shown in Figs. l0, 11 and 12, and evenly spaced. The spring tension does not cause the diamond to penetrate more than the distance of .005 of an inch but it will apparently press into the glass without cutting action, deforming the surface in a line appearing perhaps, one-ten/thousandth of an inch deep, more or less.

Minute irregularities of the diamond point apparently do not adversely affect results. A scratchy diamond point will produce lines attempted to be illustrated in cross section at Fig. 12. Diffusion or diffraction effect, however, is such that light rays passing through are distorted by the cut portion of the grating surface thereon, and such lines pass away from the eyes or the eye-piece, leaving the true diffraction effect of the undistorted surface of the eld functioning, so far as visibility and photographic purposes are concerned, about as effectively as though the grating were formed by alternate transparent and opaque lines.

In Fig. 13 the grating members f and y are manso shown as mounted in a tube T with the grating bands lh and 4k respectively at slightly different zones and the eye-piece E may comprise a suitable lens for the purpose desired.

Fig. 14 shows mounting of a grating plate or disc such as shown in Fig. 6, with the opaquecenter disc d and single grating band 4a. Here the ends of the telescoping tube formed of two parts, Tl and T2, will produce concentric rings of color or light emitting from the eye-piece hole H, where light is admitted through a small hole HI from the light source as shown at C. By graduated lines indicated conventionally at S, visible colors of the spectrum can be predetermined. Analysis of atmospheric conditions may be facilitated. The spacing of the spectrum colors with relation to the spacing between the opening Hl and rality of spectroscopic circular coaxial grating i zones on the same plane, and spaced apart predetermined distances and the lines of each zone having predetermined spacing relationships to the line spacing of another grating zone.

3. A transparent body having a planular surv face, a plurality of spaced apart concentric circular zones of diiraction lines on said surface,

the lines comprising minutely spaced grooves formed in the surface separated by uncut portions, the spacingl of the lines for each zone bethe grating 4a, may afford accurate light analysis for various purposes.

Fig. 15 shows grating zones on the opposite sides of a parallelled sided block and the light effects from a given source assume very definite contrasts as a result of change of distance from the light of the gratings affording means of measuring distance or small angle differences. y

Fig. 16 shows the use of a half disc preferably with lines so spaced that a spectrum will appear in a narrow band shown in darker lines and by which a sharp angle reading may be made, for example: the change incolor of a single light out of the line of vision of a driver in a vehicle` will appear in the form of a darkened band when seen through a window or windshield.

We do not wish to limit the scope of our present invention to the illustrative forms, scientific and decorative uses and effects described and shown except as properly distinguished from prior gratings and as defined in the appended claims.

We claim:

1. A transparent spectroscope grating having separated coaxial circular zones of grating lines of predetermined spacing and a relation to each other and uniformly spaced in each zone, Whereby diiracted light rays through one may pass through the other and be observed at a common point.

2. A transparent body having thereon a pluing uniform throughout the zone, the spacing of the lines of one zone having a predetermined relation to the spacing of the lines of adjacent zones, and thespacing resulting in diffracting color to a common point on the axis normal to the plane and concentric with the zone circles.

4. A spectroscope comprising a transparent body having parallel sides, grating lines comprising minute grooves of uniform depth formed in a circular zone on opposite sides and within concentric circular bands, the spacing of lines being such that light diffracted into the body from one band is again difracted by the second band to a focal point on an axis concentric with both zones.

FRANK J. KAEHNI. WILLIAM L. KAEHNI.'

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 551,769 Jacobson Dec. 24, 1895 FOREIGN PATENTS Number Country Date 501,645 Great Britain Feb. 28, 1939 OTHER REFERENCES Physical Optics, by R. W. Wood; 1934 edition; page 253 cited.

Light, by Lewis Wright, second edition, published 1892, pages 178 and 179 cited.

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