United States Patent [191
`Ehrenwald et al.
`
`\[11] Patent Number:
`[45] Date of Patent:
`
`4,467,172
`Aug. 21, 1984
`
`[54] METHOD AND APPARATUS FOR LASER
`ENGRAVING DIAMONDS WITH
`PERMANENT IDENTIFICATION
`MARKINGS
`[75] Inventors: Jerry Ehrenwald, 4001 Judith La.,
`Oceanside, NY. 11572; Carl B.
`Miller, Jr., Saddle Brook, NJ.
`[73] Assignee: Jerry Ehrenwald, Oceanside, N.Y.
`[21] App1.No.: 455,329
`[22] Filed:
`Jan. 3, 1983
`
`[51] Int. Cl.3 ............................................ .. B23K 27/00
`[52] U.S. Cl. ...................... .. 219/121 LH; 219/121 L]
`[58] Field of Search
`219/121 LM, 121 L, 121 LH,
`219/121 LJ, 121 LY, 121 LA, 121 LB, 121 LP,
`121 LQ, 121 LR, 121 LZ; 372/13, 22, 23, 106;
`350/397, 407, 393; 307/427; 125/30
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`2,351,932 6/1944 Deckelet al. ................ .. 350/407X
`
`3,407,364 10/1968 Turner . . . . .
`
`. . . . . .. 372/106 X
`
`219/121 LM
`3,527,198 9/1970 Takaoka
`219/121 LR X
`3,622,739 ll/l971 Steffen ....... ..
`219/121 LZ X
`3,775,586 11/1973 Flint et al.
`4,048,515 9/ 1977 Liv ...................................... .. 372/22
`
`FOREIGN PATENT DOCUMENTS
`
`0048489 4/1980 OJapan .......................... .. 219/121 LB
`
`0077989 6/1980 Japan . . . . . .
`
`. . . . . .. 219/121LZ
`
`Primary Examiner—-C. L. Albritton
`Attorney, Agent, or Firm-Natter & Natter
`
`ABSTRACT
`'
`[s7]
`A laser system for inscribing permanent identi?cation
`markings on or below the surface of a diamond. A shal
`low penetration depth and narrow line width is
`achieved by Cusing a harmonic conversion device to
`produce an output frequency which is the second har
`monic of the fundamental laser frequency in combina
`tion with a lens system having a short focal length to
`provide a high density pinpoint spot of laser energy.
`The energy intensity can be further regulated by a po
`larization attenuator. In operation, the diamond is
`mounted on a rngvable support structure which insures
`proper relationship to the laser beam. The process is
`activated by a computer which supplies positional com
`mands to the movable support and is interfaced with the
`laser for generating programmed alpha-numeric se
`
`quences.
`
`.
`
`17 Claims, 3 Drawing Figures
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`/
`2
`i / j 1 I E
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`'8
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`2B
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`LIGHT PUMP
`POWER SOURCE
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`‘
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`/
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`32
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`2'5
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`‘23
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`$4
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`‘36
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`l6
`/
`2.4 29
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`'r
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`A”
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`o- SWITCH
`26 / POWER SOURCE
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`- 1
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`METHOD AND APPARATUS FOR LASER
`ENGRAVING DIAMONDS WITH PERMANENT
`‘ IDENTIFICATION MARKINGS
`
`TECHNICAL FIELD
`This invention concerns a technique for inscribing
`indicia in precious stones and especially an application
`of light ampli?cation by stimulated emission of radia
`tion for engraving permanent identi?cation markings.
`In particular, this invention relates to a laser imprint
`ing system for depth controlled etching on or below a
`diamond surface.
`
`4,467,‘ 172
`2
`By way of further background, it should be under
`stood that in order for the electromagnetic laser radia
`tion to vaporize the diamond surface, a critical energy
`level must be reached. Radiation below this threshold
`energy level is transmitted through the diamond. When
`the laser power supply source is increased to produce
`laser energy above the critical level, the diamond sur
`face will vaporize forming carbon and pyrolithic graph
`ite which, in turn, absorbs further energy in an uncon
`trolled avalanche effect producing a deep penetration
`mark. That procedure was unacceptable when working
`with diamonds which require precise control over
`depth of cut or subsurface marking.
`
`15
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`40
`
`BACKGROUND ART
`There has been a long sought need for a reliable de
`tection procedure which would verify the identity of
`precious stones such as diamonds. Conventional meth
`ods of identifying diamonds relied upon photographs
`20
`and/or written descriptions of the physical fearures of
`the stone such as the shape, cut, weight, measurements,
`proportions and the like. It was dif?cult using these
`variables to locate and recover specific pieces of lost or
`stolen jewelry especially if the items were altered as by
`cutting, drilling or polishing.
`'
`A protection system which would provide a depend
`able method of recognition would thus be particularly
`' useful not only to jewelry owners but also to the insur
`ance industry.
`30
`' A prior scheme for identifying diamonds involved,
`the process of photographing a pattern of re?ections
`created when a low level laser light beam was passed
`through the stone. This re?ection pattern was then
`stored in a computer at a central registry for later use. A
`35
`disadvantage of this system was that by altering the
`diamond surface structure such as by repolishing a
`facet, the re?ection pattern could be changed thus de
`feating the possibility of subsequent reidenti?cation.
`Another shortcoming of that system was that local
`jewelers had to acquire the laser and photographic
`equipment for making the photographs, and further
`more later identi?cation was dependent upon veri?ca
`tion from the central registry.
`The ability to inscribe permanent markings directly in
`a diamond could have expedited the identification pro
`cedure and furthermore could also have served as a
`theft deterrent.
`‘A problem encountered in the prior art with regard
`to inscribing on diamonds was to develop an effective
`method for‘ penetrating the extremely hard surface
`without damaging the diamond. Although the use of
`laser energy was previously applied for altering the
`surface of a workpiece such as typically illustrated in
`U.S. Pat. Nos. 4,336,439 and 4,028,532, those proce
`dures were not directed to engraving in a diamond
`surface and consequently were not concerned with the
`problems inherent when inscribing in this material.
`Other attempts at laser inscribing were noted in U.S.
`Pat. Nos. 3,657,510 and 4,032,861. These last mentioned
`methods utilized a mask having a cutout portion de?n
`ing a given pattern and did not contemplate engraving
`in a diamond surface in characters that were invisible to.
`the naked eye. Another method for working diamonds
`with the use of laser energy was shown in U.S. Pat. No.
`3,537,198. That method, however, did not solve the
`problem of controlling the depth of laser penetration
`and engraved line size.
`
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`SUMMARY OF THE INVENTION
`Brie?y, the nature of this invention involves a laser
`system for providing a focussed spot of electromagnetic
`radiation on or into a diamond for engraving selected
`indicia. The diamond is rigidly mounted in an appropri
`ate ?xture which securely holds the diamond in correct
`relationship to the focussed spot of the laser beam. In
`this preferred procedure, the target surface coincides
`with the girdle portion of the gem stone. The diamond
`is programmable for movement with respect to the laser
`beam.
`The laser system encompasses a continuous-mode,
`solid state laser and an acousto-optical Q-switch for
`providing short duration high energy pulses. In addi
`tion, an optical system is incorporated whereby penetra
`tion and line width can‘ be controlled by the depth of
`?eld as opposed to beam intensity. The instant invention
`achieves a shallow penetration depth and pinpoint spot
`size by utilizing a multiple of the fundamental laser
`frequency, in this instance the second harmonic, in com
`bination with a short focal length lens.
`A further feature of the precision laser control of this
`invention includes the adaptation of a polarization de
`vice for modifying the amplitude of the output beam to
`further control energy intensity.
`Another aspect of this invention concerns the incor
`poration of a binocular viewing system to allow accu
`rate positioning and focussing of the laser beam on the
`diamond. In addition, the laser engraving operation uses
`computer programs to supply positional on and off
`commands and also to generate a selected alphanumeric
`sequence.
`'
`
`An advantage of this invention is that precise control
`can be maintained over the engraving operation which
`is of particular concern when working with precious
`materials, especially diamonds.
`Another aspect of this invention is the recognition of
`a speci?c target area on the diamond surface for engrav
`ing which does not deter from the appearance or physi
`cal characteristics of the diamond and further which
`would not subject the diamond to fracture.
`In view of the foregoing, it should be apparent that
`the present invention overcomes many disadvantages of
`the prior art and provides an improved method for laser
`engraving which is readily adapted to function as an
`identi?cation system for diamonds.
`Having thus summarized the invention, it will be seen
`that it is an object thereof to provide a protection sys
`tem for precious stones which involves the engraving of
`permanent identi?cation markings using laser energy.
`Speci?cally, it is an object of the present invention to
`provide an apparatus for vaporizing selected portions of
`the material on or below the surface of a diamond
`through the application of laser energy.
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`DESCRIPTION OF THE DRAWINGS
`25
`In the accompanying drawings in which are shown
`possible exemplary embodiments of the invention:
`FIG. 1 is a schematic view with a portion in elevation
`showing the laser engraving apparatus of this invention;
`FIG. 2 is a perspective view of a diamond which has
`been engraved in accordance with the process of this
`invention; and
`FIG. 3 is an enlarged partial sectional view taken
`substantially along line 3—-3 of FIG. 2 showing the
`material removed.
`
`35
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`40
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`4,467,172
`3
`4
`Another object of this invention is to provide con
`ration to a beam resonating state, a high power, short
`trolled depth of penetration for the laser using an opti
`duration pulse of coherent radiation is emitted produc
`cal system having a short focal length for a pinpoint
`ing the output beam 22.
`,
`focussed spot size of high energy density.
`In addition, an electromechanical shutter 28 is posi
`Another object of this invention is to provide supple
`tioned within the cavity resonator 16 so that the output
`mental laser controls for regulating the intensity of the
`beam 22 can be gate controlled by computer pro
`grammed commands.
`laser energy output.
`A still further object of this invention is to provide a
`It should be understood that the YAG rod 12 emits
`laser engraving apparatus having binocular viewing
`electromagnetic radiation having a wavelength of
`system of the target area.
`10,600 angstroms (1.06 microns). In order to achieve a
`Still another object of this invention is to provide a
`smaller focussed spot size having a greater power den
`sity and shallow depth of penetration, using a ?xed
`laser engraving method and apparatus which is reliable
`focus optical system, the coherent radiation within the
`in use and well adapted for its intended purposes.
`Other objects, features and advantages of the inven
`cavity resonator 16 is modi?ed by a second harmonic
`frequency generator 30. The harmonic frequency gen
`tion in part will be obvious and in part will be pointed
`erator 30 uses a lithium iodate crystal to effectively
`out hereinafter.
`With these ends in view, the invention ?nds embodi
`convert the 1.06 micron wavelength to 0.532 microns
`and correspondingly doubles the frequency. The num
`ment in certain combinations of elements and arrange
`ments of parts by which the objects aforementioned and
`ber of pulses within a ?xed time frame remains constant
`at 3,000—5,000 pulses per second.
`certain other objects are hereinafter attained, all as
`It will be further apparent hereinafter that, since the
`more fully described with reference to the accompany
`ing drawings and the scope of which is more particu
`spot size is a function of wavelength, this modi?cation
`larly pointed out and indicated in the appended claims.
`of the fundamental frequency to a second harmonic
`effectively tailors the wavelength to the optical system.
`With regard to amplitude modulation, coarse control
`can be obtained by regulation of the current to the light
`pump power source 15. Fine control, however, can be
`achieved, in accordance with this invention, by applica
`tion of an extracavity attenuation device 32. The attenu
`ation device 32 is comprised of a pair of polarizers 34,
`36. As an exemplary illustration, the polarizer 34 is ?xed
`and the polarizer 36 is rotatable such that the transmit
`ted energy beam 22 is a function of the vector sum of
`the relative positions of the polarizers 34, 36. It should
`thus be apparent that the amplitude of the wavelength
`can now be ?nely tuned without affecting the parame
`ter of pulse duration.
`I
`The transmitted energy beam 22 is next passed
`through a beam expander 38 which incorporates a lens
`system 23, 25 for enlarging the transmitted beam 22
`whilesimultaneously reducing the divergence to yield
`the required F/number.
`.The beam 22 is thereafter directed through an optical
`system 42 that includes a dichroic beam splitter 44
`which reflects the beam 22 90 degrees. The beam 22
`then passes through a short focal length objective lens
`46. It should be noted that the beam splitter 44 totally
`re?ects the laser radiation but simultaneously transmits
`the remaining visible light 48 which is then fed to a
`binocular viewer 50. The binocular viewer 50 is prefer
`ably equipped with an adjustable cross hair such that
`the beam 22 and cross hair can be brought into coinci
`dence. Additionally, as a safety measure, the binocular
`viewer 50 is equipped with a shutter device 52 so that
`viewing by eye is not possible when the laser engraving
`apparatus 10 is activated. A remote closed circuit televi
`sion camera (not shown) can be employed for monitor;
`ing the actual engraving procedure if desired.
`Referring now to the lens 46, it should be noted that
`this is a short focal length objective lens having a low
`system F number, e.g. 30 mm., and that the energy beam
`22 has been modulated for compatibility with the ?xed
`optical system 42.
`In operation, a diamond 54 is placed within a holding
`?xure 56 and the beam 22 is focussed on a target area or
`marginal band between a crown 55 and a pavilion 57
`and referred to as a girdle 58. The beam 22 can also be
`' focussed below the target surface.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`Referring now in detail to the drawings, the reference
`numeral 10 denotes generally the arrangement of appa
`ratus for performing the laser engraving technique in
`accordance with this invention. A solid-state laser de
`vice preferably comprised of ions of a transition metal
`such as neodymium embedded in host material of yt
`trium aluminum garnet (Y AG) and formed as a rod 12
`45
`which is optically excited or “pumped” by a linear ?ash
`lamp 14 for continuous emission of coherent electro
`magnetic wave radiation in a single transverse, mode.
`The ?ash lamp 14, such as a DC. krypton lamp, is
`controlled by an electronic light pump power source
`15.
`The YAG rod 12 and linear lamp 14 as noted in FIG.
`1 are contained within an optical cavity resonator 16
`having a pair of plane, parallel re?ective mirrors 18, 20.
`The mirror 18, however, is partially-transmitting such
`that an output beam 22 will escape through mirror 18
`upon reaching a threshold energy level or peak pulse.
`In order to achieve the high energy peak pulse, a
`Q-switch 24 is utilized within the cavity resonator 16
`and is operated by a power source 26. The Q-switch 24
`in this typical embodiment is acousto-optical in nature
`and intended for excitation by an RF (radio frequency)
`?eld which changes the index of refraction of a crystal
`material and bends the emitted radiation out of the
`cavity resonator 16 so that it will not resonate or gener
`ate the output beam 22. This results in a population
`inversion in that there are more ions in a high energy
`level within the resonator and subsequently, upon resto
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`mark 72.
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`4,467,172
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`including short focal length objective lens means for
`It has been found that the inscription of permanent
`markings within this target area 58 is substantially im
`directing the transmitted radiation to a focussed spot at
`perceptible to the naked eye although clearly visible
`the target surface, conversion means within the optical
`cavity for modifying the radiation wave length to con
`under magni?cation such as with a ten power (10X)
`loupe. Furthermore, the focussed beam 22"‘u'sing the
`form with the focal length of the lens means, said con
`version-means including a harmonic crystal generator
`short focal length lens 46 will generate a high intensity
`pinpoint spot wherein the critical density level is rap
`providing a multiple harmonic of the fundamental radi
`idly reached.
`ation frequency with the converted wave length being
`compatibly focusable by the lens means for providing a
`The holding ?xture 56 is mounted to a positioning
`shallow penetration depth in the target surface.
`table 60 having respective slide members 62, 64, each
`adapted for selective independent translatory displace
`2. A laser apparatus as claimed in claim I wherein the
`harmonic conversion produces an output frequency
`ment in perpendicular directions in a horizontal plane.
`which is the second harmonic of the fundamental radia
`The movement of the positioning‘table'60isicontrolled
`tion frequency at one-half the wave length.
`by a programmed sequence with=a"'co‘1nputer 66. In
`3. A laser apparatus as claimed in claim 2 further
`addition, the shutter 28 is interfaced with the computer
`including power attenuator means for adjusting the
`66 so that the beam 22 can be regulated for on-off gating
`radiation amplitude and corresponding energy density
`to form a series of depressions 68 (see FIG. 3) and to
`of the focussed spot.
`generate a selected alphanumeric code, typically shown
`4. A laser system as claimed in claim 3 further includ
`by letters 70 in FIG. 2. It should also be noted that the
`ing beam expander means having a lens system for en
`beam 22 is capable of producing a subsurface occluded
`larging the radiation beam while simultaneously reduc
`ing its divergence.
`5. A laser system as claimed in claim 3 wherein the
`power attenuator means includes at least one ?xed and
`at least one rotatable polarizer within the path of radia
`tion whereby the transmitted radiation is a vector sum
`of the relative polarizer positions.
`6. A laser system as claimed in claim 4 further includ
`ing beam splitter means for directing the radiation to the
`focussing lens and viewer means for monitoring the
`target surface through the beam splitter means.
`7. A laser system as claimed in claim 6 further includ
`ing positioning means for displacing the target surface
`with respect to the focussed spot, said positioning
`means including a positioning table controlled by a
`computer.
`8. A laser system as claimed in claim 7 wherein the
`computer is interfaced with a shutter for on/ off gating
`of the radiation pulses, whereby the focussed spot on a
`selected area of the target surface will conform to a
`programmed code.
`9. A laser system as claimed in claim 8 wherein the
`switch means includes an acousto-optical Q-switch.
`10. A laser system as claimed in claim 9 wherein the
`source of electromagnetic energy is solid-state neodym
`ium yttrium aluminum garnet rod.
`11. A laser apparatus as claimed in claim 10 wherein
`the harmonic generator utilizes a lithium iodate crystal.
`12. A method for laser engraving permanent identi?
`cation markings in the structure of a diamond including
`the steps of
`(a) mounting the diamond in a ?xture,
`(b) generating a beam of laser radiation at a constant
`wave length,
`(0) modifying the wave length by harmonic conver
`sion for compatibility with a ?xed short focal
`length lens system,
`(d) selectively focussing the laser beam either on or
`below a target surface area on the diamond,
`(e) displacing the ?xture with respect to the focussed
`beam in accordance with a computer program A
`sequence,
`(f) coordinating on/off laser beam transmission by
`interfacing the computer with the laser for imprint
`ing a desired format on the target surface area of
`the diamond.
`13. A method for laser inscribing identi?cation mark
`ings as claimed in claim 12 wherein the focussed laser
`
`Both the surface and subsurface marking .1Can be
`readily accomplished with precision and accuracy since
`the programmed movement of diamond 54‘with respect
`to the ?xed focussed beam produces a scan format. The '
`character size is within the range 010001-0005 inch
`(25-125 microns) in both height and width and has a line
`width of less than 0.001 inch (25 microns). The depth of
`penetration is less than 0.002 inch (50 microns) for sur
`_ face marking leaving an open cut.
`It should further be observed that the impinging elec
`tromagnetic energy stimulates the diamond atoms to
`release thermal energy and that a portion of the
`diamond in the immediate area-is thus vaporized leaving
`a track of carbon and pyrolitic graphite. The so formed
`black residue does not have an detrimental effect on the
`diamond, however removal can be achieved from the
`open cut inscription through the application of approxi‘
`mately 700 degrees centigrade of heat and hydrochloric
`acid treatment. The remaining impression than takes on
`40
`a clear to white or frosted appearance as viewed under
`magni?cation. An alternative treatment is to fill the
`newly formed depressions with a distinctive color mate
`rial so as to present a contrasting surface with the sur
`rounding diamond face. The carbon and graphite
`formed in the occluded mark 72 cannot be removed,
`however this is not detrimental to the appearance or
`value of the stone.
`Thus, it will be seen that there is provided a method
`and apparatus for laser engraving permanent identi?ca
`tion markings which achieves the various objects of the
`invention and which is well adapted to meet the condi
`tions of practical use.
`’
`Since various possible embodiments might be made of
`the present invention and various changes might be
`55
`made in the exemplary embodiments set forth, it is to be
`understood that all material set forth or shown in the
`accompanying drawings is to be interpreted as illustra- ‘
`tive and not in a limiting sense.
`Having thus described the invention, there is claimed
`as new and desired to be secured by Letters Patent:
`1. A laser apparatus for inscribing permanent mark
`ings selectively on or below a target surface comprising
`a source of coherent electromagnetic radiation in a
`continuous mode having a fundamental radiation fre
`quency, resonator means including an optical cavity,
`switch means for transmitting short duration pulses of
`said radiation from the cavity, ?xed focus optical means
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`beam forms a blackened residue on the target surface
`when vaporized, and further including the steps of
`(g) removing the residue and
`(h) ?lling the depressions with a selected material for
`contrasting with the diamond surface.
`14. A method for laser inscribing identi?cation mark
`ings as claimed in claim 13 wherein the focussed laser
`beam has a penetration depth of less than 50 microns.
`. 15. A method for laser inscribing permanent identi?
`cation markings as claimed in claim 14 wherein the
`
`8
`inscriptions have a character size within the range of
`25-125 microns.
`16. A method for laser inscribing identi?cation mark
`ings as claimed in claim 15 wherein the target surface
`area is on a girdle portion of the diamond.
`17. A method for laser inscribing identi?cation mark
`ings as claimed in claim 12 wherein the imprinted for
`mat is occluded below the target surface.
`it
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