ale-1a?
`23/30/83
`
`SR
`lie-4011876
`
`‘3R
`
`United States Patent [191
`Cooper
`
`[11]
`[45]
`
`4,401,876
`Aug. 30, 1983
`
`[54] WORKING GEMSTONES
`[76] Inventor:
`Martin Cooper, 38, Marsden Green,
`Welwyn Garden City,
`Hertfordshire, England
`[21] Appl. No.:
`264,710
`May 18, 1981
`[22] Filed:
`Foreign Application Priority Data
`[30]
`May 20, 1980 [GB] United Kingdom ............... .. 8016669
`Aug. 7, 1980 [GB] United Kingdom ............... .. 8025737
`
`[51] Int. (31.3 ............................................ .. B23K 27/00
`[52] U.S. Cl. .......................... .. 219/121 LJ; 125/30 R;
`125/39; 219/121 LH; 219/121 LZ
`[58] Field of Search
`................ .. 219/121LH, 121LJ,
`219/121 LU, 121 LW, 121 LZ; 125/30 R, 36,
`39, 23 R
`
`[56]
`
`References Cited
`‘
`_
`U.S. PATENT DOCUMENTS
`
`3,440,388 4/1969 Otstot et a1. ........................ .. 219/69
`3,527,198 9/1970 Takaoka .... ..
`.219/121LMX
`3,700,850 10/1972 Lumley et a1. .................... .. 219/121
`FOREIGN PATENT DOCUMENTS
`877326 12/1979
`130138 3/1978
`133023 11/1978
`1057127 2/1967
`1059249 2/1967
`1094367 12/1967
`1254120 11/1971
`1265241 3/1972
`
`Belgium .
`Fed. Rep. of Germany .
`Fed, Rep. of Germany .
`United Kingdom .
`United Kingdom .
`United Kingdom .
`United Kingdom .
`United Kingdom .
`
`1292981
`1324903
`_ 1326775
`1377131
`1405487
`1446806
`2052369
`
`10/ 1972
`United Kingdom .
`7/1973
`United Kingdom .
`8/ 1973
`United Kingdom .
`12/ 1974
`United Kingdom .
`9/ 1975
`United Kingdom .
`8/ 1976 United Kingdom .
`1/1981 United Kingdom ........... .. 125/30 R
`
`OTHER' PUBLICATIONS
`Laser Institute of America, “Guide for Material Pro
`cessing by Lasers” 1978.
`“Industrial Diamond Review”, Mar. 1980, pp. 90 and
`91.
`“Laser Application Notes”, vol. 1, No. l of Feb. 1979.
`“New Hyperyag”, on Model DLPY 4-System 2000
`Yag Laser.
`'
`>
`“Diamonds”: N.A.G. Press LTD, Chapter Eleven, pp.
`235, 239-242.
`Primary Examiner——C. L. Albritton
`Attorney, Agent, or Firm—Shapiro and Shapiro
`[57]
`ABSTRACT
`In order to provide a better way of ker?ng a gemstone
`such as a diamond, a high energy, high pulse rate, low
`order mode, laser beam is employed to cut the kerf.
`Apparatus for ker?ng a gemstone can in general com
`prise a laser, re?ecting means which bends the incident
`beam through a substantial angle and which is moveable
`substantially parallel to the axis of the incident beam,
`and a focusing arrangement which focuses the beam on
`the gemstone.
`
`7 Claims, 4 Drawing Figures
`
`1
`
`TIFFANY 1012
`
`

`

`U.S. Patent
`
`Aug. 30, 1983
`
`4,401,876
`
`
`
`2
`
`

`

`1
`
`WORKING GEMSTONES
`
`BACKGROUND OF THE INVENTION
`Ker?ng is forming a groove in the gemstone, which is
`done prior to cleaving; cleaving is parting a gemstone
`along a cleavage plane. There is a description of ker?ng
`and cleaving in “Diamonds”, by Eric Bruton, 2nd edi
`tion, 1978, NAG Press, London.
`It will be understood that working a gemstone with a
`laser normally involves material removal, though in
`thermal cleaving the stone may be split along the cleav
`age plane without any material being removed. '
`The present description relates speci?cally to
`diamonds, but it is believed that it is generally applica
`ble to other gemstones although some of the effects may
`be markedly different, such as in diamonds the presence
`of clear cleavage planes, the formation of graphite and
`the resulting higher absorption of energy, and the
`higher thermal and mechanical strength.
`Working gemstones with lasers is found to give a
`combination of particular problems which is not met
`with when working other materials. For instance, the
`gemstones in general have a very low absorption of the
`laser energy, giving problems in reaching the working
`temperature; wastage of the gemstone must be kept
`very low due to the value of the gemstone material;
`likewise, a clean cut reduces later wastage of gemstone
`material; and chipping and subsequent blowing off of
`pieces of the gemstone can occur and can be very
`wasteful.
`Furthermore, ker?ng gemstones requires special
`measures in that a line must be cut, which is-more diffi
`cult than machining a spot, and the line must have a
`cross-sectional shape suitable for a subsequent cleaving
`operation.
`
`5
`
`20
`
`4,401,876
`2
`at ?rst (say about 15% at room temperature), there is
`enough energy absorbed rapidly to heat the diamond
`during a single pulse, and as the energy rises, the per
`centage energy absorption increases up to a temperature
`at which graphitisation occurs. Normally, a laser beam
`will be pulsed, either by chopping the beam itself (Q
`switched) or by pulsing the energy input. The heating
`effect is assisted by a high pulse rate (i.e. repetition rate),
`which allows high rates of energy emission. Preferred
`pulse rates are from 10 Hz upwards, the higher rates of
`20, 25 or 50 Hz or more (e.g. up to 85 Hz) being pre
`ferred. The rate however can be lower than 10 Hz. At
`10 Hz, the pulse energy would have to be very high in
`order to achieve the required heating effect, and below
`10 Hz, say at 5 Hz, the pulse energy required may be so
`high as to damage the stone. For this reason, the pre
`ferred minimum rate is 20 or 25 Hz, higher repetition
`rates being more viable economically. The upper limit is
`set when too much energy is put into the stone, causing
`damage. Pulse durations are preferably from 50 usec up
`to 150 uusec, a good duration being about 75 usec
`(usec: lO—6 see).
`A suitable energy range for the laser beam is 150 to
`1000 ml per pulse, the preferred energy being around
`400 m] per pulse (mJ: l0—3 J).
`The preferred laser is a solid state laser, e.g. a
`Nd/YAG laser, which produces a beam of a wave
`length of 106p, (;1.=1O“6 m). This wavelength is pre
`ferred for working diamonds as it produces a smaller
`diameter focussed machining spot and a greater depth
`of focus than say a C02 gas laser (106g). The size of the
`focussed spot is important in minimising wastage of
`gemstone. A greater depth of focus makes focusing less
`critical. The apparatus has a ?nite depth of focus, and,
`at the start of working, the surface of the gemstone is
`positioned roughly in the middle of the focal range; as
`the cut penetrates, the beam may become slightly out of
`focus, but once (in the case of diamonds in particular)
`cutting has begun and graphitisation has occurred, this
`is not critical. As an example, the depth of focus may be
`i075 mm and the depth of a kerf 0.5 mm. In general
`terms, the beam is focussed substantially on the surface
`of the gemstone.
`Suitable high energy, high pulse rate, low order
`mode, laser output can be achieved from a Nd/Y AG
`laser in several ways. The laser may be pulse pumped
`and arranged to produce a substantially Gaussian en
`ergy distribution output by aperturing the multimode
`output (non-Gaussian) from a conventional laser optical
`resonator. Alternatively, special laser resonator optical
`designs, such as an unstable resonator or a stable resona
`tor with an intracavity telescope, may be employed to
`produce a quasi or substantially Gaussian output energy
`distribution. Permissible pulse lengths in the region
`50-150 usec may be used for such systems although
`much shorter pulse lengths (l5 usec) can also be pro
`duced to machine diamond by tailoring the pulses from
`a pulse-pumped laser. Acceptable repetition rates with
`such lasers are from 10 Hz to 150 Hz; the preferred rate
`will depend on the type and quality of diamond being
`kerfed.
`A continuously pumped Nd/Y AG laser may also be
`used with suitable resonator optics and beam aperturing
`to produce a low order mode or substantially clean
`Gaussian output energy distribution. The output from
`such a laser must be Q-switched to produce high en
`ergy, high repetition rate pulses with acceptable pulse
`
`40
`
`45
`
`THE INVENTION
`The present invention provides a method of ker?ng a
`gemstone, comprising using a high energy, low order
`mode, laser beam. The present invention also provides
`apparatus for ker?ng a gemstone, comprising a mount
`for holding the gemstone, and a laser arranged to lase
`the gemstone with a high energy, low order mode, laser
`beam.
`A single order mode beam has a Gaussian energy
`distribution across the beam section, and a low order
`mode beam (which approximates to or is close to a
`single order mode beam) has a roughly Gaussian energy
`distribution across the beam section and hence a signi?
`cantly higher energy in the centre that at the edges.
`Such a beam produces good ker?ng geometry, that is to
`say a V-cut which is moderately “clean”, i.e. smooth
`sided, and the cut is wide enough to receive the tip of a
`cleaving tool, possibly without having to index the
`beam across the width of the cut (the width being the
`, dimension normal to the length or maximum dimension
`of the cut)-the cut can for instance be 250p wide and
`300;; or 400p deep, and the included angle of the V can
`be about 35". (or say 20° for smaller kerfs). Furthermore,
`a diamond does not tend to chip and the cuts are also
`more reproducible. If the beam has low divergence, the
`size of the focussed spot'is smaller~for instance, the
`divergence of the cone of the beam which contains 90%
`of the radiation can be 0.8 mRad (milliradian).
`The high energy content of the beam causes the
`diamond to graphitise, and although the energy absorp
`tion (in the zone of the focus of the beam) is rather low
`
`3
`
`

`

`4,401,876
`4
`3
`In the apparatus of FIG. 2, there is an Nd/Y AG laser
`lengths usually in the range 50~20O nsec (nsec=l0*9
`6 which provides a substantially parallel, high energy,
`sec) and a repetition rate frequency in the range 0.5~5.0
`high pulse rate, low order mode beam indicated by the
`KHz.
`small single-headed arrows. The beam is bent through
`Due to the value of the gemstone material, small
`90° by a mirror 7 which is re?ective for the infra-red
`errors in setting up and registration can be very expen
`light of the laser but it is not as re?ective for visible
`sive, and thus a special optical system has been designed
`wavelengths. The beam then passes through a focusing
`to ensure accurate working as the beam is moved along
`arrangement 8 and is focussed onto the diamond 1,
`the kerf line-the word “optical” includes all suitable
`which is in a suitable holder such as that disclosed in GB
`laser wavelengths, particularly infra-red wavelengths.
`2 052 369 A, referred to above. The focal point can be
`The present invention also provides, whether or not
`viewed directly through the mirror 7 by way of two
`associated with the foregoing speci?c laser, apparatus
`further mirrors 9, 10 and a suitable eye piece and ?lter
`for ker?ng a gemstone, comprising a mount for holding
`11 which includes crosswires 12, the visible light being
`the gemstone, a laser arranged to lase the gemstone with
`indicated by two small double-headed arrows. The
`a laser beam, re?ecting means which bend the beam
`mirrors 9, 10 can be surface silvered in the normal way
`through a substantial angle (preferably 90°) and which
`so as to be fully re?ective.
`is moveable substantially parallel to the axis of the beam
`As indicated in a schematic manner, the focusing
`incident on the re?ecting means, for moving the beam
`arrangement 8, mirror 7 and mirror 9 are all ?xed to a
`along the line to be kerfed, and a focusing arrangement
`single support mount 13 which can be indexed in the
`which focuses the beam. Although there are other ar
`direction indicated by the large double arrows by means
`rangements for translating the focal point so as to out
`of a lead screw 14. This lead screw can be connected to
`along the line, this arrangement is especially suitable as
`a shaft encoder for control of the translatory movement
`it can provide the accuracy required for ker?ng a gem
`of the mount 13.
`stone. The beam incident on the focusing means is pref
`As part of the setting-up procedure, the diamond 1 is v
`erably substantially parallel.
`positioned so that the cross-limb of the cross 2 appears
`Preferably, the apparatus is such that the focal point
`straight, as seen in FIG. 3, and the cross 2 is in register
`can be viewed along the optical axis of the focusing
`with the cross-wires 12 (which are shown to the side of
`arrangement, e.g. by using re?ecting means which be
`FIG. 3 for clarity), the assumption being that the cross
`have differently for the laser wavelength and for at least
`limb of the cross 2 is already in register with the cutting
`one visible wavelength. A convenient arrangement is to
`line 4. However, for resetting, the lead screw 14 can be
`use a re?ecting means which re?ects the laser wave
`rotated manually to place the centre of the cross 2 on
`lengths and allows at least part of the visible wave
`the centre of the cross-wires 12. If the correct setting of
`length to pass through without re?ection. In practice, a
`the mirrors etc. is to be checked, the laser can then give
`mark is made by hand on the gemstone to indicate
`a single pulse on a test piece which is viewed through
`where the out should be initiated, and this mark can be
`the eye-piece 11 to ensure that it is the centre of the
`viewed to ensure that cutting does start on the correct
`spot, thereby ensuring accuracy and saving material.
`cross 2.
`.
`Assuming that the setting-up is correct, the laser is
`For convenience, the apparatus can include a further
`switched on and the lead screw 14 makes several com
`re?ecting means ?xed to the ?rst re?ecting means and
`plete traverses or passes, thus moving or traversing the
`moving with it and re?ecting the non-laser visible
`laser beam relative to the diamond and forming a kerf
`wavelength along the axis parallel to the axis of the
`on the diamond 1 along the line 4. FIG. 4 shows one
`incident beam referred to above. In this way, the actual
`suitable kerf, with an included angle of 35° and a depth
`viewer need not move. It will be noted that the focusing
`arrangement can also be ?xed to the two re?ecting
`of about 400 um.
`.
`It is found that it may be necessary to index the beam
`means so that all three move together. Adjustment of
`across the width of the cut as well as traversing along
`the position of the focal point in a direction at right
`the length, though this depends upon the exact type of
`angles to the cutting line can be provided using an ar
`laser beam being used.
`rangement described in detail in GB 2 052 369 A.
`In more detail, the laser 6 may be con?gured with a
`stable resonator comprising an output mirror 15, a
`Nd/Y AG laser rod 16 and a 100% re?ecting mirror 17.
`Between the rod 16 and the mirror 17 is a beam redu
`cing/beam expanding telescope 18 (an intracavity tele
`scope) with a magni?cation of 2X, and the mirror 17 is
`suf?cient distance away for suf?cient diffraction to be
`achieved to discriminate against higher order modes, to
`give a cleaner, low divergence output beam which is
`substantially single mode; the output has a quasi-Gaus
`sian beam pro?le. The pulse rate was 50 Hz.
`Instead of the eye piece 11 and cross-wires 12, a tele
`vision viewer could be used, eg with electronically
`generated cross-wires 12.
`In accordance with normal practice, a cleaving tool
`19 can have its tip inserted in the kerf and the diamond
`1 can be cleaved. A suitable holder for this is disclosed
`in GB 2 052 369 A, referred to above. The cleaving
`plane 20 is indicated.
`I claim:
`1. A method of cleaving a gemstone, comprising:
`
`PREFERRED EMBODIMENT
`A preferred embodiment of 'the invention is now
`particularly described, with reference to the accompa
`nying drawing, in which:
`FIG. 1 is a view of a diamond which has been'marked
`prior to ker?ng and then cleaving;
`FIG. 2 is a schematic side view of apparatus in accor
`dance with the invention, the diamond being shown
`greatly enlarged;
`FIG. 3 is a view of the diamond, as it would be seen
`through the cross-wires of the apparatus of FIG. 2; and
`FIG. 4 is an enlarged cross~section through the kerf,
`also showing the tip of the cleaving tool.
`In FIG. 1, the diamond has been marked with a cross
`2 to indicate the centre of the ker?ng cut. It will be seen
`that one limb of the cross is marked along an edge 3 of
`the diamond while the other limb follows the proposed
`cutting line 4, the two limbs of the cross usually not
`being at 90° to each other. The dashed line 5 indicates
`the subsequent cleavage.
`
`55
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`60
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`5
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`4
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`

`

`4,401,876
`6
`5
`with an intracavity telescope, the beam being pulsed
`mounting said gemstone in position, said gemstone
`with a pulse rate of at least 20 Hz, having a wave length
`having a surface to be kerfed;
`of about 1 pm and low divergence.
`generating a high energy, low order mode, laser
`6. The method of claim 1, wherein a substantially
`beam;
`parallel laser beam is generated, and there are provided
`focussing said beam substantially on said surface,
`re?ecting means on which said parallel beam is incident
`thereby removing gemstone material from said
`and which bend said parallel beam through a substantial
`surface;
`‘
`angle, and moving means for moving said re?ecting
`moving said beam relative to said surface, thereby
`means in a direction substantially parallel to the axis of
`cutting a kerf; and
`‘
`the said incident parallel beam, thereby moving said
`inserting the tip of a tool in said kerf and thereby
`beam relative to said surface, to cut said kerf in said
`cleaving the gemstone.
`surface.
`2. The method of claim 1, wherein said laser beam is
`7. The method of claim 6, wherein said re?ecting
`a pulsed beam having a pulse rate of at least 20 Hz.
`means is re?ective for the wavelength of said parallel
`3. The method of claim 1, wherein said laser beam has
`beam but is less re?ective for at least one visible wave
`a wave length of about 1 pm.
`length, means being provided for viewing said surface
`4. The method of claim 1, wherein said laser beam is
`of said gemstone by eye through the back of said re?ect
`generated by a Nd/Y AG laser having a stable resonator
`ing means, thereby viewing the focal point of said laser
`with an intracavity telescope.
`beam on said surface.
`5. The method of claim 1 or 4, wherein said laser
`*
`beam is generated by a laser having a stable resonator
`
`it
`
`* * *
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