CA1317642C - Optical system for laser marking - Google Patents
Optical system for laser markingInfo
- Publication number
- CA1317642C CA1317642C CA 585139 CA585139A CA1317642C CA 1317642 C CA1317642 C CA 1317642C CA 585139 CA585139 CA 585139 CA 585139 A CA585139 A CA 585139A CA 1317642 C CA1317642 C CA 1317642C
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- CA
- Canada
- Prior art keywords
- mask
- concave mirror
- optical system
- laser
- mirror
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Abstract
Abstract An optical system for laser marking and comprising - when seen in the direction of a light beam of a predetermined transverse measurement (D0) and emitted by a laser (1)-a mask (7) including a mask pattern (8), and an image-producing means (12), such as a lens, and whereby the transverse measurement of the laser beam on the mask (7) is larger than the transverse measurement of the mask pattern. A focusing means (2), such as a lens, and a concave mirror (3) are situated between the laser (1) and the mask (7), whereby the concave mirror (3) being situated with its vertex in the focal point of the focusing means (2) and with the reflecting surface (4) facing the mask (7). An inlet opening (5) is shaped about the vertex, the transverse measurement of said inlet opening being slightly larger than the transverse measurement of the focal point. The mask (7) is shaped as a mirror, preferably a plane mirror, with the reflecting surface (9) facing the concave mirror (3), and the radius of the curvature (R4) of the concave mirror (3) is longer than twice the distance (b) between the mask (7) and the concave mirror (3).
Description
-Title: An Optical System For Laser Markin~
Technical Field The invention relates to an optical system for laser marking and comprising - when seen in the direction of a S light beam of a predetermined transverse measurement and emitted by a laser - a mask including a mask pattern, and an image-producing means, such as a lens, and whereby the transverse measurement of the laser beam on the mask is slightly larger than the transverse measurement of the 10 mask pattern.
Beyond current marking the laser marking also includes all processings where a thin surface layer is removed or evaporated from an article by a laser beam passing through a mask.
15 Background Art It is generally known to use short, high-energy laser pulses for engraving marks, such as numbers or dates, on various surfaces, such as coloured paper or eloxated alumi-nium, by directing the laser beam towards a mask made of 20 for instance copper or stainless steel and in which the desired pattern is removed. In this manner a minor portion, typically less than 10~, of the laser light passes through the openings of the mask and through an image-producing optical system usually including a~lens, and is imaged on 25 the surface of the article.
Hoaever, far the ma;or portion of the laser light is re-flected by the portions of the mask not being removed, and thus the process utilizes the efficiency of the laser only to a minor degree. The radiation reflected by the mask 30 is furthermore damaging to the laser in case it is directed towards said laser, because reflected radiation can inter-:
.
-' .
fere with the operation of the laser or, in extreme cases, damage parts thereof. Therefore the mask is often made diffusely reflecting or absorbing on its surface facing the beam.
5 With respect to laser processing of highly reflecting materials US-A-4,480,168 discloses the use of a mirror system for catching ehe reflections from ~he surface of an article situated immediately below the mirror system, and for redirecting said reflectLons to ~he surface of 10 the arcicle in order thereby to increase the coupling of light into the material. Thus the publication discloses a mirror system comprising a concave upper mirror with a small opening allowing passage of a focused laser beam, and a lower mirror with a reflecting surface facing the 15 upper mirror and with a larger opening allowing the laser beam to leave the mirror system and radiate the surface of the article so as to be refleceed therefrom back to the mirror system. The surface of the article forms thus an ~i essential part of the mlrror system for achieving an 20 increased coupling of light into said surface. In other words the reflections from the surface are redirected thereto by means of the upper mirror.
If the above system is to be used for laser-marking an article, the latter must according to the publication be 25 situated very close to the lower mirror with the rather unfortunate sideeffect that the material removed by the marking squirts onto the edge of the larger opening and is deposited thereon. As a consequence thereof the opening geometry or dimension changes gradually.
30~Descr~tion of the Invention Th~e object of the iDventio~n is to~provide an optical system for l~aser-marking and exhibiting a substantial}y improved efficlency compared to the known optical systems for laser-: : :
':: , : ~' , , - : .
marking, and which improves the quality of the resultin~
mark.
The optical system according to the invention is charac-eerised in that a focusing means, such as a lens, and a 5 concave mirror are situated between the laser and the ~ask, the focusing means being situated to focus the laser beam emitted by the laser to have said transverse measure-ment on the mask after focusing the conca~e mirror being sit~ated wlth its vertex in the focal point oi the ~ocusing 10 means and with the reflecting surface facing the mask, and where an inlet opening is shaped about the vertex, the transverse measurement of said inle~ opening being slightly larger than the transverse measurement of the focal point, that the mask is shaped as a mirror, pre-15 ferably a plane mirror, with the reflecting surface facingthe concave mirror, and that the radius of the curvaeure of the concave mirror is longer than twice the distance between the mask and the concave mirror.
` .
In this manner the amoune of energy radiated through the ; 20 mask is lncreased because the portion of the laser beam not passing dlrectly through the mask openings is reflected by the reflecting surface or mirror face of the mask. The light is reflected back to the concave mirror in turn reflecting the light to the mask, whereby an additional 25 portion of the laser bea~ passes through the mask openings.
The si~e of the reflectLng surface of the concave mirror and consequently the amoun~ of the light reflected by the concave mirror are optimized by the laser beam being focused~by means of a focusing means in the small opening 30 in the vertex of the mirror.~In addition the small inlet openin~ of the concave mirror protects the laser against possible damaging reflections ~rom the mask towards said laser. Furthermore the mask pattern of ehe mask is uniform-ly radiated, and consequen~ly the energy is uniformly 35 distributed ln the light em~tted. The laeter is parti-'~ , ,.:
` 1317642 cularly due to the fact that the indicated relationship between the radius of the curvature of the concave mirror and the distance between said concave mirror and the mask ensures that the radiation reflected by the mask and subse-S quently by the concave mirror exposes the entire maskpattern the fLrst time it radLates the mask, and where it includes che highese content of energy.
According to the invention the radius of the curvature of the concave oirror may be substantially in the range of 3 10 to 10 times the distance between the concave mirror and the mask. Tescs have shown that a suicable compromise between uniform distribution of energy~and high efficiency can be-achieved.
~ oreover according to the invention an elongated, straight, 15 cylindrLcal waveguide with a reflecting inner sur~ace may extend coaxially and substantially between the concave mLrror and the mask. As a result the diseribucion of energy on the mask and thereby also of the laser beams passing through the mask openings is uniform because the waveguide 20 trLes ~o concentrate rhe radiation farthest from the optical axis, whereas the c~oncave mirror constituting a stable resonator together with the mask tries to concen-trate the radiation adjacent the optical axis . In this manner a very uniform distribution of energy is obtained 25 across the mask.
~Furthermore according to the invention the transverse measurements of the cylindrical waveguide may correspond to l to 5, preferably l.S to 2.5 times the transverse ~ measurement of the incoming~light beam on the mask. In 30 this manner the ma~imum efficiency of the waveguide is obtained depending on the focal leng~h of the concave mirror.
Moreover according to the invention the inlet opening of the concave mirror and the waveguide may be of~a transverse 35 measurement con~ruent with the laser beam, preferably a ~3176~2 rectangular transverse measurement, and especially a square transverse measurement. In this manner there is provided a compensation for the irregularities in the distribution of the laser beam leaving the laser, said irregularities 5 appearing as lines in the laser beam depending on the transverse geometry of the laser beam and the way the laser beam is generated. As a result a perfect mark is obtained on the article.
Noreover the distance between the concave mirror and the 10 mask may a~cording to the invention correspond substantial-ly to the focaI length of the focusing means. Such an embodiment provides in practice excellent results both as far as the efficiency and as far as the marking quality are concerned.
.~, 15 In addition according to the invention the focusing means may be of a focal length of between 150 and 500 mm, prefer-ably between 250 and 375 mm, said relatively long focal length reducing the risk of plasma formation both in the inlet opening of the concave mirror and in the openings 20 of the mask.
On the side facing the focusing means the concave mirror ; may comprise a frusto-conical surface with the vertex ad;acent the inlet opening. In this manner the portions of the laser beam, which might~incident on the edge of the 25 inlet opening, are prevented Erom being reflected back to the laser and thereby from subjecting said laser to pos-sible damagin~g effectsO ~ ~ ~
:
Together the concave mirror, the cylindrical waveguide, and~the mask may furthermore according ~o the invention 30 form a pressure cham~ber which~can be eupplied with pro-tecting gas, whereby an undesired oxidation of the reflect-ing surfaces is prevented, and the gas prevents plasma ~ ~ ~ formation in the inlet opening and the mask openings.
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.
Moreover according to the invention the focusing means and the image-producing means may form end walls of a pressure chamber which can be supplied with protecting gas. In this manner the risk of plasma formation imme-5 diately before the inlet opening and after the mask open-ings is eliMinated at the same time as the consumption of protecting gas is minimized.
~ Finally according to the invention the reflecting surface ; of the concave mirror may be formed by a plurality of ; 10 small, plane mirror segments, which provides 8 very uniform distributlon of energy on the mask and therefore a very ~, uniform mark on the article.
' ~ :
Brief Description of the Drawin~
:: :
The invantion is described in greater detail below with ~; 15 reference to the accompanying drawing, in which the only Figure i8 a diagrammatic view of an embodiment of the optical system according to the invention.
Descr,i~ion_of the Preferre,d Embodiments of the Invention The optical syst0m according to the invention for laser 20 marking comprises - when seen in the direction of a laser beam from a laser 1 - a focusing lens 2 situated coaxially :
to the laser beam of a preferably~rectangular, and especi-~- ally square transverse measureme~nt.~ The lens 2 is prefer-ably of a rel~aeively long~f~ocal~length~a. A concave mirror 25 3 is~situated with~the vertex~in th;e focal point of the ens, and the reflecting~surface or mirror face 4 of said concave mirror faces away~ro~m~the direction of the laser beam and is of a relatively l~arge radius of curvature R4.
An inlet opening 5 is shaped about the vertex of the ; 30 concave mirror 3 and is congruent with the transverse , ~
~ measurement of the laser beam. The inlet opening 5 allows :: `: :
13~6~
passage of the focusing laser beam and is of a transverse measurement slightly larger than the transverse measurement of the focal point. The side of the concave mirror 3 facing the focusing lens 2 comprises a frusto-conical surface 6 5 with its vertex adjacent the inlet opening. The frusto^
conical surface prevents the portions of the laser beam, which might incident on the edge of the inlet opening, from being reflected back into the laser and thereby from ~ damaging said laser.
;~ 10 Having passed the mirror 3 the laser beam is met by a mask 7 with a reflecting surface or mirror face 9 facing the concave mirror. The mask 7 may opt~onally comprise several mask portions or sections arranged behind one another and/or side by side. The distance b between the concave 15 mirror 3 and the mask 7 corresponds in this embodiment substantially to the focal length a of the focusing lens 2, whereby the transverse measurement Dl of the laser beam on the mask corresponds substantially to the trans-verse measurement of the beam leaving the laser 1. A mask 20 pattern or mask openings 8 are shaped in the mask 7, and the transverse measurement of this mask pattern is slightly smaller than the transverse measurement Dl of the laser beam on the mask.
An elongated, straight, cylindrical waveguide 10 is co-25 axially situated betwaen the concave mirror 3 and the mask 7. The waveguide is reflecting on its inner surface 11 and is of a transverse measurement being congruent with the transverse measurement of the laser beam. In the illu-strated embodiment the inner transverse measurement D of 30 the waveguide 10 corresponds substantially to ~wice the transverse measurement Dl of the laser beam on the mask 7.
A portion of the laser beam being met by the mask 7 passes directly through the mask pattern or the mask openings 8, whereas the remaining portion of the laser beam is reflect-'.
::
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~317~2 ed by the surface 9 of the mask 7 and thereby directedback towards the reflecting surface 4 of the mirror 3. In turn the reflecting surface 4 directs the light towards the mask 7, whereafter an additional portion of the laser 5 beam passes through the mask pattern 8. At the same time the reflecting inner surface 11 of the wa~eguide 10 re-flects the radiation reflected towards it by the reflecting surface 9 of the mask 7 or the reflecting surface 4.
While the reflecting surfaces 4 and 9 in general try to 10 concentrate the radiation closely about the optical axis, the waveguide 10 of a square transverse measurement tries in general to uniform the radiation or to concentrate said radiation farther away from the optical axis and thereby tries to provide a uniform distribution of energy lS across the mask 7. The latter implies furthermore that the laser radiation passing through the mask pattern 8 discloses a very uniform distribution of energy when being met by an image-producing lens 12. The image-producing lens 12 i9 situated coaxially to the optical axis after 20 the mask 7 and produces an image 13 of the mask pattern 8 on the surface of the article 14 to be marked. As a strong short laser pulse is employed, typically involving a pulse energy of about 0.5-20 joule and a pulse length of typical-ly 10-1000 ns, the laser radiation evaporates a thin 25 surface layer on the article and leaves an image of the mask on the article.
: Together the concave mirror 3,:the cylindrical waveguide 10, and the mask 7 form a pressure chamber 15 which can be supplied with a protecting gas through an inlet opening ~: 30 16. The protecting gas may leave the chamber 15 through both the inlet opening S of the concave mirror 3 and through the mask pattern 8 of the mask 7. The protecting ~;gas prevents an undesired~ oxidation of the reflecting surfaces 4, 9, 11 and prevents plasma formation in the ~ 35 inlet opening S and the mask openings 8, as said plasma : :
:: :
.,, ~317 ~4~ -might otherwise shade these openings. Gases of~a high ionic potential can be used as protecting gas.
The entire optical system is situated in such a manner in a housing not shown that the components of the optical 5 system can be very accurately adjusted, which ensures an optimum efficiency of the system and an optimum distribu-tion of energy of the beam leaving the system. These ad-justment possibilities include:
The concave mirror 3 which can be tilted about its centre 10 in two planes in order to optimize the resonator represent-ed by the concave mirror 3 and the mask 7, the mask 7 which is also tiltable about its centre in two planes in order to optimize the above resonator, ~: `
~; the lens 2 which can be moved in three axial directions 15 in order to ensure a focusing of the laser beam in the inlet opening 5, ~:
the waveguide 10 which can be situated coaxial to the mirror 3 and the mask 7, : :
the part of the optical system comprising the mirror 3, 20 the waveguide 10, and the mask 7, and which can be tilted about the centre of the~inlet opening 5 in two planes in order to ensure that the las~er beam enters said part of the system at the correct angle, the image-producing lens 12 which can be correctly posi-25~tioned in three axial directions relative to the mask 7 in ~such a manner that the maximum portion of the light leaving through the mask pattern 8 is received and image-produced in the correct dimensions~, . :: .
~ the distance m between the entire optical system and the , ~ : - :
;~,:, : , :
.:
' ~3176~
article 14 in order ~o achieve a sharp image on the surface of the areicle.
The majority of these adjustments are, of course, performed 5 by the manufacturer of the optical system so that the user thereof need only perform the absolutely necessary adjust-ments.
Tests have shown that the optical system according to the invention provides an increase in the energy of about ; 10 100~ at the same time as the sharpness of the marX produced on the article is improved by the use of a laser beam of a transverse measurement of Do - 20 times 20 mm and an optical system of the following dimensions a - b ~ 330 mm, R4 - 2000 mm, and D - 36 times 36 mm.
15 The image-producing lens 12 may be replaced by more lenses arranged in succession in case the latter is considered advantageous. Furthermore the reflecting surface of the concave mirror 3 may lnstead of being a continuous surface also comprise a plurality of small mirrors together forming 20 the reflecting surface. Furthermore lasers may be used which emit laser beams of other transverse measurements than the rectangular, such as circular, and the inlet openlng~ and the~ waveguide may be~ of other transverse measurements neither~c`on~gruent~there~to nor mutually con-25~gruent~.~ Furthe~rmore, ~ehe`waveguide~can~ be completelyomi~tt~ed.~
:
: :
~. .
~....
Technical Field The invention relates to an optical system for laser marking and comprising - when seen in the direction of a S light beam of a predetermined transverse measurement and emitted by a laser - a mask including a mask pattern, and an image-producing means, such as a lens, and whereby the transverse measurement of the laser beam on the mask is slightly larger than the transverse measurement of the 10 mask pattern.
Beyond current marking the laser marking also includes all processings where a thin surface layer is removed or evaporated from an article by a laser beam passing through a mask.
15 Background Art It is generally known to use short, high-energy laser pulses for engraving marks, such as numbers or dates, on various surfaces, such as coloured paper or eloxated alumi-nium, by directing the laser beam towards a mask made of 20 for instance copper or stainless steel and in which the desired pattern is removed. In this manner a minor portion, typically less than 10~, of the laser light passes through the openings of the mask and through an image-producing optical system usually including a~lens, and is imaged on 25 the surface of the article.
Hoaever, far the ma;or portion of the laser light is re-flected by the portions of the mask not being removed, and thus the process utilizes the efficiency of the laser only to a minor degree. The radiation reflected by the mask 30 is furthermore damaging to the laser in case it is directed towards said laser, because reflected radiation can inter-:
.
-' .
fere with the operation of the laser or, in extreme cases, damage parts thereof. Therefore the mask is often made diffusely reflecting or absorbing on its surface facing the beam.
5 With respect to laser processing of highly reflecting materials US-A-4,480,168 discloses the use of a mirror system for catching ehe reflections from ~he surface of an article situated immediately below the mirror system, and for redirecting said reflectLons to ~he surface of 10 the arcicle in order thereby to increase the coupling of light into the material. Thus the publication discloses a mirror system comprising a concave upper mirror with a small opening allowing passage of a focused laser beam, and a lower mirror with a reflecting surface facing the 15 upper mirror and with a larger opening allowing the laser beam to leave the mirror system and radiate the surface of the article so as to be refleceed therefrom back to the mirror system. The surface of the article forms thus an ~i essential part of the mlrror system for achieving an 20 increased coupling of light into said surface. In other words the reflections from the surface are redirected thereto by means of the upper mirror.
If the above system is to be used for laser-marking an article, the latter must according to the publication be 25 situated very close to the lower mirror with the rather unfortunate sideeffect that the material removed by the marking squirts onto the edge of the larger opening and is deposited thereon. As a consequence thereof the opening geometry or dimension changes gradually.
30~Descr~tion of the Invention Th~e object of the iDventio~n is to~provide an optical system for l~aser-marking and exhibiting a substantial}y improved efficlency compared to the known optical systems for laser-: : :
':: , : ~' , , - : .
marking, and which improves the quality of the resultin~
mark.
The optical system according to the invention is charac-eerised in that a focusing means, such as a lens, and a 5 concave mirror are situated between the laser and the ~ask, the focusing means being situated to focus the laser beam emitted by the laser to have said transverse measure-ment on the mask after focusing the conca~e mirror being sit~ated wlth its vertex in the focal point oi the ~ocusing 10 means and with the reflecting surface facing the mask, and where an inlet opening is shaped about the vertex, the transverse measurement of said inle~ opening being slightly larger than the transverse measurement of the focal point, that the mask is shaped as a mirror, pre-15 ferably a plane mirror, with the reflecting surface facingthe concave mirror, and that the radius of the curvaeure of the concave mirror is longer than twice the distance between the mask and the concave mirror.
` .
In this manner the amoune of energy radiated through the ; 20 mask is lncreased because the portion of the laser beam not passing dlrectly through the mask openings is reflected by the reflecting surface or mirror face of the mask. The light is reflected back to the concave mirror in turn reflecting the light to the mask, whereby an additional 25 portion of the laser bea~ passes through the mask openings.
The si~e of the reflectLng surface of the concave mirror and consequently the amoun~ of the light reflected by the concave mirror are optimized by the laser beam being focused~by means of a focusing means in the small opening 30 in the vertex of the mirror.~In addition the small inlet openin~ of the concave mirror protects the laser against possible damaging reflections ~rom the mask towards said laser. Furthermore the mask pattern of ehe mask is uniform-ly radiated, and consequen~ly the energy is uniformly 35 distributed ln the light em~tted. The laeter is parti-'~ , ,.:
` 1317642 cularly due to the fact that the indicated relationship between the radius of the curvature of the concave mirror and the distance between said concave mirror and the mask ensures that the radiation reflected by the mask and subse-S quently by the concave mirror exposes the entire maskpattern the fLrst time it radLates the mask, and where it includes che highese content of energy.
According to the invention the radius of the curvature of the concave oirror may be substantially in the range of 3 10 to 10 times the distance between the concave mirror and the mask. Tescs have shown that a suicable compromise between uniform distribution of energy~and high efficiency can be-achieved.
~ oreover according to the invention an elongated, straight, 15 cylindrLcal waveguide with a reflecting inner sur~ace may extend coaxially and substantially between the concave mLrror and the mask. As a result the diseribucion of energy on the mask and thereby also of the laser beams passing through the mask openings is uniform because the waveguide 20 trLes ~o concentrate rhe radiation farthest from the optical axis, whereas the c~oncave mirror constituting a stable resonator together with the mask tries to concen-trate the radiation adjacent the optical axis . In this manner a very uniform distribution of energy is obtained 25 across the mask.
~Furthermore according to the invention the transverse measurements of the cylindrical waveguide may correspond to l to 5, preferably l.S to 2.5 times the transverse ~ measurement of the incoming~light beam on the mask. In 30 this manner the ma~imum efficiency of the waveguide is obtained depending on the focal leng~h of the concave mirror.
Moreover according to the invention the inlet opening of the concave mirror and the waveguide may be of~a transverse 35 measurement con~ruent with the laser beam, preferably a ~3176~2 rectangular transverse measurement, and especially a square transverse measurement. In this manner there is provided a compensation for the irregularities in the distribution of the laser beam leaving the laser, said irregularities 5 appearing as lines in the laser beam depending on the transverse geometry of the laser beam and the way the laser beam is generated. As a result a perfect mark is obtained on the article.
Noreover the distance between the concave mirror and the 10 mask may a~cording to the invention correspond substantial-ly to the focaI length of the focusing means. Such an embodiment provides in practice excellent results both as far as the efficiency and as far as the marking quality are concerned.
.~, 15 In addition according to the invention the focusing means may be of a focal length of between 150 and 500 mm, prefer-ably between 250 and 375 mm, said relatively long focal length reducing the risk of plasma formation both in the inlet opening of the concave mirror and in the openings 20 of the mask.
On the side facing the focusing means the concave mirror ; may comprise a frusto-conical surface with the vertex ad;acent the inlet opening. In this manner the portions of the laser beam, which might~incident on the edge of the 25 inlet opening, are prevented Erom being reflected back to the laser and thereby from subjecting said laser to pos-sible damagin~g effectsO ~ ~ ~
:
Together the concave mirror, the cylindrical waveguide, and~the mask may furthermore according ~o the invention 30 form a pressure cham~ber which~can be eupplied with pro-tecting gas, whereby an undesired oxidation of the reflect-ing surfaces is prevented, and the gas prevents plasma ~ ~ ~ formation in the inlet opening and the mask openings.
: , ` .
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~, .
.
Moreover according to the invention the focusing means and the image-producing means may form end walls of a pressure chamber which can be supplied with protecting gas. In this manner the risk of plasma formation imme-5 diately before the inlet opening and after the mask open-ings is eliMinated at the same time as the consumption of protecting gas is minimized.
~ Finally according to the invention the reflecting surface ; of the concave mirror may be formed by a plurality of ; 10 small, plane mirror segments, which provides 8 very uniform distributlon of energy on the mask and therefore a very ~, uniform mark on the article.
' ~ :
Brief Description of the Drawin~
:: :
The invantion is described in greater detail below with ~; 15 reference to the accompanying drawing, in which the only Figure i8 a diagrammatic view of an embodiment of the optical system according to the invention.
Descr,i~ion_of the Preferre,d Embodiments of the Invention The optical syst0m according to the invention for laser 20 marking comprises - when seen in the direction of a laser beam from a laser 1 - a focusing lens 2 situated coaxially :
to the laser beam of a preferably~rectangular, and especi-~- ally square transverse measureme~nt.~ The lens 2 is prefer-ably of a rel~aeively long~f~ocal~length~a. A concave mirror 25 3 is~situated with~the vertex~in th;e focal point of the ens, and the reflecting~surface or mirror face 4 of said concave mirror faces away~ro~m~the direction of the laser beam and is of a relatively l~arge radius of curvature R4.
An inlet opening 5 is shaped about the vertex of the ; 30 concave mirror 3 and is congruent with the transverse , ~
~ measurement of the laser beam. The inlet opening 5 allows :: `: :
13~6~
passage of the focusing laser beam and is of a transverse measurement slightly larger than the transverse measurement of the focal point. The side of the concave mirror 3 facing the focusing lens 2 comprises a frusto-conical surface 6 5 with its vertex adjacent the inlet opening. The frusto^
conical surface prevents the portions of the laser beam, which might incident on the edge of the inlet opening, from being reflected back into the laser and thereby from ~ damaging said laser.
;~ 10 Having passed the mirror 3 the laser beam is met by a mask 7 with a reflecting surface or mirror face 9 facing the concave mirror. The mask 7 may opt~onally comprise several mask portions or sections arranged behind one another and/or side by side. The distance b between the concave 15 mirror 3 and the mask 7 corresponds in this embodiment substantially to the focal length a of the focusing lens 2, whereby the transverse measurement Dl of the laser beam on the mask corresponds substantially to the trans-verse measurement of the beam leaving the laser 1. A mask 20 pattern or mask openings 8 are shaped in the mask 7, and the transverse measurement of this mask pattern is slightly smaller than the transverse measurement Dl of the laser beam on the mask.
An elongated, straight, cylindrical waveguide 10 is co-25 axially situated betwaen the concave mirror 3 and the mask 7. The waveguide is reflecting on its inner surface 11 and is of a transverse measurement being congruent with the transverse measurement of the laser beam. In the illu-strated embodiment the inner transverse measurement D of 30 the waveguide 10 corresponds substantially to ~wice the transverse measurement Dl of the laser beam on the mask 7.
A portion of the laser beam being met by the mask 7 passes directly through the mask pattern or the mask openings 8, whereas the remaining portion of the laser beam is reflect-'.
::
, .
~317~2 ed by the surface 9 of the mask 7 and thereby directedback towards the reflecting surface 4 of the mirror 3. In turn the reflecting surface 4 directs the light towards the mask 7, whereafter an additional portion of the laser 5 beam passes through the mask pattern 8. At the same time the reflecting inner surface 11 of the wa~eguide 10 re-flects the radiation reflected towards it by the reflecting surface 9 of the mask 7 or the reflecting surface 4.
While the reflecting surfaces 4 and 9 in general try to 10 concentrate the radiation closely about the optical axis, the waveguide 10 of a square transverse measurement tries in general to uniform the radiation or to concentrate said radiation farther away from the optical axis and thereby tries to provide a uniform distribution of energy lS across the mask 7. The latter implies furthermore that the laser radiation passing through the mask pattern 8 discloses a very uniform distribution of energy when being met by an image-producing lens 12. The image-producing lens 12 i9 situated coaxially to the optical axis after 20 the mask 7 and produces an image 13 of the mask pattern 8 on the surface of the article 14 to be marked. As a strong short laser pulse is employed, typically involving a pulse energy of about 0.5-20 joule and a pulse length of typical-ly 10-1000 ns, the laser radiation evaporates a thin 25 surface layer on the article and leaves an image of the mask on the article.
: Together the concave mirror 3,:the cylindrical waveguide 10, and the mask 7 form a pressure chamber 15 which can be supplied with a protecting gas through an inlet opening ~: 30 16. The protecting gas may leave the chamber 15 through both the inlet opening S of the concave mirror 3 and through the mask pattern 8 of the mask 7. The protecting ~;gas prevents an undesired~ oxidation of the reflecting surfaces 4, 9, 11 and prevents plasma formation in the ~ 35 inlet opening S and the mask openings 8, as said plasma : :
:: :
.,, ~317 ~4~ -might otherwise shade these openings. Gases of~a high ionic potential can be used as protecting gas.
The entire optical system is situated in such a manner in a housing not shown that the components of the optical 5 system can be very accurately adjusted, which ensures an optimum efficiency of the system and an optimum distribu-tion of energy of the beam leaving the system. These ad-justment possibilities include:
The concave mirror 3 which can be tilted about its centre 10 in two planes in order to optimize the resonator represent-ed by the concave mirror 3 and the mask 7, the mask 7 which is also tiltable about its centre in two planes in order to optimize the above resonator, ~: `
~; the lens 2 which can be moved in three axial directions 15 in order to ensure a focusing of the laser beam in the inlet opening 5, ~:
the waveguide 10 which can be situated coaxial to the mirror 3 and the mask 7, : :
the part of the optical system comprising the mirror 3, 20 the waveguide 10, and the mask 7, and which can be tilted about the centre of the~inlet opening 5 in two planes in order to ensure that the las~er beam enters said part of the system at the correct angle, the image-producing lens 12 which can be correctly posi-25~tioned in three axial directions relative to the mask 7 in ~such a manner that the maximum portion of the light leaving through the mask pattern 8 is received and image-produced in the correct dimensions~, . :: .
~ the distance m between the entire optical system and the , ~ : - :
;~,:, : , :
.:
' ~3176~
article 14 in order ~o achieve a sharp image on the surface of the areicle.
The majority of these adjustments are, of course, performed 5 by the manufacturer of the optical system so that the user thereof need only perform the absolutely necessary adjust-ments.
Tests have shown that the optical system according to the invention provides an increase in the energy of about ; 10 100~ at the same time as the sharpness of the marX produced on the article is improved by the use of a laser beam of a transverse measurement of Do - 20 times 20 mm and an optical system of the following dimensions a - b ~ 330 mm, R4 - 2000 mm, and D - 36 times 36 mm.
15 The image-producing lens 12 may be replaced by more lenses arranged in succession in case the latter is considered advantageous. Furthermore the reflecting surface of the concave mirror 3 may lnstead of being a continuous surface also comprise a plurality of small mirrors together forming 20 the reflecting surface. Furthermore lasers may be used which emit laser beams of other transverse measurements than the rectangular, such as circular, and the inlet openlng~ and the~ waveguide may be~ of other transverse measurements neither~c`on~gruent~there~to nor mutually con-25~gruent~.~ Furthe~rmore, ~ehe`waveguide~can~ be completelyomi~tt~ed.~
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~....
Claims (11)
1. An optical system for laser marking and comprising-when seen in the direction of a light beam of a predeter-mined transverse measurement (D0) and emitted by a laser (1) - a mask (7) including a mask pattern (8), and an image-producing means (12), such as a lens, and whereby the transverse measurement (D1) of the laser beam on the mask (7) is larger than the transverse measurement of the mask pattern (8), c h a r a c t e r i s e d in that a focusing means (2), such as a lens, and a concave mirror (3) are situated between the laser (1) and the mask (7), the focusing means (2) being situated to focus the laser beam emitted by the laser (1) to have said transverse measurement (D1) on the mask (7) after focusing, the concave mirror (3) being situated with its vertex in the focal point of the focusing means (2) and with the reflecting surface (4) facing the mask (7), and where an inlet opening (5) is shaped about the vertex, the trans-verse measurement of said inlet opening being slightly larger than the transverse measurement of the focal point, that the mask (7) is shaped as a mirror, preferably a plane mirror, with the reflecting surface (9) facing the concave mirror (3), and that the radius of the curvature (R4) or the concave mirror (3) is longer than twice the distance (b) between the mask (7) and the concave mirror (3).
2. An optical system as claimed in claim 1, c h a r -a c t e r i s e d in that the radius (R4) of the curvature of the concave mirror (3) is substantially in the range of 3 to 10 times the distance (b) between the concave mirror (3) and the mask (7).
3. An optical system as claimed in claim 1, c h a r a c t e r i s e d in that an elongated, straight, cylindrical waveguide (10) with a reflecting inner surface (11) extends coaxially and substantially between the concave mirror (3) and the mask (7).
4. An optical system as claimed in claim 3, c h a r -a c t e r i s e d in that the transverse measurement of the cylindrical waveguide (10) corresponds to 1 to 5, preferably 1.5 to 2.5 times the transverse measurement (D1) of the incoming light beam on the mask (7).
5. An optical system as claimed in any one of claims 1 to 4, c h a r a c t e r i s e d in that the inlet opening (5) in the concave mirror (3) and the waveguide (10) is of a transverse measurement congruent with the laser beam, said transverse measurement preferably being rectangular and especially being square.
6. An optical system as claimed in any one of claims 1 to 4, c h a r a c t e r i s e d in that the distance (b) between the concave mirror (3) and the mask (7) corresponds substantially to the focal length (a) of the focusing means (2).
7. An optical system as claimed in any one of claims 1 to 4, c h a r a c t e r i s e d in that the focusing means (2) is of a focal length in the range of 150 to 500 mm, preferably 250 to 375 mm.
8. An optical system as claimed in any one of claims 1 to 4, c h a r a c t e r i s e d in that on the side facing the focusing means (2) the concave mirror (3) comprises a frusto-conical surface (6) with a vertex adjacent the inlet opening (5).
9. An optical system as claimed in any one of claims 1 to 4, c h a r a c t e r i s e d in that the concave mirror (3), the cylindrical waveguide (10), and the mask (7) together form a pressure chamber (15), which can be supplied with protecting gas.
10. An optical system as claimed in any one of claims 1 to 4, c h a r a c t e r i s e d in that the focusing means (2) and the image-producing means (12) form end walls of a pressure chamber which can be supplied with protecting gas.
11. An optical system as claimed in any one of claims 1 to 4, c h a r a c t e r i s e d in that the reflecting surface (4) of the concave mirror (3) is formed by a plurality of small plane mirror segments.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 585139 CA1317642C (en) | 1988-12-06 | 1988-12-06 | Optical system for laser marking |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DK6447/87 | 1987-12-08 | ||
| CA 585139 CA1317642C (en) | 1988-12-06 | 1988-12-06 | Optical system for laser marking |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1317642C true CA1317642C (en) | 1993-05-11 |
Family
ID=4139242
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 585139 Expired - Fee Related CA1317642C (en) | 1988-12-06 | 1988-12-06 | Optical system for laser marking |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1317642C (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107790877A (en) * | 2017-11-24 | 2018-03-13 | 广州新可激光设备有限公司 | A kind of economizing type laser marking structure |
-
1988
- 1988-12-06 CA CA 585139 patent/CA1317642C/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107790877A (en) * | 2017-11-24 | 2018-03-13 | 广州新可激光设备有限公司 | A kind of economizing type laser marking structure |
| CN107790877B (en) * | 2017-11-24 | 2023-09-08 | 广州新可激光设备有限公司 | Laser marking structure |
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| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |