United States Patent [19]
`Baer
`
`[11] Patent Number:
`[45] Date of Patent:
`
`5,059,764
`Oct. 22, 1991
`
`[54] DIODE-PUMPED, SOLID STATE
`LASER-BASED WORKSTATION FOR
`PRECISION MATERIALS PROCESSING
`AND MACHINING
`
`Inventor: Tom Baer, Mountain View, Calif.
`[75]
`[73] Assignee: Spectra-Physics, Inc., San Jose, Calif.
`[21] Appl. No.: 265,052
`
`Oct. 31, 1988
`[22] Filed:
`Int. Cl.5 .............................................. B23K 26/00
`[51]
`[52] U.S. Cl ........................... 219/121.68; 219/121.61;
`219/121.69; 219/121.78; 219/121.82
`[58] Field of Search ...................... 219/121.68, 121.69,
`219/121.82, 121.61, 121.62, 121.83, 121.78;
`372/71, 108
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`3,400,456 9/1968 Hanfmann.
`3,657,510 4/1972 Rothrock.
`3,753,145 8/1973 Chesler.
`3,902,036 8/1975 Zaleckas.
`3,982,201 9/1976 Rosenkrantz et al. .
`4,568,409 2/1986 Caplan.
`4,576,480 3/1986 Travis.
`4,638,145 111987 Sakuma et al. .
`4,653,056 3/1987 Baer et al. .
`4,656,635 4/1987 Baer et al. .
`4,665,529 5/1987 Baer et al. ........................... 772/108
`4,701,929 10/1987 Baer et al. .
`
`4,710,605 12/1987 Presby.
`4,734,550 3/1988 Imamura et al. .......... 219/121.82 X
`4,734,912 3/1988 Scerbak et al. .
`4,739,507 4/1988 Byer et al. .
`4,756,765 7/1988 Woodroffe.
`4,761,786 8/1988 Baer.
`4,772,121 9/1983 Trageser.
`4,794,222 12/1988 Funayama et al. .
`4,794,615 12/1988 Berger et al. .
`4,806,728 2/1989 Salzer et al. .
`4,825,034 4/1989 Auvert et al. .............. 219/121.83 X
`
`Primary Examiner-C. L. Albritton
`Attorney, Agent, or Firm-Lyon & Lyon
`
`ABSTRACT
`[57]
`A diode laser pumped, solid state laser-based system
`and related method of operation for precision materials
`processing and machining is described. A component of
`the system is a diode laser pumped, q-switched, fiber(cid:173)
`coupled, solid state laser which produces a pulsed beam
`having a pulse width of approximately 50 ns or less,
`which width is necessary for material removal by abla(cid:173)
`tion. Other components of the system include an optical
`subsystem such as a microscope, a stepper-motor con(cid:173)
`trolled workstation, an imaging subsystem such as a
`video camera coupled to a monitor, and control means
`such as a personal computer. The system can be oper(cid:173)
`ated in either a manual or an automatic mode.
`
`22 Claims, 2 Drawing Sheets
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`1
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`TIFFANY 1016
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`u.s. Patent
`US. Patent
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`Oct. 22, 1991
`Oct. 22, 1991
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`5,059,764
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`u.s. Patent
`US. Patent
`
`Oct. ‘22, 1991
`Oct. 22, 1991
`
`Sheet 2 of 2
`Sheet 2 of 2
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`5,059,764
`5,059,764
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`1
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`5,059,764
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`2
`switch to produce the pulsed output necessary for abla(cid:173)
`tion.
`The turbulence of the water cooling is problematic
`for precision materials processing and machining. This
`5 is because noise will be introduced into the pulsed laser
`beam by coolant water turbulence, which will limit the
`precision of the cuts possible.
`In addition, the high input power required will be
`problematic for the additional reason that the energy
`delivered by the laser at the short pulse width will be
`much too high for ablation and precision cuts, necessi-
`tating that the laser output be attenuated before imping(cid:173)
`ing upon the material. Lower power arc-lamp pumped
`solid state lasers are not a possible solution to the attenu(cid:173)
`ation problem since they will not produce the short
`pulse widths required for material ablation. The net
`result is that the pulse width/energy level combination
`required for successful material ablation is not achiev(cid:173)
`able with conventional, arc-lamp pumped, q-switched,
`solid state lasers.
`The combined impact of the long cavity length and
`large q-switch, the required 230 V AC hook-up, the
`water cooling of the laser, and the attenuation of the
`laser output, make the laser bulky and mechanically
`difficult to integrate into an optical system for down(cid:173)
`stream focusing, shaping, and directing of the beam
`which may be required, and also make the laser and
`system in which it is integrated unwieldy and lacking in
`portability.
`The low electrical efficiency provides for a signifi-
`cant amount of heat dissipation in the laser head of the
`laser, necessitating that a cooling system be applied to
`the laser head. A problem for precision materials pro(cid:173)
`cessing is that vibrations from the cooling system will
`35 be coupled to the laser head, causing the head to move,
`and resulting in less precise cuts.
`Finally, the arc lamp in such a laser is coupled to the
`laser head, often necessitating that the laser head be
`aligned and readjusted every time the arc lamp is re(cid:173)
`quired or serviced.
`Accordingly, it is an object of the present invention
`to provide a solid state laser for use in a workstation for
`high precision materials processing, which provides the
`proper pulse width/energy level combination for abla(cid:173)
`tion, which provides for efficient pumping in a compact
`laser cavity, which eliminates the need for water cool-
`ing with the attendant water turbulence induced noise
`to the laser output beam, which is small, compact, and
`easily integrable into an optical system for downstream
`focusing and directing of the beam, and which decou(cid:173)
`pies the vibrations of the cooling system of the pumping
`source from the laser head, enabling the laser to pro(cid:173)
`duce more precise cuts.
`
`DIODE-PUMPED, SOLID STATE LASER-BASED
`WORKSTATION FOR PRECISION MATERIALS
`PROCESSING AND MACHINING
`
`25
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates generally to a diode-pumped,
`solid state laser-based workstation for use in a variety of 10
`precision materials processing and machining applica(cid:173)
`tions, and more specifically, to a workstation employing
`a diode laser end pumped, q-switched, fiber-coupled,
`solid state laser which produces a pulsed laser beam for
`ablating, and hence making precision cuts in, the surface 15
`of the material.
`2. Background of the Invention
`Lasers have been used in a variety of materials pro(cid:173)
`cessing and machining applications. Their primary ad(cid:173)
`vantage is that they provide a directed energy beam at 20
`high average power which can be focused to micron
`beam diameters, allowing unique materials processing
`applications to be developed, such as the using lasers for
`semiconductor memory repair via link blowing, or pre-
`cision engraving applications.
`A requirement of lasers used in these types of applica(cid:173)
`tions in that the laser deliver short, high energy pulses
`having a pulse width which is short compared to the
`thermal diffusion time of the material being processed.
`This is necessary so that the material will ablate from 30
`the surface, that is evaporate without melting, enabling
`the laser to make precise and accurate cuts on the sur(cid:173)
`face of the material. In fact, laser pulse widths of 50 ns
`or lower are typically necessary to achieve material
`removal by ablation.
`Solid state lasers are particularly advantageous in
`producing a pulsed beam output since they have a long
`excited state lifetime, and hence can store energy from
`the laser pump source and then release the energy over
`a short time period through a process called q-switch- 40
`ing. To produce pulses having a short enough width for
`ablation, as is known, lasers having either a short cavity
`or high gain are required, since pulse width depends on
`the product of gain and cavity round trip time. How(cid:173)
`ever, solid state lasers used in the art are typically 45
`pumped with an arc lamp, which is a broadband source,
`and not particularly efficient in pumping a solid state
`laser since it will pump portions of the lasing medium
`which will not contribute to production of the output
`beam, and because it contains many different wave- 50
`lengths which will not be absorbed by the laser medium.
`In fact, the arc lamp electrical efficiency is typically
`only about 0.5%. The net result is that the gain per unit
`length of the system will be low, necessitating that the
`laser material be relatively long so that enough lasing 55
`material will be present for the laser to achieve the
`necessary gain required and thus produce a short pulse
`width. For example, a cavity having a I foot length is
`typically required.
`In addition, because the gain is so low, quite a bit of 60
`input power must be applied to produce a short pulse,
`necessitating in many instances that water cooling of
`the laser head take place to control heat dissipation, and
`also necessitating that the laser be coupled to a 230
`V AC outlet to produce the several kilowatts of input 65
`power which must typically be supplied to achieve the
`requisite gain. Moreover, the large cavity length implies
`a large beam diameter which will require a large q-
`
`SUMMARY OF THE INVENTION
`To achieve the foregoing objects, and in accordance
`with the purpose of the invention as embodied and
`broadly described herein, there is provided a diode(cid:173)
`laser end-pumped, solid state laser-based workstation
`for precision materials processing and machining. A key
`component of the workstation is a diode-laser end(cid:173)
`pumped, q-switched, fiber-coupled, solid state laser for
`producing a pulsed laser beam having a beam width,
`pulse width, and energy level necessary for ablation.
`End pumping is beneficial since it results in high
`efficiency pumping. This is because end pumping allows
`only those areas of the lasing medium which will con(cid:173)
`tribute to the production of the output beam to be ex-
`
`4
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`5,059,764
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`3
`cited. For precision materials processing, the TEMoo
`mode is particularly advantageous, since it has a smooth
`intensity profile, with no nodes or zeroes, and it is dif(cid:173)
`fraction limited. End pumping is particularly efficient
`for producing the TEMoo mode.
`Diode laser pumping also contributes to high effi(cid:173)
`ciency pumping, since the diode laser is monochro(cid:173)
`matic, and can be tuned to maximize its absorption by
`the laser material. In fact, compared with arc lamp
`pumping, which achieves an electrical efficiency on the 10
`order of 0.5%, diode laser pumping achieves a electrical
`efficiency on the order of 10%. Because of the higher
`electrical efficiency, the laser can be set up for liS V AC
`operation, improving its portability, and eliminating the
`need for 230 VAC operation and the attendant water 15
`cooling and turbulence noise of the output beam. In
`addition, the elimination of water cooling contributes to
`the compact size of the laser.
`The combined impact of end pumping and diode laser
`pumping is high gain at lower input power levels, en- 20
`abling the laser to produce short pulses even in a short
`cavity at the correct pulse-width/energy level combina(cid:173)
`tion required for precision material ablation. Additional
`benefits are that the laser can be made very compact,
`the need to attenuate is eliminated, forced air cooling 25
`can be substituted for water cooling, and little or no
`heat dissipation takes place in the laser head.
`The particular q-switch chosen to be used with the
`laser contributes to the compact size, gain, and effi(cid:173)
`ciency of the laser. These benefits are achieved by using 30
`a q-switch comprised of a material having a higher
`acoustic-optic figure of merit than traditional fused
`silica, which makes the q-switch more efficient, so that
`it too can be made more compact along with the laser
`cavity.
`Fiber coupling enables the laser head to be extremely
`compact, and easily integrable with an imaging system
`such as a microscope for directing and focusing of the
`laser beam. This is because the use of fiber coupling
`enables the laser head to be spaced from the diode laser 40
`so that only the laser head need be mounted in the imag(cid:173)
`ing system while the rest of the laser is kept in a central
`staging area. An additional advantage is that fiber cou(cid:173)
`pling enables the diode laser to be mounted in the power
`supply, and cooled via the forced air cooling system 45
`used to cool the power supply. The forced air cooling
`system typically includes a fan, and spacing the diode
`laser from the laser head eliminates the coupling of fan
`vibration to the laser head, which in turn, contributes to
`the precision of the system.
`The spacing of the diode laser from the laser head
`further enables the diode laser to be replaced or ser(cid:173)
`viced without requiring the laser head to be dismounted
`and realigned.
`The net result is that the laser will produce a pulsed 55
`beam having a beam width of approximately 200-300
`microns or less, a pulse width of approximately 50 ns or
`less, and an energy level of approximately 100 pJ or
`less. Moreover, the laser beam can easily be focused
`down to a width of approximately 10-30 microns, and 60
`even 1-2 microns for those applications requiring the
`most precision. An advantageous laser beam for preci(cid:173)
`sion materials processing has a beam width of as little as
`1-2 microns, a pulse width of approximately 30 ns, and
`an energy level of approximately 10 pJ. These charac- 65
`teristics are advantageous for precision materials pro(cid:173)
`cessing applications such as semiconductor memory
`link blowing and repair, since a link has a dimension on
`
`4
`the order of 1-2 microns, and a 30 ns pulse at 10 pJ will
`ablate the link. The same holds true for precision en(cid:173)
`graving applications.
`Other components of the system include an optical
`5 subsystem such as a microscope mechanically coupled
`to the laser, an aiming beam collinear to the pulsed laser
`beam, an imaging subsystem including a video camera
`electrically coupled to a monitor, a stepper-motor con-
`trolled workstation for holding and positioning the
`material being processed with respect to the pulsed
`laser beam, and control means such as a personal com-
`puter electrically coupled to the laser and to the work(cid:173)
`station. In addition, the video camera of the imaging
`subsystem is mechanically coupled to the optical sub(cid:173)
`system.
`The optical subsystem directs the pulsed beam along
`a straight path to the surface of the material held by the
`workstation. A focusing lens is placed along the optical
`path. The pulsed beam intersects the lens and is focused
`to a beam having a width of as little as 1-2 microns or
`less. The focused beam strikes the surface of the mate-
`rial, and ablates it.
`To position the pulsed beam, the aiming beam is used.
`The aiming beam is collinear with the pulsed laser
`beam, and can either be the leakage light from the diode
`laser, the laser light from the solid state laser while
`operating in continuous wave (cw) mode at low power,
`or an aiming beam from an independent light source.
`The aiming beam is also directed by the optical sub-
`system along the same straight path as the pulsed beam
`to strike but not ablate the surface of the material. The
`beam then reflects from the surface, and partially re(cid:173)
`traverses the optical path. Also placed in the optical
`35 path and spaced from the focusing lens is a beam split(cid:173)
`ter. The reflected beam intersects the beam splitter, and
`a portion of the reflected beam is directed to the video
`camera of the imaging subsystem, which directs the
`monitor to visually display an image of the surface of
`the material using the reflected portion of the beam.
`The workstation positions the material under process
`at a particular location with respect to the laser before
`the transmission of the pulsed beam in order to make a
`precise cut in the surface of the material at the particu(cid:173)
`lar location. At present, two modes of operation are
`provided: manual and automatic.
`In both modes of operation, a user controls the laser
`and the workstation through a series of commands is(cid:173)
`sued via the control means, which can be a personal
`50 computer (hereinafter "PC"). In the manual mode, a
`user positions the beam to the desired location by visu(cid:173)
`ally tracking the position of the beam via the monitor,
`and issuing commands to change the position. The user
`then directs the laser to transmit one or more pulses to
`oblate the material.
`In the automatic mode of operation, the user first
`positions the laser beam to a reference location on the
`surface of the material, either manually, by visually
`positioning the beam using the monitor as described
`above, or automatically, by invoking pattern recogni(cid:173)
`tion software resident in the Pc. In this latter instance,
`images of the surface of the material are converted to
`data descriptive of the surface, and sent to the pattern
`recognition software in the PC, which analyzes the data
`to detect whether a predetermined pattern such as a bar
`code previously marked on the surface of the material is
`present. The surface of the material is automatically
`scanned until the pattern is detected and the beam is
`
`5
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`

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`5,059,764
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`5
`positioned at the reference location indicated by the
`pattern.
`Next, the user creates data descriptive of the location
`(with respect to the reference location) and depth of
`one of more cuts to be made in the surface of the mate- 5
`rial, and loads the data into the PC. The PC then directs
`the laser to selectively transmit the pulsed beam, and
`also directs the workstation to position the material
`with respect to the pulsed beam so that the beam oblates
`and makes cuts in the surface of the material at the
`locations and depth described by the data.
`
`20
`
`6
`As explained in Baer et ai., the laser comprises a laser
`head which is pumped by a diode laser, wherein the
`laser head is spaced from and optically coupled to the
`diode laser by means of a fiber optic cable.
`The decoupling of the diode laser from the laser head
`enables the laser head to be more compact, and inserted
`easily into a standard microscope or other optical sub(cid:173)
`system. Contributing to the compact size of the laser
`head is the high pumping efficiency achievable with
`10 diode laser end-pumping, which enables the laser head
`to be extremely compact, and still have a high enough
`gain to produce short enough pulses for material obla(cid:173)
`tion. (The high pumping efficiency wiII be discussed in
`detail below.) Also contributing to the compact size is
`15 the use of a q-switch having a high diffraction effi(cid:173)
`ciency, which q-switch is made from a nontraditional
`material having a higher acoustic-optical figure of merit
`than traditional fused silica, resulting in a more com-
`pact, miniaturized q-switch.
`The compact size of the laser simplifies the mechani(cid:173)
`cal design of the system. By way of comparison, con(cid:173)
`ventional arc lamp pumped, q-switched, solid state la(cid:173)
`sers are typically 1 meter in length with a cross section
`of 20 cm. by 20 cm. In contrast, a fiber-coupled, diode
`laser end-pumped, q-switched solid state laser head can
`be as small as 8 cm. in length with a diameter of 2 cm.
`An exemplary laser head is the Spectra-Physics Model
`7950 Q-switched laser head. An exemplary laser system
`of which the laser head is a key component comprises
`the Spectra-Physics Model 7200 diode laser module, the
`Model 7250 Q-switch driver, the Model 7950 Q-
`switched laser head, and an optional frequency dou(cid:173)
`bling accessory Model 7955 allowing pulsed operation
`in the visible.
`Another benefit of fiber optic coupling in combina(cid:173)
`tion with the high pumping efficiency is that little orno
`heat dissipation will be required in the laser head. Most
`of the heat dissipation will be localized in the power
`supply or the diode laser, and any cooling required can
`be localized there. Since the diode laser is decoupled
`and spaced from the laser head, the attendant vibrations
`associated with a cooling system can be insulated from
`the laser head, enabling the laser head to produce a
`more precise cut in the material being processed or
`machined.
`Another benefit of fiber coupling is that servicing or
`replacing of the diode laser will not require dismounting
`or realigning of the laser head, and servicing of the
`laser, and hence the subject invention, will be easier.
`The advantage of end pumping is that it is very effi(cid:173)
`cient, enabling only those regions of the active media
`that will contribute to the production of a selected las(cid:173)
`ing mode to be pumped. In other words, end pumping
`provides for the best overlap of the pump volume with
`the lasing volume of the particular mode which is de(cid:173)
`sired. These principles are discussed in more detail in
`Baer et ai., but will be summarized here.
`For materials processing, the TEMoo mode is an ideal
`mode since it is a diffraction limited beam compared to
`the other modes, and can be focused down to the beam
`size required for materials processing. A major applica-
`tion of the subject invention is link blowing for semi(cid:173)
`conductor memory repair. Since a link is on the order of
`1-2 microns in thickness, a beam diameter on the order
`of 1-2 microns will be required. With the TEMoo mode,
`a beam diameter of 200-300 microns can be achieved,
`which can easily be focused to a beam having a diame(cid:173)
`ter on the order of 1-2 microns.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. I(A) shows a block diagram of a side view of an
`exemplary embodiment of the subject invention;
`FIG. I(B) shows a block diagram ofa tilted side view
`of the exemplary embodiment of FIG. I(A); and
`FIG. 2 is a block diagram of the optical subsystem of
`the subject invention.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`An exemplary embodiment of the subject invention is
`shown in FIG. 1. As illustrated in the Figure, the em(cid:173)
`bodiment comprises diode-laser end-pumped, solid state 25
`laser 1, optical subsystem 2, imaging subsystem 3, work(cid:173)
`station means 4, optical paths 5 and 6, material under
`process 7, and control means (not shown). The imaging
`subsystem advantageously comprises an aiming beam
`collinear with the pulsed laser beam, and a video cam- 30
`era electrically coupled to a monitor (not shown). The
`optical subsystem is advantageously a microscope, and
`the control means is advantageously a personal com(cid:173)
`puter ("PC"). In addition, the workstation means is
`advantageously an X-Y stepper motor-controlled work- 35
`station for stepping horizontally, vertically, or both in
`response to commands from the PC.
`As illustrated in the Figure, the laser is mechanically
`coupled to the optical subsystem, which in turn is me(cid:173)
`chanically coupled to the video camera of the imaging 40
`subsystem. In addition, the video camera is electrically
`coupled to the monitor, and is optionally electrically
`coupled to the control means. The control means is
`electrically coupled to the laser and to the workstation
`means for selectively directing the laser to transmit a 45
`pulsed laser beam, and directing the workstation means.
`to position the material with respect to the laser beam.
`The microscope or other optical subsystem directs the
`pulsed laser beam along an optical path to the surface of
`the material being processed, whereupon the beam ob- 50
`lates the surface. The microscope or other optical sub(cid:173)
`system also directs the collinear aiming beam along the
`same optical path to strike but not oblate the surface of
`the material. After the aiming beam strikes the surface,
`it will then reflect from it. The reflected beam then 55
`partly retraverses the optical path, and the optical sys(cid:173)
`tem directs a fraction of the reflected beam to the video
`camera of the imaging system, which directs the moni(cid:173)
`tor to visually display an image of the surface of the
`material at the location where the beam strikes. The 60
`visual display of the surface will be important for manu(cid:173)
`ally positioning the pulsed laser beam on the surface of
`the material.
`Diode-laser pumped, solid state laser 1 is a diodelaser
`end-pumped, q-switched, fiber-coupled, solid-state laser 65
`as described more fully in Baer et aI., U.S. Pat. No.
`4,665,529, which is herein incorporated by reference as
`though fully set forth herein.
`
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`5,059,764
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`7
`Another advantage of the TEMoo mode for materials
`processing is that it will be a uniform beam, with no
`nodes, zeroes, or other structure across the face of the
`beam, as will be present with the other modes. The
`advantage of having no structure is that the energy 5
`delivered by the laser to the material being processed
`can be more tightly controlled, enabling better control
`of the width and depth of cuts.
`The lasing volume for the TEMoo mode will depend
`on the characteristics of the laser cavity in the laser 10
`head, and specifically the radii of curvature of the mir(cid:173)
`rors on either side of the cavity. In the embodiment
`described in Baer et aI., the lasing material is a laser rod
`comprising a Nd:Y AG crystal approximately 5 mm
`long and 3 mm in diameter. The laser rod has a first and 15
`a second end, and the laser cavity is defined by two
`mirrors placed at the first and second ends, on either
`side of the rod. A flat mirror is placed at the first end,
`which can either be spaced from the first end of the
`laser rod, or formed directly on the first end of the laser 20
`rod. A concave mirror is placed at the second end of the
`rod, and spaced from the end. The radius of curvature
`of this mirror is 5 cm. These parameters define the diam(cid:173)
`eter of the TEMoo mode lasing volume, which in the
`embodiment described above, has a diameter of approx- 25
`imately 150-200 microns.
`For maximum efficiency, the pumping volume should
`overlap the lasing volume as much as possible. The
`pumping volume will be dependent on the diameter of
`the fiber cable, and the extent to which the pumping 30
`radiation diverges after being emitted from the end of
`the fiber cable, and before entering the longitudinal end
`of the solid state rod in the laser head. In the embodi(cid:173)
`ment described in Baer et aI., the diameter of the fiber
`cable is 100 microns, and the pumping volume will have 35
`a diameter in the range of 100-200 microns. In addition,
`as described above, the lasing volume for the TEMoo
`mode will be approximately 200 microns in diameter.
`Thus, substantial overlap is achieved.
`Diode pumping also contributes to the efficiency 40
`since it can be tuned to a wavelength which overlaps
`the absorption band of the Nd ion produced in the laser
`rod in the wavelength range of interest. As a result, the
`diode laser light will be almost entirely absorbed, and
`therefore contribute to the creation of a population 45
`inversion. Compared to arc lamp pumping, which has
`an electrical efficiency level of only 0.5%, diode pump(cid:173)
`ing has an electrical efficiency level of approximately
`10%.
`It is recognized that high electrical efficiency can also 50
`be achieved with diode laser side-pumped solid state
`lasers, as set forth more fully in Baer et aI., U.S. patent
`application Ser. No. 103,557 entitled "High Efficiency
`Mode Matched Solid State Laser With Transverse
`Pumping," filed Sept. 30, 1987 which is incorporated by 55
`reference as though set forth herein. Therefore, the
`subject invention is meant to encompass embodiments
`employing side-pumped as well as end-pumped solid
`state lasers.
`Because of the greater efficiency available with diode 60
`laser end-pumping, the laser will have a much higher
`gain at a given input power level. As a result, the laser
`cavity can be made extremely short in length in order to
`produce the short output pulses required for material
`ablation. As discussed earlier, for successful materials 65
`processing, the output pulses should be short compared
`to the diffusion time of the material being processed.
`For many applications, a pulse width of 50 ns or below
`
`8
`is required, for example 30 ns. With the embodiment of
`the laser described in Baer et aI., pulse widths on the
`order of 10-50 ns have been obtained.
`Another benefit of the higher efficiency is that the
`input power can be lowered. In fact, the higher effi(cid:173)
`ciency enables the laser to be operated from a 115 VAC
`outlet instead of a 230 V AC outlet. This allows delivery
`of a laser beam having the appropriate energy levels
`required for materials processing without the necessity
`of attenuating the beam. For materials processing appli(cid:173)
`cations, a laser beam having an energy level of 100 pJ or
`lower, and preferably 5-10 J-tJ, will be required in order
`to obtain precise cuts. Energy levels higher than this
`will, because of the short pulse widths involved, deliver
`too much power to the material, causing it to melt. This
`is because the power deliveri'!d by the laser will be equal
`to the energy level, which will remain approximately
`constant over many variations in the pulse width, di(cid:173)
`vided by pulse width. The net result is that diode laser
`end-pumping delivers the proper pulse width/energy
`level combination required for successful, precision
`materials processing.
`The higher electrical efficiency has significant, addi(cid:173)
`tional benefits. One benefit is that there will be little or
`no heat dissipation in the laser head, enabling the cool(cid:173)
`ing system to be moved to and localized with the power
`supply and diode laser, which in turn will decouple the
`laser head from the vibrations of the cooling system. In
`addition, there is no need for water cooling, and the
`attendant noise in the laser output caused by water
`turbulence will be eliminated. The benefit is that more
`precise cuts can be made.
`The above was a description of the laser component
`of the system. The remaining components will now be
`described. The optical subsystem directs the laser beam
`to strike the surface of material 7, and also focuses the
`laser beam. In the particular embodiment of FIG. 1, the
`optical subsystem is any standard microscope capable of
`focusing a 10-20 micron diameter beam to a diameter of
`as little as 1 micron. An exemplary microscope is Model
`No. P37,324 manufactured by Edmund Scientific. In
`addition, the video camera and monitor of the imaging
`subsystem are standard optical components known in
`the art.
`The workstation is a stepper motor controlled trans(cid:173)
`lation workstation known in the art. An advantageous
`embodiment in Model No. XY-3535-M20, manufac(cid:173)
`tured by New England Affiliate Technologies. In addi(cid:173)
`tion, the workstation is electrically coupled to the con(cid:173)
`trol means for storing, sequencing, and sending out
`commands to the workstation to position the material
`with respect to the laser beam. In the embodiment of
`FIG. 1, the computing means is a personal computer.
`The function of the microscope is two fold: I) direct(cid:173)
`ing and focusing the pulsed laser beam onto the surface
`of the material being processed in order to ablate the
`surface; and 2) directing an aiming beam collinear with
`the pulsed beam onto the surface in order to facilitate
`positioning of the pulsed beam.
`The collinear aiming beam is advantageously the
`leakage light from the diode laser, which will be collin(cid:173)
`ear with the pulsed beam. The leakage light will also be
`directed along the same optical path as the pulsed beam
`by the microscope or other optical subsystem to strike,
`but not ablate, the surface of the material. The leakage
`light will then reflect from the surface, and be directed
`by the optical subsystem along optical path 6 to the
`imaging subsystem, which will then display an image of
`
`7
`
`

`

`5,059,764
`
`9
`the surface of the material at the point of impact. A user
`is then able to visually track the positioning of the
`pulsed beam using the monitor of the imaging subsys(cid:173)
`tem, and then issue commands to the control means to
`reposition the pulsed beam. Alternative embodiments 5
`for the collinear, aiming beam, other than the diode
`laser leakage light, include operating the solid state laser
`in continuous wave (cw) mode at lower power, or alter(cid:173)
`natively, using an independent, collinear, aiming beam.
`In any of the embodiments described above, the aiming 10
`beam is used to position the laser while the pulsed beam
`is switched off. Once the laser is positioned, the pulsed
`beam is switched on to ablate the surface.
`A block diagram of the optical subsystem of the ex(cid:173)
`emplary embodiment of FIG. 1 is illustrated in FIG. 2. 15
`The diagram incorporates some of the components of
`FIG. 1, and the identifying num