US20130044779A1 - Method for tailoring the dopant profile in a laser crystal using zone processing - Google Patents

Method for tailoring the dopant profile in a laser crystal using zone processing Download PDF

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US20130044779A1
US20130044779A1 US13/210,786 US201113210786A US2013044779A1 US 20130044779 A1 US20130044779 A1 US 20130044779A1 US 201113210786 A US201113210786 A US 201113210786A US 2013044779 A1 US2013044779 A1 US 2013044779A1
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ingot
crystal
dopant
lasing medium
heating element
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Robert W. Byren
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Raytheon Co
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Raytheon Co
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Priority to US13/210,786 priority Critical patent/US20130044779A1/en
Assigned to RAYTHEON COMPANY reassignment RAYTHEON COMPANY ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: BYREN, ROBERT W.
Priority to EP12823996.9A priority patent/EP2744930B1/en
Priority to JP2014526220A priority patent/JP6087923B2/ja
Priority to PCT/US2012/051189 priority patent/WO2013025926A1/en
Publication of US20130044779A1 publication Critical patent/US20130044779A1/en
Priority to IL230316A priority patent/IL230316A/en
Priority to US14/487,295 priority patent/US9926644B2/en
Priority to US15/904,039 priority patent/US10273595B2/en
Abandoned legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • C30B13/16—Heating of the molten zone
    • C30B13/20—Heating of the molten zone by induction, e.g. hot wire technique
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • C30B13/08—Single-crystal growth by zone-melting; Refining by zone-melting adding crystallising materials or reactants forming it in situ to the molten zone
    • C30B13/10—Single-crystal growth by zone-melting; Refining by zone-melting adding crystallising materials or reactants forming it in situ to the molten zone with addition of doping materials
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B13/00—Single-crystal growth by zone-melting; Refining by zone-melting
    • C30B13/16—Heating of the molten zone
    • C30B13/22—Heating of the molten zone by irradiation or electric discharge
    • C30B13/24—Heating of the molten zone by irradiation or electric discharge using electromagnetic waves
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/12—Halides
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/10—Inorganic compounds or compositions
    • C30B29/16—Oxides
    • C30B29/22—Complex oxides
    • C30B29/28—Complex oxides with formula A3Me5O12 wherein A is a rare earth metal and Me is Fe, Ga, Sc, Cr, Co or Al, e.g. garnets
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/05—Construction or shape of optical resonators; Accommodation of active medium therein; Shape of active medium
    • H01S3/06—Construction or shape of active medium
    • H01S3/0602—Crystal lasers or glass lasers
    • H01S3/0617—Crystal lasers or glass lasers having a varying composition or cross-section in a specific direction
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/1601—Solid materials characterised by an active (lasing) ion
    • H01S3/1603—Solid materials characterised by an active (lasing) ion rare earth
    • H01S3/1611—Solid materials characterised by an active (lasing) ion rare earth neodymium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/14—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range characterised by the material used as the active medium
    • H01S3/16—Solid materials
    • H01S3/163—Solid materials characterised by a crystal matrix
    • H01S3/164—Solid materials characterised by a crystal matrix garnet
    • H01S3/1643—YAG

Definitions

  • the present disclosure relates to solid-state lasers. More specifically, the present disclosure relates to a laser crystal having a tailored dopant profile, the method of fabricating thereof, and a lasing medium fabricated from said laser crystals.
  • Solid-state lasers are currently being developed and used for a variety of military and industrial applications, including range finding, target designation/marking, illumination, three-dimensional imaging, vibration sensing, profilometry, cutting, drilling, welding, heat treating and other material processing, electro-optical and infrared countermeasures, and directed energy weapons.
  • a solid-state laser typically includes a laser amplifier medium or lasing medium disposed within an optical resonant cavity.
  • the resonant cavity or resonator provides the feedback necessary to build oscillation of electromagnetic radiation within the laser.
  • the bulk lasing medium is typically in the shape of a slab, rod, or disk. When pumped, the medium provides amplification by a process of stimulated emission.
  • the provision of reflective surfaces or gratings at the ends of the lasing medium provides a resonator.
  • an incoherent light source imparts energy to the lasing medium, which produces light in which the waves are in phase through particular electron transitions. Where the lasing medium is properly designed, this “coherent light” is emitted as a beam.
  • laser gain media typically comprise single crystals having substantially uniform dopant concentration, such as Nd:YAG (neodymium doped yttrium-aluminum-garnet).
  • Developmental lasers are being designed with optical-quality poly-crystalline ceramic lasing media which offer size and cost advantages over conventional single-crystal media.
  • Solid-state lasing media, doped with an active ion often use one or more flash lamps or laser diodes to provide “pump light.” The diode pump light excites the active ions in the doped crystalline or ceramic lasing medium to a higher energy state.
  • a “pump cavity” typically contains a uniformly doped lasing medium, which may be a crystal or glass or polycrystalline ceramic element fabricated in the shape of a rod, slab, or disk, and other elements, such as a pump light reflector or relay optics. Pump light is coupled into the cavity, typically with one or more flash lamps or laser diodes, either from the side of the cavity (i.e., side pumping) or the end of the cavity (i.e., end pumping).
  • Efficient absorption in which nearly all of the pump light is absorbed by the doped medium, is a primary goal of laser designers.
  • One method of attaining efficient absorption is by using high-absorption (highly doped) laser materials.
  • a ray of pump light going through a doped crystal one time is known as a “pass.”
  • a pump light ray makes only one or two passes through the doped crystal before escaping, necessitating the use of high-absorption materials to achieve efficient absorption.
  • Absorption is governed by an exponential function.
  • ASE amplified spontaneous emission
  • extraction efficiency
  • mode control beam quality
  • End pumping In which pump light comes into a pump cavity along its longitudinal axis. End pumping requires high-brightness pump diodes and durable dichroic coatings, since the pumping and laser light extraction take place through the same optical surfaces (i.e. the ends of the rod) while requiring quite different reflectivity characteristics.
  • pump “bleaching” can occur, in which a large fraction of the active ions have been excited and correspondingly fewer ions are in the ground state available for pump light absorption, resulting in reduced absorption for both side- and end-pumping geometries.
  • a laser crystal having a tailored concentration profile may be especially useful for laser applications which may use a high-aspect-ration slab geometry for the lasing medium.
  • the slab geometry is the planar waveguide (PWG) which is advantageous for applications requiring high gain, high average power, and high efficiency.
  • PWG planar waveguide
  • the PWG has a planar geometry, which guides light only in the thin dimension of the slab.
  • the dopant absorbs the pump energy along the length of the medium and releases it radiatively as photons and non-radiatively as heat.
  • heat is a function of both the energy pumped into the laser material and the dopant level of the laser material.
  • a tailored longitudinal concentration profile (of active ion dopant) is needed.
  • Lasing media with different concentrations along the length thereof have been used. For example, multiple single crystal segments each having a different concentration are bonded together to form a lasing medium with a stepped dopant concentration profile. However, these lasing media are bonded at interfaces that cross the laser beam axis, resulting in media that are more expensive to fabricate and prone to damage.
  • One embodiment of this disclosure provides a method of fabricating a single, contiguous laser crystal having a tailored dopant concentration profile.
  • the method includes arranging a plurality of polycrystalline segments together to form an ingot.
  • the polycrystalline segments each have dopant distributed therein.
  • the method further includes providing a crystal seed at a first end of the ingot and moving a heating element along the ingot starting from the first end to a second end of the ingot.
  • the moving heating element creates a moving molten region within the ingot while passing therealong.
  • Another embodiment provides a single crystal having a tailored dopant concentration profile, produced by a process that includes the steps of arranging a plurality of polycrystalline segments together to form an ingot.
  • the polycrystalline segments each have dopant distributed therein.
  • the steps also include providing a crystal seed at a first end of the ingot and moving a heating element along the ingot starting from the first end to a second end of the ingot.
  • the moving heating element creates a moving molten region within the ingot while passing therealong.
  • a lasing medium that includes a single crystal having a continuous body having a selected length, wherein the crystal comprises dopant distributed along the length of the body to define a dopant concentration profile that results in a uniform heating profile.
  • the lasing medium may be produced by machining the single crystal using processes known in the art such as core drilling, saw cutting, grinding, polishing, and coating to produce a final lasing medium with a desired shape and optical characteristics.
  • FIG. 1 a illustrates a starting ingot formed from a plurality of polycrystalline segments
  • FIG. 1 b illustrates a heating element passing through the ingot and creating a liquid zone therein during float zone processing
  • FIG. 2 illustrates a liquid zone and post-melt and pre-melt regions of the ingot during float zone processing
  • FIG. 3 schematically depicts the liquid zone and the post-melt and pre-melt regions of the ingot during float zone processing and identifies the parameters used in corresponding mathematical equations;
  • FIG. 4 is a plot of a final concentration profile for a laser crystal
  • FIG. 5 is a plot of comparisons between a target concentration, a concentration profile resulting from float zone processing performed on a uniform ingot, and a concentration profile resulting from float zone processing performed on multiple segments having different dopant concentrations.
  • Lasing media can be fabricated to have a tailored dopant concentration profile.
  • the lasing media includes an elongated, single crystal having a continuous body having a selected length.
  • the crystal may include dopant distributed along the length of the body and may have a dopant concentration profile in accordance with a target dopant concentration profile.
  • the lasing medium may be fabricated using float zone processing or zone melting.
  • Float zone processing has been used in the semiconductor industry to purify crystals by melting a narrow region of the crystal. This molten zone is then moved along an ingot by moving a heating element along the longitudinal axis of the crystal. As the molten region moves through the ingot, this molten region melts impure solids and leaves behind a single crystal region of purer materials as it solidifies. As a result, the impurities concentrate in the melt, and are moved to one end of the ingot.
  • the purifying process works on the principle that, since the segregation coefficient k, which is the ratio of an impurity in the solid phase to that in the liquid phase, is usually less than one, the impurity atoms will diffuse to the liquid region at the solid/liquid boundary. Thus, by passing a crystal boule through a thin section of furnace very slowly, such that only a small region of the boule is molten at any time, the impurities may be segregated at the end of the crystal.
  • FIGS. 1 a - 1 b illustrates using float zone processing to tailor the concentration of active lasing species (or dopants) within a laser crystal.
  • dopants are typically inserted into a substance in order to alter the electrical properties or the optical properties of the substance.
  • the atoms of the dopant commonly take the place of elements that were in the crystal lattice of the material.
  • YAG which is also known as yttrium aluminum garnet (Y 3 Al 5 O 12 )
  • Y 3 Al 5 O 12 is a popular synthetic crystal material that is usually doped with some element to form a laser crystal.
  • the yttrium ions in YAG can be replaced with laser-active rare earth ions (e.g., neodymium) up to some concentration limit without strongly affecting the lattice structure.
  • concentration limit is determined by size of the dopant ion (e.g., neodymium) relative to that of the substituted ion (e.g., yttrium).
  • These dopant ions may essentially carry out the lasing process in the crystal.
  • the other atoms in the crystal i.e., the yttrium, aluminum, and oxygen atoms
  • a variety of crystal materials may be used, for example, Y 3 Al 5 O 12 , YLiF 4 , or Gd 3 Ga 5 O 12 .
  • a variety of dopants may also be used, just for example, ytterbium, erbium, thulium, or holmium.
  • starting ingot 10 is formed from plurality of polycrystalline segments 12 .
  • the starting ingot may be oriented such that its longitudinal axis is vertical.
  • each polycrystalline segment 12 has a different dopant concentration from the other segments.
  • segments 12 may have the same dopant concentration or alternatively may be a single polycrystalline segment. It should be appreciated that the number of segments 12 may vary in other embodiments.
  • the length of each segment 12 and the concentration in each segment 12 may also vary to achieve the target concentration profile. Segments 12 may be vertically stacked without bonding or sintering and held in place only by gravity.
  • Single seed crystal 14 may be provided at first end 16 of ingot 10 and arranged with segments 12 to form ingot 10 .
  • Seed crystal 10 may be substantially pure or doped with a concentration of dopant. Seed crystal 14 lattice orientation is the same as the desired orientation of the resulting lasing crystal. Ingot 10 may also include a second end 18 opposite first end 16 . Heating element 20 may be used to form liquid zone 22 . In one embodiment, ingot 10 is oriented such that its longitudinal axis is vertical with seed crystal at the top, the end of seed crystal not adjacent to a polycrystalline segment is clamped or bonded to a holding fixture to offset the force of gravity, and heating element 20 is moved vertically from top to bottom while ingot 10 is held stationary.
  • heating element 20 is near the interface between the seed crystal 14 and the adjacent polycrystalline segment 12 ′ such that end 16 of seed crystal 14 remains a crystallized solid and defines the crystal structure and lattice orientation of the resulting lasing crystal.
  • Heating element 20 may be provided by RF induction or any other methods or apparatuses.
  • heating element 20 may be induction coils, ring-wound resistance heaters, or gas flames.
  • ingot 10 may be heated radiatively using an induction-heated tungsten ring.
  • an electric current may be passed through the ingot while it is suspended in a magnetic field with the current controlled such that the material is magnetically levitated to minimize gravity sag in the liquid zone 22 .
  • the liquid zone 22 formed by heating element 20 may similar to the “molten zone” described above with respect to purification of crystals. Liquid zone 22 moves through ingot 10 and disperses the dopants through ingot 10 to form the dopant concentration profile.
  • FIG. 1 b shows heating element 20 moving through ingot 10 in the direction of A, and thus moving liquid zone 22 through ingot 10 . As heating element 20 moves liquid zone 22 through ingot 10 , a resulting crystal portion 24 having the desired concentration profile is formed.
  • Seed crystal 14 and each segment 12 of ingot 10 may be doped with a selected active lasing species, which behaves as the “impurity” in the float zone purification process described above.
  • the process of FIG. 1 produces a single crystal having a desired or target one-dimensional dopant profile.
  • the resulting profile may be achieved by selecting the proper dopant concentration within each segment 12 such that the natural diffusion of active lasing species within the liquid zone and the difference in solubility of active lasing species between solid and liquid phases results in the desired profile.
  • the difference in solubility of active lasing species between solid and liquid phases which gives rise to the lowering of concentration in the single crystal region is characterized by the segregation coefficient for the particular dopant within the particular crystal.
  • seed crystal 14 should be doped with the same concentration as desired at first end 16 of the resulting crystal and segments 12 near seed crystal 14 that will be melted first should have a higher concentration of dopant than the target concentration.
  • segments 12 closer to second end 18 of ingot 10 may have less concentration of dopant.
  • the concentrations of segments 12 are decreasing from first end 16 to second end 18 .
  • the smoothness of the doping profile may depend on the steepness of the desired concentration gradient and the number of polycrystalline segments 12 in ingot 10 .
  • FIG. 2 shows an expanded view of the region around liquid zone 22 where the dopant species are mixed within the liquid during melting.
  • Region 21 represents a pre-melt region or condition and has a concentration of C I .
  • C I represents the initial concentration of dopant species by weight.
  • C I can be a constant if a single uniformly-doped segment is used. Alternatively, if multiple segments 12 having different dopant concentrations are used, C I may be a function of distance along the length of ingot 10 in the direction of A.
  • Region 23 represents the post-melt region or condition having a concentration of C F .
  • C F represents the final concentration, which is a function of distance along the length of the resulting crystal.
  • the final concentration of the resulting crystal may be tailored by varying the length of each polycrystalline segment, varying the concentration of the dopant in each polycrystalline segment, varying the length of the liquid zone, varying the number of passes that the heating element is moved along the ingot, and varying other factors that will be described below. Accordingly, C I represents the pre-melt condition and C F represents the post-melt condition.
  • Float zone processing that is performed on polycrystalline segments 12 can convert polycrystalline lasing material to a single crystal where a standard growth process (e.g., Czochralski growth process) is impossible, impractical from a size standpoint, and/or results in unwanted stress regions within the crystal.
  • a standard growth process e.g., Czochralski growth process
  • neodymium-doped YAG formed by the Cazochralski growth process has a stressed region formed along the center of the crystal that is not useable for lasing media.
  • the resulting crystal formed by the float zone processing of multiple polycrystalline segments 12 has a continuous body, a tailored dopant concentration profile along the length of the body, and no substantially stressed regions.
  • the resulting crystal may be a single crystal with the identical crystal structure and lattice orientation as crystal seed 14 and a concentration profile that can be arbitrarily tailored with precision by varying any of the factors or parameters described below.
  • FIG. 3 shows the same region as FIG. 2 and shows the parameters used to analyze the doping profile.
  • the parameters are defined as below:
  • k segregation coefficient (ratio of dopant concentration in solid to that in liquid across solidus/liquidus interface)
  • the molten region propagates from left to right in the direction of A as heater 20 is moved accordingly.
  • dx the amount of dopant added to liquid zone 22 from the ingot is C I (x)A ⁇ dx.
  • the above equations can be solved for any given concentration profile for the polycrystalline ingot. That is, to tailor the concentration profile, the above equations may be used to determine the value of the parameters. Alternatively, the input values of the parameters may be used to determine the resulting concentration profile.
  • the resulting lasing medium is neodymium-doped yttrium aluminum garnet (Nd:YAG).
  • Nd:YAG offers substantial laser gain even for moderate excitation levels and pump intensities. The gain bandwidth may be relatively small, but this allows for a high gain efficiency and thus low threshold pump power.
  • the area of the ingot might not be a factor in the analysis, but the interfaces between the solid and the liquid phases should be relatively flat and normal to the direction of A. This may prevent or minimize a lateral component to the concentration gradient, which may not be desirable.
  • the resulting crystal may have features or performance characteristics that vary based on the float zone processing apparatuses, the physical and thermal design of the laser pump head, and the handling and thermal robustness of laser crystal 12 .
  • the crystal may have the following parameters:
  • FIG. 4 plots the final concentration profile for a laser crystal with the above parameters. That is, FIG. 4 plots the final concentration profile for laser crystal 12 for several liquid zone lengths after a single pass of heating element 20 along the length of the starting ingot that was doped at 1 atomic percent neodymium.
  • FIG. 4 shows the concentration profiles for crystals having liquid zone lengths of 0.5 cm, 1 cm, and 1.5 cm.
  • Plot A shows the concentration profile for crystals having liquid zone length of 0.5 cm
  • plot B shows the concentration profile for crystals having liquid zone length of 1 cm
  • plot C shows the concentration profile for crystals having liquid zone length of 1.5 cm.
  • the mass density is 4.56 g/cm 3 .
  • the segregation coefficient of neodymium in YAG is 0.18.
  • FIG. 5 shows a comparison of a resulting crystal having a final concentration produced by using multiple segments of different concentrations versus the resulting crystal having a final concentration produced by a simple float zone process with a uniformly doped starting ingot 10 .
  • the target concentration shown in this Figure represents a near-optimal concentration profile for a small 5 cm long laser crystal designed to be the active layer of a high aspect ratio PWG slab structure.
  • the resultant concentration profile for the uniformly-doped ingot is also shown in FIG. 5 , where the starting concentration of the ingot (1.95 ⁇ 10 19 atoms/g) is tailored to give the same final concentration as the target profile at the lean end (3.32 ⁇ 10 18 atoms/g).
  • the resultant concentration for the segmented ingot is also shown where each segment is 0.5 cm long and has the following concentration:
  • the extra segment at the end may be sacrificed to allow the float zone to pass through the entire useful region of the slab without discontinuity.
  • the concentration profile produced by float zone processing on multiple segments of different dopant concentrations as described above is closer to the target concentration than the concentration produced by a simple float zone process on a uniformly doped starting ingot 10 . Accordingly, the dopant concentration profile of a single crystal may be tailored by performing float zone processing on a plurality of polycrystalline segments.
  • uniformly doped lasing media may result in the material in the pump end receiving the most energy and producing the most heat, thus resulting in localized heating.
  • the tailored dopant levels within the single crystal produced by the float zone processing described above may result in uniform heating and uniform laser emission throughout the crystal. That is, the tailored dopant profile of the single crystal may result in a strong, robust lasing medium having a uniform heating profile that can produce higher output power.

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US13/210,786 2011-08-16 2011-08-16 Method for tailoring the dopant profile in a laser crystal using zone processing Abandoned US20130044779A1 (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US13/210,786 US20130044779A1 (en) 2011-08-16 2011-08-16 Method for tailoring the dopant profile in a laser crystal using zone processing
EP12823996.9A EP2744930B1 (en) 2011-08-16 2012-08-16 Method for tailoring the dopant profile in a laser crystal using zone processing
JP2014526220A JP6087923B2 (ja) 2011-08-16 2012-08-16 ゾーン処理を用いてレーザー結晶内のドーパントプロファイルを調節する方法
PCT/US2012/051189 WO2013025926A1 (en) 2011-08-16 2012-08-16 Method for tailoring the dopant profile in a laser crystal using zone processing
IL230316A IL230316A (en) 2011-08-16 2014-01-05 A method for coordinating a doping profile in a laser crystal by region processing
US14/487,295 US9926644B2 (en) 2011-08-16 2014-09-16 Method for tailoring the dopant profile in a laser crystal using zone processing
US15/904,039 US10273595B2 (en) 2011-08-16 2018-02-23 Method for tailoring the dopant profile in a laser crystal using zone processing

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CZ306311B6 (cs) * 2015-07-16 2016-11-23 Fyzikální Ústav Av Čr, V. V. I. Optické elementy pro konstrukci výkonových laserových systémů a jejich příprava
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EP2744930A4 (en) 2015-12-30
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US10273595B2 (en) 2019-04-30
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