Patent Description:
In recent years, with increase in output power of a laser oscillator, cooling of an optical material used in the laser oscillator has become a problem. A temperature gradient generated in an optical material causes a thermal lens effect, thermal aberration, thermal birefringence, and the like. As a result, the temperature gradient degrades quality of laser light. Therefore it is desired to make the temperature gradient in the optical material as gentle as possible. Accordingly, development of techniques for efficiently cooling an optical material in a laser oscillator is underway. For example, Non Patent Literature <NUM> discloses a bonded body in which transparent sapphire (a cooling material) having excellent thermal conductivity is bonded at both ends of Yb:YAG (an optical material). Joining materials by diffusion bonding is further disclosed in Non Patent Literature <NUM> and Patent Literature <NUM> to <NUM>.

It is known that when light enters an interface where substances having different refractive indices come in contact with each other, part of the light is reflected from the interface (Fresnel reflection). The bonded body in Non Patent Literature <NUM> is formed by bonding an optical material to a cooling material and therefore has a problem that an amount of loss caused by a Fresnel reflection is large when light is transmitted through the bonded body. Such a problem exists not only in a case of causing a bonded body formed by bonding Yb:YAG to sapphire to transmit light but also in a case of causing a composite material formed by combining materials capable of transmitting light to transmit light.

The present disclosure has been made based on such a background, and an objective of the disclosure is to provide a joined body, a laser oscillator, a laser amplifier, and a joined body manufacturing method that provide sufficient optical quality even when materials capable of transmitting light are combined. This objective is solved by a joined body, a laser oscillator, a laser amplifier, and a joined body manufacturing method, comprising the features of the independent claims.

In order to achieve the aforementioned objective, a joined body according to a first aspect of the present disclosure includes a first material and a second material that are capable of transmitting light and are joined together,
wherein, at a joining interface between the first material and the second material, the joined body is capable of transmitting light, and also wherein parts of atoms contained in each one of the materials diffusively enter correspondingly the other one of the materials in such a degree that an interference fringe is not generated in the joined body.

A diffusive entry length of an atom contained in the first material into the second material is in a range from approximately <NUM> to approximately <NUM>.

Assuming a wavelength λ of laser light emitted from a laser interferometer used for measuring transmission wave surface precision to be <NUM>, transmission wave surface precision of the first material and the second material may be approximately λ or less.

The first material may be a polycrystal, and the second material may be a monocrystal.

The polycrystal may be YAG or YAG doped with a rare-earth ion, and
the monocrystal may be sapphire, aluminum nitride, gallium nitride, silicon carbide, or diamond.

The first material may be a phosphor or a magneto-optical material, and the second material may be a material having a thermal conductivity higher than that of the first material.

In order to achieve the aforementioned objective, a laser oscillator according to a second aspect of the present disclosure includes:.

In order to achieve the aforementioned objective, a laser amplifier according to a third aspect of the present disclosure includes:.

In order to achieve the aforementioned objective, a joined body manufacturing method according to a fourth aspect of the present disclosure
is a method for manufacturing a joined body including a first material and a second material that are capable of transmitting light and are joined together, wherein parts of atoms contained in each one of the materials diffusively enter correspondingly the other one of the materials in such a degree that an interference fringe is not generated in the joined body, the joined body manufacturing method including:.

The predetermined pressure may be in a range from approximately <NUM> MPa to approximately <NUM> GPa.

The predetermined temperature may be in a range from approximately <NUM> to approximately <NUM>.

The predetermined time may be in a range from approximately <NUM> minutes to approximately <NUM> hours.

The present disclosure can provide a joined body, a laser oscillator, a laser amplifier, and a joined body manufacturing method that provide sufficient optical quality even when materials capable of transmitting light are combined.

Embodiments of a joined body, a laser oscillator, a laser amplifier, and a joined body manufacturing method according to the present disclosure will be described in detail below with reference to drawings. In each drawing, the same sign is given to the same or equivalent parts.

<FIG> is a perspective view illustrating a structure of a joined body <NUM> according to Embodiment <NUM>. The joined body <NUM> includes an optical material <NUM> (first material) and a pair of cooling materials <NUM> (second materials) each of which is joined to each of the two ends of the optical material <NUM>. Each of the optical material <NUM> and the cooling material <NUM> is formed of a material capable of transmitting light and, more specifically, is formed of a transparent material. The optical material <NUM> and the cooling material <NUM> are joined to each other without involving means for bonding materials, such as an adhesive.

"Joining" means binding materials in contact with each other by diffusive entry of atoms from at least one of the materials to the other material. "Joining" does not include a case of binding materials by involving means for bonding the materials, such as an adhesive. At a joining interface in the joined body <NUM>, part of atoms of the optical material <NUM> diffusively enter the cooling material <NUM>, or part of atoms of the cooling material <NUM> diffusively enter the optical material <NUM>. Consequently, the optical material <NUM> is firmly joined to the cooling material <NUM>.

Further, "joining" also includes a case of, when atoms diffusively enter from one material to another material, an intermediate layer originating in the atoms constituting the materials being formed between the materials in contact with each other and the materials being bound through the intermediate layer. Further, it is also included that a case of placing an intermediate layer (such as a SiO<NUM> layer) causing diffusion and entry of atoms with one material and the other material between the one material and the other material, and binding the materials through the intermediate layer.

For example, each of the optical material <NUM> and the cooling material <NUM> is disk-shaped and is formed at the same outer diameter. By using a manufacturing method of the joined body <NUM> to be described later, an unprecedentedly large-sized joined body <NUM> can be produced. The outer diameter of the joined body <NUM> may be approximately <NUM> or greater, may be, for example, approximately <NUM> to approximately <NUM>, and may preferably be approximately <NUM> to approximately <NUM>. Further, when defined by an area, for example, the size of the joined body <NUM> may be in a range from approximately <NUM><NUM> to <NUM><NUM>.

The optical material <NUM> is a laser medium in a laser oscillator. The laser medium amplifies light by absorbing light emitted from a pumping light source and causing induced emission. The laser medium is formed of a phosphor absorbing light at a specific wavelength and emitting light at another wavelength based on the specific wavelength.

For example, the optical material <NUM> is a polycrystal such as yttrium aluminum garnet (YAG) or Nd:YAG. Nd:YAG is in a same material type relation with YAG and is acquired by doping YAG with neodymium (Nd) and replacing part of yttrium (Y) with neodymium. Polycrystals such as YAG and Nd:YAG have excellent light absorbance. Therefore, increasing in output power of a laser oscillator can be achieved by using the polycrystals. For example, the thickness of the optical material <NUM> is approximately <NUM> to approximately <NUM>.

Further, a polycrystal constituting the optical material <NUM> may be a material acquired by doping a basic material such as YAG, lutetium aluminum garnet (LuAG), Y<NUM>O<NUM>, Lu2O<NUM>, or CaF<NUM> with a rare-earth ion such as Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, or Yb. The basic material may be co-doped with a plurality of types of rare-earth ions.

The cooling material <NUM> is a material capable of transmitting light, transfers heat generated in the optical material <NUM>, and emits the heat to the outside. In order to efficiently absorb heat generated in the optical material <NUM>, the cooling material <NUM> is formed of a material having a thermal conductivity higher than that of the optical material <NUM>. For example, the cooling material <NUM> is a monocrystal such as sapphire, aluminum nitride, gallium nitride, silicon carbide, or diamond. For example, the thickness of the cooling material <NUM> is approximately <NUM> to approximately <NUM>.

Sapphire has a property of having a higher damage threshold value compared with YAG. The damage threshold value is a threshold value of an amount of energy per unit area that can be supplied without damaging the material. By sandwiching the optical material <NUM> formed of YAG by cooling materials <NUM> formed of sapphire, damage to the joined body <NUM> caused by application of energy can be effectively prevented even when the optical material <NUM> is formed of YAG.

A degree of diffusive entry of atoms at the joining interface in the joined body <NUM> is evaluated by an index called a "diffusive entry length" including a case of providing an intermediate layer between one material and the other material. For example, a diffusive entry length is expressed by √Dt in a case of fitting, by Equation (<NUM>) below, a one-dimensional concentration distribution of atoms acquired when atoms contained in one material of the joined body <NUM> diffusively enter the other material. Math <NUM> <MAT>.

Note that Cx denotes concentration (in any units) of the atoms at a distance x, Co denotes the concentration (in any units) of the atoms at a distance x = <NUM>, x denotes a distance (m), x<NUM> denotes a distance (m) of a position where the concentration of the atoms is C<NUM>/<NUM>, D denotes a diffusion coefficient (m<NUM>/sec), and t denotes time (sec).

The diffusive entry length of atoms of the joined body <NUM> is set in such a degree that the optical material <NUM> and the cooling material <NUM> are firmly joined together. At the same time, transparency and absorbency of the optical material <NUM> and the cooling material <NUM> are not affected. According to the invention, a diffusive entry length of atoms of the joined body <NUM> satisfying the condition described above is in a range from approximately <NUM> to approximately <NUM> or may be in a range from approximately <NUM> to approximately <NUM>.

When the laser oscillator operates at high output power, the central part of the optical material <NUM> reaches a high temperature, and therefore a temperature gradient is generated in a radial direction. A temperature gradient generated in the optical material <NUM> causes thermal expansion, a refractive index gradient, and the like. As a result, the temperature gradient causes degradation in beam quality and decrease in laser output. However, the joined body <NUM> is formed in such a way that the cooling materials <NUM> arranged in an oscillation direction of laser light sandwich the optical material <NUM>, and therefore heat generated in the central part of the optical material <NUM> can be efficiently discharged.

As described above, the cooling materials <NUM> are joined to both ends of the optical material <NUM> in the joined body <NUM> according to Embodiment <NUM>, and therefore thermal resistance at the interface is lower compared with a case of bonding the two. Accordingly, heat generated in the optical material <NUM> can be conducted to the cooling material <NUM> and can be efficiently discharged to the outside.

Further, the optical material <NUM> is joined to the cooling material <NUM> without involving the air, an adhesive, or the like in the joined body <NUM> according to Embodiment <NUM>, and therefore sufficient optical quality can be acquired by suppressing Fresnel loss and intensity can be sufficiently secured.

Furthermore, the optical material <NUM> is formed of a polycrystal, and the cooling material <NUM> is formed of a monocrystal in the joined body <NUM> according to Embodiment <NUM>. Accordingly, even though the optical material <NUM> is formed of a polycrystal, damage to the joined body <NUM> can be prevented by sandwiching the optical material <NUM> by the cooling materials <NUM> formed of monocrystals.

<FIG> is a diagram illustrating a structure of a laser oscillator <NUM> according to Embodiment <NUM>. The laser oscillator <NUM> includes a joined body <NUM> including a laser medium, a resonator <NUM> placed in such a way as to sandwich the joined body <NUM>, and pumping light sources <NUM> supplying pumping light to the joined body <NUM> and causing laser light to resonate in the resonator <NUM>.

The resonator <NUM> includes a reflecting mirror <NUM> totally reflecting light and an output mirror <NUM> capable of taking out part of light to the outside. The reflecting mirror <NUM> and the output mirror <NUM> are placed in such a way as to face each other with the joined body <NUM> in between. Further, the pumping light sources <NUM> are placed in such a way as to face each other in a radial direction of the joined body <NUM> with the joined body <NUM> in between. The laser oscillator <NUM> amplifies laser light by induced emission every time the laser light passes through the joined body <NUM>, by causing the laser light to repeatedly reflect between the reflecting mirror <NUM> and the output mirror <NUM>, and emits part of the laser light through the output mirror <NUM>.

The laser oscillator <NUM> includes the joined body <NUM> and therefore can efficiently discharge heat generated in the central part of the optical material <NUM> in a propagation direction of laser light through the cooling material <NUM>. Accordingly, heat can be effectively discharged even when the laser oscillator <NUM> is downsized, and therefore a small-sized laser device such as a microchip laser can be provided.

Next, a manufacturing method of the joined body <NUM> will be described with reference to <FIG> and <FIG>. The joined body <NUM> is manufactured by use of pulsed electric current sintering (PECS). PECS is a method of joining materials to be joined to each other by supplying pulse current generated by ON/OFF switching of direct current and heating the materials while mechanically pressurizing the materials.

PECS causes diffusion of atoms between the materials and joins materials to be joined to each other by simultaneously performing pressurization and heating of the materials. PECS causes a punch and a die for pressurizing materials to generate heat and heats the materials by heat conduction of the punch and the die. Therefore PECS allows more rapid heating compared with a case of using an electric furnace or the like. Accordingly, structural change, such as grain growth, occurring due to exposing materials in a high-temperature environment for a long time can be suppressed.

<FIG> is a diagram illustrating a structure of a manufacturing device <NUM> for manufacturing the joined body <NUM>. The manufacturing device <NUM> is a device being installed in a vacuum or in an inert gas and manufacturing the joined body <NUM> by pressurizing materials to be joined and heating the materials by supplying pulse current to the materials.

The manufacturing device <NUM> includes a pair of vertically placed spacers <NUM>, a pair of punches <NUM> pressurizing materials to be joined to each other, each punch being fixed at the end of a spacer <NUM>, a die <NUM> internally housing the pair of punches <NUM> and the materials, and a pulse current source <NUM> supplying pulse current from one spacer <NUM> to the other spacer <NUM>.

The spacer <NUM> holds the punches <NUM> and presses the materials from a vertical direction through the punches <NUM>. Further, each spacer <NUM> is electrically connected to the pulse current source <NUM> and supplies pulse current from one punch <NUM> to the other punch <NUM>. The lower spacer <NUM> is installed on a base of the manufacturing device <NUM>. The upper spacer <NUM> is fixed to a moving mechanism (unillustrated) of the manufacturing device <NUM> and is formed in such a way as to be movable in a vertical direction relative to the lower spacer <NUM>.

The punch <NUM> is a member being in direct contact with a material and pressing the material and at the same time supplying pulse current from the spacer <NUM> to the material. For example, the punch <NUM> is a cylindrical member and is formed of an electroconductive material such as graphite. The diameter of the punch <NUM> corresponds to the diameter of the joined body <NUM> and, for example, is approximately <NUM> to approximately <NUM> and is preferably approximately <NUM> to approximately <NUM>.

The die <NUM> is a member internally housing materials and supplying pulse current supplied from the punch <NUM> to the outer peripheral surface of the materials. The die <NUM> is a tubular member including a through hole being capable of housing materials and allowing the punches <NUM> to be inserted. For example, the die <NUM> is formed of an electroconductive material such as graphite. The inside diameter of the die <NUM> is set in such a way that the outer peripheral surface of the materials and the outer peripheral surface of the punch <NUM> come in contact with the inner peripheral surface of the die <NUM>.

<FIG> is a flowchart illustrating a flow of a manufacturing process of the joined body <NUM> manufactured by use of the manufacturing device <NUM>. A flow of the manufacturing process of the joined body <NUM> will be described below with reference to <FIG>.

First, an optical material <NUM> and cooling materials <NUM> are integrally assembled (Step S1). The optical material <NUM> and the cooling materials <NUM> may be integrally assembled by placing a cooling material <NUM> at each of two ends of the optical material <NUM> and applying an adhesive to the outer peripheral surface of a part where the optical material <NUM> is in contact with the cooling material <NUM>. Further, the two may be bonded by bonding surfaces of the optical material <NUM> and the cooling materials <NUM> together in an activated state.

The integrally assembled optical material <NUM> and the cooling materials <NUM> are formed in such a way as to have predetermined transmission wave surface precision. Assuming a wavelength of laser light emitted from a laser interferometer used for measuring transmission wave surface precision to be λ = <NUM>, for example, the transmission wave surface precision is approximately λ or less, is preferably approximately λ/<NUM> or less, and is more preferably approximately λ/<NUM> or less. For example, the lower limit of the transmission wave surface precision may be approximately λ/<NUM> or less.

Next, the materials assembled in Step S1 are placed at a predetermined position in the manufacturing device <NUM> (Step S2). More specifically, first, the materials are placed inside the through hole of the die <NUM> in such a way that a direction in which the optical material <NUM> and the cooling material <NUM> are laid on top of each other matches an axial direction of the through hole of the die <NUM>. Subsequently, the materials are placed in the manufacturing device <NUM> by inserting the pair of punches <NUM> into the through hole of the die <NUM>.

Next, the materials are pressurized at a predetermined pressure by moving the upper spacer <NUM> downward (Step S3). The materials are pressurized in the direction in which the optical material <NUM> and the cooling material <NUM> are laid on top of each other. For example, the predetermined pressure is in a range from approximately <NUM> MPa to approximately <NUM> GPa, is preferably in a range from approximately <NUM> MPa to approximately <NUM> GPa, and is more preferably in a range from approximately <NUM> MPa to approximately <NUM> GPa.

Next, the materials in a pressurized state are heated to a predetermined temperature by supplying pulse current to the materials (Step S4). More specifically, the punches <NUM> generate heat by supplying pulse current to the punches <NUM>, the heat is conducted to the materials, and the materials are quickly heated. Consequently, As a reason for that the temperature of the optical material <NUM> and the cooling material <NUM> in the pressurized state rises, diffusion of atoms occurs at the joining interface, and therefore joining of the optical material <NUM> and the cooling material <NUM> progresses.

For example, the manufacturing device <NUM> can raise the temperature of the materials at <NUM>/min. The predetermined temperature and the temperature rise rate are set in consideration of types, shapes, sizes, a state of the contact surface, and the like of the optical material <NUM> and the cooling material <NUM>. For example, the predetermined temperature is in a range from approximately <NUM> to approximately <NUM>, is preferably in a range from approximately <NUM> to approximately <NUM>, and is more preferably in a range from approximately <NUM> to approximately <NUM>.

After the materials are heated to the predetermined temperature, the state of the materials being pressurized at the predetermined pressure and being heated at the predetermined temperature is continued for a predetermined time. The predetermined time is set in such a way that a desired diffusive entry length is acquired, in consideration of the types, the shapes, the sizes, the state of the contact surface, and the like of the optical material <NUM> and the cooling material <NUM>. For example, the predetermined time is in a range from approximately <NUM> minutes to approximately <NUM> hours and is preferably in a range from approximately <NUM> hour to approximately <NUM> hours.

Next, whether the predetermined time has elapsed since a point of the materials reaching the predetermined temperature is determined (Step S5). When the predetermined time has elapsed since the point of the materials reaching the predetermined temperature (Step S5; Yes), the pressure on the materials is gradually decreased and, at the same time, the temperature of the materials is gradually decreased (Step S6). It is preferable in Step S6 to gradually cool and gradually decompress the materials at a predetermined temperature fall rate and at a predetermined decompression rate. The temperature fall rate and the decompression rate are set in consideration of the types, the shapes, the sizes, the state of the contact surface, and the like of the optical material <NUM> and the cooling material <NUM>.

On the other hand, when the predetermined time has not elapsed since the point of the materials reaching the predetermined temperature (Step S5; No), the pressurization of the material at the predetermined pressure and the heating of the materials at the predetermined temperature are continued until the predetermined period elapses.

Next, the materials cooled in Step S6 are removed from the manufacturing device <NUM> (Step S7), and by performing optical polishing on the reflection surface of the materials (Step S8), the manufacture of the joined body <NUM> ends. The above is the flow of the manufacturing process of the joined body <NUM> using the manufacturing device <NUM>.

Known methods of joining materials together include a thermal diffusion joining method and a normal temperature joining method, and it is conceivable to apply the techniques to the manufacturing process of the joined body <NUM>. However, the thermal diffusion joining method heats materials by use of an electric furnace or the like and therefore requires high-temperature heat treatment for a long time; and it is difficult to make a diffusive entry length of atoms at the joining interface approximately <NUM> or less. Further, thermal expansion occurs in a clamp for pressurizing materials at a high temperature in the thermal diffusion joining method, and therefore it is difficult to control pressure actually applied to the materials. Furthermore, thermal expansion occurs in the materials themselves at a high temperature in the thermal diffusion joining method, and therefore it is difficult to join different types of materials with different thermal expansion coefficients to each other.

The normal temperature joining method requires extremely high surface precision for joining interfaces to each other. More specifically, denoting a wavelength of laser light emitted from a laser interferometer used for measuring transmission wave surface precision by λ, transmission wave surface precision required of materials is required to be approximately λ/<NUM> or less. It is difficult to form materials having a wide area with high surface precision, and therefore it is difficult to achieve upsizing of a joined body (such as approximately <NUM><NUM> or greater) by the normal temperature joining method. Further, the normal temperature joining method does not heat materials, and therefore it is difficult to make a diffusive entry length at a joining interface approximately <NUM> or greater. Furthermore, the normal temperature joining method requires a high degree of vacuum, and therefore a manufacturing cost is high.

On the other hand, the manufacturing method according to Embodiment <NUM> can perform heat treatment on materials in a short period of time by use of pulse current and therefore can easily join the materials together in a short period of time. Further, As a reason for that the manufacturing method according to Embodiment <NUM> uses pulse current for heating materials, thermal expansion does not occur in the punch <NUM> and the die <NUM>, and the pressure applied to the materials can be accurately controlled even at a high temperature.

Furthermore, by adjusting a predetermined pressure, a predetermined temperature, and a predetermined time, the manufacturing method according to Embodiment <NUM> can control a diffusive entry length of atoms at a joining interface of materials to a desired range (such as from approximately <NUM> to approximately <NUM>) and can suppress structural change, such as grain growth, in a polycrystal under heat treatment. Moreover, the manufacturing method according to Embodiment <NUM> can achieve upsizing of the joined body <NUM> (such as an area of approximately <NUM><NUM> or greater) since materials can be joined to each other even when transmission wave surface precision at a joining interface is approximately λ or less and can suppress a manufacturing cost since a high degree of vacuum is not required.

Structures of a joined body <NUM> and a laser oscillator <NUM> according to Embodiment <NUM> of the present disclosure will be described with reference to <FIG>. The joined body <NUM> according to Embodiment <NUM> differs from the joined body <NUM> according to Embodiment <NUM> in joining a saturable absorber <NUM> (second material) to an optical material <NUM> (first material).

The joined body <NUM> includes the optical material <NUM> being a laser medium and the saturable absorber <NUM> joined to one surface of the optical material <NUM>. The saturable absorber <NUM> acts as an absorber for low-intensity incident light and acts as a transparent body for high-intensity incident light by saturation of an ability as an absorber. For example, the saturable absorber <NUM> is formed of YAG doped with Cr (Cr:YAG).

The laser oscillator <NUM> includes a reflecting mirror <NUM> being placed on the optical material <NUM> side of the joined body <NUM> and totally reflects laser light, and an output mirror <NUM> being placed on the opposite side of the reflecting mirror <NUM> with the joined body <NUM> in between and partially reflecting laser light. The reflecting mirror <NUM> and the output mirror <NUM> constitute a resonator <NUM> resonating laser light inductively emitted by the joined body <NUM>.

When the saturable absorber <NUM> is irradiated with a light pulse, the central part of the pulse having high intensity passes through the saturable absorber <NUM>, whereas the foot part of the pulse having low intensity is absorbed by the saturable absorber <NUM>. Accordingly, a pulse width (time duration) of laser light in the laser oscillator <NUM> becomes shorter, and, for example, a light pulse with a width of the order of picoseconds to nanoseconds is emitted.

As described above, the laser oscillator <NUM> according to Embodiment <NUM> includes the saturable absorber <NUM> joined to the optical material <NUM>. Accordingly, the laser oscillator <NUM> can provide sufficient optical quality by suppressing Fresnel loss and can achieve pulse shortening of laser light.

Structures of a joined body <NUM> and a laser oscillator <NUM> according to Embodiment <NUM> of the present disclosure will be described with reference to <FIG>. The joined body <NUM> according to Embodiment <NUM> differs from the joined bodies <NUM> according to Embodiments <NUM> and <NUM> in joining a spontaneous emission absorber <NUM> (second material) in such a way that the spontaneous emission absorber <NUM> surrounds the outer periphery of an optical material <NUM> (first material).

The joined body <NUM> includes the optical material <NUM> being a laser medium and the spontaneous emission absorber <NUM> being joined around the optical material <NUM> and absorbing light from the laser medium. For example, the spontaneous emission absorber <NUM> is formed of Sm:YAG or Cr:YAG.

When pumping energy is supplied to the optical material <NUM>, amplified spontaneous emission (ASE) may be generated. ASE is light generated by spontaneous emission generated in a laser medium propagating through the laser medium. When pumping energy is further supplied, ASE may cause resonance (parasitic oscillation) in a direction other than an oscillation direction of laser light. When ASE and parasitic oscillation are generated, energy used for light amplification is wastefully consumed, and therefore laser output of the laser oscillator <NUM> decreases.

The spontaneous emission absorber <NUM> is joined in such a way as to surround the outer periphery of the optical material <NUM> in the joined body <NUM> according to Embodiment <NUM>; and therefore spontaneous emission is absorbed by the spontaneous emission absorber <NUM>, and, as a result, ASE and parasitic oscillation are suppressed. Further, the spontaneous emission absorber <NUM> itself is a non-heat-generating material and therefore can absorb heat generated by the optical material <NUM> and discharge the heat to the outside.

As described above, the laser oscillator <NUM> according to Embodiment <NUM> includes the spontaneous emission absorber <NUM> joined in such a way as to surround the outer periphery of the optical material <NUM>. Accordingly, even when ASE is generated and light enters the spontaneous emission absorber <NUM> from the optical material <NUM>, parasitic oscillation can be suppressed, and at the same time, the optical material <NUM> can be cooled. As a result, decrease in laser output in the laser oscillator <NUM> can be suppressed.

Structures of a joined body <NUM> and a laser amplifier <NUM> according to Embodiment <NUM> of the present disclosure will be described with reference to <FIG>. The laser amplifier <NUM> is a device amplifying laser light entering from the outside with a laser medium and emitting the amplified light to the outside. Unlike the laser oscillators <NUM> according to Embodiments <NUM> to <NUM>, the laser amplifier <NUM> does not include a resonator <NUM>.

The laser amplifier <NUM> includes the joined body <NUM>, a pumping light source <NUM>, and an amplified light source <NUM>. The pumping light source <NUM> emits light to the joined body <NUM> in such a way as to pump the joined body <NUM>. The amplified light source <NUM> introduces light to the joined body <NUM> in such a way that the light is amplified by the joined body <NUM>. The light emitted from the amplified light source <NUM> is amplified by an optical material <NUM> in the joined body <NUM> pumped by the pumping light source <NUM> and is emitted from the joined body <NUM>. At this time, cooling materials <NUM> are joined to both sides of the optical material <NUM>, and therefore heat generated in the central part of the optical material <NUM> can be efficiently discharged in a propagation direction of the laser light through the cooling material <NUM>.

As described above, the laser amplifier <NUM> includes the joined body <NUM> in which the optical material <NUM> is joined to the cooling materials <NUM> and therefore can effectively cool the optical material <NUM> pumped by the pumping light source <NUM>. Accordingly, heat can be effectively discharged even when the laser amplifier <NUM> is downsized, and thus downsizing of the laser amplifier <NUM> can be achieved.

The present disclosure will be specifically described below by citing Examples. However, the present disclosure is not limited to Examples.

An experiment performed for evaluating success or failure of joining of a joined body and the result thereof will be described with reference to <FIG> and <FIG>.

In this verification, first, a <NUM>% Nd:YAG polycrystal and a sapphire monocrystal were worked into disk shapes having the same outer diameter. The <NUM>% Nd:YAG polycrystal is acquired by doping YAG with <NUM>% of neodymium. Next, a bonded body was acquired by laying the worked Nd:YAG polycrystal and sapphire monocrystal on top of each other and applying an adhesive to the outer peripheral part.

<FIG> indicates conditions for temperature and pressure in PECS for each sample of a joined body. A sample of a joined body (may be hereinafter referred to as an Nd:YAG/sapphire joined body) was produced by processing a bonded body integrated by an adhesive, in accordance with a condition in <FIG>. Next, success or failure of joining was determined for each produced sample by confirming existence of an interference fringe and measuring a transmission spectrum for each sample.

<FIG> is a graph for illustrating success or failure of joining in the samples produced under the conditions in <FIG>. The vertical axis of <FIG> represents pressure (MPa) in PECS, and the horizontal axis represents temperature (°C) in PECS. A symbol × in <FIG> represents a sample <NUM> (<NUM>, <NUM> MPa), a symbol Δ represents a sample <NUM> (<NUM>, <NUM> MPa), a symbol of "double circle" represents a sample <NUM> (<NUM>, <NUM> MPa), and a symbol o represents a sample <NUM> (<NUM>, <NUM> MPa). An interference fringe was observed in the entire sample <NUM>. Further, an interference fringe was observed on the periphery of the sample <NUM> and the sample was slightly blackish. On the other hand, an interference fringe did not exist at all in the sample <NUM>, and the most excellent result was exhibited. Further, while an interference fringe did not exist at all in the sample <NUM>, the sample was slightly blackish.

Accordingly, it is understood that a joined body in an excellent joining state without an interference fringe is acquired when pressure and temperature are in an "excellent joining" region in <FIG>. A slope of a straight line including a point representing the sample <NUM> and a point representing the sample <NUM> in <FIG> is (<NUM> - <NUM>)/(<NUM> - <NUM>) = -<NUM>, and therefore a condition imposed on pressure P and temperature T for acquiring a joined body without an interference fringe is expressed by Equation (<NUM>) below in a range from the temperature T = <NUM> to <NUM>.

From the above, it is confirmed in this verification that a joined body in an excellent joining state without an interference fringe is acquired by adjusting temperature and pressure in PECS.

Next, an experiment for measuring a transmission spectrum in each sample of an Nd:YAG polycrystal, a bonded body, and a joined body, and the result thereof will be described with reference to <FIG>. Note that the bonded body is acquired by laying a sapphire monocrystal and an Nd:YAG polycrystal on top of each other and applying an adhesive to the outer peripheral surface, and the joined body is an Nd:YAG/sapphire joined body acquired under the condition of <NUM> and <NUM> MPa providing the most excellent result in Example <NUM>.

A transmission spectrum indicates a transmissivity of a sample for each wavelength of incident light entering the sample; and a transmissivity is a ratio of incident light at a specific wavelength transmitted through the sample. Part of incident light entering a sample is reflected from the surface of the sample, the joining interface of materials, and the like. Accordingly, intensity of transmitted light transmitted through the sample decreases compared with that of the incident light entering the sample. In this verification, a transmission spectrum of each sample was generated by measuring a radiant emittance of transmitted light transmitted through each sample and calculating a ratio between radiant emittances of transmitted light and incident light for each wavelength of incident light. Note that a radiant emittance is an emission flux per unit area emitted from an emitter.

<FIG> is a graph illustrating transmission spectra in an Nd:YAG polycrystal, a bonded body, and a joined body. The vertical axis of <FIG> represents a transmissivity (%), and the horizontal axis represents a wavelength (nm) of incident light. Further, a solid line in <FIG> represents an actually measured transmissivity, and a dotted line represents a theoretical value of transmissivity. As illustrated in <FIG>, across the entire wavelength range, a transmissivity of the joined body had a value higher than that of the bonded body by approximately <NUM>% and a value higher than that of the Nd:YAG polycrystal. The reason the transmissivity of the joined body was higher than the transmissivities of the bonded body and the Nd:YAG polycrystal is that Fresnel loss was suppressed by a sapphire monocrystal being joined to the Nd:YAG polycrystal.

For example, when irradiated with a wavelength of <NUM>, the transmissivity (experimental value) of the joined body was <NUM>%, whereas the transmissivity (experimental value) of the bonded body was <NUM>%, and the transmissivity (experimental value) of the Nd:YAG polycrystal was <NUM>%. Since the transmissivity (theoretical value) of the joined body was <NUM>%, the transmissivity (theoretical value) of the bonded body was <NUM>%, and the transmissivity (theoretical value) of the Nd:YAG polycrystal was <NUM>%, the experimental result on transmission spectra is confirmed to be valid.

From the above, it is confirmed in this verification that a joined body produced by PECS has a higher transmissivity compared with a bonded body before undergoing PECS and has excellent optical quality.

Next, an experiment performed for observing an internal structure of a joined body and the result thereof will be described with reference to <FIG> and <FIG>. In this verification, an image of a joining interface in an Nd: YAG/sapphire joined body produced under a condition of <NUM> and <NUM> MPa was captured by a scanning electron microscope (SEM), and the joining interface in the SEM image was observed. Further, an elementary analysis of the Nd: YAG/sapphire joined body was performed by performing a fluorescent X-ray analysis by use of a fluorescent X-ray analysis device.

<FIG> is a diagram illustrating an SEM image including the joining interface in the joined body. The left side of <FIG> represents an Nd:YAG polycrystal, and the right side represents a sapphire monocrystal. As illustrated in <FIG>, it is confirmed that there is no space at the joining interface between the sapphire monocrystal and the Nd:YAG polycrystal, and the two are excellently joined together even at a micro level.

<FIG> is a graph illustrating the result of the elementary analysis in the joined body. The vertical axis of <FIG> represents intensity (in any units) of characteristic X-rays, and the horizontal axis represents a distance (nm) from the surface of the Nd:YAG polycrystal. The left side of <FIG> represents an Nd:YAG region, the central part represents a region of the interface between Nd:YAG and sapphire, and the right side represents a sapphire monocrystal region. In <FIG>, a state of a solid line indicating intensity of characteristic X-rays related to yttrium (Y) sloping from upper left toward lower right in the interface region is observed. The above indicates that yttrium contained in the Nd:YAG polycrystal diffusively entered the sapphire monocrystal.

From the above, it is confirmed in this verification that diffusion and entry of yttrium from the Nd:YAG polycrystal to the sapphire monocrystal occur at the joining interface in the joined body acquired by PECS, and at the same time the sapphire monocrystal is excellently joined to the Nd:YAG polycrystal without a space at the joining interface.

Next, a laser oscillation experiment performed by use of each sample of an Nd:YAG polycrystal, a bonded body, and a joined body, and the result thereof will be described with reference to <FIG> and <FIG>. The bonded body and the joined body are similar to those in Example <NUM>. In this verification, a laser oscillation experimental system incorporating each sample was operated, and laser output for each case was measured.

<FIG> illustrates an example of the laser oscillation experimental system incorporating the joined body. The experimental system includes a pumping semiconductor laser (LD), an optical fiber, a lens system, an Nd:YAG/sapphire joined body, a dichroic mirror (DM), an output mirror (OC), and a thermal sensor. The LD emits continuous light (CW) having a wavelength λ of <NUM> and a laser output of <NUM> W. The optical fiber has a diameter of approximately <NUM> and transmits laser light from the LD toward the lens system. The lens system causes laser light supplied from the optical fiber to converge toward Nd:YAG. The thermal sensor receives laser light emitted from the OC and measures laser output.

<FIG> is a graph illustrating an input-output characteristic of the laser oscillation experimental system. The vertical axis of <FIG> represents laser output (W) output from the experimental system, and the horizontal axis represents current (A) applied to the LD. A symbol o in <FIG> represents a measured value when the Nd:YAG polycrystal is used, a symbol Δ represents a measured value when the bonded body is used, and a symbol □ represents a measured value when the joined body is used. The laser output when the Nd:YAG polycrystal was incorporated into the laser oscillation experimental system was <NUM> W, whereas the laser output when the joined body was incorporated into the laser oscillation experimental system was <NUM> W. Incorporation of the joined body into the laser oscillation experimental system increased laser output by approximately <NUM>% compared with the case of the Nd:YAG polycrystal.

Further, the maximum pump current when the Nd:YAG polycrystal was used was <NUM> A, whereas the maximum pump current when the joined body was used was <NUM> A. Further, the maximum pump current when the bonded body was used was also <NUM> A. The above indicates that the maximum pump current increased due to a conduction cooling effect by sapphire contained in the joined body and the bonded body. It is further understood that when the joined body was used in the laser oscillation system, laser output also increased with increase in the maximum pump current.

From the above, it is confirmed in this verification that incorporation of an Nd:YAG polycrystal/sapphire monocrystal joined body into a laser oscillator enables increase in the maximum pump current that can be applied to a pumping light source and, as a result, enables increase in laser output.

Next, an experiment for recognizing the lower limit of a diffusive entry length of an yttrium element at a joining interface in an Nd:YAG/sapphire joined body and the result thereof will be described with reference to <FIG>. In this verification, one-dimensional concentration distribution of an yttrium element was acquired by irradiating a joining interface in an Nd:YAG/sapphire joined body produced under the same condition as that in Example <NUM> with an electron beam by an electron microscope and measuring fluorescent X-rays generated from the yttrium element. Subsequently, a diffusive entry length of the yttrium element was calculated, based on the one-dimensional concentration distribution of the yttrium element.

<FIG> is a graph illustrating the one-dimensional concentration distribution of the yttrium element acquired by electron microscope observation. The vertical axis of <FIG> represents concentration (in any units) of the yttrium element, and the horizontal axis represents a distance (nm) from a predetermined position in Nd:YAG, the position not being affected by the joining. The concentration of the yttrium element is normalized to <NUM> in a part in Nd:YAG, the part not being affected by the joining. The left part separated by a dotted line in the vertical direction represents an Nd:YAG region, and the right part represents a sapphire monocrystal region.

A solid line in <FIG> represents a one-dimensional concentration distribution of the yttrium element, and a broken line is acquired by fitting the one-dimensional concentration distribution of the yttrium element represented by the solid line by Equation (<NUM>). Concentration Cx of the yttrium element is normalized in <FIG>, and therefore C<NUM> = <NUM>. For example, a diffusive entry length is defined by √Dt in Equation (<NUM>), and therefore the diffusive entry length √Dt in <FIG> is <NUM>.

From the above, it is understood that a diffusive entry length of an yttrium element in an Nd: YAG/sapphire joined body is roughly <NUM> or greater. Further, calculation of a diffusive entry length using Equation (<NUM>) is applicable not only to the case of an Nd:YAG/sapphire joined body but also to a case of calculating a diffusive entry length of another joined body.

The present disclosure is not limited to the aforementioned embodiments, and modified examples described below may also apply.

While a case of joining different types of materials (different-type materials) together have been described as an example in the aforementioned embodiments, the present disclosure is not limited thereto. The same-type materials may be joined together to form a joined body <NUM>. For example, the same-type materials include a material acquired by doping a basic material with an active element, such as Nd:YAG for YAG.

While the optical material <NUM> has been sandwiched by a pair of cooling materials <NUM> in the aforementioned embodiments, the present disclosure is not limited thereto. For example, the cooling material <NUM> may be joined to one surface of the optical material <NUM>, or the cooling material <NUM> may be joined to the outer peripheral surface of the optical material <NUM>. Further, the cooling material <NUM> may be joined to the front of the optical material <NUM>.

While the optical material <NUM> and the cooling material <NUM> are disk shapes having the same outer diameter in the aforementioned embodiments, the present disclosure is not limited thereto. The optical material <NUM> and the cooling material <NUM> may be disk-shaped members having different outer diameters. Further, for example, the optical material <NUM> and the cooling material <NUM> may be rectangular or polygonal plate-shaped members. Furthermore, the optical material <NUM> and the cooling material <NUM> may have shapes different from each other; and for example, a plurality of elongated cylindrical-shaped optical materials <NUM> may be joined to a pair of cooling materials <NUM> in such a way as to be sandwiched by the cooling materials <NUM>, as illustrated in <FIG>.

While the optical material <NUM> is formed of a polycrystal, and the cooling material <NUM> is formed of a monocrystal in the aforementioned embodiments, the present disclosure is not limited thereto. Each of the optical material <NUM> and the cooling material <NUM> may be any one of a monocrystal, a polycrystal, and a glass body as long as the material is capable of transmitting light. For example, the cooling material <NUM> may be formed of a polycrystal such as aluminum nitride.

While the joined body <NUM> is cylindrically formed in the aforementioned embodiments, the present disclosure is not limited thereto. For example, the joined body <NUM> may be cut in such a way that an end has Brewster's angle.

While the resonator <NUM> in the laser oscillator <NUM> includes the reflecting mirror <NUM> and the output mirror <NUM>, and the pumping light sources <NUM> in the laser oscillator <NUM> and the laser amplifier <NUM> cause side pumping in the aforementioned embodiments, the present disclosure is not limited thereto. For example, anti-reflection (AR) coating or high-reflection (HR) coating may be applied to both ends of the joined body <NUM> in the laser oscillator <NUM>, and a resonator may be formed in the joined body <NUM>. Further, the pumping light sources <NUM> in the laser oscillator <NUM> and the laser amplifier <NUM> may be placed in such a way as to cause end pumping.

While the optical material <NUM> and the cooling material <NUM> are combined and then are installed in the manufacturing device <NUM> in the aforementioned embodiments, the present disclosure is not limited thereto. For example, the optical material <NUM> and the cooling material <NUM> may be installed at predetermined positions in the manufacturing device <NUM> in such a way as to be laid on top of each other in order, without being combined in advance.

While pressure and temperature of the optical material <NUM> and the cooling material <NUM> are gradually decreased after a predetermined time elapses in the aforementioned embodiments, the present disclosure is not limited thereto. For example, pressurization and heating of the optical material <NUM> and the cooling material <NUM> may be stopped after a predetermined time elapses. In this case, the materials may be cooled by natural air cooling, or the materials may be cooled by blowing air.

While the optical material <NUM> is a laser medium in the aforementioned embodiments, the present disclosure is not limited thereto. For example, the optical material <NUM> may be a magneto-optical material. For example, the magneto-optical material may be a material rotating a polarization plane by the Faraday effect for use in an optical isolator and a Faraday rotator. Further, the magneto-optical material may be a material elliptically polarizing reflected light by the magneto-optical Kerr effect for use in polarizer glass and the like.

Further, the optical material <NUM> may be a phosphor changing a color tone of laser light emitted from the laser oscillator. After entering an excited state by absorbing energy of light from the outside, the phosphor emits light having different energy in a process of returning to a ground state. The phosphor may be doped with an active element. The phosphor may be used for adjusting a color tone of a light emitting diode (LED) lamp.

While the manufacturing device <NUM> is operated in a vacuum in the aforementioned embodiments, the present disclosure is not limited thereto. For example, the manufacturing device <NUM> may be operated in an atmosphere of an inert gas such as argon and nitrogen.

Further, while the spontaneous emission absorber <NUM> is used in aforementioned Embodiment <NUM>, the present disclosure is not limited thereto. For example, a scatterer scattering oscillation light around the optical material <NUM> may be joined in order to suppress parasitic oscillation.

While a case of applying the joined body <NUM> to the laser oscillator <NUM> and the laser amplifier <NUM> has been described as an example in the aforementioned embodiments, the present disclosure is not limited thereto. For example, the joined body <NUM> may be applied to a laser amplifier, an optical isolator, and a Faraday rotator.

The foregoing describes some example embodiments for explanatory purposes. Although the foregoing discussion has presented specific embodiments, persons skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the invention as defined in the appending claims. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined only by the included claims.

Claim 1:
A joined body (<NUM>) comprising a first material (<NUM>) and a second material (<NUM>, <NUM>) that are capable of transmitting light and are joined together,
wherein, at a joining interface between the first material (<NUM>) and the second material (<NUM>, <NUM>), the joined body (<NUM>) is capable of transmitting light, and also parts of atoms contained in each one of the materials (<NUM>) diffusively enter correspondingly the other one of the materials (<NUM>, <NUM>) in such a degree that an interference fringe is not generated in the joined body (<NUM>),
characterized in that
a diffusive entry length of the atoms of the joined body (<NUM>) is in a range from approximately <NUM> to approximately <NUM>.