Abstract:
A method for joining optical members, comprising a step of forming one dielectric thin film on a joining surface of one optical member, a step of forming another dielectric thin film on a joining surface of another optical member, and a step of making contact without scattering light between the one dielectric thin film and the another dielectric thin film together, wherein optical wavelength property as required can be obtained by joining the another dielectric thin film with the one dielectric thin film.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a method for joining optical members, and to a laser oscillation device comprising the optical members. 
         [0002]    In recent years, there have been strong demands on the development of a laser oscillation device of smaller size and with higher output. As the laser oscillation device designed in smaller size and for easily oscillating a laser beam, there is a solid-state laser oscillation device, and this solid-state laser oscillation device comprises a plurality of optical members (solid-state laser media). Also, with the development of the optical members of smaller size, the optical members are integrated with each other by joining the optical members together. 
         [0003]    In the past, integration of a plurality of optical members has been performed by joining of the optical members by using an adhesive agent. With the development of the laser oscillation device in smaller size, on the other hand, the development of the laser oscillation device with higher output has been promoted. With the development of the laser oscillation device with higher output, high-energy laser beams enter the optical members, and the optical members are exposed to higher temperature. 
         [0004]    In general, compared with the optical members, the adhesive agent is more easily deteriorated by laser beams or by high temperature. When the adhesive agent is used for integrating the optical members in the laser oscillation device with lower output, the deterioration of the adhesive agent does not cause problems particularly because energy of the laser beam is low and the temperature of the optical members is also low. However, in the laser oscillation device with high output, the deterioration of the adhesive agent tends to shorten the service life of the optical members, and has been a problem. 
         [0005]    An example of a laser oscillation device, which uses optical members and generates laser beams with high output, is disclosed in JP-A-2004-111542. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the present invention to provide a method for integrating optical members, which are highly resistant to the deterioration caused by high-output laser beam or to high temperature, and also to provide a laser oscillation device with a plurality of optical members integrated with each other. 
         [0007]    The present invention provides a method for joining optical members, comprising a step of forming one dielectric thin film on a joining surface of one optical member, a step of forming another dielectric thin film on a joining surface of another optical member, and a step of making contact without scattering light between the one thin dielectric film and another dielectric thin film together, wherein optical wavelength property as required can be obtained by joining the another dielectric thin film with the one dielectric thin film. The present invention also provides a method for joining optical members, wherein a dielectric film formed by joining the one dielectric thin film with another dielectric thin film is a multi-layer film. Further, the present invention provides a method for joining optical members, wherein the contact without scattering light is optical contact. Also, the present invention provides a method for joining optical members, wherein the contact without scattering light is diffusion bonding. Further, the present invention provides a method for joining optical members, wherein the contact without scattering light is ultrasonic bonding. 
         [0008]    Further, the preset invention provides a structure for integrating optical members, comprising one dielectric thin film formed on a joining surface of one optical member, another dielectric thin film formed on a joining surface of another optical member, wherein the two optical members are joined together via contact without scattering light by joining the one dielectric thin film with the another dielectric thin film, and wherein a dielectric thin film with optical wavelength property as required is formed by joining the one dielectric thin film with the another dielectric thin film. Also, the present invention provides a structure for integrating optical members, wherein the dielectric film comprises multi-layer dielectric thin films, and one layer of the multi-layer films is formed by joining the one dielectric thin film with the another dielectric thin film by contact without scattering light. Further, the present invention provides a structure for integrating optical members, wherein the dielectric film comprises multi-layer dielectric thin films, wherein the one dielectric thin film and the another dielectric thin film are joined together via contact without scattering light, and wherein two adjacent layers of the multi-layer films are formed by the one dielectric thin film and the another dielectric thin film. Also, the present invention provides a structure for integrating optical members, wherein the one optical member is a laser crystal for emitting a fundamental light by means of an excitation light from a light source, the another optical member is a wavelength conversion crystal for converting wavelength of the fundamental light, and the dielectric thin films allow the fundamental light to pass through and reflect a wavelength-converted light. Further, the present invention provides a structure for integrating optical members, wherein the contact without scattering light is optical contact. Also, the present invention provides a structure for integrating optical members, wherein the contact without scattering light is diffusion bonding. Further, the present invention provides a structure for integrating optical members, wherein the contact without scattering light is ultrasonic bonding. 
         [0009]    Further, the present invention provides a laser oscillation device, comprising a laser crystal for emitting a fundamental light by means of an excitation light from a light source, a wavelength conversion crystal being integrated with the laser crystal via a third dielectric film and for converting wavelength of the fundamental light, a first dielectric film formed on an incident surface of the laser crystal, and a second dielectric film formed on an exit surface of the wavelength conversion crystal, wherein the first dielectric film allows the excitation light to pass through and reflects the fundamental light, the third dielectric film is formed by joining a film on the laser crystal with a film on the wavelength conversion crystal by contact without scattering light, wherein the third dielectric film allows the fundamental light to pass through and reflects the wavelength conversion light, and wherein the second dielectric film reflects the fundamental light and allows the wavelength conversion light to pass through. Also, the present invention provides a laser oscillation device, wherein the contact without scattering light is optical contact. Further, the present invention provides a laser oscillation device, wherein the contact without scattering light is diffusion bonding. Also, the present invention provides a laser oscillation device, wherein the contact without scattering light is ultrasonic bonding. 
         [0010]    According to the present invention, there are provided a step of forming one dielectric thin film on a joining surface of one optical member, a step of forming another dielectric thin film on a joining surface of another optical member, and a step of making contact without scattering light between the one dielectric film and another dielectric thin film together, and optical wavelength property as required can be obtained by joining another dielectric thin film with the one dielectric thin film. As a result, it is possible to abolish the use of adhesive agent for the joining of optical members and to prevent the shortening of the service life of the optical members caused by the deterioration of the adhesive agent. 
         [0011]    Also, according to the present invention, there are provided one dielectric thin film formed on a joining surface of one optical member, another dielectric thin film formed on a joining surface of another optical member, and the two optical members are joined together via contact without scattering light by joining the one dielectric thin film with the another dielectric thin film, and a dielectric thin film with optical wavelength property as required is provided by joining the one dielectric thin film with the another dielectric thin film. As a result, it is possible to abolish the use of adhesive agent for the joining of optical members and to prevent the shortening of the service life of the optical members caused by the deterioration of the adhesive agent. 
         [0012]    Further, according to the present invention, the dielectric film comprises multi-layer dielectric thin films, the one dielectric thin film and the another dielectric thin film are joined together via contact without scattering light, and two adjacent layers of the multi-layer films are formed by the one dielectric thin film and the another dielectric thin film. As a result, contact without scattering light can be attained between homogeneous films, and high-quality joining can be accomplished. 
         [0013]    Also, according to the present invention, there are provided a laser crystal for emitting a fundamental light by means of an excitation light from a light source, a wavelength conversion crystal being integrated with the laser crystal via a third dielectric film and for converting wavelength of the fundamental light, a first dielectric film formed on an incident surface of the laser crystal, and a second dielectric film formed on an exit surface of the wavelength conversion crystal, wherein the first dielectric film allows the excitation light to pass through and reflects the fundamental light, the third dielectric film is formed by joining a film on the laser crystal with a film on the wavelength conversion crystal by contact without scattering light, the third dielectric film allows the fundamental light to pass through and reflects the wavelength conversion light, and the second dielectric film reflects the fundamental light and allows the wavelength conversion light to pass through. As a result, it is possible to abolish the use of adhesive agent for the joining of optical members, to prevent the deterioration of adhesive agent caused by high-output laser beam, to attain stable laser beam output, and to ensure longer service life of the laser oscillation device. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a schematical block diagram of a laser oscillation device, in which the present invention is carried out; 
           [0015]      FIG. 2  is a drawing to explain an optical resonator where two optical members are integrated; 
           [0016]      FIG. 3  is a schematical drawing to show a dielectric film formed on the optical member; and 
           [0017]      FIG. 4  is a partial enlarged view of the dielectric film shown in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    Description will be given below on the best mode for carrying out the present invention referring to the attached drawings. 
         [0019]    First, referring to  FIG. 1 , description will be given on general features of a laser oscillation device, in which the present invention is carried out. 
         [0020]      FIG. 1  shows an LD pumped solid-state laser device of one-wavelength oscillation type, which is an example of a laser oscillation device  1 . 
         [0021]    In  FIG. 1 , reference numeral  2  denotes a light emitting unit, and numeral  3  represents an optical resonator. The light emitting unit  2  comprises an LD light emitter  4  and a condenser lens  5 . Further, the optical resonator  3  comprises a first optical crystal (laser crystal  8 ) where a first dielectric reflection film  7  is formed, a second optical crystal (nonlinear optical crystal (NLO); (wavelength conversion crystal  9  for second harmonic wave)), and a concave mirror  12  where a second dielectric reflection film  11  is formed. At the optical resonator  3 , a laser beam is pumped, resonated, amplified and outputted. As the laser crystal  8 , Nd:YVO 4  or the like is used, and as the wavelength conversion crystal  9  for second harmonic wave, KTP (KTiOPO 4 ; potassium titanyl phosphate) or the like is used. 
         [0022]    The light emitting unit  2  emits a laser beam with wavelength of 809 nm, for instance, and the LD light emitter  4 , which is a semiconductor laser, is used. Also, the LD light emitter  4  has the function as a pumping light generator  8 . for generating an excitation light  17 . The light emitting unit  2  is not limited to a semiconductor laser, and any type of light source means may be adopted so far as the light source means can generate a laser beam. 
         [0023]    The laser crystal  8  is to generate a fundamental wave  18  with a predetermined wavelength from the excitation light  17 . As the laser crystal  8 , Nd:YVO 4  with oscillation line of 1064 nm is used. In addition to this, YAG (yttrium aluminum garnet) doped with Nd 3+  ions or the like may be adopted. YAG has oscillation line of 946 nm, 1064 nm, 1319 nm, etc. Also, Ti (Sapphire) or the like with oscillation line of 700 to 900 nm may be used. 
         [0024]    On an end surface (an incident surface) of the laser crystal  8  closer to the LD light emitter  4 , the first dielectric reflection film  7  is formed. On an exit surface of the laser crystal  8 , a third dielectric reflection film  13  is formed. The second dielectric reflection film  11  is formed on the concave mirror  12 . 
         [0025]    The first dielectric reflection film  7  is highly transmissive to a laser beam (an excitation light  17 ) from the LD light emitter  4 , and the first dielectric reflection film  7  is highly reflective to an oscillation wavelength (a fundamental wave  18 ) of the laser crystal  8 . 
         [0026]    The third dielectric reflection film  13  is highly transmissive to the fundamental wave  18 , and the third dielectric reflection film  13  is highly reflective to a second harmonic wave  19  (SECOND HARMONIC GENERATION (SHG)), which is converted by the wavelength conversion crystal  9  for second harmonic wave. 
         [0027]    The concave mirror  12  is arranged at a position to face toward the laser crystal  8 . The surface of the concave mirror  12  closer to the laser crystal  8  is designed in a shape of a concave spherical mirror with an adequate radius, and the second dielectric reflection film  11  is formed on the surface of the concave mirror  12 . The second dielectric reflection film  11  is highly reflective to the fundamental wave  18 , and the second dielectric reflection film  11  is highly transmissive to the second harmonic wave  19 . 
         [0028]    As a dielectric material to make up the reflection film, TiO 2  (n=2.3 to 2.55) or the like is used as a high refractive material, and MgF 2  (n=1.32 to 1.39) or the like is used as a low refractive material. The high refractive material and the low refractive material make up together an alternately deposited multi-layer film. 
         [0029]    A linearly polarized excitation light  17  is emitted from the light emitting unit  2 . The excitation light  17  passes through the first dielectric reflection film  7  and enters the laser crystal  8 , and the fundamental wave  18  is oscillated. Then, the fundamental wave  18  is pumped between the first dielectric reflection film  7  and the second dielectric reflection film  11 . Further, the fundamental wave  18  enters the wavelength conversion crystal  9  for second harmonic wave, and the second harmonic wave  19  is generated. 
         [0030]    The second harmonic wave  19  is projected after passing through the second dielectric reflection film  11  and is reflected by the third dielectric reflection film  13 . Then, the second harmonic wave  19  is projected after passing through the second dielectric reflection film  11 . When the laser beam passes through the laser crystal  8 , the polarizing condition is changed. However, the second harmonic wave  19  is reflected by the third dielectric reflection film  13  and the second harmonic wave  19  does not pass through the laser crystal  8 , therefore the polarizing condition of the second harmonic wave  19  is maintained. And then a linearly polarized second harmonic wave (laser beam) is projected from the light resonator  3 . 
         [0031]    As described above, the first dielectric reflection film  7  of the laser crystal  8  is combined with the second dielectric reflection film  11  of the concave mirror  12  and the laser beam from the LD light emitter  4  is pumped to the laser crystal  8  through the condenser lens  5 , and the light is reciprocally projected between the first dielectric reflection film  7  of the laser crystal  8  and the second dielectric reflection film  11  of the concave mirror  12 . As a result, the light is confined for long time, and the light can be resonated and amplified. 
         [0032]    Within the light resonator  3 , which comprises the first dielectric reflection film  7  of the laser crystal  8  and the second dielectric reflection film  11  of the concave mirror  12 , the wavelength conversion crystal  9  for second harmonic wave is inserted. A strong coherent light such as a laser beam enters the wavelength conversion crystal  9  for second harmonic wave, and a second harmonic wave is generated, which doubles frequency of the light. The generation of the second harmonic wave is called “second harmonic generation”. Therefore, when the laser beam enters the laser crystal  8  and the fundamental wave  18  of 1064 nm is oscillated, a laser beam with wavelength of 532 nm (green laser beam) is projected from the laser oscillation device  1 . 
         [0033]      FIG. 2  shows the optical resonator  3 , in which the laser crystal  8 , i.e. an optical member, and the wavelength conversion crystal  9  for second harmonic wave are integrated. In  FIG. 2  and  FIG. 3 , the same component as shown in  FIG. 1  is referred by the same symbol. 
         [0034]    The laser crystal  8  and the wavelength conversion crystal  9  for second harmonic wave are integrated with each other via the third dielectric reflection film  13  by contact without scattering light of joining method. Also, as contact without scattering light, optical contact (contact without scattering light between optical interfaces), diffusion bonding and ultrasonic bonding, etc. are included. 
         [0035]    On an incident surface of the laser crystal  8 , the first dielectric reflection film  7  is formed, and on an exit surface of the wavelength conversion crystal  9  for second harmonic wave, the second dielectric reflection film  11  is formed. Because the second dielectric reflection film  11  is formed on the exit surface of the wavelength conversion crystal  9  for second harmonic wave, the concave mirror  12  is omitted. 
         [0036]    After entering the laser crystal  8 , the excitation light  17  is pumped as the fundamental wave  18  between the first dielectric reflection film  7  and the second dielectric reflection film  11 . Further, at the wavelength conversion crystal  9  for second harmonic wave, the fundamental wave  18  is oscillated to generate the second harmonic wave  19 , and the second harmonic wave  19  is projected after passing through the second dielectric reflection film  11 . 
         [0037]    Next, referring to  FIG. 3 , description will be given on integration of the laser crystal  8  with the wavelength conversion crystal  9  for second harmonic wave. Also, following description is a case that contact without scattering light is optical contact. 
         [0038]    The first dielectric reflection film  7 , the third dielectric reflection film  13  and the second dielectric reflection film  11  are deposited in multiple layers respectively so that thin films of the materials used can have optical wavelength property as required. As a result, optical performance characteristics as required are provided. 
         [0039]    For example, Ta 2 O 5  and SiO 2  are alternately deposited in several tens of layers, and the first dielectric reflection film  7  is formed. In  FIG. 3 , the first dielectric reflection film  7 , the third dielectric reflection film  13  and the second dielectric reflection film  11  are represented each in four layers for convenience purpose. 
         [0040]    It is supposed that the third dielectric reflection film  13  comprises thin films  13   a ,  13   b ,  13   c  and  13   d . A boundary exists in one of the thin films  13   a ,  13   b ,  13   c  and  13   d , the laser crystal  8  and the wavelength conversion crystal  9  are jointed together via optical contact of the boundaries. 
         [0041]    For instance, when it is supposed that a boundary  14  is at an intermediate position of the thin film  13   b , a thin film  13   b ′, which is a part of the thin film  13   b  and the thin film  13   a , are deposited on the exit surface of the laser crystal  8 . On the incident surface of the wavelength conversion crystal  9  for second harmonic wave, a thin film  13   b ″, which is the rest part of the thin film  13   b , and the thin films  13   c  and  13   d  are deposited. 
         [0042]    The exit surface of the laser crystal  8  and the incident surface of the wavelength conversion crystal  9  for second harmonic wave are finished to have such flatness and flat surface roughness as capable of optical contact. It is designed that the flatness and the flat surface roughness as capable of optical contact can be maintained after the thin film  13   b ′ and the thin film  13   b ″ have been deposited. 
         [0043]    By cleaning up the joining surface of the thin film  13   b ′ and the joining surface of the thin film  13   b ″ and by putting the thin film  13   b ′ and the thin film  13   b ″ closer to each other, the laser crystal  8  and the wavelength conversion crystal  9  for second harmonic wave are pressed tightly to each other. 
         [0044]    By achieving optical contact between the thin films  13   b ′ and  13   b ″, the laser crystal  8  and the wavelength conversion crystal  9  for second harmonic wave are joined together. Under the joined condition, the thin film  13   b  is made up with the thin films  13   b ′ and  13   b ″. The joining between the thin films  13   b ′ and  13   b ″ is the joining by homogeneous materials, and high affinity is assured. No shearing occurs due to the difference of thermal expansion between the thin films  13   b ′ and  13   b″.    
         [0045]    After the joining, the thin films  13   b ′ and  13   b ″ fulfill the function as the thin film  13   b . Further, the thin films  13   a ,  13   b ,  13   c  and  13   d  fulfill the function as the third dielectric reflection film  13 . 
         [0046]    In the embodiment as described above, joining is achieved within one layer of thin film, while joining via optical contact may be made at the boundary between thin films. For instance, joining may be accomplished between the thin film  13   b  and the thin film  13   c.    
         [0047]    As the joining method without scattering light, for example, the surfaces to be joined are pressed against each other under heated condition. Or, a certain type of liquid, e.g. pure water, is interposed between the thin film  13   b ′ and the thin film  13   b ″, and the thin film  13   b ′ and the thin film  13   b ″ are pressed together and heated further to remove the liquid. Then optical contact is attained. 
         [0048]    Further, as the joining method, diffusion bonding or ultrasonic bonding may be used. 
         [0049]    As the cleaning method to clean up the joining surface of the thin film  13   b ′ and the joining surface of the thin film  13   b ″ and further to make active the thin film  13   b ′ and the thin film  13   b ″, cleaning by using a material with HF group or OH group, cleaning by using ultrasonic vibration, cleaning by using ion sputter, cleaning by using plasma, etc., may be employed.