Abstract:
An optically pumped semiconductor laser is assembled in an enclosure comprising a base, a first mounting frame attached to the base, a second mounting frame attached to the first mounting frame and a cover attached to the second mounting frame. The assembly base, frames, and cover forms an undivided enclosure, with the frames contributing to walls of the enclosure. Components of the laser are assembled sequentially on the base and the frames. The frames are irregular in height to permit flexibility in the mounting-height of components. This reduces the extent to which compactness of the enclosure is limited by any one component.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates in general to enclosures for housing optical apparatus or electro-optical apparatus. The invention relates in particular to enclosures for housing laser apparatus. 
       DISCUSSION OF BACKGROUND ART 
       [0002]    Laser apparatus is usually part of an optical system for performing some operation using the laser apparatus. Such operations include laser machining, optical inspection of semiconductor circuits, interferometry, and microscopy. Because of this, there is a constant demand to reduce the size of laser apparatus, for example, for correspondingly reducing the size, or for increasing the portability of the overall optical system. 
         [0003]    One approach to reducing the size of laser apparatus is described in U.S. Pat. No. 7,952,806, assigned to the assignee of the present invention and the complete disclosure of which is hereby incorporated by reference. In this apparatus the output of four semiconductor lasers, each emitting radiation of a different color is combined to provide illumination for microscopy. The apparatus is housed in an enclosure divided into three compartments arranged one above another. Lasers are located in a base compartment, electronics are located on the floor of the next compartment, and a beam combining arrangement including a compact, monolithic, pentagonal beam-combining prism is mounted on the floor of the upper compartment. 
         [0004]    A limit to compactness in this arrangement is that the area of footprint of the enclosure is determined by the area required of the biggest compartment. Vertical floor-spacing is determined by the tallest compartment on any one floor. In order to achieve any further compacting, a more flexible approach to such housing or packaging is required. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention is directed to compact packaging of optical apparatus in an enclosure, the optical apparatus including a plurality of components. In one aspect of the invention the enclosure comprises a base-member, configured to provide a floor of the enclosure. One or more open frame-members are stacked on the base-member and form walls of the enclosure. A cover-member covers the enclosure. At least one of the components is mounted on one of the one or more frame-members. 
         [0006]    In another aspect of the invention optical apparatus includes a plurality of optical components contained in a housing having an undivided internal volume. The housing includes a rigid base and a rigid wall. At least one the optical components is mounted on the rigid wall. 
         [0007]    The term components as applied to the optical apparatus is intended to include but not be limited to optical components such as lenses, minors, solid-state gain-media and semiconductor gain-structures, and optically nonlinear crystals for frequency conversion; electro-optical components such as semiconductor-lasers, detectors, Q-switches, and optical modulators; and mechanical components such as optical mounts. 
         [0008]    In one preferred embodiment of the invention, the optical apparatus is a frequency-doubled optically pumped semiconductor (OPS) laser having a multiply-folded resonator. The enclosure or housing has two frame-members. Components of the laser are mounted on the base-member and each of the two frame-members. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The accompanying drawings, which are incorporated in and constitute a part of the specification, schematically illustrate a preferred embodiment of the present invention, and together with the general description given above and the detailed description of the preferred embodiment given below, serve to explain principles of the present invention. 
           [0010]      FIG. 1  schematically illustrates a prior-art, planar layout of an intra-cavity frequency-doubled optically pumped semiconductor (OPS) laser including a semiconductor gain-structure, a diode-laser array and associated optics for pumping the gain-structure, a resonator including an optically nonlinear crystal for the frequency-doubling, an end mirror and a dichroic fold-mirror for outputting frequency-doubled radiation, and a birefringent filter for selecting the wavelength of radiation to be frequency-doubled. 
           [0011]      FIG. 2  is a three-dimensional perspective view schematically illustrating a base-member of an optical apparatus enclosure in accordance with the present invention wherein the optical apparatus is an intra-cavity frequency-doubled OPS-laser including components of the laser of  FIG. 1 , with the semiconductor gain-structure, and the diode-laser array and associated optics for pumping the gain-structure, mounted on the base-member. 
           [0012]      FIG. 3  is a three-dimensional perspective view schematically illustrating a first frame-member attached to the base member of  FIG. 2 , with the birefringent filter and a first auxiliary fold-minor, mounted on one side-wall of the first frame-member and a second auxiliary fold-mirror, mounted on an opposite side-wall of the first frame-member. 
           [0013]      FIG. 4  is a three-dimensional perspective view schematically illustrating a second frame-member attached to the first frame-member of  FIG. 3 , with the optically nonlinear crystal mounted a one side-wall of the second frame-member, the resonator end-mirror mounted on an opposite side-wall of the second frame member, and the dichroic minor mounted on an end-wall of the second frame-member. 
           [0014]      FIG. 4A  is a three-dimensional perspective view schematically illustrating further detail of the mounting of the optically nonlinear crystal and the resonator end-mirror in the frame members of  FIG. 4 . 
           [0015]      FIG. 4B  is a three-dimensional perspective view schematically illustrating still further detail of the mounting of the optically nonlinear crystal and the resonator end-mirror in the frame members of  FIG. 4 . 
           [0016]      FIG. 5  is a three-dimensional perspective view illustrating a cover-member attached to the second frame-member of  FIG. 4  for completing the enclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Referring now to the drawings, wherein like components are designated by like reference numerals,  FIG. 1  schematically illustrates a prior-art, planar layout of an intra-cavity frequency-doubled optically pumped semiconductor (OPS) laser  10  having a laser-resonator  11 . Laser  10  includes an OPS structure  12  including a mirror structure  14  surmounted by a semiconductor gain-structure  16 . The OPS structure is supported on a heat-sink  18 . Gain structure  16  is optically pumped by radiation P from a diode-laser array  22  including fast- and slow-axis collimating optics (not shown in  FIG. 1 ). Here, the collimated pump radiation is focused onto the gain-structure by lenses  30  and  32 . 
         [0018]    Laser-resonator  11  is formed between mirror structure  14  of the OPS structures and an end-mirror  34 . The resonator is once-folded by a fold-mirror  36  for compactness and convenience of output. In response to the optical pumping of gain-structure  16 , radiation having a fundamental wavelength characteristic of materials of the gain-structure circulates in resonator  11  as indicated by arrowheads F. A birefringent filter  38  is configured to select a particular fundamental wavelength from a relatively broad gain-bandwidth of the gain-structure. An optically nonlinear crystal  40  converts the fundamental radiation to second-harmonic (2H) radiation by frequency-doubling. The 2H-radiation is indicated in  FIG. 1  by double arrowheads 2H. Fold-mirror  36  is a dichroic mirror, highly reflective for the fundamental radiation and highly transmissive for the 2H radiation. This allows the 2H radiation be delivered from resonator  11  as output radiation. 
         [0019]    It should be noted here that only sufficient description of laser  10  is provided to explain how such a laser and other optical apparatus can be packaged in an enclosure in accordance with the present invention. A detailed description of such a laser is not required for understanding principles of the present invention and accordingly is not presented herein. A detailed description of OPS lasers including frequency-doubled such lasers is provided in U.S. Pat. No. 6,097,742, assigned to the assignee of the present invention, and the complete disclosure of which is hereby incorporated herein by reference. 
         [0020]    The present invention is described below with an example of repackaging the prior-art laser of  FIG. 1  into an inventive compound enclosure of the type summarized above. The description begins with reference to  FIG. 2  which schematically illustrates a base-member  42 , here, a rectangular base-member, of the enclosure. Base-member  42 , here has low side-walls  44 A and  44 B, an end-wall  46 A having the same height as the side-walls and a raised, thickened end-wall  46 B. These walls surround a rigid floor  48  of the base-member. 
         [0021]    The purpose of the low walls is primarily to provide sufficient thickness for blind threaded holes (not shown) which could be used for attaching other enclosure members. These low walls also contribute to providing rigidity of base-member  42 . End-wall  46 B is raised and thickened to allow the end-wall to be machined to provide a mount for OPS-structure  12 . The wall is machined at an angle to the floor of the base member and at an angle to the longitudinal direction of the base-member to satisfy a particular fold arrangement of the laser-resonator. 
         [0022]    Diode-laser array assembly  20  is attached to floor  48  of the base-member. The diode laser bar assembly includes a heat-sink  22  and a top-contact  24 . The actual diode-laser array (diode-laser bar) is not visible as it is clamped between the heat-sink and the top contact and obscure by a collimating optics assembly  26 , which includes a cylindrical, fast-axis collimating lens  27  and an array of slow-axis collimating lenses  28 . Diode-laser array assemblies, with collimating optics of this type, are commercially available from a number of commercial suppliers. 
         [0023]    Focusing lenses  30  and  32  are supported on a mount  50  including a platform  52  to which the lenses are bonded. Platform  52  is bonded to floor  48  via a positive temperature coefficient (PTC) heating element  54 . This type of mounting device uses the PTC element to soften solder bonds, allowing the optics (here lenses  30  and  32 ) to be aligned. After alignment the PTC element is allowed to cool to harden the solder bonds to fix the alignment. This type of mount is well known in the laser art and is described in detail in U.S. Pat. No. 5,930,600, assigned to the assignee of the present invention, and the complete disclosure of which is hereby incorporated herein by reference. Other type of optics mount may be used for these or other components of the re-packaged laser without departing from the spirit and scope of the present invention. 
         [0024]      FIG. 3  schematically illustrates a first rigid frame-member  60 , here, rectangular, attached to the base-member  42  of  FIG. 2  in a next step of assembling the laser, and the enclosure. In  FIG. 3 , only components added to those depicted in  FIG. 2  are identified, for simplicity of illustration, the previously described components being easily recognizable due to the detail level of the drawings. 
         [0025]    Frame-member  60  includes opposite side-walls  62 A and  62 B, and opposite end-walls  64 A and  64 B. The frame-member is an “open”, frame, i.e., the frame does not have a floor. 
         [0026]    Birefringent filter (BRF)  38  of the laser is mounted on a raised portion  65  of wall  62 B via a complex mount  68 . A lowered region  66  of wall  62 A facilitates access to mount  68  for aligning and adjusting the birefringent filter. Mount  68  includes a bracket  70  on which the BRF is bonded. Bracket  70  is bonded to an intermediate member  74  via a temperature control element  72 , for example a thermoelectric coupler. Intermediate member  74  is bonded to a base member  76  which is affixed to, or alternatively part of, wall  62 B. Base member  76  has a triangular cross-section which establishes the incidence angle for the BRF at the Brewster angle. Adjustment of the transmission wavelength of the BRF is made by adjusting the angle of the optical axis of the BRF relative to the polarization plane of the resonator mode. 
         [0027]    Fold-minors  35  and  37  are provided for the laser-resonator. Mirrors  35  and  37  are attached to walls  62 B and  62 A, respectively, by mounts  80  and  82 , respectively. These mounts are of the PTC type discussed above. The resonator beam-path is indicated by a bold line  11 A. It can be seen from the drawing that a beam of radiation leaving OPS chip  12  is incident first on minor  35  and next on minor  37 . Minor  37  directs the beam through BRF  38  to other resonator components (not shown) which are (or will be) attached to another frame-member. Fold minors  35  and  37  and the BRF are aligned with respect to OPS-structure  12 , i.e., with respect to mirror-structure  14  thereof. Techniques for performing such alignment are well known in the art and include the use of visible alignment lasers, pinholes and other fixtures. 
         [0028]      FIG. 4  schematically illustrates a second rigid frame-member  90  attached to frame-member  60  of  FIG. 3  in a next step of assembling the laser, and the enclosure. Here again, only components added to those depicted in  FIG. 3  are identified, for simplicity of illustration. 
         [0029]    Frame-member  90  includes opposite side-walls  92 A and  92 B, and opposite end-walls  94 A and  94 B. Here again, the frame-member is an “open”, frame. Cut-out portions  95  and  97  are provided in walls  92 A and  94 B respectively to facilitate access for component mounting and alignment. Dichroic minor  36  is mounted on end-wall via a PTC type mount  98  on a bracket or post  99 . Minor  36  directs fundamental radiation in the laser beam-path  11 A back through optically nonlinear crystal  40  to resonator end mirror  34 . 
         [0030]    Crystal  40  is held in a C-shaped, thermal contact clamp  100 , which is bonded to a platform or holder  102 . Holder  102  is supported on a mount  104  including a heating element  106  for maintaining the crystal at a phase-matching temperature. The mount comprises a base  108 , and a post  110 , which is attached to wall  92 B. 
         [0031]    Referring now to  FIG. 4A  and  FIG. 4B  for detail, resonator end-minor  34  is mounted on wall  92 A via a PTC-type mount  112 . The resonator functions as described above for the laser of  FIG. 1 . 2H-radiation generated by crystal  40  is transmitted through dichroic minor  36  and a window  112  in wall  94 A of frame-member  90  as output radiation of the laser. 
         [0032]    Referring in particular to  FIG. 4B  wherein wall  92 A of frame-member  90  is depicted as cut-away to provide visibility, crystal  40  is inclined at an angle to beam path  11 A with end faces  40 A and  40 B of the crystal cut for optimum phase-matching. Here, the beam from dichroic mirror  36  is incident on crystal  40  via end-face  40 A; is refracted by the surface along the longitudinal axis of the crystal; and exits end-face  40 B thereof parallel to the incidence direction. The beam is returned by reflection from end-mirror  34  along the same path. Cutting and orientation of optically nonlinear crystals for phase matching in frequency conversion is well known in the art and a detailed description thereof is not required for understanding principles of the present invention accordingly no such description is presented herein. 
         [0033]    At the point depicted in  FIG. 4 , the assembly of the laser is complete, and the base and frame-members have formed an almost-complete enclosure  114  for the laser. The enclosure is completed as schematically depicted in  FIG. 5  by a cover-member  118  to provide an inventive laser  120  in what is essentially an integral enclosure. 
         [0034]    Those skilled in the art will recognize that base and frame-members must be stiff enough to hold components of the laser in relative alignment as components are added and frame-members are attached to each other to form the enclosure. Accordingly, materials such as aluminum titanium and magnesium with a high stiffness to weight ratio are preferred for forming the base and frame-members. Composite materials may also be considered. Regarding attaching the base and frame-members together, options include the use of screws attaching one member to the next, or bonding or welding the members together, if maintenance of the laser is not contemplated. These or any such options may be exercised without departing from the spirit and scope of the present invention. 
         [0035]    One unique aspect of the present invention is that the laser and the enclosure thereof are actually assembled together, step by step. This differs significantly from normal practice where all components are assembled on a stiff base then covered with a can-type enclosure. The use of a sequence of open frame-members for forming the enclosure, in addition to providing sites for component mounting, optimizes the use of the undivided volume of the enclosure for compactly arranging, in this case, the laser, and generally any other optical system. 
         [0036]    In practice, an optical system can be theoretically folded into the smallest practical volume in space, and then a compound enclosure in accordance with the present invention can be designed specifically for that system to enclose that volume. This promises a significant advance in the quest to reduce the size of optical systems. 
         [0037]    By way of example, the OPS-laser described herein would have performance comparable to a Genesis-MX™ laser available from Coherent Inc. of Santa Clara, Calif., the assignee of the present invention. This laser has a 2H-output power of up to about 8 Watts (W), and is contained in an enclosure having dimensions 4.75 inches by 1.73 inches by 2.75 inches. The inventive enclosure for the laser described above can, in theory at least, have corresponding dimensions 2.17 inches by 0.79 inches by 1.1 inches, i.e., less than half of the linear dimensions and about one-tenth of the volume. These dimensions may need to be increased to accommodate heat dissipation measures. Nevertheless the reduction in size and volume can still be expected to be commercially significant. 
         [0038]    It is emphasized here that while the present embodiment is described above with reference to assembling a frequency-doubled OPS-laser in the inventive disclosure, the invention enclosure and assembly technique is applicable to assembling any multi-component optical apparatus active or passive for which requires or would benefit from an enclosure. In summary, the invention is not limited to the embodiment described above. Rather the invention is defined by the claims appended hereto.