Abstract:
A laser beam dump dissipates laser energy. The laser dump includes a cradle for holding the laser and an open cavity lined with a laser energy absorbing material. Laser emissions are directed from the laser into the laser dump cavity where the laser energy is dissipated.

Description:
GOVERNMENT CONTRACT 
     The United States Government has certain rights to this invention pursuant to Contract No. N61331-00-C-0022 awarded by the Department of Navy. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a laser dump which absorbs laser energy. 
     BACKGROUND INFORMATION 
     Laser systems often require reshaping of the laser beam. Some of the rays of the laser beam may be separated or stripped from the beam of interest and the energy contained therein must be safely dissipated. In high power laser systems, such energy is substantial and the construction of a suitable heat absorbing device, commonly known as a laser dump, can present significant problems. 
     Many conventional laser dumps use a liquid coolant to absorb the incident radiant energy to keep the temperature of the dump material within allowable working limits. However, liquid cooling requires complex cooling channel networks and associated piping connections for the coolant. To increase the heat transfer rate, the coolant is usually forced through the cooling channels at a very high velocity under great pressure, which necessitates the use of a high pressure pump. U.S. Pat. Nos. 4,267,523 and 4,271,396 disclose laser dumps which utilize cooling fluids. 
     Other types of conventional laser dumps utilize reflective surfaces to control energy dissipation. One such design directs laser energy to a pointed reflective surface which reflects the energy to a hemispherical absorber. However, this design may result in excessive heat build up at the apex of the reflector. Another laser dump which utilizes reflective surfaces is disclosed in U.S. Pat. No. 4,511,216. This design controls the angles at which the beam is introduced to an internal cylindrical surface, and provides reflective and absorbing zones. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention is to provide a laser beam dump comprising a cavity lined with a laser beam absorbing material, and a cradle for receiving a laser such that laser beam emissions from the laser are directed into the cavity and are contained within the cavity. 
     Another aspect of the present invention is to provide a laser beam dump system comprising a laser, and a laser beam dump positioned adjacent to the laser for accepting laser beam emissions from the laser, the laser beam dump comprising a cavity lined with a laser beam absorbing material and a cradle structured and arranged to receive the laser. 
     A further aspect of the present invention is to provide a method of dissipating laser energy. The method comprises mounting the laser on a laser beam dump and directing a laser fan beam from the laser into the laser beam dump, wherein the laser beam dump includes a cavity lined with a laser beam absorbing material and a cradle for receiving the laser. 
     These and other aspects of the present invention will be more apparent from the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partially schematic side view of a laser mounted on a laser beam dump in accordance with an embodiment of the present invention. 
         FIG. 2  is an isometric view of a laser beam dump in accordance with an embodiment of the present invention. 
         FIG. 3  is a top view of the laser beam dump of  FIG. 2 . 
         FIG. 4  is a sectional view taken through line  4 - 4  of  FIG. 3   
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a laser beam dump system in accordance with an embodiment of the present invention. The system includes a laser  5  which may be any conventional laser such as a neodymium: YAG type, Class 1, 2, 3a, 3b or 4 laser. The laser  5  may be a high power laser having a fan beam output, e.g., with an output level of less than 40 Watts. The laser  5  is positioned over the laser beam dump  10  in such a manner that a portion of the laser energy B generated by the laser  5  is emitted from a region  6  of the laser into the laser beam dump  10 . 
     As shown in  FIGS. 1 and 2 , the laser beam dump  10  includes feet  12  which may be height-adjustable, e.g., from 0.5 to 3 inches. The laser beam dump  10  also includes side handles  14  which may be used to transport and adjust the orientation of the laser beam dump  10 . 
     As shown in  FIG. 2 , the laser beam dump  10  includes opposing side walls  22   a  and  22   b , and opposing front  24   a  and back  24   b  walls. Top edge portions  26   a  and  26   b  may be fastened by any suitable means such as mechanical fasteners or adhesives to the side walls  22   a  and  22   b  and/or the front and back walls  24   a  and  24   b . A semicircular cradle  30  is formed in the front wall  24   a  and back wall  24   b . A resilient sealing or padding strip  32  lines the cradle  30 . 
     As shown in  FIG. 2 , the laser beam dump  10  has a height H of any suitable dimension, for example, from about 1 to about 3 feet. The width W of the laser beam dump  10  may be, for example, from about 1 to about 3 feet. The length L of the laser beam dump  10  may be, for example, from about 6 inches to about 2 feet. The cradle  30  has a diameter D which may vary depending upon the dimensions of the laser  5 . For example, the diameter D of the cradle  30  may be from about 6 inches to about 3 feet. The shape of the cradle  30  shown in  FIG. 2  is generally semicircular, however, the cradle  30  may have any other suitable shape such as square, rectangular or curved, depending on the geometry of the laser to be held by the cradle. The bottom of the cradle  30  is located at a height C from the base of the laser beam dump  10 , which may range from about 6 inches to about 3 feet. The above-noted dimensions may be adjusted depending on the type and configuration of the laser. 
       FIG. 3  is a top view of the laser beam dump  10  showing its internal cavity  28 . In accordance with a preferred embodiment of the present invention, the cavity  28  is generally rectangular. Furthermore, the cavity  28  preferably does not include mirrors or other reflective surfaces for contacting the incoming laser beam. The cavity  28  has a suitable laser absorbing internal surface area, e.g., from about 1 m 2  to about 2 m 2 . The cavity  28  has a suitable volume, e.g., from about 0.5 to about 0.75 m 3 . 
     As shown in  FIGS. 3 and 4 , the cavity  28  of the laser beam dump  10  is lined with a laser absorbing material. The cavity may be partially lined or fully lined with the absorbing material. In the embodiment shown in  FIGS. 3 and 4 , the side walls  22   a  and  22   b  are lined with absorbing panels  23   a  and  23   b , and the front and back walls  24   a  and  24   b  are also lined with absorbing panels  25   a  and  25   b . As shown in  FIG. 4 , the base  20  of the laser beam dump  10  is lined with a laser beam absorbing panel  21 . 
     The components of the laser beam dump  10  may be made of any suitable materials. For example, the side walls  22   a  and  22   b , front wall  24   a , back wall  24   b , top edges  26   a  and  26   b  and base  20  may be made of plywood, sheet metal and/or plastic. The absorbing liners  23   a ,  23   b ,  25   a ,  25   b  and  21  may be made of any suitable laser beam energy absorbing material such as concrete wall board or other special laser absorbing material. For example, the laser beam energy absorbing material may be wall board sold under the designation Durock by USG Co. The resilient strips  32  may be made of any suitable material such as rubber weather stripping or plastic moulding. 
     The following example is intended to illustrate various aspects of the present invention, and is not intended to limit the scope of the invention. 
     EXAMPLE 
     A Class 4 laser fan beam comprising an environmentally sealed pod housing, environmental control unit and power supplies is positioned above or laser beam dump as shown in  FIGS. 1-4 . The laser beam dump has a height H of 25.5 inches, a width W of 26 inches, and a length L of 12 inches. The semicircular cradle has a diameter D of 20 inches and is elevated a height C of 15.5 inches from the base of the laser beam dump. The sides, front, back, base and top edges are made of ¾ inch thick plywood lined with ½ inch thick cement wall board sold under the designation Durock. The semicircular cradle is lined with rubber weather strip to protect the surface of the laser/pod housing from scratches and to protect against laser light leakage through the seam interface. 
     The laser and laser beam dump are operated as follows. The laser is mounted internal to the pod housing which is supported (suspended) by a special work stand, or in this case by the stores mounting structure of a helicopter. During the conduct of the test, the laser fan beam must be captured and contained without posing a health risk to test personnel or causing damage to assets or equipment. The laser beam dump is positioned under the pod at the appropriate region to capture laser energy B at the laser output port. If desired, a calorimeter can also be installed internal to the laser beam dump to enable measurements to be taken of the actual laser output power. After installation of the laser beam dump, height adjustments can be made to ensure a tight fit between the cradle  30  and the laser/pod surface  6  at which point the test may begin. Testing is performed without any anomalies for long durations, no laser light is released and no significant heating is experienced. 
     Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.