Patent Publication Number: US-2011051209-A1

Title: Beam irradiation apparatus and laser radar

Description:
This application claims priority under 35 U.S.C. Section 119 of Japanese Patent Application No. 2009-197471 filed Aug. 27, 2009, entitled “BEAM IRRADIATION APPARATUS AND LASER RADAR”. The disclosure of the above applications is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a beam irradiation apparatus which irradiates a target region with light and a laser radar on which the beam irradiation apparatus is mounted. 
     2. Related Art 
     In recent years, a laser radar is mounted on a household automobile or the like in order to enhance safety while driving. In general, the laser radar makes a laser beam scan within a target region and detects presence/absence of an obstacle at each scanning position based on presence/absence of reflected light from each scanning position. Further, a distance to the obstacle is detected based on a time needed from an irradiation timing of a laser beam at each scanning position to a reception timing of reflected light. 
     A beam irradiation apparatus for making a laser beam scan on a target region is incorporated into the laser radar. In a case where the laser radar is mounted on an automobile, detection accuracy in the horizontal direction is improved in comparison with that in the vertical direction. Therefore, the beam irradiation apparatus mounted on the laser radar of such type irradiates the target region with a beam having a shape which is longer in the vertical direction and narrower in the horizontal direction. 
     When a laser diode is used as a light source of the beam irradiation apparatus, a divergence angle of an output laser beam is large in the direction perpendicular to a pn junction surface (hereinafter, referred to “short side direction”) and is small in the direction parallel with the pn junction surface (hereinafter, referred to “longitudinal direction”). Therefore, when the laser diode is used as the light source of the beam irradiation apparatus, a configuration for adjusting a shape of a beam on the target region to a desired shape is needed. In this case, a beam shaping lens such as a cylindrical lens may be used in addition to a convergent lens. 
     However, if the beam shaping lens such as the cylindrical lens is needed in addition to the convergent lens as described above, a problem that a shape of the beam on the target region is distorted due to an aberration caused by the cylindrical lens or the like may arise. Further, if distortion is caused in a beam profile on the target region, there is a risk that an accuracy of detecting an obstacle is deteriorated. 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention relates to a beam irradiation apparatus. The beam irradiation apparatus according to the first aspect of the invention includes a light source which outputs a laser beam, a convergent lens into which the laser beam output from the light source is entered, and a scanning portion which makes the laser beam transmitted through the convergent lens scan on a target region. In the beam irradiation apparatus, the laser light source is arranged such that a pn junction surface of a laser chip is parallel with the vertical direction. Length of the laser beam in the vertical direction on the target region is set by length of a light emitting portion of the laser light source in the direction parallel with the vertical direction. Further, a wavefront aberration of the convergent lens with respect to the laser beam is set to be 0.15 λrms or less. 
     A second aspect of the invention relates to a laser radar. The laser radar according to the second aspect of the invention includes the beam irradiation apparatus according to the first aspect and a light reception portion which receives light from the target region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-described and other objects and novel characteristics of the invention are made obvious more perfectly by reading the following description of embodiment and the following accompanying drawings. 
         FIGS. 1A and 1B  are views for explaining a method of configuring a laser light source according to the embodiment. 
         FIG. 1C  is a view illustrating a scanning of a laser beam on a target region. 
         FIGS. 2A and 2B  are diagrams for explaining a method of configuring a convergent lens according to the embodiment. 
         FIGS. 3A and 3B  are diagrams for explaining a method of configuring the convergent lens according to the embodiment. 
         FIGS. 4A and 4B  are diagrams for explaining a method of configuring the convergent lens according to the embodiment. 
         FIG. 5  is an exploded perspective view illustrating a configuration of a mirror actuator according to the embodiment. 
         FIGS. 6A and 6B  are perspective views illustrating a configuration of the mirror actuator according to the embodiment. 
         FIG. 7A  is a view illustrating a configuration of an optical system of a beam irradiation apparatus according to the embodiment.  FIGS. 7B and 7C  are views illustrating an arrangement of a laser chip of the beam irradiation apparatus according to the embodiment. 
         FIGS. 8A and 8B  are views illustrating a configuration of the optical system of the beam irradiation apparatus according to the embodiment. 
         FIG. 9  is a diagram illustrating a configuration of a laser radar according to the embodiment. 
     
    
    
     It is to be noted that the drawings are exclusively intended to explain the invention only and are not intended to limit a range of the invention. 
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereinafter, an embodiment of the invention will be described with reference to drawings. Note that a beam irradiation apparatus according to the invention is mounted on a laser radar for an automobile. 
       FIGS. 1A and 1B  are views for explaining a method of configuring a laser light source in the beam irradiation apparatus. In  FIGS. 1A and 1B , a convergent lens is a convex lens having a predetermined focal distance. A lens surface of the convergent lens has a rotational symmetrical shape about an optical axis. 
     If a laser chip of the laser light source (laser diode) is arranged at a focal position of the convergent lens as shown in  FIG. 1A , the following relationship is established among a divergence angle θL 0  of a laser beam in the longitudinal direction (the direction parallel with a pn junction surface) after the laser beam transmits through the convergent lens, a half value Y 0  of length of the laser chip in the longitudinal direction (length of a light emitting portion) and a focal distance f 0  of the convergent lens. It is to be noted that the following relational expressions are satisfied when the divergence angle θL 0  is a value close to zero. 
         Y 0 =f 0·tan(θ L 0)  (1)
 
       θ L 0=tan −1 ( Y 0 /f 0)  (2)
 
     In this case, the divergence angle of the laser beam in the short side direction (the direction perpendicular to a pn junction surface) after the laser beam transmits through the convergent lens is zero. That is to say, the laser beam which is output so as to be spread in the short side direction transmits through the convergent lens, and then, travels parallel with the optical axis. In this case, the laser beam enters into the lens as shown in  FIG. 1B , for example. 
       FIG. 1C  is a view illustrating a scanning form of the laser beam on a target region. 
     Irradiation blocks of three stages in the vertical direction are set as the target region. Each block has an elongated shape in the vertical direction. The laser beam output from the beam irradiation apparatus sequentially scans each block on the target region row by row in the horizontal direction from left to right, for example. As shown in  FIG. 1C , the irradiation region of the laser beam on the target region is set to be slightly larger than each block. The beam irradiation apparatus pulse-emits the laser beam at a timing where a scanning position corresponds to a position of each block. 
     With the above expressions (1) and (2), if the laser chip is arranged on the focal position of the convergent lens, the laser beam has a predetermined divergence angle θL 0  in the longitudinal direction. Therefore, the laser chip is desired to be arranged such that the longitudinal direction is in parallel with the vertical direction in order to make the laser beam on the target region have an elongated shape in the vertical direction as shown in  FIG. 1C . With this, the length of the laser beam in the vertical direction on the target region can be set to a desired length by adjusting the half value Y 0  of the length of the laser chip in the longitudinal direction (vertical direction) or the focal distance f 0  of the lens. 
     In this case, a width of the laser beam in the horizontal direction on the target region can be adjusted by moving the position of the laser chip from the position as shown in  FIG. 1A  toward the convergent lens as shown by a dashed-line arrow as shown in  FIG. 1A . Here, the position as shown in  FIG. 1A  indicates a position of the focal distance f 0  of the convergent lens. That is to say, if the position of the laser chip is made close to the convergent lens from the focal position of the convergent lens, the divergence angle θs 0  of the laser beam in the short side direction (horizontal direction) after the laser beam transmits through the convergent lens can be obtained by the following expression. 
       θ As 0=λ/(πω)  (3)
 
     In the expression, λ indicates a wavelength of the laser beam and ω indicates a radius of beam waist at a virtual image position. Note that the expression is satisfied when the width of the laser chip in the short side direction is small and the laser chip is regarded as a point light source. 
     With the above expression (3), the width of the laser light in the horizontal direction on the target region can be set to a desired width by making the position of the laser chip close to the convergent lens from the focal position of the convergent lens and adjusting the divergence angle θs 0  in the short side direction (horizontal direction). 
     In this case, the divergence angle θs 0  can be set to a desired value by slightly moving the position of the laser chip from the position of the focal distance of the convergent lens. Therefore, the divergence angle θL 0  of the laser beam in the longitudinal direction (vertical direction) as shown in  FIG. 1A  is not so different from that in a case where the laser chip is at the position of the focal distance even when the position of the laser chip is moved in such a manner. Accordingly, the length of the laser beam in the vertical direction on the target region can be kept to be a desired length even if the position of the laser chip is moved in order to adjust the divergence angle θs 0  in the short side direction (horizontal direction). 
     The shape of the laser beam on the target region can be made an elongated shape in the vertical direction by arranging the laser chip such that the longitudinal direction is in parallel with the vertical direction as described above. Further, with the above expressions (1) and (2), the length of the laser beam in the vertical direction on the target region can be set to a desired length by adjusting the half value Y 0  of the length of the laser chip in the longitudinal direction (vertical direction) or the focal distance f 0  of the lens. The length of the laser beam in the horizontal direction on the target region can be adjusted to a desired length by making the position of the laser chip close to the convergent lens from the focal position of the convergent lens. 
     In the embodiment, the half value Y 0  of the length of the laser chip in the longitudinal direction (vertical direction) or the focal distance f 0  of the lens is adjusted and the position of the laser chip with respect to the focal position of the convergent lens is adjusted such that a size of the irradiation region of the laser beam on the target region is a predetermined size. In the embodiment, since a shape of the beam can be set by a configuration and an arrangement of the laser chip in such a manner, a lens for shaping the beam is not needed. Therefore, a beam profile of the laser beam on the target region is not deteriorated due to an aberration caused by the beam shaping lens. Further, the laser beam output from the laser chip is entered into the convergent lens not through an aperture for shaping the beam. Therefore, a beam profile of the laser beam on the target region is not also deteriorated due to diffraction by the aperture. 
     Further, in the embodiment, the beam profile of the laser beam on the target region is further stabilized by setting characteristics of the convergent lens as follows. 
       FIG. 2A  through  FIG. 4B  are diagrams illustrating results of simulations made by the inventors in order to set the characteristics of the convergent lens. Conditions of the simulations are set as follows. 
     
       
         
           
               
             
               
                   
               
               
                 &lt;Condition 1&gt; 
               
               
                   
               
             
            
               
                 (a) Convergent lens 
               
            
           
           
               
               
               
            
               
                 A. 
                 Lens specification 
                 Both-side aspherical single lens 
               
               
                 B. 
                 Focal Distance 
                 10 mm 
               
               
                 C. 
                 Opening Number (NA) 
                 0.35 
               
            
           
           
               
            
               
                 (b) Laser chip 
               
            
           
           
               
               
               
            
               
                 D. 
                 Wavelength of 
                 905 mm 
               
               
                   
                 output light 
               
               
                 E. 
                 Light emitting portion 
                 Short side direction thereof is 
               
               
                   
                   
                 regarded as point light source 
               
               
                 F. 
                 Laser divergence angle 
                 40 degree horizontal, 14 degree 
               
               
                   
                 (1/e2 TOTAL ANGLE) 
                 vertical 
               
            
           
           
               
            
               
                 (c) Divergence angle and position of laser chip 
               
            
           
           
               
               
               
            
               
                 G. 
                 Divergence angle and 
                 0.1 degree in short side direction 
               
               
                   
                 position of laser chip 
               
               
                 H. 
                 Position of laser chip 
                 Position at which divergence angle 
               
               
                   
                   
                 in short side direction is 0.1 degree 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                   
               
               
                 &lt;Condition 2&gt; 
               
               
                   
               
             
            
               
                 (a) Convergent lens 
               
            
           
           
               
               
               
            
               
                 A. 
                 Lens specification 
                 Both-side aspherical single lens 
               
               
                 B. 
                 Focal Distance 
                 16 mm 
               
               
                 C. 
                 Opening Number (NA) 
                 0.35 
               
            
           
           
               
            
               
                 (b) Laser chip 
               
            
           
           
               
               
               
            
               
                 D. 
                 Wavelength of 
                 905 mm 
               
               
                   
                 output light 
               
               
                 E. 
                 Light emitting portion 
                 Short side direction thereof is 
               
               
                   
                   
                 regarded as point light source 
               
               
                 F. 
                 Laser divergence angle 
                 40 degree horizontal, 14 degree 
               
               
                   
                 (1/e2 TOTAL ANGLE) 
                 vertical 
               
            
           
           
               
            
               
                 (c) Divergence angle and position of laser chip 
               
            
           
           
               
               
               
            
               
                 G. 
                 Divergence angle and 
                 0.1 degree in short side direction 
               
               
                   
                 position of laser chip 
               
               
                 H. 
                 Position of laser chip 
                 Position at which divergence angle 
               
               
                   
                   
                 in short side direction is 0.1 degree 
               
               
                   
               
            
           
         
       
     
     A focal distance of the convergent lens as shown in the above condition 2 indicates a focal distance which is needed to take a laser beam from the laser chip into the convergent lens having a standard size (lens effective diameter=about 13 mm) in current beam irradiation apparatuses for automobiles. That is to say, if the focal distance is 16 mm or less, the convergent lens can take all of the laser beam having the divergence angle as shown in F in the above condition 2. On the other hand, if the focal distance is larger than 16 mm, the convergent lens cannot take a part of the laser beam having the above divergence angle. 
     It is to be noted that the simulations are performed on the assumption that other optical devices such as a beam shaping lens and an aperture are not arranged between the laser chip and the convergent lens at all as shown in  FIG. 1A . 
       FIGS. 2A and 3A  are results of the simulations performed as follows. That is, a beam profile in the short side direction when the laser beam is output from the laser chip in each of the optical systems configured in accordance with each of the above condition 1 and condition 2 is obtained at a position which is 10 m ahead of the convergent lens. In  FIGS. 2A and 3A , a horizontal axis indicates a distance from the center of the beam and a vertical axis indicates an intensity of the laser beam at each distance. Each result of the simulations is normalized by setting an intensity at the center of the beam to 1. Further, in each of  FIGS. 2A and 3A , results of the simulations obtained when wavefront aberrations of the convergent lens are changed at nine stages. 
     Here, the wavefront aberrations of the convergent lens set in the simulations are 0.4 (λrms), 0.3 (λrms), 0.2 (λrms), 0.14 (λrms), 0.1 (λrms), 0.08 (λrms), 0.06 (λrms), 0.04 (λrms), and 0.02 (λrms). In each of  FIGS. 2A and 3A , an outermost waveform is a simulation result when the wavefront aberration is 0.4 (λrms), and an innermost waveform is a simulation result when the wavefront aberration is 0.02 (λrms). The wavefront aberrations of the inner side waveforms become smaller. 
     In each simulation, the beam profiles are obtained till a weak intensity at which a relative intensity is 1.0×10 −4 . When the beam irradiation apparatus is mounted on the laser radar for an automobile, high detection accuracy is needed. In this case, the beam having such weak intensity may affect the detection accuracy. 
     In the laser radar, the target region is desired to be irradiated with a laser beam having clear contour without blurring on the periphery of the beam. Accordingly, in each of the simulation results in  FIGS. 2A and 3A , the beam profile is desired to be formed into a spike form as sharp as possible such that skirt portions are not spread in the left-right directions. In each of the simulation results, the wavefront aberration of 0.02 (λrms) is considered to be substantially aberration-free. The beam profile in this case has a sharp spike form such that skirt portions are not spread. As the wavefront aberration of the convergent lens is larger, the beam profile has a gentler mountain-like shape such that skirt portions are spread. That is to say, as the wavefront aberration of the convergent lens is larger, blurring on the periphery of the laser beam irradiated onto the target region is larger. 
       FIGS. 2B and 3B  are simulation results obtained by dividing each of the intensities of the beam profiles having the wavefront aberrations as shown in  FIGS. 2A and 3A  by the intensity of the beam profile having a wavefront aberration of 0.02 (λrms) as an ideal waveform. As is obvious from these simulation results, as the wavefront aberration of the convergent lens is larger, the beam profile has a gentler mountain-like waveform such that skirt portions are spread. The degree of spreading of the beam profile, that is, the degree of blurring of the laser beam on the target region is recognized from the size of the mountain in each waveform. As the mountain is larger, the laser beam can be evaluated to be blurred on the target region. 
       FIGS. 4A and 4B  are graphs obtained by plotting the heights of the mountains (maximum value in the vertical axis) in  FIGS. 2B and 3B  for each wavefront aberration. In  FIGS. 4A and 4B , a straight line is added with dashed line for convenience of explanation. 
     Referring to  FIG. 4A , when the focal distance of the convergent lens is set to 10 mm, maximum values of the waveforms in  FIG. 2B  change in a linear fashion until the wavefront aberration reaches to around 0.18 (λrms) and the maximum values of the waveforms in  FIG. 2B  change so as to be larger in an exponential fashion after the wavefront aberration is beyond around 0.18 (λrms). 
     Referring to  FIG. 4B , when the focal distance of the convergent lens is set to 16 mm, maximum values of the waveforms in  FIG. 3B  change in a linear fashion until the wavefront aberration reaches to around 0.15 (λrms) and the maximum values of the waveforms in  FIG. 3B  change so as to be larger in an exponential fashion after the wavefront aberration is beyond around 0.15 (λrms). 
     The wavefront aberration of the convergent lens thus changes due to arrangement errors with respect to the optical system, change in temperature of the convergent lens, or the like. Therefore, the wavefront aberration of the convergent lens is desired to be set in a range where the maximum value of the waveform as shown in  FIG. 2B  does not largely change even when the wavefront aberration of the convergent lens changes due to arrangement errors, change in temperature of the convergent lens, or the like. 
     From this viewpoint, when the focal distance of the convergent lens is 10 mm, the wavefront aberration of the convergent lens is desired to be set to a range of 0.18 (λrms) or less as is seen from  FIG. 4A . By setting in this manner, even when the wavefront aberration changes due to arrangement errors with respect to the optical system, change in temperature of the convergent lens, or the like, the maximum value of the waveform as shown in  FIG. 2B  does not largely change and the laser beam on the target region can be prevented from being significantly blurred. Further, if the wavefront aberration of the convergent lens is set to a range of 0.18 (λrms) or less, the maximum value of the waveform as shown in  FIG. 2B  is 3 or less. Therefore, the target region can be irradiated with a laser beam having clear contour in a state where blurring on the periphery of the beam is suppressed. 
     Accordingly, when the focal distance of the convergent lens is 10 mm, the following effects can be obtained by setting the wavefront aberration of the convergent lens to a range of 0.18 (λrms) or less. That is, the target region can be irradiated with a laser beam having clear contour in a state where blurring on the periphery of the beam is suppressed and the laser beam on the target region can be prevented from being significantly blurred even if the wavefront aberration of the convergent lens changes due to arrangement errors of the convergent lens with respect to the optical system, change in temperature of the convergent lens, or the like. 
     From the same viewpoint, when the focal distance of the convergent lens is 16 mm, the wavefront aberration of the convergent lens is desired to be set to a range of 0.15 (λrms) or less as is seen from  FIG. 4B . By setting in this manner, even when the wavefront aberration changes due to arrangement errors with respect to the optical system, change in temperature of the convergent lens, or the like, the maximum value of the waveform shown in  FIG. 3B  does not largely change and the laser beam on the target region can be prevented from being significantly blurred. Further, if the wavefront aberration of the convergent lens is set to a range of 0.15 (λrms) or less, the maximum value of the waveform as shown in  FIG. 3B  is 3 or less. Therefore, the target region can be irradiated with a laser beam having clear contour in a state where blurring on the periphery of the beam is suppressed. 
     Accordingly, when the focal distance of the convergent lens is 16 mm, the following effects can be obtained by setting the wavefront aberration of the convergent lens to a range of 0.15 (λrms) or less. That is, the target region can be irradiated with a laser beam having clear contour in a state where blurring on the periphery of the beam is suppressed and the laser beam on the target region can be prevented from being significantly blurred even if the wavefront aberration of the convergent lens changes due to arrangement errors of the convergent lens with respect to the optical system, change in temperature of the convergent lens, or the like. 
     From the results of the above two studies, when the focal distance of the convergent lens is 16 mm or less so as to take all of the laser beam from the laser chip, the wavefront aberration of the convergent lens is desired to be set be 0.15 (λrms) or less. Therefore, the target region can be irradiated with a laser beam having high intensity and clear contour and the laser beam on the target region can be prevented from being significantly blurred. Accordingly, an obstacle on the target region can be stably detected with high accuracy while enhancing safety. It is to be noted that the same tendency as the above configuration can be obtained if the wavelength of the laser beam is set to around 900 nm±100 nm. 
     Specific Configuration Example 
     Hereinafter, a specific configuration example of the beam irradiation apparatus according to the embodiment is described. 
     At first, a configuration of a mirror actuator  100  for making a laser beam scan on a target region is described with reference to  FIG. 5 . 
     In  FIG. 5 , a reference numeral  110  corresponds to a tilt unit. The tilt unit  110  includes a supporting shaft  111 , a bearing portion  112 , coil supporting plates  113 ,  114 , coils  115 ,  116  and a connecting portion  117 . The bearing portion  112  is rotatably attached to the supporting shaft  111 . The coil supporting plates  113 ,  114  are arranged at positions so as to be symmetric with respect to the bearing portion  112 . The coils  115 ,  116  are attached to the coil supporting plates  113 ,  114 , respectively. The connecting portion  117  connects the bearing portion  112  and the coil supporting plates  113 ,  114 . 
     A shaft hole  112   a  penetrating through in the left-right direction is provided on the bearing portion  112 . The supporting shaft  111  is put through the shaft hole  112   a . The bearing portion  112  is attached to a center portion of the supporting shaft  111 . Further, a hole  112   b  is provided on an upper face of the bearing portion  112 . 
     Flange portions projecting in the left-right direction are formed on the upper side faces of the coil supporting plates  113 ,  114 . Holding holes  113   a ,  114   a  are provided on the respective flange portions. The holding holes  113   a ,  114   a  are provided at positions so as to be symmetric with respect to the bearing portion  112 . Positions of the holding holes  113   a ,  114   a  in the up-down direction and front-rear direction are the same as each other. 
     Coils  115 ,  116  each of which is wound into a square form are attached to the coil supporting plates  113 ,  114 , respectively. An output terminal of the coil  115  is connected to an input terminal of the coil  116  with a signal line (not shown). 
     A reference numeral  120  corresponds to a pan unit. The pan unit  120  includes a recess  121 , a bearing portion  122 , a reception portion  123 , a coil  124 , a supporting shaft  125 , an E ring  126  and a balancer  127 . The recess  121  accommodates the tilt unit  110 . The bearing portion  122  is continuously connected to an upper portion of the recess  121 . The reception portion  123  is continuously connected to a lower portion of the recess  121 . The coil  124  is attached to a rear face of the recess  121 . 
     A shaft hole  122   a  penetrating through in the up-down direction is provided on the bearing portion  122 . As described later, the supporting shaft  125  is put through the shaft hole  122   a  in the up-down direction when the tilt unit  110  and the pan unit  120  are assembled. As shown in  FIG. 5 , a groove  125   a  with which the E ring  126  is fastened is formed on the supporting shaft  125 . A thread groove  125   b  to which the balancer  127  is attached is formed on an upper portion of the supporting shaft  125 . 
     Holding holes  123   a ,  123   b  are provided on the reception portion  123 . The holding holes  123   a ,  123   b  are provided at positions so as to be symmetric with respect to the supporting shaft  125 . Positions of the holding holes  123   a ,  123   b  in the up-down direction and the front-rear direction are the same as each other. A recess  123   c  is formed on a lower edge of the reception portion  123 . A gap of the recess  123   c  in the front-rear direction has substantially the same dimension as the thickness of a transparent body  200 . An upper portion of the transparent body  200  is attached to the recess  123   c.    
     A coil attachment portion (not shown) is formed on a rear face of the pan unit  120 . A coil  124  which is wound into a square form is attached to the coil attachment portion. 
     A reference numeral  130  corresponds to a magnet unit. The magnet unit  130  includes a recess  131 , grooves  132 ,  133 , eight magnets  134  and two magnets  135 . The recess  131  accommodates the pan unit  120 . The grooves  132 ,  133  engage with both edges of the supporting shaft  111 . The eight magnets  134  apply magnetic fields to the coils  115 ,  116 . The two magnets  135  apply a magnetic field to the coil  124 . 
     The eight magnets  134  are attached to left and right inner side faces of the recess  131  so as to be divided into two stages of the upper side and the lower side. Further, the two magnets  135  are attached to the inner side faces of the recess  131  so as to be inclined in the front-rear direction as shown in  FIG. 5 . Further, holes  136 ,  137  to which power supply springs  151   a ,  151   b ,  152   a ,  152   b  are inserted are formed on the recess  131 . 
     When the mirror actuator  100  is assembled, the tilt unit  110  is assembled, at first. That is to say, the supporting shaft  111  is attached to the shaft hole  112   a  and the coils  115 ,  116  are attached to the coil supporting plates  113 ,  114 , respectively. 
     Thereafter, the assembled tilt unit  110  is accommodated in the recess  121  of the pan unit  120 . Then, the supporting shaft  125  is inserted from the upper side in a state where the hole  112   b  of the tilt unit  110  and the shaft hole  122   a  of the pan unit  120  are matched with each other in the up-down direction. A lower edge of the supporting shaft  125  is fixed to the hole  112   b . Then, the E ring  126  is fastened to the groove  125   a  so that the supporting shaft  125  does not move downwardly from a position at which the E ring  126  is fastened with respect to the pan unit  120 . Thus, the pan unit  120  is rotatably supported with respect to the tilt unit  110  by the supporting shaft  125 . 
     Thereafter, the balancer  127  is fastened to the thread groove  125   b  of the supporting shaft  125 . Further, the transparent body  200  is attached to the recess  123   c . A mirror  140  is attached to a front face of the pan unit  120 . Thus, the tilt unit  110 , the pan unit  120  and the mirror  140  are completely assembled as shown in  FIG. 6A . 
     Note that the balancer  127  is a portion for adjusting the constituent components of the mirror actuator  100  which rotates about the supporting shaft  111  so as to rotate in a balanced manner when the constituent components of the mirror actuator  100  rotates about the supporting shaft  111 . The balance of such rotation is adjusted by weight of the balancer  127 . In addition, a position of the balancer  127  in the up-down direction is fine-adjusted by the thread groove  125   b  of the supporting shaft  125  so that the balance of the rotation is adjusted. 
     Thereafter, a configured body as shown in  FIG. 6A  is attached to the magnet unit  130 . 
     Returning to  FIG. 5 , both edges of the supporting shaft  111  are fixed to the grooves  132 ,  133  of the magnet unit  130 , from the upper side. Engagement portions which engage with the grooves  132 ,  133 , are formed on the both edges of the supporting shaft  111 . When these engagement portions are fitted into the grooves  132 ,  133 , the supporting shaft  111  is fixed to the grooves  132 ,  133  without rotating. 
     Subsequently, the power supply springs  151   a ,  151   b ,  152   a ,  152   b  are put through the holes  136 ,  137  from the rear face side of the recess  131 . In this case, distal edges of the power supply springs  151   a ,  151   b  are locked by the holding holes  113   a ,  114   a  of the tilt unit  110 . Further, the distal edges of the locked power supply springs  151   a ,  151   b  are electrically connected to the input terminal of the coil  115  and the output terminal of the coil  116 , respectively, with solders or the like. Rear edges of the power supply springs  151   a ,  151   b  are locked by the holding holes provided on the rear face side of the magnet unit  130 . 
     On the other hand, distal edges of the power supply springs  152   a ,  152   b  are locked by the holding holes  123   a ,  123   b  of the pan unit  120 , respectively. Further, the distal edges of the locked power supply springs  152   a ,  152   b  are electrically connected to an input terminal and an output terminal of the coil  124 , respectively, with solders or the like. Rear edges of the power supply springs  152   a ,  152   b  are locked by the holding holes provided on the rear face side of the magnet unit  130 . 
     When an interconnect substrate is arranged on the rear face of the magnet unit  130 , the rear edges of the power supply springs  151   a ,  151   b ,  152   a ,  152   b  are locked to holding holes formed on the interconnect substrate. 
     A beryllium copper or the like having small resistance value and excellent durability is used as materials of the power supply springs  151   a ,  151   b ,  152   a ,  152   b . In the embodiment, a coil spring obtained by winding a wire rod having excellent conductivity into a coil form is used as each of the power supply springs  151   a ,  151   b ,  152   a ,  152   b.    
     In such a manner, the mirror actuator  100  is completely assembled as shown in  FIG. 6B . If the assembled mirror actuator  100  is arranged such that the up-down direction as shown in  FIG. 5  is parallel with the vertical direction, the supporting shaft  111  and the supporting shaft  125  are parallel with the left-right direction and the up-down direction as shown in  FIG. 5 , respectively and the mirror  140  faces to the front side. 
     Lengths, spring coefficients, and the like of the power supply springs  151   a ,  151   b ,  152   a ,  152   b  are set such that the mirror  140  of the mirror actuator  100  after assembled faces to the front side. Further, the power supply springs  151   a ,  151   b ,  152   a ,  152   b  are set so as to have expanding and contracting allowances in a allowable range where the mirror  140  rotates after the mirror actuator  100  is assembled. 
     Referring to  FIG. 5  and  FIGS. 6A and 6B , when the pan unit  120  rotates about the supporting shaft  125  with respect to the tilt unit  110 , the mirror  140  rotates in accompanied therewith. Further, when the tilt unit  110  rotates about the supporting shaft  111  with respect to the magnet unit  130 , the pan unit  120  rotates in accompanied with the rotation of the tilt unit  110  and the mirror  140  rotates integrally with the pan unit  120 . Thus, the mirror  140  is rotatably supported by the supporting shafts  111 ,  125  which are perpendicular to each other and rotates about the supporting shafts  111 ,  125  by applying currents to the coils  115 ,  116 ,  124 . At this time, the transparent body  200  attached to the pan unit  120  rotates in accompanied with the rotation of the mirror  140 . 
     In the assembled state as shown in  FIG. 6B , the eight magnets  134  are arranged and polarities thereof are adjusted such that a rotational force about the supporting axis  111  is generated on the tilt unit  110  by applying currents to the coils  115 ,  116  through the power supply springs  151   a ,  151   b . Accordingly, if currents are applied to the coils  115 ,  116 , the tilt unit  110  rotates about the supporting axis  111  with electromagnetic driving forces generated on the coils  115 ,  116 . 
     Further, in the assembled state as shown in  FIG. 6B , the two magnets  135  are arranged and polarities thereof are adjusted such that a rotational force about the supporting axis  125  is generated on the pan unit  120  by applying current to the coil  124 . Accordingly, if current is applied to the coil  124 , the pan unit  120  rotates about the supporting axis  125  with an electromagnetic driving force generated on the coil  124 . Further, the transparent body  200  rotates in accompanied therewith. 
     Next, the optical system of the beam irradiation apparatus is described with reference to  FIGS. 7A ,  7 B,  8 A and  8 B. 
     A scanning optical system is described with reference to  FIG. 7A , at first. In  FIG. 7A , a reference numeral  500  corresponds to a base. In  FIG. 7A , an upper face of the base  500  is horizontal. An opening  503   a  is formed on the base  500  at an arrangement position of the mirror actuator  100 . The mirror actuator  100  is attached onto the base  500  such that the transparent body  200  is inserted to the opening  503   a . The mirror actuator  100  is attached to the base  500  such that the up-down direction as shown in  FIG. 5  corresponds to the vertical direction as shown in  FIG. 7A . 
     A laser light source  410  and a convergent lens  430  are arranged on the upper face of the base  500 . The laser light source  410  is attached to a substrate  420  for the laser light source. The substrate  420  is arranged on the upper face of the base  500 . The laser light source  410  outputs a laser beam having a wavelength of about 900 nm. The convergent lens  430  is a convex lens having a predetermined focal distance. A lens surface of the convergent lens  430  has a rotationally symmetric shape about an optical axis. 
     The convergent lens  430  corresponds to the convergent lens as shown in  FIGS. 1A and 1B . The focal distance and wavefront aberration of the convergent lens  430  are set to be in a range as described with reference to  FIG. 2A  through  FIG. 4B . That is to say, a both-sided aspherical single lens of the standard size is used as the convergent lens  430 . The focal distance of the convergent lens  430  is set to 16 mm or less and the wavefront aberration (ideal design value) thereof is set to 0.15 (λrms) or less. 
     As schematically showing in  FIG. 7B , a laser chip  411  is arranged in a CAN of the laser light source  410 . The laser light source  410  is arranged such that the longitudinal direction of the laser chip  411  is parallel with the vertical direction. Here, the length L of the laser chip  411  in the longitudinal direction is adjusted such that the laser beam has a desired shape on the target region as described with reference to  FIGS. 1A and 1B . Further, the laser chip  411  is positioned to be slightly close to the convergent lens  430  from a position of the focal distance of the convergent lens  430  such that the laser beam transmitted through the convergent lens  430  spreads in the horizontal direction by a predetermined angle. 
     Note that although one laser chip  411  is arranged in the CAN of the laser light source  410  here, a plurality of laser chips may be arranged in the CAN so as to be aligned in the longitudinal direction. In this case, the entire length L of the light emitting portion composed of these laser chips in the vertical direction is adjusted such that the laser beam has a desired shape on the target region. With this configuration, an incident region of the laser beam onto the convergent lens  430  can be spread in the vertical direction. When the target region is irradiated with the laser beam, all of the laser chips emit lights simultaneously.  FIG. 7C  illustrates a configuration in which two laser chips  411 ,  412  are arranged in one CAN so as to be aligned in the longitudinal direction. 
     The laser beam (hereinafter, referred to as “scanning laser beam”) output from the laser light source  410  enters onto the convergent lens  430  not through other optical devices such as a beam shaping lens, an aperture or the like. The laser beam transmitted through the convergent lens  430  travels to the target region in a state where the laser beam is slightly diverged in the vertical direction and the horizontal direction such that the size of the laser beam becomes a predetermined size (for example, about 2 m long and about 1 m wide) on the target region. In this case, the target region is set to a position about 100 m ahead of the beam emitting port of the beam irradiation apparatus, for example. 
     The scanning laser beam transmitted through the convergent lens  430  enters into the mirror  140  of the mirror actuator  100  and is reflected by the mirror  140  toward the target region. The mirror  140  is biaxially driven by the mirror actuator  100  so that the scanning laser beam is scanned on the target region. 
     When the mirror  140  is at a neutral position, the mirror actuator  100  is arranged such that the scanning laser beam from the convergent lens  430  enters into a mirror surface of the mirror  140  at an incident angle of 45 degree in the horizontal direction. The expression “neutral position” indicates a position of the mirror  140  at which the mirror surface is parallel with the vertical direction and the scanning laser beam enters into the mirror surface at the incident angle of 45 degree with respect to the horizontal direction. The mirror  140  is positioned at the neutral position in a state where currents are not applied to the coils  115 ,  116 ,  124 . 
     A circuit substrate  300  is arranged on a lower face of the base  500 . Further, circuit substrates  301 ,  302  are arranged on a back face and a side face of the base  500 , respectively. 
       FIG. 8A  is a partial plan view when the base  500  is seen from the back face side. A servo optical system arranged on the back side of the base  500  and configurations peripheral to the servo optical system are illustrated in  FIG. 8A . 
     As shown in  FIG. 8A , walls  501 ,  502  are formed on back side edges of the base  500 . A center portion between the walls  501 ,  502  corresponds to a flat face  503  which is lower than the walls  501 ,  502  by one step. An opening for attaching a laser diode  303  is formed on the wall  501 . A circuit substrate  301  to which the laser diode  303  has been attached is attached to an outer face of the wall  501  in such a manner that the laser diode  303  is inserted into the opening. On the other hand, a circuit substrate  302  to which a PSD  308  has been attached is attached in the vicinity of the wall  502 . 
     A condensing lens  304 , an aperture  305 , and a neutral density (ND) filter  306  are attached to the flat face  503  at the backside of the base  500  with an attachment  307 . Further, the above opening  503   a  is formed on the flat face  503 . The transparent body  200  attached to the mirror actuator  100  projects to the back side of the base  500  through the opening  503   a . Here, when the mirror  140  of the mirror actuator  100  is at the neutral position, the transparent body  200  is positioned such that two flat faces are parallel with the vertical direction and are inclined at 45 degree with respect to the output light axis of the laser diode  303 . 
     The laser beam (hereinafter, referred to as “servo beam”) output from the laser diode  303  is transmitted through the condensing lens  304 . Then, a beam diameter thereof is restricted by the aperture  305 . Further, the laser beam is extinguished by the ND filter  306 . Then, the servo beam is entered into the transparent body  200  so as to be subjected to a refraction action by the transparent body  200 . Thereafter, the servo beam transmitted through the transparent body  200  is received by the PSD  308  and a position detection signal in accordance with the light reception position is output from the PSD  308 . 
       FIG. 8B  is a view schematically illustrating a configuration in which a rotation position of the transparent body  200  is detected by the PSD  308 . Note that only the transparent body  200 , the laser diode  303  and the PSD  308  in  FIG. 8A  are illustrated in  FIG. 8B  for convenience of explanation. 
     The servo beam is refracted by the transparent body  200  arranged so as to be inclined with respect to the laser beam axis and received by the PSD  308 . When the transparent body  200  is rotated as shown by a dashed line arrow, an optical path of the servo beam changes to a path as shown by a solid line from a path shown by the dotted line in  FIG. 8B  and a reception position of the servo beam on the PSD  308  changes. Therefore, a rotation position of the transparent body  200  can be detected by the reception position of the servo beam, which is detected by the PSD  308 . The rotation position of the transparent body  200  corresponds to a scanning position of the scanning laser beam on the target region. Accordingly, the scanning position of the scanning laser beam on the target position can be detected based on a signal from the PSD  308 . 
       FIG. 9  is a view illustrating a configuration of a laser radar on which the beam irradiation apparatus having the above configuration is mounted. As shown in  FIG. 9 , the laser radar includes a beam irradiation apparatus  1  having the above configuration, a light reception portion  2 , a PSD signal processing circuit  3 , a servo LD driving circuit  4 , an actuator driving circuit  5 , a scan LD driving circuit  6 , a PD signal processing circuit  7  and a DSP  8 . 
     As the configurations in the beam irradiation apparatus  1 , only the laser light source  410 , the mirror actuator  100 , the laser diode  303 , and the PSD  308  are illustrated in  FIG. 9  for convenience of explanation. The light reception portion  2  includes a condensing lens  440  which condenses a scanning laser beam reflected from the target region and a Photo Detector (PD)  450  which receives the condensed scanning laser beam. 
     The PSD signal processing circuit  3  generates a position detection signal from an output signal from the PSD  308  and outputs the generated signal to the DSP  8 . 
     The servo LD driving circuit  4  supplies a driving signal to the laser diode  303  based on a signal from the DSP  8 . To be more specific, when the beam irradiation apparatus  1  is operated, the servo beam having a constant output is output from the laser diode  303 . 
     The actuator driving circuit  5  drives the mirror actuator  100  based on a signal from the DSP  8 . To be more specific, a driving signal for making the scanning laser beam scan on the target region along a predetermined trajectory is supplied to the mirror actuator  100 . 
     The scan LD driving circuit  6  supplies a driving signal to the laser light source  410  based on a signal from the DSP  8 . To be more specific, the laser light source  410  pulse-emits at a timing where the scanning position of the scanning laser beam is at a predetermined position on the target region. 
     The PD signal processing circuit  7  amplifies and digitalizes a signal from the PD  450  to supply the obtained signal to the DSP  8 . 
     The DSP  8  detects a scanning position of the scanning laser beam on the target region based on the position detection signal input from the PSD signal processing circuit  3  so as to control driving of the mirror actuator  100 , driving of the laser light source  410 , and the like. Further, the DSP  8  judges whether an obstacle is present on the irradiation position with the scanning laser on the target region based on the signal input from the PD signal processing circuit  7 . At the same time, the DSP  8  measures a distance to the obstacle based on a time difference between an irradiation timing of the scanning laser beam output from the laser light source  410  and a light reception timing of the reflected light from the target region, which is received on the PD  450 . 
     According to the embodiment, the laser light source is arranged such that the pn junction surface of the laser chip is parallel with the vertical direction so that the divergence angle of the laser beam in the vertical direction can be easily adjusted. In this case, the laser beam from the laser chip is entered into the convergent lens not through other optical devices such as a beam shaping lens, an aperture, or the like. Therefore, according to the embodiment, distortion due to the aberration caused by the beam shaping lens, diffraction caused by the aperture, or the like is not caused in the laser beam so that the target region can be appropriately irradiated with the laser beam. 
     Further, according to the embodiment, the wavefront aberration of the convergent lens is adjusted in a manner as described above with reference to  FIG. 2A  through  FIG. 4B . Therefore, the target region can be irradiated with a laser beam having high intensity and clear contour. In addition, the laser beam on the target region can be prevented from being significantly blurred. Accordingly, an obstacle on the target region can be stably detected with high accuracy while enhancing safety. 
     As described above, according to the embodiment, the target region can be irradiated with a laser beam with a stable beam profile and the detection accuracy of an obstacle on the target region can be enhanced. 
     Although the embodiment of the invention has been described above, the invention is not limited to the above embodiment. Further, the embodiment of the invention can variously modified into modes other than the above embodiment. 
     For example, in the above embodiment and specific configuration example, the divergence angle of the laser beam in the horizontal direction is adjusting by making the position of the laser chip close to the convergent lens from the position of the focal distance of the convergent lens. However, the divergence angle of the laser beam in the horizontal direction may be adjusted by adjusting length of the light emitting portion in the short side direction as in the longitudinal direction. In this case, the length of the light emitting portion in the short side direction can be adjusted by stacking the laser chips in the short side direction. 
     Further, all or a part of the PSD signal processing circuit  3 , the servo LD driving circuit  4 , an actuator driving circuit  5  and the scan LD driving circuit  6  in the configuration shown in  FIG. 9  may be included as configurations in the beam irradiation apparatus  1 . 
     In addition, the embodiment of the invention can be appropriately modified in a range of claims.