Patent Publication Number: US-2011051756-A1

Title: Beam irradiation apparatus

Description:
This application claims priority under 35 U.S.C. Section 119 of Japanese Patent Application No. 2009-197473 filed Aug. 27, 2009, entitled “BEAM IRRADIATION APPARATUS”. The disclosure of the above application 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, particularly relates to a beam irradiation apparatus which is suitably mounted on a laser radar. 
     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 the number of parts and cost are increased arises. Further, a problem that a shape of the beam on the target region is distorted because of an aberration caused by the cylindrical lens or the like may also arise. 
     SUMMARY OF THE INVENTION 
     A beam irradiation apparatus according to a 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. Further, 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 vertical direction. 
     A beam irradiation apparatus according to a second aspect of the invention includes a light source in which a plurality of laser chips is arranged so as to be aligned in the vertical direction such that pn junction surfaces are parallel with the vertical direction, a convergent lens into which the laser beam output from the light source is entered, a scanning portion which makes the laser beam transmitted through the convergent lens scan on a target region and a light source controller which controls the light source. The light source controller makes all of the plurality of laser chips emit light simultaneously when the target region is irradiated with the laser light. 
    
    
     
       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. 
         FIG. 1  is a view illustrating a mounting form of a beam irradiation apparatus according to an embodiment. 
         FIGS. 2A through 2D  are views for explaining a method of configuring a laser light source according to the embodiment. 
         FIGS. 3A through 3D  are views for explaining a method of configuring the laser light source according to the embodiment. 
         FIGS. 4A through 4D  are views for explaining a method of configuring the laser light source 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 the beam irradiation apparatus according to the embodiment.  FIG. 7B  is a view 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. 
       FIG. 1  is a view illustrating a mounting form of the beam irradiation apparatus according to the embodiment. 
     As shown in  FIG. 1 , a beam irradiation apparatus  1  is arranged at a front side of an automobile B 1  and irradiates a target region set at a front side in a traveling direction with a laser beam. 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  1  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. 1 , the irradiation region of the laser beam on the target region is set to be slightly larger than each block. The beam irradiation apparatus  1  pulse-emits the laser beam at a timing where a scanning position corresponds to a position of each block. 
       FIGS. 2A through 2D  are views for explaining a method of configuring a laser light source in the beam irradiation apparatus  1 . In  FIGS. 2A through 2D , 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. 2A , 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. 
     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. 2A  toward the convergent lens as shown by a dashed-line arrow as shown in  FIG. 2A . Here, the position as shown in  FIG. 2A  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 s 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. 2A  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. 
     For example, the divergence angle of a laser beam after the laser beam passes through the convergent lens can be enlarged from θL 0  to θL 1  by making the focal distance of the convergent lens short from f 0  to f 1  as shown in  FIG. 2C . However, in this case, a beam diameter of the laser beam when the laser beam is entered into the convergent lens is made smaller as shown  FIG. 2D . If the beam diameter is made small in such a manner, the laser beam is easily affected by dusts, water drops, or the like adhering to the convergent lens. Therefore, there is a risk that the target region cannot be appropriately irradiated with the laser beam. 
     Further, the divergence angle of a laser beam after the laser beam passes through the convergent lens can be enlarged from θL 0  to θL 2  by making the half value of length of the laser chip in the longitudinal direction (vertical direction) large from Y 0  to Y 2  as shown in  FIG. 3C . In  FIGS. 3A and 3B , the same views as those as shown in  FIGS. 2A and 2B  are illustrated for comparison. However, with a configuration as shown in  FIG. 3C , a divergence angle β of a laser beam in the longitudinal direction when the laser beam is output from the laser chip is made smaller than a divergence angle α in the case of  FIG. 3A . Therefore, in this case, as shown in  FIG. 3D , a beam diameter of the laser beam when the laser beam is entered into the convergence lens is also smaller than that in the case of  FIGS. 3A and 3B . 
     Problems arising with configurations as shown in  FIGS. 2C and 3C  can be solved by employing a configuration as shown in  FIG. 4C . In  FIGS. 4A and 4B , the same views as those as shown in  FIGS. 2A and 2B  are illustrated for comparison. 
     In the configuration as shown in  FIG. 4C , two laser chips are arranged so as to be aligned in the longitudinal direction (vertical direction) such that pn junction surfaces are parallel with the longitudinal direction (vertical direction). In such a manner, the half value of the entire length of the laser chips (light emitting portion) in the longitudinal direction (vertical direction) are made large from Y 0  to 2·Y 0 . Therefore, the divergence angle of the laser beam after the laser beam passes through the convergence lens is enlarged from θL 0  to θL 3 . In this case, a divergence angle α of the laser beam when the leaser beam is output from each laser chip is the same as that in  FIG. 4A . Therefore, as shown in  FIG. 4D , a beam diameter of the laser beam when the laser beam is entered into the convergence lens is larger than that in the case of  FIGS. 4A and 4B . 
     As described above, the laser chip is desired to be arranged such that the longitudinal direction is in parallel with the vertical direction in order to irradiate the target region with a laser beam having an elongated shape in the vertical direction. In this case, the following method is desired to be employed in order to adjust length of the laser light on the target region in the vertical direction. That is, a plurality of laser chips is arranged so as to be aligned in the longitudinal direction (vertical direction) such that pn junction surfaces are parallel with the longitudinal direction (vertical direction). With this configuration, the length of each laser chip in the longitudinal direction and the number of the laser chips arranged in the longitudinal direction are appropriately adjusted in accordance with the length of the laser beam in the vertical direction on the target region. Therefore, the target region can be irradiated with a laser beam having a desired shape while keeping the beam diameter of the laser beam when the laser beam is entered into the convergent lens to be large. 
     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 predetermined wavelength. 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. 
     As schematically showing in  FIG. 7B , two laser chips  411 ,  412  are arranged so as to be aligned in a CAN of the laser light source  410  such that pn junction surfaces are parallel with each other. The entire length L of the two laser chips  411 ,  412  in the direction parallel with the pn junction surfaces is adjusted such that the laser beam on the target region has a desired shape as described above with reference to  FIG. 4C . The laser light source  410  is arranged such that these two laser chips  411 ,  412  are aligned in the vertical direction. Further, the two laser chips  411 ,  412  are 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 the two laser chips  411 ,  412  are arranged in the CAN of the laser light source  410  here, three or more laser chips may be arranged in the CAN of the laser light source  410 . In this case, the entire length L of the light emitting portion composed of these laser chips in the vertical direction is also adjusted such that the laser beam on the target region has a desired shape. As the other configuration, only one laser chip may be arranged in the CAN of the laser light source  410 . In such a case, the length L of the laser chip (light emitting portion) in the vertical direction is adjusted such that the laser beam on the target region has a desired shape. 
     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 a beam shaping lens or an aperture. 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 diode  303  pulse-emits at a timing where the scanning position of the scanning laser beam is at a predetermined position on the target region. That is to say, the laser beams are emitted from the two laser chips  411 ,  412  arranged in the laser light source  410  simultaneously at a timing where the scanning position reaches to the irradiation position as shown in  FIG. 1 . 
     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. Additionally, the following effects can be obtained by aligning two laser chips  411 ,  412  in the vertical direction to adjust the entire length L of the light emitting portion as in the specific configuration example. That is, the beam diameter of the laser beam when the laser beam is entered into the convergence lens  430  is made smaller as described above with reference to  FIGS. 4C and 4D  so that affects by dusts, water drops, or the like adhering to the convergent lens  430  on the laser beam can be suppressed. Therefore, with this configuration, the target region can be appropriately irradiated with a laser beam, thereby enhancing detection accuracy of an obstacle on the target region. 
     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.