Patent ID: 7558180

Claim:
A light source apparatus comprising: a light source by which a light flux whose emitting angle is different in a horizontal direction and in a vertical direction is projected, and a beam shaping element, for converting the light flux into a light flux whose emitting angle is almost equal in both the horizontal direction and the vertical direction and projecting, of a single lens formed of plastic in which a linear expansion coefficient α n satisfies the following expression (1) 5.0×10 −5 <α n <8.0×10 −5 (1), and a part of the beam shaping element is fixed and arranged to the light source, so that an astigmatism generated following the refractive index change of the beam shaping element generated by a temperature change is suppressed by an interval change, which is generated by the linear expansion of the beam shaping element, between the light source and the incident surface of the beam shaping element, wherein, in the beam shaping element, an outgoing surface is fixed so that a distance in the optical axis direction from the beam shaping element to the light source is almost constant in a range of the temperature change, wherein the beam shaping element is structured so that the astigmatism generated by the temperature change is suppressed by using the astigmatism generated following a shape change due to the temperature change of the beam shaping element, wherein a fixing member for fixing the beam shaping element outgoing surface is formed of a material having a linear expansion coefficient satisfying 10×10 −5 <α n <3.0×10 −5 , wherein, in the beam shaping element, a cross sectional shape in the horizontal direction or in the vertical direction of at least one optical surface of the incident surface and the outgoing surface is a non-circular arc, wherein the surface shape of the beam shaping element incident surface satisfies the following Math-1 or Math-2, ( Z - R x ) 2 + X 2 = ( R x - Y 2 R y ( 1 + 1 - ( 1 + k y ) ⁢ Y 2 / R y 2 ) + ∑ i ⁢ A yi ⁢ Y i ) 2 [ Math ⁢ - ⁢ 1 ] ( Z - R y ) 2 + Y 2 = ( R y - X 2 R x ( 1 + 1 - ( 1 + k x ) ⁢ X 2 / R x 2 ) + ∑ A xi ⁢ X i ) [ Math ⁢ - ⁢ 2 ] wherein: Z is a distance in a Z-axis direction, Z corresponds to the optical axis direction, and Z is positive in an advancing direction of the light emitted by the light source, X and Y are distances in an X-axis direction, which corresponds to the horizontal direction, and a Y-axis direction, which corresponds to the vertical direction, the X and Y distances indicate a height from the optical axis in each of the X- and Y-axes, R x is a paraxial radius of curvature on the XZ surface, R y is a paraxial radius of curvature on YZ surface, and k x , k y , A xi , and A yi are non circular arc coefficients.