LIGHT-CONDENSING OPTICAL ELEMENT, LIGHT-CONDENSING DEVICE, PHOTOVOLTAIC DEVICE, AND PHOTOTHERMAL CONVERSION DEVICE

PROBLEM TO BE SOLVED: To provide new light-condensing means capable of utilizing light energy efficiently.SOLUTION: A light-condensing optical element 10 comprises an A member 11 having optical transparency and a plurality of particulate B members 12 having optical transparency and dispersed in the A member. Particle sizes of the B members are 0.1 λ to 10 λ, where a wavelength of incident light is denoted by λ. When an axis extending in the thickness direction is denoted by y axis, axes orthogonal to this axis are denoted by x axis and z axis, a refractive index for light whose electric field amplitude is in the xy plane and travelling in the y axis direction in the A member is denoted by naxy, a refractive index for light travelling in the x axis direction in the A member is denoted by nayx, a refractive index for light travelling in the axial direction tilted by an angle from the y axis in the A member is denoted by nax , a refractive index for light travelling in the y axis direction in the B members is denoted by nbxy, a refractive index for light travelling in the x axis direction in the B members is denoted by nbyx, and a refractive index for light travelling in the axial direction tilted by the angle from the y axis in the B members is denoted by nbx , the light-condensing optical element is so constituted as to satisfy naxy≠nbxy, nayx≠nbyx, nax =nbx , and sin >(1/nax ).