Off-axis three-mirror optical system with freeform surfaces

An off-axis three-mirror optical system with freeform surfaces comprising:

• an aperture located on an incident light path, and the aperture defining an aperture center;
• a primary mirror located on an aperture side that is away from an object space and configured to reflect an incident light to form a first reflected light, and the first reflected light defining a first reflected light path;
• a secondary mirror located on the first reflected light path and configured to reflect the first reflected light to form a second reflected light, and the second reflected light defining a second reflected light path;
• a tertiary mirror located on the second reflected light path and configured to reflect the second reflected light to form a third reflected light, and the third reflected light defining a third reflected light path;
• and
• a detector located on the third reflected light path and configured to receive the third reflected light;
• wherein a first three-dimensional rectangular coordinates system (x1, y1, z1) is defined, and the aperture center is a first three-dimensional rectangular coordinates system (x1, y1, z1) origin;
• a second three-dimensional rectangular coordinates system (x2, y2, z2) is defined for a primary mirror location and a tertiary mirror location;
• a third three-dimensional rectangular coordinates system (x3, y3, z3) is defined for a secondary mirror location;
• and a fourth three-dimensional rectangular coordinates system (x4, y4, z4) is defined for a detector location;
• a primary mirror reflective surface and a tertiary mirror reflective surface have a same freeform surface analytical expression, and the freeform surface equation is a fifth-order polynomial of x2y2;
• a secondary mirror reflective surface is a fifth-order polynomial of x3y3;
• and the first reflected light path, the second reflected light path and the third reflected light path overlap with each other.