Patent ID: 6930975

Claim:
An optical irradiation head comprising: a trapezoidal prism having a pair of trapezoidal principal surfaces parallel to each other, a rectangular bottom surface, a rectangular top surface parallel to said rectangular bottom surface, and a pair of oblique side surfaces connecting said rectangular top surface, said rectangular bottom surface, and said trapezoidal principal surfaces, said trapezoidal prism being formed of a first material; and a cover member for covering said trapezoidal principal surfaces and said oblique side surfaces of said trapezoidal prism, said cover member being formed of a second material; said first and second materials being related so as to satisfy n 1 2 −k 1 2 >0, k 1 <0.01, and n 2 2 −k 2 2 <0 where n 1 and n 2 are the refractive indices of said first and second materials, respectively, k 1 and k 2 are the extinction coefficients of said first and second materials, respectively, and n 1 −j·k 1 and n 2 −j·k 2 (j 2 =−1) are the complex indices of refraction of said first and second materials, respectively.