Diamond micro-optics: microlenses and antireflection structured surfaces for the infrared spectral region

Fabrication and evaluation of a subwavelength grating in diamond, designed to reduce the Fresnel reflection, is demonstrated. The antireflection (AR) structures are designed to reduce the surface reflection at an illuminating wavelength of 10.6 microm. With this AR-treatment, where no other material is introduced (i.e., no thin film coating), the unique properties of diamond can be fully used. The fabricated AR structures were optically evaluated with a spectrophotometer. The transmission through a diamond substrate with AR structures on both sides was increased from 71% to 97%, with a theoretical value of 99%. Microlenses in diamond are also demonstrated. The lenses are evaluated with interferometers and show good performance. The micro-optical structures were fabricated by electron-beam lithography or photolithographic methods followed by plasma etching.