Diamond micro-optics for high-power lasers

Abstract

We have developed a method for fabricating any type of optical surfaces in diamond. The method consists of the following steps: First, a polymer film, spun onto diamond substrates of optical quality, is patterned by lithographic processes. Next, the surface relief is transferred into the underlying diamond by use of inductively coupled plasma dry etching in an oxygen/argon chemistry. Using this technique, we have successfully demonstrated the fabrication of diamond spherical microlenses, blazed gratings, Fresnel lenses, subwavelength gratings and diffractive beam-shaping elements. The spherical microlenses had apertures of 100 µm and f-number of 3.7. The phase error, measured with a Twyman-Green interferometer at 633 nm, was found to be less than 31 nm. The RMS value of the surface roughness over the spherical surface was measured to be 6 nm. The diffraction efficiency for the blazed grating was measured to be 68% at 400 nm, with a theoretical maximum of 71%. The subwavelength grating was designed for reducing surface reflections at a wavelength of 10.6 µm. Photospectrometric results show that the optical transmission was increased from 70%, using a non-structured diamond substrate, to 81%, using our subwavelength structured diamond. The transmission can be further increased by structuring both sides of the substrate. Finally, the beam-shaping element has been tested with a 6kW carbon-dioxide laser, to microstructure pieces of PMMA. The results are excellent, showing diffraction limited spots.We have developed a method for fabricating any type of optical surfaces in diamond. The method consists of the following steps: First, a polymer film, spun onto diamond substrates of optical quality, is patterned by lithographic processes. Next, the surface relief is transferred into the underlying diamond by use of inductively coupled plasma dry etching in an oxygen/argon chemistry. Using this technique, we have successfully demonstrated the fabrication of diamond spherical microlenses, blazed gratings, Fresnel lenses, subwavelength gratings and diffractive beam-shaping elements. The spherical microlenses had apertures of 100 µm and f-number of 3.7. The phase error, measured with a Twyman-Green interferometer at 633 nm, was found to be less than 31 nm. The RMS value of the surface roughness over the spherical surface was measured to be 6 nm. The diffraction efficiency for the blazed grating was measured to...