Continuous-relief diffractive microlenses for laser beam focusing.

Microscale, continuous-profile, diffractive lenses have been fabricated and characterized. Lenses designed to operate at λ0 = 405 nm were created by focused ion beam milling of a glass substrate. The micro-structured profile was analysed by confocal microscopy and optical performance was quantified by measurements of the transmitted laser beam profile. Lenses of size 125 μm × 125 μm, containing up to 18 annuli and focusing at 400 μm, 450 μm and 500 μm have been made. Measured focused beams were in excellent agreement with the predicted performance. A maximum diffraction efficiency of 84 % and side-lobe suppression down to the 10-4 level can be achieved. The suitability of the lenses for interfacing with trappedion systems is outlined.