Fabrication of microlenses in bulk chalcogenide glasses

Abstract

width is varied from 33 ns to 62 ns while maintaining constant energy per pulse. Without aperturing, the laser beam size before entering the focusing lens is 10 mm. A mechanical aperture is used to shrink the unfocused laser beam size, and values of 7.5 mm to 6.5 mm were chosen. These three beam sizes correspond to a minimum laser focus spot size of 7.46, 9.94, and 11.47 p m respectively. The bump shape is measured by an interferometric optical surface profiler and results are summarized in Fig. 3. It can be seen that at 1.11 pj/pulse with an unapertured 10 mm beam, the laser power is close to the threshold of bump formation and changes in the pulse duration do not greatly affect the bump height. At laser powers that generate bump heights around 22 nm, bump height (BH) and bump depth (BV) increase while the bump size (BD) decreases as a function of laser pulse duration. Aperturing ofthe laser beam changes the beam size, which only affects BD. In other words, beam clipping has the same effect as changing the beam diameter by the use of a beam expander. As the bump size increase to 12 p m by beam clipping, a sharp BV decrease is observed. This is the region where the laser bump shape starts changing from a crater to a Sombrero. Sombrero bump formation has been explained by the interaction of the thermocapillary effect and the chemicapillary effects.' Figure 4 shows the 3-D profile of a crater bump formed by laser texture.