Terrace formation with a picoliter sol–gel droplet for spherical cavity Raman laser

Abstract

We have successfully made terrace-microspheres for laser emission: micrometer-size spherical cavity laser having terrace-shaped pumping-light entrance. Organic–inorganic hybrid materials in the binary system of 3-methacryloxypropyltrimethoxysilane (MOPS) and tetramethoxysilane (TMOS) were used for preparing the terrace on glass microspheres by sol–gel technique. To make terrace portion, a picoliter sol was supplied with a micro-capillary suppliers into the bottom of spheres and subsequently the terrace-shaped sol was solidified. In the MOPS-TMOS binary system, essential sol properties such as viscosity change and sol–gel transformation rate determine the terrace structures. Compositions and volumes of the sol remarkably influenced viscosity increase and subsequent solidification. In this study, we showed that the control of the terrace structure for spherical cavity Raman lasers was possible by choosing the suitable compositions of picoliter-volume sol droplets. Terrace-microspheres from high-refractive-index glass spheres (nD = 1.93) was pumped with a CW Ar+ laser (514.5 nm wavelength), and stimulated Raman emission was demonstrated above the threshold of 2.5 mW.