Experimental and theoretical study on the driving force and glass flow by laser-induced metal sphere migration in glass

Light is able to remotely move matter. Among various driving forces, laser-induced metal sphere migration in glass has been reported. The temperature on the laser-illuminated side of the sphere was higher than that on the non-illuminated side. This temperature gradient caused non-uniformity in the interfacial tension between the glass and the melted metal as the tension decreased with increasing temperature. In the present study, we investigated laser-induced metal sphere migration in different glasses using thermal flow calculations, considering the temperature dependence of the material parameters. In addition, the velocity of the glass flow generated by the metal sphere migration was measured and compared with thermal flow calculations. The migration velocity of the stainless steel sphere increased with increasing laser power density; the maximum velocity was 104 μm/s in borosilicate glass and 47 μm/s in silica glass. The sphere was heated to more than 2000 K. The temperature gradient of the interfacial tension between the stainless steel sphere and the glass was calculated to be -2.29 × 10-5 N/m/K for borosilicate glass and -2.06 × 10-5 N/m/K for silica glass. Glass flowed in the region 15-30 μm from the surface of the sphere, and the 80-μm sphere migrated in a narrow softened channel.