Laser glass marking - influence of pulse characteristics

Laser glass marking is currently used in several glass materials for different purposes, such as bar codes for product tracking, brand logos or just decoration. Systems with a variety of different laser sources, with inherent power ranges, wavelengths and pulse regimes have been used, namely CO(2), Nd:YAG, Excimer, Ti-Sapphire lasers. CO(2) Lasers systems, although being a reliable tool for materials processing, and very compact in the case of sealed low power lasers, are usually associated with a localized thermal loading on the material, causing brittle materials like glass to crack around the irradiated area. In this experimental study a pulsed CO(2) laser was used to direct marking the glass surface. The temporal characteristics of the laser pulse - pulse length, period and duty cycle were varied, and glass materials with different thermal properties were used in order to correlate the marking process - cracking or softening with or without material removal with the laser and material characteristics. Glass materials with major industrial application, such as soda-lima, borosilicate (PYREX (R)) glasses and crystal have been investigated. Laser marked areas have been characterized in terms of surface optical properties, like diffuse and direct reflectance and transmittance for white light, directly related with marked surface quality.