Fused silica F Theta lenses in ghost free design

18. April 2018

In principle optical designers differ between optical glass and two types of fused quartz glass. On the one hand melted minerals containing silicon oxide are the basic for natural fused quartz. 

On the other hand synthetic fused silica emerges from the oxidation from chemicals containing gaseous silicon (silicon tetrachloride). This fused silica is the mostly favored material for optical applications. Fused silica is ideal for laser applications while optical glasses are better for machine vision tasks. Their consistent transmission for the visual region and a possible color correction makes optical glasses attractive for the use of broad band light sources with wavelengths between 400 nm and 700 nm.

The transmission and absorption factor for specific wavelengths are important values of materials for laser applications. The main advantage of fused silica is the very low absorption for the UV‑region but also for longer wavelengths i.e. IR-region. Therefore this material is optimal for UV, IR lasers and especially for lasers with short pulses and high peak pulse energy. In contrast optical glass would heat too much so that there would be an enormous thermal focus shift and a damage of the anti‑reflection coating and the lens material. Because of the much better temperature stability of fused silica the thermal dilatation is even low at high temperatures. A mainly temperature‑independent working distance with a high importance for the performance results. Because of the multi‑photon absorption caused by internal back reflections and the resulting dielectric breakdown, a ghost free design is most important for the use of ultrashort pulsed lasers. In the worst case this temperature rise can result in damages of the lens material or of the coating. For more information visit the Technicon section on our homepage.

Sill Optics created a new special series of F‑Theta lenses for applications with UKP lasers. Three different types are optimized for wavelengths of 355 nm, 532 nm and 1064 nm. Of course the lenses are ghost free and only with fused silica elements. The focal length (125 mm) is relatively short, which is a quality characteristic for laser material processing. Short focal lengths mean a small spot sizes at the working surface. The product portfolio of Sill Optics consists of much more fused silica F‑Theta lenses for UKP lasers. We also offer custom solutions specially designed to your requirements.