Thermal lensing measurement of a thermal lens compensation high power laser objective

An effort was under taken to mitigate thermal lensing and have an easy and compact means of monitoring thermal lensing in a high power laser system. Utilizing the negative temperature coefficient of refractive index in CaF2 with the nearly opposing positive temperature coefficient of refractive index in SiO2, a multi-element focusing objective was fabricated to reduce the amount of thermal lensing experienced with a multi-kilowatt, cw fiber laser. In addition, an all-passive optical design beam analyzer was developed to accurately measure the focus shift of an all SiO2 lens objective in contrast to the CaF2/SiO2 multi-element lens to compare their perspective thermal lensing values.