Careful Optical-System Design Enables Cutting-Edge High-Power Laser Applications
The increasing demand for high-power lasers (100 W up to kilowatts) in laser materials
processing presents a technical challenge for optical components such as f-theta lenses, beam expanders, and Faraday isolators. As a result, thermally induced beam-degradation effects are playing an increasing role in a variety of high-power laser and related applications.
The most prominent artifact in high-power laser applications is thermal lensing, producing a focus shift. An intense laser beam passing through the optical glasses of an f-theta lens or the magneto-optical crystal in a Faraday isolator can locally heat the optical material. This local heating is largely dependent on the laser power density and absorption of the optical material, and causes thermally induced dispersion of the refractive index. The laser beam profile, absorption, and heat dissipation result in a transverse refractive-index gradient in the optical medium, which generates a significant refractive index difference in the center compared to the edge of the optical material, resulting in an undesired gradient-index (GRIN) lens.
Additional lensing effects that frequently occur for laser crystals, optics, and coating materials include refractive-index changes caused by thermally induced mechanical stress, as well as mechanical stress and thermal expansion leading to bulging of the end faces of the gain medium or of optical parts.
Read the March issue of Laser Focus World to hear from our experts about how proper design and analysis can minimize the negative effects that high-power lasers can have on optical components in materials-processing systems. By using various design tools, combined with a deep knowledge of material properties and continuous control of the materials and processes, a balanced tradeoff between performance requirements for the optical parts and maintenance of the required high-end beam quality can be achieved to ensure optimal results for high-power lasers and applications. View the article online at Laser Focus World.