High performance ErYb:Glass for eye-safe lasers

Abstract

ABSTRACT Phosphate glasses are known to produce high gain for the Er 3+ emission into 1540nm , especially when sensitized with Yb. Unfortunately, the phosphate glass matrix tends to be weaker than other available amorphous materials. Unlike crystalline materials, glass chemical structure around the active ion can be optimized for both mat erial strength and laser output. Reported here is the result from a design of experiment that was completed in order to strengthen the glass structure of a commercially available phosphate laser glass without impacting its laser output efficiencies . Laser output per formance results for the glass that met the targeted thermal and mechanical limits are presented. This effort concludes with a scalable material that is ultimately released to the commercial market. Keywords: Eye -safe, laser g lass, phosphate laser glasses, erbium laser spectroscopy, erbium laser gain 1. INTRODUCTION Retina -safe operation in open -air is of high interest to the next generation of lasers that are being utilized for many industrial, defense and medical applications. Those wavelength s that are considered to be the best for retina safe operations (also called eye -safe ) fall in the range between 1400nm and1800nm . For laser s in medicine, the targeted wavelength regimes coincide with the absorption features of hemoglobin, melanin, and hydroxyl groups in the tissues [1] . Wavelengths ab ove 1400nm are easily absorbed by tissues, making it possible for rapid thermal heating below the skin which is useful for aesthetic and surgical lasers. The trivalent Er ion can produce direct emission into the 1540 nm wavelength, thus, it is the rare -ear th emitter of choice for many eye -safe applications. In recent years, the need for high beam quality under passive operation in open air applications have renewed interest in Er -doped bulk glasses as the gain material o f choice for solid -state eye -safe las ers . The increasing need for higher energy outputs and improved repetition rates is the motivation for seeking a new material in the phosphate glass space. Thus, a study was initiated in order to strengthen a commercially available laser glass (SCHOTT LG940) by adding modifiers that increase the short -range order in the starting phosphate glass structure . However, it is well known that the addition of the elements that drive the glass stability will decrease the laser gain obtained . It is also known that Er