Glasses for Laser Applications doped with REEs

I was recently perusing several online articles in an effort to respond to a question a colleague asked about rare earth lasers – a query more related to which lasers are used for what applications. I fortunately came across a SCHOTT (one of the world’s glassmaking leaders) PDF from 2013. The two-pager briefly describes their wide range of “active and passive laser glasses for high power, ultra-short pulse, laser range finding and medical applications.” I thought I’d share a few modestly-edited excerpts, as they provide a taste of some of the complexities of chemistry, physics and material science that underlie laser glasses. For example, did you know that:
           

• Glass is a uniquely suitable host material for rare earth ions to provide the laser action in optically pumped lasers. Glass types can be tailored to specific applications, with unique characteristics needed to excel in high energy, high average power or integrated optics uses.

• Platinum-particle-free melting permits high fluence (a stream of particles crossing a unit area, usually expressed as the number of particles per second) operation of phosphate laser glass components without laser-induced damage. Phosphate-based laser glasses generally exhibit high laser cross section, low nonlinear refractive index, and athermal (does not involve either heat or a change in temperature) characteristics that can meet the needs of the high energy solid state laser community.

• Phosphate-based laser glass for high power and ultra-short pulse applications enjoys enhanced thermal mechanical properties desirable in high average power applications. The broad emission bandwidth of this material has been utilized in femtosecond (10-15) regime laser systems.

• ‘Eye-Safe’ laser glasses are an erbium–ytterbium–chromium–cerium doped phosphate-based laser glass used in flashlamp pumped and diode pumped solid-state laser systems. Laser pumping is the act of energy transfer from an external source into the gain medium of a laser. The energy is absorbed in the medium, producing excited states in its atoms. Phosphate glasses generally offer higher solubility of rare earth dopants, thus the amount of active ions can be significantly increased.

• Silicate-based laser glass classically features a high cross section, high ultraviolet transmission and high resistance to solarisation (a reversal of gradation in a photographic image obtained by intense or continued exposure). This glass is commonly employed in high repetition rate solid state laser systems. These glasses have particularly found applications with such rare earth ions as erbium, ytterbium, praseodymium and their combinations.

• Laser cavity materials are used as laser pumping cavity filters. They absorb undesired pumping light in the UV and infrared, preventing solarization of the laser glass. By absorbing the neodymium laser light, these filters reduce amplified spontaneous emission and eliminate parasitic oscillation, thereby increasing lasing efficiencies and powers. These materials can be chemically strengthened to increase their mechanical strength and thermal shock resistance fourfold.

• Samarium-doped glasses block the 1.06 micron wavelength and ultraviolet (UV) pump light from neodymium lasing elements, such as Nd: YAG or Nd:glass rods and slabs. Samarium-doped silicate glasses (with 10% doping recommended for most applications, 5% doping usually reserved for elements thick) and clear, cerium-doped silicate glass also serve as UV cut-off materials.

• ZERODUR® is a glass ceramic for applications calling for a near-zero coefficient of thermal expansion over a fairly wide temperature range. It is a homogeneous material that exhibits practically no measurable variations in its thermal and mechanical properties.

I trust you will share my take that lasers, with their complexities of chemistry, physics, material science and advanced materials, applications and the folks that bring them together certainly warrant our respect!

Until soon… Ian