SCHOTT solutions no. 2/2014 > Laser glass

Laser glass is becoming increasingly important for use as both a gain medium for the resonator and as an amplifier for ultra-high-performance applications. SCHOTT offers a wide range of laser glasses for many different applications. Photo: SCHOTT/J. Stevens

A material with a great future

SCHOTT ranks among the world’s leading suppliers of laser glass for use in industry, at universities and public institutions. Close collaboration with customers and intensive research and development will continue to open up promising prospects for laser glass as a medium in the future.

Dr. Gregory Flinn

The realization that certain combinations of glass and rare earth dopants such as neodymium, erbium, and ytterbium also make exceptionally good laser gain media was made in the early 1960s by Elias Snitzer, the scientist and pioneer in the area of laser glass research at the American Optical Company, shortly after the advent of the laser. The principal reasons for this are the broad spectral absorption/emission profiles of dopants in glass that allow for efficient pumping using broadband discharge lamps. The high dopant solubility and large emission cross sections also mean that pulsed laser action is relatively easy to achieve, and that the variable chemical makeup of glass allows adaptation of the spectral and physical properties to best suit the application. ”These factors have all helped nurture a steadily growing interest in laser glass, both as a gain medium for the resonator itself, and as an amplifier in ultra-high peak power applications,” says laser glass expert Dr. Simi George from SCHOTT Research & Development (R & D) in North America.
Photo: SCHOTT/J. Stevens

Many years of expertise

Drawing on over 40 years of R&D, SCHOTT’s expertise in the field of laser glass is now unmatched. Neodymium-doped glasses, as used for laser amplifier systems, have been the dominant product in the laser glass portfolio of the Business Unit SCHOTT Advanced Optics. Today, there are three principal types of phosphate-based laser glasses available suitable for high energy, high-power and ultrashort pulse applications. More recent developments include ’eye-safe’ laser glasses for medical technology, celestial/terrestrial range finding and medical/cosmetic applications at a wavelength around 1.5 µm. Further to these mainstream laser glass categories, SCHOTT also offers a silicate-based laser glass for high-repetition rate, solid-state laser applications, and both phosphate and silicate-based glass types optimized for fabrication of active guiding structures in integrated optics applications.
Zeige Details

Otto Schott Research Award for laser glass pioneers

Lawrence Livermore National Laboratory, Planung von Petawatt-Lasern
As a partner on developing laser glass components, SCHOTT Advanced Optiocs is involved in large projects such as those that Lawrence Livermore National Laboratory (on the left) is working on or in planning petawatt lasers at the European level (on the right). Photo on the left: SCHOTT/National Energetics, Photo on the right: SCHOTT/ LNLL | National Energetics
In addition to production in Mainz, Germany, SCHOTT Advanced Optics manufactures the majority of its laser glasses in Duryea, Pennsylvania. The Research  & Development center for these  products is also based there. Distinguished glass experts, such as Dr. Joseph S. Hayden, who has made a significant contribution to SCHOTT’s leading market position, also research glass and its properties in Duryea. Hayden, an internationally renowned laser glass expert, joined SCHOTT in 1985, where his work on compositional modifications and the identification of special post-processing treatments was crucial in expanding the operational window for laser glasses.

But SCHOTT’s success in the field has also been influenced by other factors, as Hayden himself acknowledges. Now a Research Fellow in Duryea, he was in July 2014 honored with the Stookey Award of the American Ceramic Society (ACerS) for lifetime contributions in the field of glass and glass-ceramics. In his Lecture of Discovery presentation, Hayden paid tribute ”to the many scientists, engineers and technicians involved in these collaborations who have individually or collectively contributed to the progress in the field.” Of particular note was the frequent technical and financial support of John H. Campbell and other researchers at Lawrence Livermore National Laboratory (LLNL).

Laser glass expert Dr. Simi George: ”We can thank the many international ventures on large-scale laser projects around the world for providing the necessary drive to further develop laser glass materials.” In most of them, SCHOTT is involved as a partner and has developed the required laser glass components, e. g. at the LLNL and the French Commissariat à l'Énergie Atomique (CEA). ”SCHOTT is also actively involved in the planning of projects exceeding the PW (petawatt) level,” continues George, ”but here we are not simply faced with the challenge of just ’bigger and better’ glass. Instead the laser glass needs to provide sufficient gain width for the incredibly short pulses – we are going to be cooking up new glasses!”
Labor SCHOTT Standort Duryea, USA
Look into the measurement lab: the SCHOTT site in Duryea, Pennsylvania, serves as the center for developing laser glasses and their manufacturing capabilities. Photo: SCHOTT/ J. Stevens
Subsequently, a consortium led by National Energetics, Inc., in partnership with Ekspla UAB, has been awarded a contract valued in excess of $40 million to develop and install an ultra-intense laser system for the European Union’s Extreme Light Infrastructure (ELI) facility near Prague in the Czech Republic. The laser system will yield pulse energies in excess of 1.5 kJ and pulse widths of approximately 150 fs delivered at a repetition rate of one shot per minute. SCHOTT will supply laser glass for use in the large aperture laser amplifiers. The development of new laser glasses has previously taken a time consuming, reiterative ‘melt and test’ approach. Thankfully, new predictive tools exist that drastically accelerate the identification of suitable glass compositions.

First, the influence of varying glass composition on laser properties has been studied so systematically that optimized glass properties for any new laser design can now be determined quickly. Secondly, by rendering the lasing and thermomechanical material parameters together in a ’Figure of Merit’ approach, the suitability of a new or existing laser glass to any one application can be better assessed. Finally, statistical tools can be used to map out the corresponding compositional space with a minimum of experimental trials. Taken together with advances in production processes, laser glasses can now be realized that would otherwise have been too costly to develop in the required volumes.
Grosser Lasereffekt

Greater laser effect

Prospects for laser glass

Currently, and aside from the large-scale projects, much of the developmental input comes from the defense and cosmetic/medical technology markets. The penetration of laser technology into these and other new applications, the demand for new wavelengths in practical and reliable laser formats, trends such as weight reduction and transportability as well as a desire for more simplified systems, all have a direct influence on the performance and size requirements of the gain media. Critically, in developing a new laser glass, it is not important to exactly reproduce the favorable optical and material parameters found in, for example, alternative gain media. Instead, it is only necessary to achieve an appropriate performance envelope using the tools described above. Using this type of approach it is now possible to realize gain media that, for example, permit the high repetition rates common to many of the (crystal-based) picosecond and femtosecond ultrashort pulse laser systems that are currently rapidly gaining recognition for industrial processing applications. Acutely, as the pulse lengths in ultrashort pulse laser systems are reduced, there is also a need to avoid an issue called gain narrowing, i.e. that the available emission profile does not provide for adequate gain across the entire spectrum of an ultrashort pulse. SCHOTT is currently pursuing options to realize this in a single gain medium. Dr. William James, Supervisor Materials Development SCHOTT R&D in North America: ”Glass is probably the only material that provides the necessary flexibility to achieve this – that is, to be able to vary the composition, physical format, and manufacturing processes in order to reach the desired goal.” <