Alexander J. Marker

Radiation resistant optical glasses

Abstract Hostile environments created by short wavelength elcctromagnetic radiation, for example UV. X-ray and γ-radiation, or from particle fluxes, for example α-particles. s-particles. protons and neutrons, can produce defects within optical glasses. This loss of transmission is detrimental to the performance of the optical system and must eliminated or reduced to a manageable level. For applications within these hostile environments, radiation-stabilized optical glasses have been developed. Radiation test results will be presented, discolouration of stabilized and not stabilized glasses will be compared and colour-centers will be discussed.

Thermal expansion and internal quality of a proposed EUVL mask substrate material: Zerodur

Detailed thermal expansion measurements and internal homogeneity measurements of the glass-ceramic material Zerodur were undertaken to examine its usefulness for EUVL. Repeat measurements on 100-mm long samples from three castings exhibit an expansion of approximately 12 +/- 2 ppb/K 2 (sigma) in the temperature range of interest for EUVL, corresponding to Class C of the draft SEMI 3148 standard. Internal homogeneity measurements reveal extremely small refractive index variations, suggesting comparably small compositional variations. This in turn is viewed as a necessary but not sufficient condition for high CTE uniformity, a factor required by EUVL applications.

Engineering of glass for optimized optical and physical properties

The ability to vary glass properties by adjusting composition continues to make glass a leading material for application as both active and passive elements, in bulk as well as in guided-wave laser systems. We consider here how glass is engineered for specific intracavity and extracavity laser applications. Mention also is made of process and manufacturing techniques which result in glasses with improved or special properties critical for applications involving laser systems.

Elimination Of Metallic Platinum In Phosphate Laser Glasses

Until recently all laser glasses were characterized by a high density of microscopic metallic platinum inclusions which became macroscopic fracture sites when the glass was used in high fluence applications. These inclusions are directly related to the utilization of metallic platinum in the construction of optical glass melters, a practice of critical importance if the resultant glass castings are to be produced with the high homogeneity required for laser applications. Substantial improvements have been made in reducing the number and size distribution of metallic platinum particles in many phosphate laser glasses. This reduction in platinum particle density has been achieved without compromising the physical, optical, or laser properties of these glasses.

Analysis and Diagnosis of Local Defects

The decomposition of raw materials during glass melting yields large quantities of gases [6.1]. Most of these gases, especially water vapour, sulphur dioxide, carbon dioxide, and air, are released into the furnace atmosphere, while a smaller portion either remains dissolved within the glass melt or forms bubbles. But this not the only bubble-forming mechanism.

Low-expansion filter glass ceramics for the suppression of ASE

In large laser systems such as NOVA at Lawrence Livermore National Laboratory the active laser glass is surrounded by a cladding glass. The purpose of this glass is to absorb 1.06 micrometers laser light and prevent parasitic laser action from occurring due to amplified spontaneous emission (ASE). Currently, the cladding glass utilizes the base composition equivalent to the active laser glass with copper doping. The copper produces the required absorption coefficient, approximately 2.8/cm. The cladding glass has a high coefficient of thermal expansion which results in the degradation of the optical properties of the laser disc due to thermally induced strain. To eliminate this problem the concept of a near zero expansion glass-ceramic cladding material was developed.

Radiation-resistant optical glasses

Hostile environments created by short wavelength electromagnetic radiation (UV, X-ray and gamma-radiation) or from particle fluxes (alpha-particles, beta-particles, protons, and neutrons), can produce discoloration within optical glasses. The associated loss in transmission is detrimental to the performance of any optical system and must be eliminated or reduced to a manageable level. For applications within these hostile environments, radiation-stabilized optical glasses have been developed. To optimize system performance, optical glasses which have been stabilized for applications within the particular radiation environment must be selected. If the environment is a mixture of radiation fields, compromises are called for.