Glass and Light. Hong Li, Mark J. Davis,* and Alexander J. Marker, III. Joseph S. Hayden

Transcription

1 International Journal of Applied Glass Science 1 [1] (2010) DOI: /j x Glass and Light Hong Li, Mark J. Davis,* and Alexander J. Marker, III SCHOTT North America Inc., 400 York Avenue, Duryea, Pennsylvania Joseph S. Hayden Consultant, 107 Fox Run Circle, Clarks Summit, Pennsylvania We discuss glass as an engineered material in its traditional role to control the propagation of and to spectrally modify light in the performance of optical functions. Next, we consider fluorescence, which provides the capability to convert absorbed light of a particular frequency to emitted light of a lower frequency and as a necessary condition for light amplification through spontaneous emission of radiation. Finally, we consider glass in the framework of high-energy particle physics experiments, including its use as a scintillator material and as a Cerenkov radiation detector. Optics and Glass For the last 125 years, optical glasses have been engineered to achieve refractive index values that allow optimization of lens system in optical instruments. The refractive index is the ratio of the velocity of light in vacuum to the velocity of light in the glass. As can be seen in Fig. 1, the refractive index is wavelength dependent. The chemical composition can be varied to achieve not only desired values of the refractive index, but also the shape of the dispersion curve. Historically, optical systems were designed with the eye as the detector. Therefore, the shape of the dispersion curve in the visible region, nm, is of critical importance. *mark.davis@us.schott.com r 2010 The American Ceramic Society and Wiley Periodicals, Inc. Figure 2 gives a pictorial representation of the refractive index and its relation to the shape of the dispersion curve. Optical glass is generally specified by n d, the value of the refractive index at the helium yellow line ( nm) and the Abbe value, n d. The Abbe value is defined by v d ¼ðn d 1Þ=ðn F n C Þ ð1þ where n F is the refractive index at the blue end of the spectral range, n C is the refractive index at the red end of the spectral region and (n F n C ) defines the principal dispersion. There exist hundreds of optical glass compositions that have been developed to achieve specific refractive indices and dispersion curve properties. These compositions reflect the utilization of approximately 60% of the elements in the periodic table. The anion contribution to the composition runs the gamut of

2 64 International Journal of Applied Glass Science Li, et al. Vol. 1, No. 1, 2010 Fig. 1. Dispersion curves for three optical glasses. being all oxygen to very little oxygen and almost totally fluorine. Another critical functionality that glass provides to the manipulation of light utilizes its transmission properties to modify the spectrum of the transmitted light. Figure 3 give the internal transmittance of three optical glasses. The internal transmittance results from correcting the actual transmission of the glass for losses due to reflections at the surfaces. Thus, the internal transmission is independent of the refractive index and the dispersion properties of the glass. The cut-on of transmission at shorter wavelengths is determined by electronic transitions that are dependent on the composition of the glass while the cut-off at longer wavelengths is determined by the vibronic properties of the glass. Optical glasses are engineered to have no absorbing species in the visible spectral range ( nm). Because of the elements used to achieve a high refractive index, the cut-on often extends into the blue end of the visible spectrum. Further, these glasses have slightly yellow tints due to the absorption of blue light, N-SF66 being an example as shown in Fig. 3. Fig. 2. The glass map for optical glasses. 20

3 Glass and Light 65 Fig. 3. Internal transmittance of the three optical glasses appearing in Fig. 1. For certain applications, the transmission properties of glasses can be even further engineered to modify the spectrum of the transmitted light. One such application is cut-on filters. These filters are designed to absorb light up to some specified wavelength ( turn-on wavelength) and transmit the remaining portion of the spectrum. Examples of cut-on filter glasses are given in Fig. 4. The base composition of all the filters in Fig. 4 is the same. These filters undergo a heat-treatment process ( striking ) whereby semiconducting colloids are formed. The time/temperature profiles result in different size colloids that lead to the sharp cut-on at various wavelengths. Some applications require only a relatively small portion of the visible spectrum to be transmitted and that all wavelengths below and above certain values be absorbed. To achieve the desired transmission properties, ionic colorants are utilized. Many of these colorants are redox-state dependent thus the choice of the base glass composition is critically important. Figure 5 displays the transmission characteristics of three of these band-pass colored glass filters. Neutral density filters are ionically colored glass filters with the unique transmission design characteristic that they reduce the intensity of the incoming light uniformly over a relatively wide range of wavelengths. For example, in Fig. 6 the transmission curve is flat in the spectral region from nm. Thus, all wavelengths of light in this spectral band will have their intensity reduced by the same amount. These filters are often used with measurement equipment in cases were the intensity of the incoming light is high enough that it would damage the detector. Figure 7 is the transmission curve for a color enhancement filter. These filters utilize ionic colorants to provide a transmission band for the three primary colors, blue, green, and red, while absorbing as much light as possible in the spectral region outside these bands. These filters are utilized as filters on avionic displays to improve daylight readability. Fig. 4. glasses. Internal Transmittance of selected colloidal colored filter Fig. 5. Internal transmittance of selected ionically colored bandpass filter glasses.

4 66 International Journal of Applied Glass Science Li, et al. Vol. 1, No. 1, 2010 Fig. 6. Internal transmittance of selected neutral density filters. Lasers and Glass LASER is an acronym for light amplification by the stimulated emission of radiation. The first working solid-state laser was reported in 1960 by Maiman. 1 Maiman utilized a crystalline host (Cr:Al 2 O 3 ); but soon after, Snitzer extended the demonstration of laser action to glass systems. 2 Since then, numerous laser glasses have been reported, doped with single or a multiple number of active ions. 3 Whereas at least one active ion is responsible for the laser activity, the others typically act as sensitizers through the absorption of some portion of the excitation energy that drives the laser and the subsequent transfer of this energy to the lasing ion(s). Table I summarizes many reported laser ions in various solid-state materials along with their corresponding emission lines and the commonly used sensitizers. 4 The primary advantages of glass over crystalline hosts for lasing ions is the possibility of engineering material properties through the adjustment of composition and processing parameters and the availability of large pieces of laser glass of the highest optical quality. Despite the availability of other lasing ions, historically Nd:glass has received the widest attention in research and commercial applications because of the following characteristics inherent to the Nd 31 ion: (a) well-understood 4f 3 electron transitions and absorption spectrum from the ultraviolet (B350 nm or B28,570 cm 1 ) to the infrared region (B900 nm or B11,110 cm 1 ) as illustrated in Fig. 8, overlapping well with high-brightness Xe-flashlamp pumping sources; (b) emission wavelength in the vicinity of 1.06 mm that is of interest in laser inertial confinement experiments and capable of large energy storage owing to a combination of favorable energy-level dynamics; and (c) the stimulated emission cross section for the Nd 31 laser transition is in the intermediate regime, large enough to provide a gain in reasonable-sized am- Fig. 7. Transmission of a color enhancement glass filter.

5 Glass and Light 67 Table I. Active ion Laser Wavelengths from Selected Active Ion Systems 4 Approximate emission wavelength (lm) Sensitizing ion (s) Nd , 1.06, 1.35 Cr 31, Mn 21, Ce 31, Eu 31,Tb 31,U 31,Bi 31 Gd Er , 1.54, 1.72, 2.75 Cr 31, Yb 31, Nd 31 Yb Nd 31, Cr 31 Dy (Er 31 ) Sm (Tb 31 ) Ho , 1.38, 2.05 (Cr 31 ), Er 31, Yb 31, (Tm 31 ) Tm , 1.47, 1.95, 2.25 (Cr 31 ), Er 31, Yb 31 Tb Ce 31, (Gd 31 ), Cu 1 Pr , 1.04, 1.34 Sensitizers in parentheses are reported for crystalline host materials and the rest for glass host materials. plifiers, but not so large as to create problems of amplified spontaneous emission (ASE), a common problem to most lasers. 5 Commercial laser glass development over the last 30 years is summarized in Fig. 9. This figure follows the transition from the initial silicate-based host glasses, popular up to the early 1980s, to phosphate-based host glasses, and by around 1986 the subsequent availability of these glasses in a form completely free of platinum inclusions, which allowed laser fluence levels to be increased by roughly a factor of 10 without observation of damage to the laser glass components. 6 Also demonstrated in Fig. 9 is the development of manufacturing capability over the same time period. Along with the shift in host glass type and the development of platinum particle-free glass, has been a steady increase in the size of available laser glass components, culminating with the development of continuous melting technology capable of producing thousands of meter-class amplifier slabs per year in support of programs such as the National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in the United States. 7 The simplest solid-state laser device is an oscillator consisting of a gain material between two mirrors, at least one of which is only partially reflecting. The initial conditions of a laser oscillation are given by R 1 R 2 exp½ðbn aþ=2lš ¼1 ð2þ where L is the length of laser rod, R 1 and R 2 are the reflectance of the mirrors, b is the gain coefficient, and a is the loss from reflection, absorption, and scattering. The lasing ions within the active solid-state material are optically pumped from its ground state to the excited state N 3, as shown in Fig. 10. For optical pumping, a minimum of three levels is required as marked by N 1, N 2, and N 3, for which the emission results from a radiative decay of the excited ions N 2 in the metastable state to the ground state N 1. On the other hand, in a Fig. 8. Nd Spectra in aluminoborosilicate glass with various Nd 2 O 3 contents and transition band assignments.

6 68 International Journal of Applied Glass Science Li, et al. Vol. 1, No. 1, 2010 Fig. 9. The evolution of laser glass over roughly 40 years from the first silicate glass of Snitzer to the meter-class slabs produced for inertial confinement fusion research at the Lawrence Livermore National Laboratory. four-level laser, the emission results from radiative decay from the excited ions N 2 to a lower state N 1 above the ground state N 0. The gain coefficient b is defined by DNs em, where DN 5 N 2 N 1 40 and s em is the emission cross section of the gain media. It implies that the gain for light intensity is provided by the induced emission of lasing ions from an upper energy state to some lower energy state. In a laser glass design, one of the critical parameters is emission cross section. The local chemical environments of the host glass surrounding the lasing ions affect the emission cross section, and hence the glass laser performance. The lasing ion local chemistry in glass is not uniquely defined because the host network is amorphous, that is, the lack of a long-range order. Despite the complexity and difficulty in actually identifying the lasing ion local structures, Judd Ofelt (J O) theory 8,9 has been widely applied to qualitatively describe relative environmental changes of the lasing ions in glass as a function of host glass composition, concentration of lasing ions, and host glass systems. Directly affecting the emission cross section of the laser glass is its line intensity, which is a linear function of the J O parameters (O 2, O 4, O 6 ). Specifically, by changing the glass composition, either the lasing ion concentration or the host glass composition or both, the J O parameters vary, for which O 2 is primarily associated with ligand-field asymmetry, O 4 is affected by the network over a longer range, and O 6 is related to the bond covalency of the lasing ion with the surrounding anions. Examples are given in Fig. 11, illustrating the effects of composition change (varying Al 2 O 3 content) in silicate glass on the J O parameters for Er 31 ions, 10 and the effect of varying Nd 2 O 3 content on O 2 of Nd 31 ions in alumino borosilicate glasses, with and without Na 2 O. 11 The effect of overall host matrix effect, in terms of ionic packing ratio, has also been studied for silicate, borate, and phosphate glasses. 12 Development of the laser glass focuses on both laser and thermomechanical properties. 13 An index or figure of merit (FOM) that describes a laser glass overall laser performance has been defined by FOM laser ¼ðDl abs =Dl em Þðt o Qs em =n 2 Þ Fig. 10. Energy level diagrams for three- and four-level lasers. ðrc p =aþ 1=4 ð3þ

7 Glass and Light 69 Fig. 11. Lasing ion local environment change in glasses: (a) O 2, O 4, O 6 as a function of Al 2 O 3 in silicate glasses 10 and (b) O 2 in aluminoborosilicate glasses with and without Na 2 O as a function of Nd 2 O 3 concentrations, in which 1/3 represents the saturation limit of Nd 2 O 3 in the borate-rich environment based on rare earth metaborate local structural model. 11 where Dl abs /Dl em is the ratio of composite bandwidths between the absorption bands and the emission bands, t o is the excited state lifetime at the zero-doping-concentration limit, Q is the quenching effect on the lifetime, n 2 is the nonlinear refractive index, r is the glass density, C p is the glass specific heat, and a is the coefficient of thermal expansion coefficient. For a quick evaluation of a glass laser performance, a simplified version FOM laser can be also used in the form of (t o Qs em /n 2 ). Another index that describes a laser glass overall thermomechanical performance is defined as FOM TM ¼ K IC kð1 uþ=ae ð4þ where K IC is the glass fracture toughness, k is the glass thermal conductivity, u is the Poisson s ratio, and E is the glass Young s modulus. Similarly with FOM laser, various simplified versions are possible, with the most dominant term in driving the FOM TM as found, for example, with phosphate glasses, to be simply (1/a). As described previously, through the adjustment of glass composition, it is possible to identify different glass compositions that are optimized for specific applications. Table II compares four commercial high-power laser glasses. The APG-glasses have high values for FOM TM, thus are optimized for applications involving high repetition rate where thermal loading and ultimately glass fracture limit the performance window. On the other hand, the LG-glasses place more emphasis on FOM laser, and are more suitable for high peak energy applications such as those required for the NIF. Overall, LG-770 has the best laser performance and APG-2 the best thermo-mechanical performance based on their FOM laser and FOM TM (expressed here relative to LG-750), respectively. To ensure glass processibility and achieving a final glass product with a high optical quality that is free of Pt inclusions, the development process can also use a third index, FOM prod, as one of the screening tools for candidate glass composition selection, defined by kð1 uþ 2 1 FOM prod ¼ K IC F Pt F dur F Dvit ae T g ð5þ

8 70 International Journal of Applied Glass Science Li, et al. Vol. 1, No. 1, 2010 Table II. Comparisons of Glass Properties among SCHOTT High-Power Laser Glasses Laser property LG-750 LG-770 APG-1 APG-2 Emission peak l (nm) Emission width Dl em (nm) Radiative lifetime t rad (ms) Emission cross-section s em (10 20 cm 2 ) Zero concentration lifetime t o (ms) Quenching constant Q (10 20 cm 3 ) Nonlinear refractive index at 1054 nm, n 2 (10 13 esu) FOM laser /FOM laser (LG 750) Thermo-mechanical properties Density r (gm/cm 3 ) Thermal conductivity (901C) k 901C (W/mK) Young s modulus E (GPa) Poisson s ratio u Fracture toughness, K IC (MPa m 1/2 ) Heat capacity (251C), Cp 251C (J/gm 1C) Thermal expansion coefficient a C (10 7 1C 1 ) Glass transition temperature, T g (1C) FOM TM /FORM TH(LG 750) t o and Q are used to describe the fluorescence lifetime, t, as a function of neodymium content in the glass by t o /(11(N d /Q) 2 ), where N d is the N d concentration in units of ions/cm 3. FOM, figure of merit. where T g is the glass transition temperature, F Pt is a factor related to the Pt solubility limit in the glass melt, F dur is a factor measuring glass chemical durability, and F Dvit is a factor measuring the tendency of glass crystallization during slow cooling. For candidate glass composition screening, it is convenient to set F dur and F Dvit being 0 for poor chemical durability and the high tendency of crystallization or 1 for good chemical durability and high resistance to crystallization. In the future, there will be a continual push for active glasses that allow operation at ever-higher repetition rates but that still offer reasonably good laser performance. This requires identifying glasses that, for example, offer the thermomechanical properties of a glass like APG-2 with the laser properties of a glass like LG-770. Glass for High-Energy Particle Physics The use of glass in high-energy particle physics dates back many decades now, taking the form of both detector and shielding in a wide variety of applications. This section specifically reviews the use of glass for electron photon calorimeters as well as Cerenkov radiation detectors. Both applications rely on several key factors inherent to glass, as noted above, the ability to produce large pieces with high homogeneity at a reasonable cost. Moreover, the relatively high transparency of glass and the ability to tune properties through an engineering approach to glass chemistry prove decisive in many applications. As suggested by Rabin, 14 a useful calorimeter for high-energy physics experiments must combine the ability of the overall detector system to ensure that all or nearly all energy of the impinging particle is lost to the system, plus the crucial factor that the loss process must be quantifiable with high fidelity. Given the wide range of particle types and energies, a vast array of detector technologies have arisen over the years. Additionally, a wide array of materials have been evaluated for these technologies, including glass, crystals, polymers, noble gases, and ionic liquids. As pointed out by Griscom 15 many years ago, there is a richness of phenomena inherent to the interaction of high-energy radiation with matter in general, and glass is no exception. Figure 12 presents a flow diagram of

9 Glass and Light 71 Fig. 12. Schematic flow diagram of radiation damage processes in glasses (Griscom 15 ). such processes, some of which are directly exploited in detection schemes, including the formation of electronhole pairs, recombination, and light emission. The latter is often enhanced through the use of a dopant with cerium being the common choice, owing in part to its short decay time (10 s of nanoseconds), thereby allowing for accurate timing measurements of particle medium interaction. Generally, at very low photon energies ( ev), coherent Rayleigh scattering and the photoelectric effect predominate. At low energies ( MeV), Compton scattering is dominant, while finally at high energies (410 MeV level), pair production is dominant. 14 The charged particles thus formed via these processes in turn lose their energies through a downward cascade of lower energy processes until the initial particle energy (E o ) is completely absorbed by the material, provided the material is sufficiently thick. One may also define a critical energy (E crit ), at which there is a significant transition in the absorption cross sections for these processes, from lowto high-energy portions of the spectrum. E crit is typically of the order of 10 MeV for solids and liquids considered for high-energy particle detection. 14 As the average energy of the shower particles becomes lower than E crit, further particle multiplication ceases. Although there are many key parameters required for a quantitative evaluation of properties for highenergy particle detection, the following are critical. The radiation length, X o, provides a measure of the material thickness necessary for an energetic electron to lose 1/e ( %) of its original energy, and can be roughly estimated via: X o ðg=cm 2 Þ¼180ðA=Z 2 Þ ð6þ where A and Z are the atomic weight and number of the element. Multicomponent compositions, such as glasses, require average values to be used in this equation, weighted by the atomic number. 14 X o is typically B1 cm for most solid-state materials (e.g., X o cm for elemental Pb and is 1.70 cm for SF6, a high-lead glass), and in scintillator glass is largely set by the BaO content. 16 The maximum number of particles (N max ) produced via a complex cascade process at a given depth in the absorbing material can be estimated from: N max ¼ E o =E crit ð7þ The depth (t max ) at which this maximum number of particles is attained is estimated as: t max ¼ lnðe o =E crit Þ= ln 2 ð8þ

10 72 International Journal of Applied Glass Science Li, et al. Vol. 1, No. 1, 2010 where t max is given in terms of radiation length (X o ). As an example, a 1 GeV particle would be expected to produce about 100 lower energy particles at a depth of 6.6 radiation lengths during the energy cascade event. At greater depths, the number of particles produced begins to decrease. 14 Finally, the expected transverse energy distribution (R m ), or the lateral spatial spread in the particle cascade event, can be estimated via: R m ¼ X o ðe s =E crit Þ ð9þ where E s ( 5 21 MeV) is a constant in the theory of multiple Coulomb scattering. 14 A common value for R m is B3 cm for solids like crystals and glass. Additional criteria for high-energy particle physics relate to the specific mechanism by which the event is recorded. For glass scintillators, one monitors the number and energy of photons per unit energy imparted to the detector. Highly efficient crystalline scintillating materials, such as CsI, create over 10 4 photons/mev for the incoming high-energy particle (thus one speaks of a light yield of 10 4 photons/mev). Cerium-doped, high-pb glasses typically have lower light yields (B100 photons/mev). However, as we note below, other important attributes associated with scintillator selection often mitigate the lower light yield for glasses. Table III presents a brief summary of some of the more important properties of representative materials. Radiation detectors based on the Cerenkov effect invariably use lead glass as the detector of choice, owing to its ability to absorb high-energy particles, high uniformity, high transmission, and the ability to produce meter-class pieces. The Cerenkov effect itself is the photonic analog to an acoustic shock wave: when a highenergy particle encounters a material at a velocity higher than the inherent photonic phase velocity of the material, Cerenkov radiation is emitted as an electromagnetic shock wave. 17 The angle (y) with which emitted photons make with respect to the initial, high-energy particle trajectory is given by: cos y ¼ 1=bn ð10þ where b is the ratio of the initial particle velocity to that of the speed of light in a vacuum and n is the refractive index of the medium. Cerenkov radiation is continuous in its spectral output, with shorter wavelengths typically being of higher intensity in the visible part of the spectrum. The probability that a material will absorb a given high-energy particle saturates at a value equal to (1 1/n 2 ). For a typical lead glass (SF5), this equates to a maximum probability of 65% that a Cerenkov photon is emitted, provided the particle has an energy exceeding 2 MeV. Below this energy threshold, the probability of Cerenkov radiation drops rapidly. 14 Whereas Ce is used as an active agent in the detection process for scintillators, Cerenkov radiation glasses do not require any active additives, although Ce may be added to enhance radiation damage resistance. However, there is a loss in transmission in the blue region of the spectrum, precisely where the Cerenkov radiation has the highest intensity in the visible part of the spectrum. Once the material emits Cerenkov photons, the transparency of the absorber becomes of paramount importance for a practical detection scheme. In some cases, there is a satisfactory tradeoff between the absorbing power and the transparency. In one study, the glass Table III. Property Summary of Scintillating Material Properties for High-Energy Particle Physics Experiments Crystals Polymer Glass Density Units (gm/cm 3 ) CsI (Tl) BGO BaF 2 NE110 (PVT) HED1 SF6 Radiation length cm R m cm E crit MeV Light yield Photons/MeV 50,000 B10,000 B4,000 10, Luminescence decay time Nanoseconds Radiation damage Poor Good Excellent Poor Excellent Uniformity Fairly good Excellent Sources: Rabin 19 and Loehr et al. 16

11 Glass and Light 73 F2 was chosen over SF5, owing to the higher transmission in the former, even though SF5 has a shorter radiation length. 18 Higher transmission equates to superior photon count yields. Furthermore, glass was chosen over various crystals and scintillating fibers in this same study on the basis of cost, handling, and ease of manufacturing concerns. 18 Block-to-block uniformity in terms of energy discrimination was checked over about 40 blocks ranging in volume from 1 to 15 L in volume each and was determined to be excellent. Conclusions We have presented a selected set of applications to demonstrate that by varying the chemical composition and processing, glass can be engineered to meet very divergent sets of properties. Acknowledgment Some of the results described here were performed under the auspices of the U.S. Department of Energy/ Lawrence Livermore National Laboratory (LLNL) under contract No. W-7405-Eng-48. References 1. T. H. Maiman, Stimulated Optical Radiation in Ruby, Nature, 187, (1960). 2. E. Snitzer, Optical Maser Action of Nd 13 in a Barium Crown Glass, Phys. Rev. Lett., 7, (1961). 3. E. Snitzer, Glass Lasers: Part 1, Glass Industry, 1, (1967). 4. M. J. Weber, CRC Handbook of Laser Science and Technology. Vol. 1: Lasers and Masers. CRC Press, Boca Raton, D. C. Brown, High Peak Power Nd:Glass Laser Systems. Springer-Verlag, Berlin, J. H. Campbell, et al. Elimination of Platinum Inclusions in Phosphate Laser Glasses UCRL Lawrence Livermore National Laboratory, Livermore, CA, J. H. Campbell et al., Continuous Melting of Phosphate Laser Glasses, J. Non-Cryst. Solid, 263, (1999). 8. B. R. Judd, Optical Absorption Intensities of Rare Earth Ions, Phys. Rev., 127, (1962). 9. G. S. Ofelt, Intensities of Crystal Spectra of Rare-Earth Ions, J. Chem. Phys., 37, (1962). 10. S. Tanabe, Optical Transitions of Rare Earth Ions for Amplifiers: How the Local Structure Works in Glass, J. Non-Cryst. Solid, 259, 1 9 (1998). 11. H. Li, L. Y. Li, and D. M. Strachan, Structural Aspects of Judd-Ofelt Oscillator Strength Parameters: Relationship between Nd Dissolution and its Local Environments in Borosilicate Glasses, Phys. Chem. Glass., 46, (2004). 12. Y. Nageno, H. Takebe, and K. Morinaga, Correlation between Radiative Transition-Probabilities of Nd 31 and Composition in Silicate, Borate, and Phosphate Glasses, J. Am. Ceram. Soc., 76, (1993). 13. J. S. Hayden, J. H. Campbell, and S. A. Payne, Development of a Laser glass for the National Ignition Facility, Conference on Window and Dome Technologies and Materials X, Orlando, FL, Proceedings of the Society of Photo- Optical Instrumentation Engineers (SPIE), Vol. 6545, ed. R. W. Tustison. SPIE, Bellingham, WA, , N. V. Rabin, Electron-Photon Calorimeters Main Properties (Review), Instrum. Experim. Tech., 35, 1 42 (1992). 15. D. L. Griscom, Nature of Defects and Defect Generation in Optical Glasses, Radiation Effects in Optical Materials, Vol. 541, ed., P. W. Levy. SPIE, Albuquerque, 38 59, S. R. Loehr, P. Nass, and B. Speit, Glasses for High Energy Particle Detectors, The Properties of Optical Glass, eds., H. Bach, and N. Neuroth. Springer-Verlag, Berlin, , D. Grischkowsky, Ultrafast THz Photonics and Applications, Springer Handbook of Laser and Optics, eds., F. Trager. Springer, New York, , L. Bartoszek et al., The E760 Lead-Glass Central Calorimeter - Design and Intial Test-Results, Nucl. Instrum. Methods Phys. Res. Sec. A-Accelerators Spectrometers Detectors Assoc. Equipment, 301, (1991). 19. N. V. Rabin, Electron-Photon Calorimeters Properties of Detector Materials for Calorimeters (Review), Instrum. Experim. Tech., 35, (1992). 20. SCHOTT North America Inc., Abbe Diagram, Version 1.8 (2009). Available at website (accessed January 18, 2010).