Abstract:
In a high energy laser system utilizing phosphate laser glass components tomplify the laser beam, the laser system requires a generated laser beam having an emission bandwidth of less than 26 nm and the laser glass components consist essentially of (on an oxide composition basis): 
     
       ______________________________________ 
     
           Mole %______________________________________  P 2  O 5         50-75  Al 2  O 3         &gt;0-10  K 2  O        &gt;0-30  MgO   0-30  CaO   0-30  Li 2  O        0-20  Na 2  O        0-20  Rb 2  O        0-20  Cs 2  O        0-20  BeO   0-20  SrO   0-20  BaO   0-20  ZnO   0-20  PbO   0-20  B 2  O 3         0-10  Y 2  O 3         0-10  La 2  O 3         0-8  Ln 2  O 3         0.01-8______________________________________ 
     wherein 
     the sum of MgO and CaO is &gt;0-30; 
     the sum of Li 2  O, Na 2  O, Rb 2  O, and Cs 2  O is 0-20; 
     the sum of BeO, SrO, BaO, ZnO, and PbO is 0-20; 
     the sum of B 2  O 3  and Y 2  O 3  is 0-10; and 
     Ln 2  O 3  represents the sum of the oxides of active lasing lanthanides of atomic number 58-71.

Description:
Government Rights 
     The United States government has rights in this invention pursuant to Contract No. W-7405-ENG-48. 
    
    
     SUMMARY OF THE INVENTION 
     This invention relates to a high energy laser system and a method of generating a laser beam using phosphate laser glasses, typically neodymium-doped, which possess an advantageous combination of property qualities desirable from both laser application and manufacturability points of view. The invention also relates to phosphate laser glasses suitable for use in high energy laser systems. 
     The term &#34;laser&#34; refers to the amplification of light by the stimulated emission of radiation. In a laser, an active material, for example, a glass suitably doped with an active atomic species such as neodymium, is placed in a cavity resonator formed by two reflecting, or at least partially reflecting, mirrors. 
     The glasses utilized in the invention offer a combination of properties which are desirable for application in high energy lasers such as high cross section for stimulated emission, low concentration quenching of the excited state lifetime, low nonlinear refractive index, small emission bandwidth, high heat capacity, and low coefficient of thermal expansion. The latter two properties are particularly desirable for applying glasses of this invention as a cladding material. 
     In accordance, with the invention, solid state lasers used for the generation of high levels of total energy per pulse require that the active material possess a maximum value of the following laser figure-of-merit, FOM laser , expressed by ##EQU1## where α is the thermal expansion; 
     ρ is the glass density; 
     C p  is the glass heat capacity; 
     σ is the cross section for stimulated emission; 
     Q is a measure of lifetime concentration quenching of the excited state; 
     n 2  is the nonlinear refractive index; 
     Δλ abs  is the average absorption bandwidth; and 
     Δλ em  is the emission bandwidth. 
     It should be noted that this laser figure-of-merit has been developed in accordance with the invention to provide guidance in selecting glasses for use in high energy laser systems. It is not intended to provide an exact and precise assessment of each glass. Still, the importance of this laser figure-of-merit can be seen from the following discussion. 
     Laser glasses for application in high energy laser systems preferably have a higher level of cross section for stimulated emission compared to current state-of-the-art laser glasses. Although a large cross section implies a high extraction of stored energy as amplified laser light, a low cross section is known to imply better energy storage ability. The optimum cross section for any particular laser system design thus varies; however, current state-of-the-art high energy laser system designs call for a cross section greater than 3.5×10 -20  cm 2 . This is considered to be a high cross section in comparison to the range of cross sections typically observed in phosphate laser glasses. 
     The cross section for stimulated emission, σ, is a particularly important parameter in large fusion laser systems based on Nd-doped glass since larger cross sections are associated with higher extraction efficiencies which are expected to lead to lower overall system costs. 
     It is desirable in high energy laser systems that the active material have a high value for the concentration quenching factor, Q, which describes the well-known phenomena of nonradiative depletion of the excited laser state by adjacent neodymium ions in the active glass. Using the concentration quenching factor, the emission lifetime quenching curve can be described by: ##EQU2## where τ 0  is the lifetime for a sample containing nearly no neodymium, N is the neodymium doping level in the glass, and Q is a numerical factor expressed in cm -3  which best fits experimental data collected on a number of samples of different neodymium concentration. See, e.g., &#34;Spectroscopic Properties of Nd +3  Dopant Ions in Phosphate Laser Glasses,&#34; Payne et al., Lawrence Livermore National Laboratory, UCRL-JC-105473, May 1991. 
     The value of nonlinear refractive index, n 2 , is preferably low since this factor is directly correlated to internal damage of optical components including laser glass by the self focusing of a propagating laser beam. It arises from the change in the refractive index of the glass induced at high intensity, e.g., 
     
         n=n.sub.o +n.sub.2 φ 
    
     where n is the refractive index, n o  is the refractive index in the absence of a propagating laser beam and φ is an indication of the intensity of the propagating laser beam. Additionally, low nonlinearity in the refractive index dependent on laser intensity implies reduced distortion of beam quality as the beam propagates through laser glass components being used to amplify the laser beam. 
     In state-of-the-art high energy laser system designs, a variant of the glass composition employed as the active laser medium but doped with an ion or ions which absorb strongly in the region of laser activity, e.g., Cu, is attached with adhesives to the edges of slabs or discs fabricated from the active laser glass. During and after excitation of the laser glass there is considerable heating of this bordering or cladding material relative to the active laser material it surrounds. This uneven heating leads to optical distortion of the complete laser glass/cladding glass element due to the uneven heating and expansion of the two glasses. Maximizing the quantity of ##EQU3## minimizes the amount of optical distortion which results for a given temperature increase of the cladding glass relative to the active laser glass it surrounds. 
     It is also desirable to maximize the absorption bandwidth for the active species in the glass in order to maximize the absorption of flashlamp light and increase the pumping efficiency into the excited state of the laser transition. Since only a fraction (e.g., about 20%) of the total light emitted from flashlamps is actually absorbed by the laser glass, materials characterized by greater average absorption bandwidth, Δλ abs , will lead to a greater fraction of the flashlamp light being absorbed. 
     Furthermore, it is desirable to minimize the emission bandwidth for the excited species in the glass to maximize the extractable energy stored in the excited stage. Measurements performed at Lawrence Livermore National Laboratory suggest that Nd-doped laser glasses with smaller bandwidths, Δλ em , are characterized by higher extraction efficiencies. 
     As fusion laser technology advances, the need exists for Nd-doped glass that can be used in laser systems that will likely produce more than five or even ten times as much output energy as the current state-of-the-art fusion laser systems (i.e., ≧0.5 or 1.0 megajoules (MJ) versus 0.1 MJ at a wavelength of 355 mm from the NOVA laser at Lawrence Livermore National Laboratory). 
     New high energy laser systems require large quantities of active laser glass (e.g., at least about 200, 300, 500, 1000, 2000, 3000, or 4000 optical glass components each of, for example, at least about 10 l in volume) which preferably can be produced in a short time period with high manufacturing yield, thereby minimizing the cost of the material to the end user. Solid state laser materials for these high energy laser systems should also preferably offer, in combination with good laser properties as discussed above, outstanding properties from the point of view of manufacturability. Thus, the glasses utilized in the present invention, simultaneously with offering good characteristics for laser application, also preferably possess desirable characteristics related to manufacturability such as high thermal conductivity, low Poisson&#39;s ratio, small coefficient of thermal expansion, low Young&#39;s modulus, high fracture toughness, a low glass transformation point, good water resistance of the glass surface, high solubility for platinum, and high stability by being resistant to devitrification and crystallization during melting and forming. 
     Therefore, it is desirable that, in accordance with the invention, the glasses exhibit a maximum value of the following production figure-of-merit, FOM prod , expressed by 
     
         FOM.sub.prod =β.sup.2 K.sub.1c ·D.sub.Pt ·F.sub.Wdur ·1/T.sub.g ·F.sub.Dvit 
    
     where ##EQU4## κ is thermal conductivity; ν is Poisson&#39;s Ratio; 
     α is thermal expansion; 
     E is Young&#39;s modulus; 
     K 1c  is fracture toughness; 
     T g  is glass transformation point; 
     F Wdur  is durability of the glass to water; 
     F Dvit  is the crystallization and devitrification tendency of the glass; and 
     D pt  is a measure of the ability of the glass to dissolve platinum. 
     It should be noted that this production figure-of-merit has been developed in accordance with the invention to serve as a guide in the selection of laser glasses. It is not intended to suggest an exact precise assessment of each glass. This production figure-of-merit in accordance with the invention is, however, important as can be seen from the following discussion. 
     The production figure-of-merit, FOM prod , described above includes a term β where ##EQU5## and κ is thermal conductivity, ν is Poisson&#39;s Ratio, α is the thermal expansion, and E is Young&#39;s modulus. This is a well known thermal-mechanical figure-of-merit which is an indication of the likelihood that glass will break while incurring thermal and mechanical stresses associated with the manufacturing steps of annealing, grinding, polishing, cutting, routine handling, etc. This term appears twice in the expression for FOM prod , once to reflect its importance in annealing of glass, and once with K 1c , the fracture toughness of the glass, as a reflection of its importance as a thermal shock figure-of-merit in the important manufacturing steps of fabricating, e.g., polishing, cutting, handling, etc., a final block, slab, disc, rod, etc. 
     The FOM prod  expression also includes 1/T g  to reflect the reduced time and effort needed to fully anneal large castings of glass which have a small transformation temperature. 
     Also included in FOM prod  are the important measures of platinum solubility, D pt , and devitrification tendency, F Dvit . 
     D pt  is evaluated by submerging a section of platinum into a molten glass melt, e.g., at temperatures of 1300° C. to 1400° C. depending on the viscosity of each glass under evaluation for 4 hours with the melt under an oxygen atmosphere. Platinum dissolution into the glass melt is evidenced by a yellow coloration of the samples, corresponding to absorption of the glass in the blue part of the spectrum. The resultant ability to dissolve platinum is evaluated by measuring the absorption coefficient of glass samples at 400 nm. See, e.g., &#34;Platinum Solubility in Phosphate Laser Glass,&#34; Hayden et al , Lawrence Livermore National Laboratory, UCRL-JC-105475, June 1991. 
     During the development of this invention, F Dvit  was not precisely quantitatively evaluated. Instead, glasses were accepted or rejected (that is to say, F Dvit  was set equal to 1 or 0, respectively) based on microscopic visual inspection of a platinum strip containing samples of the glass under evaluation which had been placed in a gradient furnace covering, temperatures from 600° C. to 1000° C., for a time sufficient so that any tendency toward devitrification or crystallization was evident upon removal of the strip from the furnace. It is also possible to identify glasses with a severe devitrification tendency by Differential Thermal Analysis (DTA) which detects and displays exothermic or endothermic reactions within a small sample of the glass under evaluation. See, e.g., &#34;Thermal-Mechanical and Physical Chemical Phosphate Laser Glasses,&#34; Elder et al , Lawrence Livermore National Laboratory, UCRL-JC-105474, July 1991. 
     A glass which is more aggressive to platinum is easier to produce in a form free of metallic platinum particles which, upon absorption of laser radiation, become damage sites within the final glass element, potentially rendering the material useless as a high quality optical element. In a similar manner, a stable glass which is not prone to devitrification during manufacturing is easier to produce in a form free of crystals and free of phase separation, which is important for production of glasses with the high optical quality essential for laser glass used in high energy laser systems. 
     Also appearing in FOM prod  is a measure of glass durability toward attack by water, F Wdur . This parameter is evaluated by submerging a sample of the glass to be tested in 50° C. water for 24 hours, measuring the weight loss, and normalizing the result per square centimeter of tested area. The weight loss per square centimeter of tested area is referred to as D wdur . See, e.g., Elder et al., supra. 
     Potentially, a somewhat higher solubility in water is an advantage during the glass polishing; however, it is desirable that F Wdur  not be so large that the glass is readily attacked by sources of water such as humidity to which surfaces might be exposed during storage or actual use. Consistent with this, glasses with values of D wdur   &gt;0.3 mg/cm 2  /day were rejected; that is, the value of F Wdur  was set equal to 0. 
     It is known for some time that phosphate laser glasses have a low threshold value for the laser effect, and phosphate glass compositions have been commercially available for some time as optical components for use in laser systems. 
     Nevertheless, a need has remained for improved development of phosphate compositions, e.g., to simultaneously improve both the thermal-mechanical properties and the laser properties of phosphate laser glasses, thus making available glasses which combine in the same material properties desirable both for manufacturability with a high production yield and for application as an active laser material. 
     Prior art phosphate laser glasses contain a wide variety of components including, for example, Al 2  O 3 , SiO 2 , alkali metal oxides (Na 2  O, K 2  O, Li 2  O, especially), alkaline earth metal oxides, etc., in addition to the base component, P 2  O 5 . Prior art glasses having the good laser properties desirable high energy solid state laser systems are described in U.S. Pat. Nos. 4,075,120; 4,248,732; and 4,239,645. However, the glasses of these inventions are thermomechanically somewhat undesirable from the manufacturability point of view. These glasses do not emphasize the identity or the amount of alkali and alkaline earth metal oxides. 
     Other phosphate laser glasses place emphasis on the use of K 2  O and BaO to impart pronounced athermal character to the laser glass. See, e.g., U.S. Pat. No. 4,022,707; U.S. Pat. No. 4,076,541; and U.S. Pat. No. 4,108,673. While other publications require the use of Li 2  O, e.g., U.S. Pat. No. 4,929,387, and/or MgO, e.g., U.S. Pat. No. 5,032,315, to obtain glasses with exceptional properties for use in high average power laser systems. Still another publication, U.S. Pat. No. 4,333,848, emphasizes the use of Li 2  O with BaO to achieve this athermal characteristic in a laser glass. 
     Still other laser glass publications exist which prescribe the necessary use of SiO 2 , e.g., U.S. Pat. No. 4,820,662, DE 34 35 133, JP 51-107312, and DE 36 09 247, and/or B 2  O 3 , e.g., U.S. Pat. No. 4,661,284, to obtain improvements in the characteristics desirable in laser glasses for high power solid state laser systems. 
     Many other laser phosphate publications exist which describe a wide variety of glasses such as JP 49-114615(4), JP 60-191029(3), JP 51-107311, JP 50-3411, JP 51-30812, SU-355,916, U.S. Pat. No. 3,846,142. In these patents, no particular emphasis is placed on alkali metal oxides. Further patents equate all metal oxides, e.g., U.S. Pat. No. 4,120,814, U.S. Pat. No. 3,979,322, U.S. Pat. No. 4,225,459, U.S. Pat. No. 3,580,859, and U.S. Pat. No. 4,470,922. 
     JP 54-38311 indicates a preference for Li 2  O, but in phosphate glasses containing components such as CuO and V 2  O 5 . 
     It has now been discovered that the requirements for high energy laser systems can be satisfied through the employment of phosphate glasses having a desirable combination of laser properties and simultaneously having a desirable combination of properties for manufacturability. 
     The invention thus relates to a high energy laser system using a phosphate glass possessing desirable properties such as high cross section for stimulated emission, low emission bandwidth, low concentration quenching of the excited state lifetime, low nonlinear refractive index, high heat capacity and low coefficient of thermal expansion, in combination with desirable characteristics related to manufacturability such as high thermal conductivity, low Poisson&#39;s ratio, small coefficient of thermal expansion, low Young&#39;s modulus, high fracture toughness, a low glass transformation point, good water resistance of the glass surface, high solubility for platinum and high stability as shown by being resistant to devitrification and crystallization during melting and forming. 
     In accordance with one aspect, the invention relates to a high energy laser system utilizing phosphate laser glass components in which the parameters of the laser system and the beam generated thereby require that the phosphate laser glass components have an emission bandwidth of less than 26 nm, and wherein the glass consists essentially of (on an oxide composition basis): 
     
         ______________________________________         Mole %                          Especially         General                Preferred Preferred______________________________________P.sub.2 O.sub.5 50-75    55-75     60-70Al.sub.2 O.sub.5           &gt;0-10    1-9       2-6K.sub.2 O       &gt;0-30    8-28      10-24MgO             0-30     0-24      0-20CaO             0-30     0-24      0-20Li.sub.2 O      0-20     0-15      0-10Na.sub.2 O      0-20     0-15      0-10Rb.sub.2 O      0-20     0-15      0-10Cs.sub.2 O      0-20     0-15      0-10BeO             0-20     0-15      0-10SrO             0-20     0-15      0-10BaO             0-20     0-15      0-10ZnO             0-20     0-15      0-10Pbo             0-20     0-15      0-10B.sub.2 O.sub.3 0-10     0-8       0-5Y.sub.2 O.sub.3 0-10     0-8       0-5La.sub.2 O.sub.3           0-8      0-5       0-4Ln.sub.2 O.sub.3           0.1-8    0.1-8     0.1-8Sum RO          &gt; 0-30   4-24      5-20(R = Mg, Ca)Sum R&#39;.sub.2 O  0-20     0-15      0-10(R&#39; = Li, Na, Rb, Cs)Sum R&#34;O         0-20     0-15      0-10(R&#34; = Be, Sr, Ba, Zn, Pb)Sum R&#34;&#39;.sub.2 O.sub.3           0-10     0-8       0-5(R&#34;&#39; = B, Y)______________________________________ 
    
     Ln 2  O 3  represents the sum of the oxides of active lasing lanthanides of atomic number 58-71. The preferred active lasing species is Nd 2  O 3 . It is also possible to use nonlanthanide active lasing species (e.g., Ti or V) in place of Ln 2  O 3 . 
     In accordance with the invention, the laser system preferably can operate at an energy level of at least about 0.1 MJ, particularly at least 0.5 MJ, 1.0 MJ, 1.5 MJ, or 2.0 MJ, and especially up to at least 3.0 MJ, 4.0 MJ or 5.0 MJ (for example, about 0.2-10 nanosecond pulse lengths at an energy level of at least 0.5 MJ and a wavelength of 355 nm). Further, the laser system preferably focuses at least about 100 beams on a target and use at least 200 laser glass components. 
     Laser systems operating at such energy levels require laser glass exhibiting high extraction efficiencies. For this reason, it has been determined that laser glass components having a low Δλ em , preferably &lt;26 nm, are needed. A high cross section, e.g., &gt;3.5×10 -20  cm 2 , is also advantageous. 
     In other preferred aspects, the glass also has the following important properties: 
     
         ______________________________________Damaging inclusions per liter                 essentially zeroStability to devitrification                 highStability to crystallization                 highκ, thermal conductivity                 &gt;0.5 W/mKν, Poisson&#39;s ratio &lt;.28α, thermal expansion from 20-300° C.                 &lt;145 × 10.sup.-7 /KE, Young&#39;s modulus    &lt;50 GPaK.sub.1c, fracture toughness                 &gt;0.40 MPa m.sup.1/2ρ, glass density  &gt;2.60 g/cm.sup.3C.sub.p, glass heat capacity                 &gt;0.50 J/gKσ, cross section                 &gt;3.5 × 10.sup.-20 cm.sup.2Q, concentration quenching factor                 &gt;7 × 10.sup.20 cm.sup.-3n.sub.2, nonlinear refractive index                 &lt;1.2 × 10.sup.-13 esuΔλ.sub.abs                 &gt;17 nmΔλ.sub.em                 &lt;26 nmT.sub.g, glass transformation point                 &lt;460° C.D.sub.Wdur, durability of the glass to water                 &lt;0.20 mg/cm.sup.2 dayD.sub.Pt, platinum solubility (@400 nm)                 &gt;0.03 cm.sup.-1______________________________________ 
    
     It is further preferred that these properties exceed even these goals, e.g., 
     
         ______________________________________κ, thermal conductivity                  &gt;0.55 W/mKα, thermal expansion from 20-300° C.                  &lt;140 × 10.sup.-7 /KE, Young&#39;s modulus     &lt;45 GPaK.sub.1c , fracture toughness                  &gt;0.50 MPa m.sup.1/2σ, cross section &gt;4.0 × 10.sup.-20 cm.sup.2Q, concentration quenching factor                  &gt;8 × 10.sup.20 cm.sup.-3n.sub.2, nonlinear refractive index                  &lt;1.1 × 10.sup.-13 esu______________________________________ 
    
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the following discussion and the accompanying drawings wherein: 
     FIGS. 1a, 1b and 1c show the values of FOM laser&#39; , defined below, for the glass examples of Tables 1, 2, and 3, respectively; 
     FIGS. 2a, 2b and 2c show the values of FOM prod&#39; , defined below, for the glass examples of Tables 1, 2, and 3, respectively; 
     FIGS. 3a, 3b and 3c show the values of FOM laser&#39; , for the glass examples of Tables 4 and 5; 
     FIGS. 4a, 4b and 4c show the values of FOM prod&#39; , for the glass examples of Tables 4 and 5; 
     FIGS. 5a, 5b, 5c and 5d show the values of FOM prod&#39; , for the glass examples of Tables 6 and 7; 
     FIGS. 6a, 6b, 6c and 6d show the values of FOM laser&#39; , for the glass examples of Tables 6 and 7; and 
     FIG. 7 shows the values of D wdur  for some glass examples of Tables 6 and 7. 
    
    
     DETAILED DESCRIPTION 
     Special emphasis in this invention is placed on those properties which appear in the following, abbreviated FOM formulae: ##EQU6## wherein the meaning of each is discussed above. 
     Also emphasized are the properties of emission bandwidth, platinum solubility, and devitrification tendency. Preferably, FOM laser&#39;  is &gt;25 (esu.cm) -1 , FOM prod&#39;  is &gt;0.60×10 -6  m 2  /sec, bandwidth for emission is &lt;26 nm, D pt  is &gt;0.025 cm -1  at 400 nm, and the glass exhibits good stability as evaluated by visual inspection for the presence of crystallization, devitrification, phase separation, etc. 
     These glass compositions employ P 2  O 5  as the principle glass former. The level of P 2  O 5  is preferably maximized. Generally, the P 2  O 5  content is 50-75, preferably 55-75, especially 60-70 mole %. The P 2  O 5  content can also be defined in terms of 51, 52, 53, 54, 56, 57, 58, 59, 61, 62, 63, 64, 65, 66, 67, 68, 69, 71, etc., mole %. 
     Al 2  O 3  is also an important component. It imparts to the glass better chemical durability and better thermomechanical properties such as κ and α. However, the amount of Al 2  O 3  should not be so high as to induce crystallization. The level of Al 2  O 3  is generally &gt;0 to 10%, preferably 1-9%, especially 2-6 mole %. Other levels of Al 2  O 3  are 3, 4, 5 and 7 mole %. 
     FIGS. 1a, 1b and 1c show the results of FOM laser&#39;  evaluations for glass compositions in Tables 1, 2 and 3. As can be seen in FIG. 1a, high levels of P 2  O 5  and minimal utilization of Al 2  O 3  provide a high value of FOM laser&#39;  due to a reduction in the value of n 2 , while increasing Q and σ. FIG. 1b shows that a reduction in modifier content, in this case, K 2  O and BaO, has a detrimental impact of FOM laser&#39; . FIG. 1c indicates that a high level of P 2  O 5 , over modifier content, is preferred. 
     FIGS. 2a, 2b and 2c show the results of FOM prod&#39;  evaluations for glass compositions in Tables 1, 2 and 3. FIG. 2a shows that, in addition to high levels of P 2  O 5 , some level of Al 2  O 3  increase still offers a slight improvement in FOM prod&#39; . FIG. 2b and FIG. 2c demonstrate the preference in these glasses for high P 2  O 5  in order to increase the value of FOM prod&#39; . 
     The alkali metal content and identity are particularly important. In particular, the presence of potassium is important for meeting the parameters necessary for simultaneously raising the figures of merit for both laser application and manufacturability. Generally, the amount of K 2  O is &gt;0 to 30%, preferably 8-28%, especially 469 10-24 mole %. The amount of K 2  O can also be 1, 2, 3, 4, 5, 6, 7, 9, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 25, etc., mole %. 
     Small additions of sodium are generally tolerable, e.g., less than about 3 to 5 mole % Na 2  O. The amount acceptable will vary somewhat as a function of base glass composition. Low amounts of lithium are also acceptable in the glasses. In general, less than about, e.g., 3 to 5 mole % Li 2  O, is consistent with producing a glass with the mentioned desirable characteristics for manufacturability and application in high energy laser systems. In general, the total amount of the alkali metal oxides Li 2  O, Na 2  O, Rb 2  O and Cs 2  O will be 0-20%, preferably 0-15%, especially 0-10 mole %, e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 16, etc., mol %. 
     As can be seen in FIG. 3a, FIG. 3b and FIG. 3c, incorporation of high molecular weight alkali metals provides a high value of FOM laser&#39; , due to reduction in the value of n 2 , simultaneously with increasing and marginally impacting the value of Q. On the other hand, low molecular weight alkali metal species impart to a glass desirable thermomechanical properties which lead to a high value for FOM prod&#39; . See FIG. 4a, FIG. 4b and FIG. 4c. 
     The alkaline earth metal content and identity are also of particular importance. In particular, the presence of CaO and/or MgO is desirable for meeting the parameters necessary for simultaneously offering a high figure-of-merit for both laser application and manufacturability. Generally, the amount of MgO is 0-30 mole %, preferably 0-24 mole %, especially 0-20 mole %, e.g., 0-7 mole %. Similarly, the amount of CaO is generally 0-30%, preferably 0-24%, especially 0-20 mole %, e.g., 7-30 mole %. The combined amount of MgO and CaO, however, is preferably &gt;0-30%, particularly 4-24%, especially 5-20%. Other possible amounts for either MgO or CaO are 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, etc., mole %. 
     It is possible to have MgO or CaO present without the other. For example, the glass can contain &gt;0-30 mole % MgO without any CaO, or &gt;0-30 mole % CaO without any MgO, such as 5-20 mole % CaO or 10-15 mole % CaO. 
     Barium, BaO, can also be present; the amount acceptable will vary somewhat as a function of base glass composition. In general, the amount of BaO is 0-20%, preferably 0-15%, especially 0-10 mole %, for example, about 3 to 5 mole % or less BaO is consistent with producing a glass with the mentioned desirable characteristics for manufacturability and application in laser systems for producing high energy levels. 
     As can be seen in FIGS. 3a, 3b, and 3c, incorporation of high molecular weight alkaline earth metals provides only a slightly higher value of FOM laser&#39; , due to an increase in the value of n 2 , combined with minimal impact on the value of Q and an increase in the value of σ. However, as demonstrated in FIGS. 4a, 4b, and 4c, low molecular weight alkali metal species also impart desirable thermomechanical properties to the glass leading to a higher value for FOM prod&#39; . 
     The addition of SiO 2  and B 2  O 3  while not required can improve thermomechanical properties. The impact of SiO 2  and B 2  O 3  substitutions for either P 2  O 5  or Al 2  O 3  are similar, as shown in FIGS. 5a-5d and FIGS. 6a-6d. 
     Substitutions of SiO 2  and B 2  O 3  for Al 2  O 3  are advantages for laser properties. See, e.g., FIGS. 6a and 6c, which shows substitutions of SiO 2 . Substitution of B 2  O 3  for Al 2  O 3  results in an increase in FOM laser&#39;  due to a smaller value of n 2  and larger values for Q and σ. The inclusion of SiO 2  and B 2  O 3  is, however, detrimental to durability of the glass to attack by water, as seen in FIG. 7. Here, the increase in glass dissolution rate, expressed as mg of material lost per square centimeter of tested surface per day of exposure, is documented for partial, e.g., 50%, and complete replacement of Al 2  O 3  by B 2  O 3  and SiO 2 . 
     With respect to BeO, SrO, BaO, ZnO and PbO, the amount of these metal oxides are each generally within the range 0-20%, preferably 0-15%, especially 0-10 mole %, with their total combined amount also being generally 0-20%, preferably 0-15%, especially 0-10 mole %. 
     The amounts of B 2  O 3  and Y 2  O 3  present are each generally 0-10%, preferably 0-8%, especially 0-5 mole %. Similarly, the total combined amount of B 2  O 3  and Y 2  O 3  is generally 0-10%, preferably 0-8%, especially 0-5 mole %. 
     As mentioned above, it is desirable for the glass to have a maximal P 2  O 5  content and, in turn, to possess a high amount of P 2  O 5  relative to modifiers. Therefore, the value of P 2  O 5  /(3ΣR 2  O 3  +MgO), wherein R is Al, La, Ln, Y and B, is preferably at least about 1.5, particularly at least about 2.0, and especially at least about 2.3. 
     When used as a lasing medium, the amount of a lasing species or lasing system (e.g., a lasing species/energy transfer species combination) present in the glass is effective for lasing, e.g., often 0.01-8 mole % (on an oxide basis) in total. Optionally, higher amounts can be used, e.g., up to 10% or even up to 20% or higher in total. 
     Nd 2  O 3 , the most preferred lasing species, is added to the glasses in sufficient quantity to achieve the desired lasing activity, as is true for other lasing species and systems. At excessively high concentration levels (Nd 2  O 3  or other lasing species), quenching of the fluorescence emission will occur. As a result, there is a corresponding drop in fluorescence lifetime of the excited state involved in the lasing transition. Suitable upper limits in a given case can be routinely determined. For example, the glass can contain 0.01, 0.05, 0.08, 0.1, 0.3, 0.5, 0.8, 1.0, 1.3, 1.5, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0 mole %, etc. 
     Any conventional glass lasing species, lanthanide or nonlanthanide, can be used, e.g., Nd, Tm, Yb, Dy, Pm, Tb, Er, Ho, Ti, V, Cr, Eu, Sm, etc. In another embodiment of the present invention, the laser compositions can contain suitable co-dopants along with primary lasing ions. These include transition metals such as chromium and vanadium or lanthanide ions such as thulium and erbium. These have broad and intense absorption bands and resultant co-dopant fluorescence bands which overlap with the primary lasing ion absorption levels. This phenomena leads to a more efficient conversion of pump radiation into the excited state population of lasing ions. 
     The total amount of these active ions alone or in combination is 0.01-8 mole % (on an oxide basis), typically. However, as noted above, higher amounts can be used where appropriate, e.g., 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 25 mole %, etc. See, for example, Physics of Laser Fusion, Volume IV, &#34;The Future Development of HighPower Solid State Laser Systems,&#34; Emmett et al , Lawrence Livermore National Laboratory, UCRL-53344, November 1982. 
     Addition of La 2  O 3  allows direct substitution of Nd 2  O 3   or other lasing or energy transfer lanthanide species by another oxide which is nearly an exact structural replacement of, e.g., Nd 2  O 3 . This allows the manufactured glass to be produced with a broad range of neodymium or other lasing species doping levels while minimizing the change from this adjustment on the physical, optical, and thermal properties of the produced glasses. Thus, La 2  O 3  amounts typically are 0-8 mole %, preferably 0-5 mole %, especially 0-4 mole %, for example, 0.1, 0.2, 0.3, 0.5, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0 mole %, etc. However, higher contents are possible, e.g., up to 10% or even 20%, as a replacement for the lanthanide lasing species. 
     It is further possible to add small amounts, e.g., 0.1-0.3 wt. %, of conventional refining agents such as As 2  O 3  and Sb 2  O 3  to the composition to aid in manufacturing while not compromising the combination of properties achieved in the present invention. It is additionally possible to add small antisolarization effective amounts, e.g., 0.1-1.5 wt. %, of conventional antisolarants such as TiO 2 , CeO 2  and Nb 2  O 5  (as well as others, e.g., SiO 2  and Sb 2  O 2 ) to suppress solarization of these glasses during exposure to intense UV radiation common during application as an active lasing material. 
     It is also possible to omit a lasing species entirely within the glass, e.g., when it is desired to use the glass in other applications (such as in optical elements, e.g., lenses, mirrors, undoped laser fiber cladding glasses, analogous to the cladding glasses of U.S. Pat. No. 4,217,382, etc.), where their exceptional combination of properties is beneficial. For example, a suitable optical glass component would correspond to the phosphate laser glass composition described above except that the lasing species is omitted and is replaced by 0.01-8 mole % La 2  O 3 . 
     It is also possible to omit the lasing species entirely and to instead dope the glass with one or more metal species, e.g., Cu or Sm, which impart light-filtering characteristics to the glass, e.g., for their use in other applications, such as filters, doped laser glass claddings for large discs, slabs, or other forms (see, e.g., U.S. Pat. No. 4,849,036), fibers (see, e.g., U.S. Pat. No. 4,217,382), etc., where their exceptional combination of properties is beneficial. 
     A suitable doped laser glass cladding, for example, would correspond to the above phosphate laser glass composition except that the active lasing species would be omitted and replaced by a component that would not adversely affect the heat capacity and thermal expansion coefficient (e.g., 0.01-8 moles La 2  O 3 ) and the glass would further contain a dopant capable of absorbing the laser wavelength, for example, &gt;0.0-2.0 wt. % of Cu 2  O, e.g., 0.1, 0.3, 0.5 or 1 wt. % or about 10-30 wt. % Sm 2  O 3 , e.g., 10, 15, 20, 25 or 30 wt. % for a lasing wavelength of Nd in phosphate glasses, i.e., 1.05-1.06 microns. 
     The laser phosphate glass composition described above can also be used as a glass waveguide. For example, the glass could be used to provide a plate waveguide wherein a certain region of the glass plate is treated (e.g., by ion exchange) to provide regions having different refractive indexes such that light will be guided through a specific region of the glass plate. 
     The phosphate laser glass composition may also be used as an incident light detector by virtue of its characteristic luminescence. In a glass containing fluorophores, absorbed incident light will induce the fluorophores to luminesce thereby indicating absorption of incident light. 
     Of course, as is clear from the foregoing discussion, the glasses of this invention are completely compatible with current state-of-the-art manufacturing methods for phosphate laser glasses. The melting, refining, homogenizing and casting of these glasses can be accomplished using the current standard procedures employed by the glass industry. The highly thermal stress resistant glasses of this invention can be formed into slabs, rods, discs, fibers, and other shapes required by the laser community and others by conventional forming techniques well known in the glass industry. The resultant glasses are of high thermal conductivity, low thermal coefficient of expansion, low Young&#39;s modulus, high cross section for stimulated emission, low nonlinear refractive index, and exhibit reduced concentration quenching of the upper state involved in the laser transition. In addition, the resultant glasses have a high solubility rate for platinum and are stable against devitrification and crystallization. Thus, these glasses are readily fabricated in large volume pieces free of metallic particles and crystalline inclusions which can become macroscopic damage sites when used in a high energy laser system. 
     The glasses of this invention can be fully conventionally prepared by mixing the appropriate amounts of each constituent to form a batch composition which is then charged into a fused silica crucible and melted by induction heating from, e.g., 1100° C. to as much as 1500° C., depending on the chosen composition. The glass can then be refined at temperatures exceeding, e.g., 1300° C. from typically 2 to 4 hours, again depending on composition and melt viscosity, with equal intervals of gas bubbling and stirring. The glass is then typically cast into steel molds and annealed at the transformation temperature plus about 20° C. for about 2 hours followed by cooling at about 30° C./hour. These procedures were followed in the examples below. 
     As noted above, the examples of this application are melted in a fused silica crucible. Under such melting conditions, as is well known, there will be some silica added from the crucible to the final glass composition. Accordingly, whereas all compositions given in this disclosure refer to the component contents as added to the batch as is conventional (batch compositions), where a fused silica crucible is employed, the final composition will contain some silica, regardless of whether SiO 2  is added as a batch component. This conventional difference from the initial batch composition is analogous to other differences between final glass compositions and batch compositions, e.g., due to the volatilization of ingredients, etc. The additional amount of silica over and above the amount included in the batch compositions will generally be no more than about 3.5, 3, 2.5, 2, 1.5, 1, 0.5 mole %, etc., especially not more than about 3 mole % and most especially not more than about 2 mole % (all on a renormalized basis). In a preferred aspect of this invention, there is no silica added to the batch compositions, and the final composition contains no more than 3 mole % silica, especially not more than 2 or 1 mole % silica (on the mentioned basis) due to the effect of silica dissolution from the crucible. Of course, where a nonsilica-containing crucible is employed, this effect will not occur. 
     The silica contribution from the crucible will vary conventionally with melt temperature and melting time. For example, in a melt of about 2 hours at a temperature of about 1300° C., about 2 wt. % of silica will be contributed from a quartz crucible, the precise amount being determined by the precise conditions involved such as glass volume exposed, crucible surface area, glass composition, degree of agitation in the melt, etc. 
     Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize this invention to its fullest extent. The following preferred specific embodiments are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever. 
     In the foregoing and in the following examples, all temperatures are set forth uncorrected in degrees Celsius and unless otherwise indicated, all parts and percentages are by weight. 
     The entire texts of all applications, patents and publications cited above are hereby incorporated by reference. 
     EXAMPLES 
     It will be noted that several of the examples achieve properties falling outside the ranges described above as desirable. These examples thus demonstrate the importance of certain factors discussed above in achieving the desired properties. Most importantly, such examples provide valuable guidance as to how routine experimentation may be utilized to select compositions within the general composition space defined for this invention. Fully conventional consideration will, of course, be given by skilled workers in any study of these examples to the experimental errors involved in measuring the disclosed properties, e.g., ±4% for thermal conductivity and ±1% for thermal coefficient of expansion. 
     
                       TABLE 1______________________________________Oxide/Melt No.        1        2        3      4______________________________________P.sub.2 O.sub.5        67       63       59     55SiO.sub.2Al.sub.2 O.sub.3        0        4        8      12B.sub.2 O.sub.3Li.sub.2 ONa.sub.2 OK.sub.2 O    15       15       15     15BaO          15       15       15     15MgOCaONd.sub.2 /La.sub.2 O.sub.3        3        3        3      3Total        100      100      100    100n.sub.d (@587.6 nm)        1.53178  1.53513  1.54005                                 1.54691Abbe No.     65.84    65.88    65.84  66.18Tg (°C.) DTA        384.3    432.8    467    487.8density (g/cm.sup.3        2.8987   2.9354   2.9829 3.0524κ (W/mK) (@90° C.)        .46      .53      .52    .55Poisson&#39;s ratio (ν)        .27      .27      .27    .26α (10.sup.-7 /K)        147.6    133.2    128.7  119.8(@20-300° C.)E (10.sup.6 GPa)        40.3     44.9     49.6   54.7n.sub.2 (10.sup.-13 esu)        1.18     1.18     1.19   1.21C.sub.p (J/gK)        .59      .61      .59    .63K.sub.1c (MPa m.sup.1/2)        .54      .45      .39    .33D.sub.Pt (cm.sup.-1) (@400 nm)                 .0452    .0306  .0284D.sub.Wdur (mg/cm.sup.2 /day)        .1923    .0594    .0302  .0505σ (10.sup.-20 cm.sup.2)        4.45     4.04     3.61   3.26Δλ.sub.em (nm)        23.31    24.73    26.62  28.36τ (rad) μsec        325.7    335.9    348.6  357.5τ.sub.0 (μsec)        336.5    352.6    361.7  368.8Q (10.sup.20 cm.sup.-3)        9.14     7.91     7.9    6.62Devit. Coeff. (0 or 1)        1        1        1      0Durabil. Coeff.        0        1        1      1(0 or 1)______________________________________ DTA = Differential Thermal Analysis 
    
     
                       TABLE 2______________________________________Oxide/Melt No.        5        6        3      7______________________________________P.sub.2 O.sub.5        51.4     55.4     59     63SiO.sub.2Al.sub.2 O.sub.3        0        4        8      12B.sub.2 O.sub.3Li.sub.2 ONa.sub.2 OK.sub.2 O    22.8     18.8     15     11BaO          22.8     18.8     15     11MgOCaONd.sub.2 /La.sub.2 O.sub.3        3        3        3      3Total        100      100      100    100n.sub.d (@587.6 nm)        1.53901  1.53837  1.54005                                 1.5389Abbe No.     64.38    65.27    65.84  66.33Tg (°C.) DTA        373.6    422.2    467    528.3density (g/cm.sup.3        3.0816   3.0163   2.9829 2.823κ (W/mK) (@90° C.)        .43      .47      .52    .60Poisson&#39;s ratio (ν)        .30      .28      .26    .25α (10.sup.-7 /K)        184.7    154      128.7  121.6(@20-300° C.)E (10.sup.6 GPa)        38.2     43.4     49.6   54.7n.sub.2 (10.sup.-13 esu)        1.23     1.2      1.19   1.18C.sub.p (J/gK)        .57      .58      .59    .62K.sub.1c (MPa m.sup.1/2)        .34      .4       .39    .58D.sub.Pt (cm.sup.-1) (@400 nm)                 .0335    .0306  .0251D.sub.Wdur (mg/cm.sup.2 /day)        .74581   .1403    .0302  .0521σ (10.sup.-20 cm.sup.2)        3.92     3.89     3.61   3.43Δλ.sub.em (nm)        25.69    25.49    26.62  28.21τ (rad) μsec        334.5    337.1    348.6  345.7τ.sub.0 (μsec)        346.2    357      361.7  362.1Q (10.sup.20 cm.sup.-3)        5.72     7.83     7.9    7.1Devit. Coeff. (0 or 1)        1        0        1      1Durabil. Coeff.        0        0        1      1(0 or 1)______________________________________ DTA = Differential Thermal Analysis 
    
     
                                           TABLE 3__________________________________________________________________________Oxide/Melt No.        8    9    3    10   11__________________________________________________________________________P.sub.2 O.sub.5        67   63   59   55   51SiO.sub.2Al.sub.2 O.sub.3        8    8    8    8    8B.sub.2 O.sub.3Li.sub.2 ONa.sub.2 OK.sub.2 O    11   13   15   17   19BaO          11   13   15   17   19MgOCaONd.sub.2 /La.sub.2 O.sub.3        3    3    3    3    3Total        100  100  100  100  100n.sub.d (@587.6 nm)        1.53602             1.53736                  1.54005                       1.544                            1.,54699Abbe No.     66.23             65.4 65.84                       65.59                            64.97Tg (°C.) DTA        499.2             492  467  480  443density (g/cm.sup.3        2.8865             2.9216                  2.9829                       3.0336                            3.0966κ (W/mK) (@90° C.)        .56  .54  .52  .54  .50Poisson&#39;s ratio (ν)        .26  .27  .26  .28  .28α (10.sup.-7 /K) (@20-300° C.)        112.4             115.9                  128.7                       139.4                            143E (10.sup.6 GPa)        52.6 50.7 49.6 49.8 49.4n.sub.2 (10.sup.-13 esu)        1.17 1.18 1.19 1.21 1.23C.sub.p (J/gK)        .62  .61  .59  .59  .61K.sub.1c (MPa m.sup. 1/2)        .46  .45  .39  .32  .29D.sub.Pt (cm.sup.-1) (@400 nm)        .0435     .0306     .0315D.sub.Wdur (mg/cm.sup.2 /day)        .0136             .0153                  .0302                       .0707                            .0963σ (10.sup.-20 cm.sup.2)        3.78 3.7  3.61 3.52 3.44Δλ.sub.em (nm)        25.45             26.19                  26.62                       27.35                            27.91τ (rad) μsec        346.4             345.6                  348.6                       344.1                            344.3τ.sub.0 (μsec)        359.5             359.9                  361.7                       358.1                            351.6Q (10.sup.20 cm.sup.-3)        8.03 8.14 7.9  6.91 7.53Devit. Coeff. (0 or 1)        0    1    1    1    0Durabil. Coeff. (0 or 1)        1    1    1    1    1__________________________________________________________________________ DTA = Differential Thermal Analysis 
    
     
                                           TABLE 4__________________________________________________________________________Oxide/Melt No.        4    12   13   3    14   15__________________________________________________________________________P.sub.2 O.sub.5        55   55   55   59   59   59SiO.sub.2Al.sub.2 O.sub.3        12   12   12   8    8    8B.sub.2 O.sub.3Li.sub.2 O             15             15Na.sub.2 OK.sub.2 O    15   15        15   15BaO          15             15MgO               15   15        15   15CaONd.sub.2 /La.sub.2 O.sub.3        3    3    3    3    3    3Total        100  100  100  100  100  100n.sub.d (@587.6 nm)        1.54691             1.52111                  1.53833                       1.54005                            1.51963                                 1.53692Abbe No.     66.18             67.25                  66.14                       65.84                            67.41                                 66.47Tg (°C.) DTA        487.8             523.7                  469.8                       467  529  478.3density (g/cm.sup.3        3.0524             2.6984                  2.6955                       2.9829                            2.6638                                 2.6799κ (W/mK) (@90° C.)        .55  .67  .86  .52  .64  .82Poisson&#39;s ratio (ν)        .26  .25  .28  .26  .24  .23α (10.sup.-7 /K) (@20-300° C.)        119.8             106.5                  89.8 128.7                            110.5                                 93.6E (10.sup.6 GPa)        54.7 58.4 71.2 49.6 55.3 69n.sub.2 (10.sup.-13 esu)        1.21 1.09 1.18 1.19 1.08 1.16C.sub.p (J/gK)        .63  .73  .74  .59  .68  .75K.sub.1c (MPa m.sup.1/2)        .33  .47  .4   .39  .49  .57D.sub.Pt (cm.sup.-1) (@400 nm)        .0284          .0306                            .0254                                 .0118D.sub.Wdur (mg/cm.sup.2 /day)        .0505             .123 .0378                       .0302                            .037 .006σ (10.sup.-20 cm.sup.2)        3.26 3.05 3.03 3.61 3.4  3.26Δλ.sub.em (nm)        28.36             29.36                  29.77                       26.62                            27.75                                 29.24τ (rad) μsec        357.5             379.3                  369.4                       348.6                            360.5                                 348τ.sub.0 (μsec)        368.8             393.2                  386.3                       361.7Q (10.sup.20 cm.sup.-3)        6.62 5.98 5.26 7.9  7.5  7Devit. Coeff. (0 or 1)        0    1    0    1    1    1Durabil. Coeff. (0 or 1)        1    0    1    1    1    1__________________________________________________________________________ DTA = Differential Thermal Analysis 
    
     
                       TABLE 5______________________________________Oxide/Melt No.        2        16       17     18______________________________________P.sub.2 O.sub.5        63       63       63     63SiO.sub.2Al.sub.2 O.sub.3        4        4        4      4B.sub.2 O.sub.3Li.sub.2 O                            15Na.sub.2 OK.sub.2 O    15       15       15BaO          15MgO                            15     15CaO                   15Nd.sub.2 /La.sub.2 O.sub.3        3        3        3      3Total        100      100      100    100n.sub.d (@587.6 nm)        1.53513  1.51947  1.5177 1.53503Abbe No.     65.88    66.39    67.09  65.98Tg (°C.) DTA        432.8    452      502.7  462density (g/cm.sup.3        2.9354   2.637    2.6502 2.6591κ (W/mK) (@90° C.)        .53      .55      .62    .80Poisson&#39;s ratio (ν)        .27      .25      .25    .22α (10.sup.-7 /K)        133.2    121.8    116.5  97.6(@20-300° C.)E (10.sup.6 GPa)        44.9     48.2     52.2   65.3n.sub.2 (10.sup.-13 esu)        1.18     1.1      1.08   1.17C.sub.p (J/gK)        .61      .66      .7     .75K.sub.1c (MPa m.sup.1/2)        .45      .52      .6     .69D.sub.Pt (cm.sup.-1) (@400 nm)        .0452                    .0202D.sub.Wdur (mg/cm.sup.2 /day)        .0594    .2       .0624  .0371σ (10.sup.-20 cm.sup.2)        4.04     3.93     3.66   3.55Δλ.sub.em (nm)        24.73    25.35    26.41  26.9τ (rad) μsec        335.9             355    349.8τ.sub.0 (μsec)        352.6             364.6  367.1Q (10.sup.20 cm.sup.-3)        7.91     8.27     7      7.76Devit. Coeff. (0 or 1)        1        0        1      0Durabil. Coeff.        1        0        1      1(0 or 1)______________________________________ DTA = Differential Thermal Analysis 
    
     
                                           TABLE 6__________________________________________________________________________Oxide/Melt No.        3    19   20   21   22   23   24__________________________________________________________________________P.sub.2 O.sub.5        59   55   51   59   59   53   47SiO.sub.2         8    16   4    8    6    12Al.sub.2 O.sub.3        8    4         4         8    8B.sub.2 O.sub.3Li.sub.2 ONa.sub.2 OK.sub.2 O    15   15   15   15   15   15   15BaO          15   15   15   15   15   15   15MgOCaONd.sub.2 /La.sub.2 O.sub.3        3    3    3    3    3    3    3Total        100  100  100  100  100  100  100n.sub.d (@587.6 nm)        1.54005             1.53465                  1.53391                       1.53518                            1.53624                                 1.54072                                      1.54286Abbe No.     65.84             65.81                  65.23                       65.88                            65.76                                 65.74                                      65.44Tg (°C.) DTA        467  452  419.6                       448.5                            419  482.1                                      483.5density (g/cm.sup.3        2.9829             2.9443                  2.9497                       2.9477                            2.947                                 3.002                                      3.0195κ (W/mK) (@90° C.)        .52  .51  .49  .51  .50  .54  .55Poisson&#39;s ratio (ν)        .26  .27  .27  .27  .27  .26  .26α (10.sup.-7 /K) (@20-300° C.)        128.7             134.4                  137.7                       134  139  131.6                                      125.2E (10.sup.6 GPa)        49.6 45.1 43.6 45.3 43.4 49.3 51.5n.sub.2 (10.sup.-13 esu)        1.19 1.18 1.18 1.17 1.18 1.19 1.21C.sub.p (J/gK)        .59  .61  .62  .62  .59  .61  .58K.sub.1c (MPa m.sup.1/2)        .39  .49  .77  .42  .39  .38  .43D.sub.Pt (cm.sup.-1) (@400 nm)        .0306               .0406D.sub.Wdur (mg/cm.sup.2 /day)        .0302             .2588                  14.05                       .07065                            .3887                                 .1445                                      .175σ (10.sup.-20 cm.sup.2)        3.61 3.87 3.89 3.89 4.07 3.41 3.22Δλ.sub.em (nm)        26.62             25.3 25.02                       25.47                            24.76                                 27.65                                      28.9τ (rad) μsec        348.6             341.2                  345.2                       337.9                            332.5                                 352.5                                      357.2τ.sub.0 (μsec)        361.7             357.5     351.8                            346.6                                 363.7                                      369.6Q (10.sup.20 cm.sup.-3)        7.9  7.88      8.92 8.62 7.1  6.5Devit. Coeff. (0 or 1)        1    1    0    1    1    1    0Durabil. Coeff. (0 or 1)        1    0    0    1    0    0    0__________________________________________________________________________ DTA = Differential Thermal Analysis 
    
     
                                           TABLE 7__________________________________________________________________________Oxide/Melt No.        3    25   26   27   28__________________________________________________________________________P.sub.2 O.sub.5        59   59   59   53   47SiO.sub.2Al.sub.2 O.sub.3        8    4    0    8    8B.sub.2 O.sub.3   4    8    6    12Li.sub.2 ONa.sub.2 OK.sub.2 O    15   15   15   15   15BaO          15   15   15   15   isMgOCaONd.sub.2 /La.sub.2 O.sub.3        3    3    3    3    3Total        100  100  100  100  100n.sub.d (@587.6 nm)        1.54005             1.53624                  1.53437                       1.54298                            1.54892Abbe No.     65.84             65.64                  66.02                       66.02                            65.89Tg (°C.) DTA        467  449  423.5                       488.3                            512.2density (g/cm.sup.3        2.9829             2.9354                  2.9091                       3.0068                            3.043κ (W/mK) (@90° C.)        .52  .51  .53  .54  .61Poisson&#39;s ratio (ν)        .26  .27  .27  .27  .26α (10.sup.-7 /K) (@20-300° C.)        128.7             133.3                  138.7                       123.6                            123.8E (10.sup.6 GPa)        49.6 46.2 43.6 51.9 55.2n.sub.2 (10.sup.-13 esu)        1.19 1.18 1.16 1.21 1.21C.sub.p (J/gK)        .59  .59  .65  .62  .59K.sub.1c (MPa m.sup.1/2)        .39  .42  .42  .43  .29D.sub.Pt (cm.sup.-1) (@400 nm)        .0306     .0383     .0213D.sub.Wdur (mg/cm.sup.2 /day)        .0302             .133 .265 .1079                            .075σ (10.sup.-20 cm.sup.2)        3.61 3.81 3.95 3.48 3.22Δλ.sub.em (nm)        26.62             25.78                  25.22                       27.36                            28.66τ (rad) μsec        348.6             342  336.5                       349.5                            356.5τ.sub.0 (μsec)        361.7             354  351.1                       375.6                            371.2Q (10.sup.20 cm.sup.-3)        7.9  8.59 8.01 5.83 6.33Devit. Coeff. (0 or 1)        1    1    0    1    0Durabil. Coeff. (0 or 1)        1    0    0    0    1__________________________________________________________________________ DTA = Differential Thermal Analysis 
    
     
                                           TABLE 8__________________________________________________________________________       29   30   16   31   32   33   34__________________________________________________________________________Mole % OxideP.sub.2 O.sub.5       63   63   63   63   67   65   57.6Al.sub.2 O.sub.3       4    4    4    4    4    2    8.8Li.sub.2 ONa.sub.2 OK.sub.2 O   25   20   15   10   13   15   17.1MgOCaO         5    10   15   20   13   15BaO                                       13.7Nd.sub.2 /La.sub.2 O.sub.3       3.0  3.0  3.0  3.0  3.0  3.0  3.0Sb.sub.2 O.sub.3As.sub.2 O.sub.3Nb.sub.2 O.sub.5Total       100  100  100  100  100  100  100.2Propertyκ (@ 90° C.) [W/mK]       .4929            .5186                 .5516                      .5855                           .5645                                .5301                                     .5120Poisson&#39;s ratio, ν       .268 .262 .252 .246 .249 .256 .263α [10.sup.-7 /°C.]:(@ 20-300° C.)       155.5            138.3                 121.8                      108.4                           114.7                                123.8                                     131.0(@ 20-40° C.)E [ 10.sup.6 GPa]       38.8 42.8 48.2 52.2 48.8 45.1 50.0K.sub.1c [MPa m.sup.1/2 ]       .41  .56  .52  .55  .52  .56  .40den [g/cm.sup.3 ]       2.596            2.615                 2.637                      2.657                           2.639                                2.615                                     2.959Tg [°C.]       399  416  449  475  448  415  452C.sub.p [J/gK]       .690 .730 .660 .700 .710 .720 .610Dur [mg/cm.sup.2 /day]       .66  .38  .20  .13  .12  .34  .04Devit. Test (0 or 1)       1    1    1    1    1    1    1D.sub.Pt [cm.sup.-1 ] (@ 400 nm)σ [10.sup.-20 cm.sup.2 ]       4.34 4.16 3.93 3.73 3.99 4.12 3.68Q [10.sup.20 cm.sup.3 ]       7.72 7.86 8.58 6.90 7.30 7.81 7.50n.sub.2 [10.sup.-13 esu]       1.03 1.06 1.10 1.13 1.10 1.07 1.17Δλ.sub.em [nm]       24.23            24.71                 25.35                      26.29                           24.59                                24.63                                     25.99τ.sub.0 [μsec]       352.4            354.8                 357.1                      372.8                           357.7                                353.5                                     360.7τ.sub.r [μsec]       330.8            334.7                 343.5                      347.6                           343.2                                338.4                                     349.0n.sub.d     1.50686            1.51259                 1.51947                      1.52667                           1.52064                                1.51670                                     1.53795Abbe No.    67.46            67.04                 66.39                      66.20                           66.77                                67.11                                     66.27__________________________________________________________________________ 
    
     
                                           TABLE 9__________________________________________________________________________       35   36   37   38   39__________________________________________________________________________Mole % OxideP.sub.2 O.sub.5       65   65   65   65   65Al.sub.2 O.sub.3       4    4    4    4    4Li.sub.2 ONa.sub.2 OK.sub.2 O   14   14   21   14   18MgO              14   7    7    5CaO         14             7    5BaONd.sub.2 /La.sub.2 O.sub.3       3.0  3.0  3.0  3.0  3.0Sb.sub.2 O.sub.3As.sub.2 O.sub.3       .1   .1   .1   .1   .1Nb.sub.2 O.sub.5       .1   .1   .1   .1   .1Total       100.2            100.2                 100.2                      100.2                           100.2Propertyκ (90° C.) [W/mK]       .5630            .6187                 .5440                      .5993                           .5514Poisson&#39;s ratio, ν       .250 .259 .268 .254 .261α [10.sup.-7 /°C.]:(@ 20-300° C.)       118.7            116.1                 142.5                      115.5                           131.1(@ 20-40° C.)            95.2 107.0                      100.1                           120.7E [10.sup.6 GPa]       48.1 51.1 42.6 50.3 45.6K.sub.1c [MPa m.sup.1/2 ]       .55  .48  .50  .57  .64den [g/cm.sup.3 ]       2.637            2.640                 2.610                      2.630                           2.620Tg [°C.]       456  463  412  460  425C.sub.p [J/gK]       .650 --   --   --   --Dur [mg/cm.sup.2 /day]       .17  .08  .17  .09  .13Devit. Test (0 or 1)       1    1    1    1    1D.sub.Pt [cm.sup.-1 ] (@ 400 nm)       .0330            .0516                 .0745                      .0264                           .0499σ [10.sup.-20 cm.sup.2 ]       3.84 3.76 4.24 3.83 3.99Q [10.sup.20 cm.sup.-3 ]       8.13 8.21 8.83 8.17 8.60n.sub.2 [10.sup.-13 esu]       1.09 1.06 1.04 1.08 1.05Δλ.sub.em [nm]       25.63            25.36                 24.17                      25.45                           24.61τ.sub.0 [μsec]       356.0            355.6                 349.6                      356.0                           351.8τ.sub.r [μsec]       344.9            361.1                 344.7                      356.5                           350.0n.sub.d     1.51959            1.51696                 1.50917                      1.51838                           1.51347Abbe No.    66.87            67.71                 67.62                      67.17                           67.56__________________________________________________________________________ 
    
     The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples. 
     From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.