of 10 14 esu as measured by the aforementioned technique of degenerate four wave mixing table ii__________________________________________________________________________1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16__________________________________________________________________________ u03c1 7 891 7 783 7 913 7 904 7 402 7 210 7 186 6 693 6 882 6 445 6 654 6 132 5 931 5 813 7 449 6 570n sub d 2 44 2 35 2 27 2 27 2 28 2 22 x sup 3 71 u00b1 11 88 u00b1 13 40 u00b1 6 32 u00b1 5 __________________________________________________________________________ it is noteworthy that the value of x sup 3 for example 3 88 u00d7 10 14 esu is to the best of our knowledge the largest nonlinear susceptibility that has been measured for any oxide glass and is roughly 250 u00d7 that of vitreous silica based upon an overall review of physical properties and melting and forming characteristics the preferred compositions of the present inventive glasses consist essentially in cation percent on the oxide basis of a 38 60 tlo 0 5 10 45 bio 1 5 5 30 geo 2 and 5 10 gao 1 5 the sum of tlo 0 5 bio 1 5 geo 2 gao 1 5 constituting at least 90 of the total composition b 20 40 teo 2 5 20 sio 2 0 50 tlo 0 5 and 10 65 pbo the sum of teo sub 2 sio 2 tlo 0 5 pbo constituting.