Cladding glass ceramic for use in high powered lasers

A method of preparing a glass ceramic composition capable of absorbing light at a wavelength of 1.06 .mu.m and having a coefficient of thermal expansion of 0.+-.0.1.times.10.sup.-6 /K. at 0-50.degree. C., said process comprising:

• subjecting a glass composition consisting essentially of (on an oxide basis):
• ______________________________________ Wt. % ______________________________________ SiO.sub.2 50-65 Al.sub.2 O.sub.3 18-27 P.sub.2 O.sub.5 0-10 Li.sub.2 O 2-6 Na.sub.2 O 0-2 K.sub.2 O 0-2 B.sub.2 O.sub.3 0-1 MgO 0-4 ZnO 0-5 CaO 0-4 BaO 0-5 TiO.sub.2 1-3 ZrO.sub.2 1-3 As.sub.2 O.sub.3 0-1.5 Sb.sub.2 O.sub.3 0-1.5 ______________________________________
• wherein the total amount of SiO.sub.2, Al.sub.2 O.sub.3 and P.sub.2 O.sub.5 is 80-89 wt. %, and
• said glass composition has a dopant 0.1-3 wt. % CuO, 0.1-1 wt. % Fe.sub.2 O.sub.3 or a combined CuO+Fe.sub.2 O.sub.3 amount of 0.1-4 wt. % to a heating treatment from room temperature to 620.degree. C. at a rate of about 4.degree. C. per minute, heating said glass from 620.degree. C. to 830.degree. C. at a heating rate of about 0.13.degree. C. per minute, holding said glass at a temperature of about 830.degree. C. for about 3 hours, subsequently cooling the glass from 830.degree. C. to room temperature.