Through the look­ing glass

Focus-Science and Technology - - Eye Opener - RICHARD F CARIS MIR­ROR LAB­O­RA­TORY, UNIVER­SITY OF ARI­ZONA, USA

This pic­ture shows the ‘raw’ glass that will even­tu­ally form one of the mir­rors for the Gi­ant Mag­el­lan Tele­scope (GMT) at Chile’s Las Cam­panas Ob­ser­va­tory.

Due to com­mence stargaz­ing op­er­a­tions in 2025, the fin­ished ’scope will have seven 8.4m mir­rors that com­bine to give it an ef­fec­tive aper­ture of 24.5m. This en­ables the GMT to pro­duce in­frared im­ages that are 10 times sharper than those cap­tured by the Hub­ble Space Tele­scope.

That level of op­ti­cal pre­ci­sion can only be achieved through the use of high-qual­ity ma­te­ri­als and an ex­act­ing pro­duc­tion process. Here, blocks of low-ex­pan­sion E6 glass made by Ja­pan’s Ohara Cor­po­ra­tion, weigh­ing a to­tal of 17,481kg, have been placed in­side a hexag­o­nal mould and are about to be heated to 1,165°C in a gi­ant furnace that spins at 5rpm.

The glass will take around four hours to melt and set­tle into the mould, af­ter which the furnace will ro­tate more slowly as the glass is care­fully cooled over the course of three months.

Once this stage is com­plete, the mir­ror will be ready for shap­ing and pol­ish­ing.


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