Question: Can I simplify a variable power of a matrix?

Hi, guys. 

I have a question with D(D)^k, where D is a diagonal matrix,k>=0,for example

D:=<<6, 0> | <0, -1>>

I want Dk to be simplified to the form

<<6k, 0> | <0, (-1)k>>

How can I get it?

TKS in advance!

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