Remove interpolation outside the border

[Krystianchwirot]

Hi,
I try to remove interpolation analysis outside the border but I don't know how. I use method Toolbox>Spatial Analyst Tools>Interpolation>Spline with barriers. Somebody know how to do this? I attach screens to this post. I use ArcGIS 10.1

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[SteveLynch]

use the ExtractByMask tool on the output