Principal Components in ArcGIS perform Principal Component Analysis (PCA) on a set of raster bands and generate a single multiband raster as output. If I need PC1 as only a raster band, then how do I get it?
When you run the tool, in the geoprocessing pane, there is an option to specify the number of Principal Components (or bands) that you need. This would be equivalent to the number of bands or axes that are created, so just write 1 of you want a 1 band image that summarizes most of the variation of the input images.