TSQL pattern or reg expression to ensure all rows returned for varchar column are strictly alphanumeric

I have researched this, but the most obvious answer on stackoverflow is for a converse question, and I can't quite get it to match my situation.

I need a TSQL reg expression to ensure all rows returned for a particular varchar column(denoted col1 here) are strictly alphanumeric (that is, any row with even one non-alphanumeric char is excluded)

Something like

where col1 like 'regExpGoesHere'