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

i have researched this, obvious answer on stackoverflow converse question, , can't quite match situation.

i need tsql reg expression ensure rows returned particular varchar column(denoted col1 here) strictly alphanumeric (that is, row 1 non-alphanumeric char excluded)

something

where col1 'regexpgoeshere' 

where value not match string containing not letter or number:

where f not '%[^a-z0-9]%' 

^{(these patterns, not regular expressions)}