We report low pump power high-efficiency frequency doubling of a fundamental laser beam at 795 nm, corresponding to the rubidium D1 line, to generate UV light at 397.5 nm using a periodically poled KTiOPO4 (PPKTP) crystal in a ring cavity. We obtain maximum stable output power of 49 mW for mode-matching pump power of 110 mW, corresponding to 45% raw efficiency (56% net efficiency when considering the output coupling mirror's 80% transmission). This is the highest efficiency obtained at this wavelength in PPKTP with such low pump power. We obtain 80% beam coupling efficiency to single-mode fiber, demonstrating high beam quality.