Frequency doubler and short wave laser source using the same and optical data processing apparatus using the short wave laser source

A optical data processing apparatus comprising a short wave laser source with a semiconductor laser and a frequency doubler, and a data recording or reproducing medium, said frequency doubler including a nonlinear crystal substrate having formed therein (a) periodic domain inverted regions having a first nonlinear coefficient, (b) a nonlinear degradation layer having a second nonlinear coefficient which is much smaller than the first nonlinear coefficient, and (c) a waveguide, said nonlinear crystal substrate having an outer surface and having a third nonlinear coefficient which is substantially equal to said first nonlinear coefficient, said nonlinear degradation layer being formed in said waveguide on a side near to the outer surface of said crystal substrate, wherein when a fundamental wave from said semiconductor laser is introduced into said waveguide, a TM.sub.10 mode of a high harmonic wave which is produced in said waveguide is emitted from an end face of the waveguide, and a beam of the high harmonic wave is irradiated onto the said recording or reproducing medium.