Improved multipass second harmonic generation (SHG) is provided by the use of an inverting, self-imaging telescope which ensures parallelism of all passes of all beams within the nonlinear medium. Improved multipass SHG is also provided by the use of a wedged phasor which provides a simple adjustment of the relative phase of the pump beam and second harmonic beam between passes. Improved multipass SHG is provided by the use of an inverting self-imaging telescope in combination with a wedged phasor which provides a simple adjustment of the relative phase of the pump beam and second harmonic beam between passes, ensures parallelism of all passes of all beams within the nonlinear medium. A further embodiment includes an OPO and at least one phasor and preferably first and second telescope assemblies.