Abstract: A method for sum-frequency conversion of coherent radiation includes generating two linearly polarized waves at different first f1 and second f2 frequencies (f2>f1), respectively, which coaxially propagate and are characterized in common case by arbitrarily located polarization planes. The waves are further guided through an optical active crystal which rotates their polarization planes at different angles ?1 and ?2 determined as ?1=?(f1)·L and ?2=?(f2)·L, where L is a length of the optical active crystal, and ?(f1) and ?(f2) specific rotations at respective frequencies f1 and f2. Finally the waves with the rotated polarization planes are incident on a non-linear crystal configured to generate a third frequency.

Abstract: A method for sum-frequency conversion of coherent radiation includes generating two linearly polarized waves which collinearly propagate in respective first and second non-coinciding planes at different first and second frequencies f1?/f2, respectively. The waves are further guided through an active crystal which rotates the waves at different angles ?1 and ?2 determined as ?1=?(f1)·L ?2=?(f2)·L, where L is a length of the active crystal, and ?(f1) and ?(f2) specific rotations of respective frequencies f1?/f2. Finally the rotated waves are incident on a non-linear crystal configured to sum frequency the wave to generate a third harmonic.