Dye solution oscillation occurs [1][2][3][4][5] in excitation by giant laser pulses. Such l a s e r s produce wavelengths g r e a t e r than those of the exciting source.Here we report frequency shift by dye solutions and mixing of the dye radiation with that from a ruby l a s e r by KDP single c r y s t a l s , as well as tuning of the transformed frequency in the short-wave range.A dye solution can oscillate in a cavity longitudinal or t r a n s v e r s e with respect to the pumping. Figure 1 shows an optical system for producing sum and doubled frequencies on longitudinal excitation of a dye. The oscillation occurs in the same direction as the ruby laser emission. M i r r o r s 1 and 2 are plane-paral[el plates of T F -5 glass 4 m m thick, which are used simultaneously in the ruby and dye cavities. The glass plate 3 is the second m i r r o r in the liquid l a s e r and provides optimum oscillation conditions. The longitudinal excitation system is very convenient in examining transformation, as beams coincident in time are readily produced in the crystal. The dye solution was placed in a cylindrical cell 20 mm long with planeparallel quartz walls and a window diameter of 20 mm. In mixing experiments one needs appropriate power from the dye and ruby l a s e r s , the ruby radiation being residual after passage through the dye solution. The mixing conditions are best if the two radiations have the same power level. The energy of each beam was about 0.3 J, corresponding to powers of about 7 MW.In the t r a n s v e r s e system, the dye flux is perpendicular to the exciting flux. In that case, a rectangular cell 10 • 24 x 30 mm was used, with the oscillation layer 24 m m thick. The dye cavity (base 40 cm) ! 2 3 I HH Fig. 1 t0 -p