Transformation of energy spread of laser pumping via phase conjugation

Nonlinear reflection of ultrashort high-energy laser radiation pulses leaving in the interaction space is more effective than that of continuous-wave radiation, but depends largely on the statistical spread of energy fluctuation. Therefore, transformation of the spread of pumping energy into the spread of energy in the conjugate wave plays an important role in the process. An experimental study was made of this transformation in a laser on a resonant dye of the polymethine group. The pumping source was a PPGS-1 single-mode parametric laser emitting pulses of 30-40 ps duration and 50 mJ energy. A semitransparent mirror with a reflection coefficient R = 0.45 split the laser beam into two approximately equal parts, each guided by a set of swivel prisms into a test cell with 3955 polymethine dye from exactly opposite directions a reference pumping waves, and a small part of the order of 0.04 guided by a wedge, an optical delay line, and a mirror with a reflection coefficient R = 1.0 into the interaction space as probing wave. All three coherent waves excited in the millimeter thick layer of 3955 dye in ethanol solution were equalized by means of two other optical delay lines. The results show the dependence of phase conjugation efficiency on the power density of the pumping waves, with the reflection coefficient for the conjugate wave peaking within some range of the pumping intensity and also within some range of the dye concentration.