Study of the mode-control of random lasers by photo-reaction

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An optical memory effect by interference of multiple scattered light in a random media was combined with a random laser with the aim of controlling the wavelength, the wave-front, and the polarization state of the output of the random laser. By detecting the optical memory effect through the scattered light, it was confirmed that the loss of light in the sample was decreased for the light of the same condition as the writing light. If the laser oscillation occurs in such a medium, the oscillation condition will be controlled by the writing. For the purpose, an photo-reactive material that is not influenced by the strong laser light is needed. However, we have not obtain materials which show reproducible optical memory effect. Then, a random laser was mixed with saturable dye which is regarded as an transient photo-reactive material, and its effect was confirmed. A computer simulation by the FDTD method was carried out, and the hole shape (intensity correlation function) was calculated. As for the width of the hall, it agreed well with the value expected from the theory and the experiment, and it was confirmed that this calculation gives the result corresponding to the optical memory effect and effective to the calculation of the electromagnetic field in a random medium.