Interpretation of direct writing M center HD curve characteristics of photodichroic NaF crystals

Hurter-Driffield curves for a number of photodichroic NaF crystals containing M centers are obtained at room temperature in the direct writing mode. The data from most of the samples are fit reasonably well by a simple one-parameter reorientation model in which the transitions from the original to the final polarization states are made indirectly via the side states. Reciprocity in the photographic sense is observed to obtain; this tends to confirmthe single photon aspect of this model. The correspondence of the reorientation parameter to exposureis not unique; impurities seem to enhance sensitivity. On a obtenu des courbes Hurter-Driffield a la temperature ambiente, par le mode d'ecriture directe, pour plusieurs cristaux photodichroiques de NaF qui contiennent des centres M. Les resultats pour la plupart des echantillons correspondent bien a un modele de reorientation a un seul parametre dans lequel les transitions des etats initiaux de polarisation auxetats finaux sont faites indirectement a travers les etats lateraux. La reciprocite, au sens photographique, est valable. Ceci confirme le caractere a photon unique de ce modele. La relation entre le parametre de reorientation et l'illumination n'est pas unique, les impuretes accroissent la sensibilite.