Light diffraction by transient gratings during multimode pumping of systems with phase memory

S. A. Moiseev, N. L. Nevelskaya, E. I. Shtyrkov

H. Paerschke, K. -E. S�sse, B. Wilhelmi

Ilja Rückmann, K. Jarašiūnas, Eugenijus Gaubas

Abstract Transient light‐induced gratings due to free carriers and excitons are created in CdSe in a medium density range of 1015 to 1017 cm−3 by two coherent intense (ns) IR‐pump beams. Detailed investigations of probe‐beam diffraction due to thin excitonic gratings in the spectral region just below the An = 1 ‐exciton line at 85 K and its dependence on sample temperature and on the excitation level are presented. First‐order diffraction efficiences up to 5% and a nonlinear dependence of diffraction on the excitation level can be observed. For the first time numerical calculations of probe‐beam diffraction due to excitonic phase and amplitude gratings are presented. The comparison with the experiment shows, that the damping of a dense exciton gas increases proportional to the excitation intensity in the case of two‐photon interband excitation, and that the light‐induced absorptive changes Δ due to dense excitons dominate over the dispersive changes Δn in the spectral region under consideration.

Sergey A. Moiseev, E. I. Shtyrkov

Multipulse excitation of a resonant medium by a laser field is considered. It is shown that one stable long-lived grating with an ultrashort period, i.e., a period much shorter than the wavelength of the exciting laser radiation, can form in such a medium. A study is reported of the interaction of light with gratings of this type and of generation of transient signals by these gratings.

Timo Jääskeläinen

Shang-qi Kuang, Chunshui Jin, Chun Li

In order to obtain an atomic grating which can diffract light into the high-order directions more efficiently, a gain-phase grating (GPG) based on the spatial modulation of active Raman gain is theoretically presented. This grating is induced by a pump field and a standing wave in ultracold atoms, and it not only diffracts a weak probe field propagating along a direction normal to the standing wave into the high-order directions, but also amplifies the amplitude of the zero-order diffraction. In contrast with electromagnetically induced grating or electromagnetically induced phase grating, the GPG has larger diffraction efficiencies in the high-order directions. Hence it is more suitable to be utilized as an all-optical router in optical networking and communication.