Q. Shu

COOPERATIVE OPTICAL BISTABILITY IN THE DIMER SYSTEM CS3Y2BR9:10% YB3+

In single crystals of the dimer compound Cs3Y2Br9:10% Yb3+ below 31 K, both visible (VIS) and near‐infrared (NIR) luminescence intensities were found to exhibit hysteresis as a function of incident NIR intensity and temperature. The optical bistability is intrinsic to Cs3Y2Br9:10% Yb3+ and not a result of an external feedback. Lowering the temperature to 11 K strongly enhances the all‐optical switching behavior. The switching on VIS cooperative upconversion and NIR luminescence transitions occurs simultaneously and with opposite polarity reflecting the competition of both emission processes. On/Off switching ratios of up to 4.8 and 1.7 were observed for VIS and NIR luminescence intensities. Using NIR luminescence spectroscopy, differences in the internal sample temperature of up to 7 K were found between the upper and lower branches of the hystereses. A two‐level density‐matrix model is developed which includes ground‐ and excited‐state interactions and shows that the intrinsic bistability due to a local ...

High-gain nondegenerate two-wave mixing in Cr:YAlO 3

A gain of 22 times was obtained by nondegenerate two-wave mixing in Cr:YAlO(3). To our knowledge, this is the largest cw two-wave mixing gain obtained in a bulk solid-state nonphotorefractive material. The measured gain appears to be limited by beam breakup that is due to spatial nonuniformities in the nonlinear refractive-index change that are the result of inhomogeneities in the crystal. Predictions based on our data indicate that gain in excess of 200 times should be possible in Cr:YAlO(3) if a homogeneous crystal can be obtained.

Two-beam coupling by nitrogen-vacancy centers in diamond

A new method for two-beam coupling measurements based on acousto-optic modulation with subhertz tuning capability is applied to study excited-state dynamics of the nitrogen-vacancy center in diamond. Results yield fundamental decay constants and the nonlinear refractive index and are in good agreement with the calculated dual grating response to resonances in the microscopic susceptibility due to intersystem crossing and spin-lattice relaxation.

Nonlinear dispersion of avalanche upconversion

Two-beam coupling measurements of an avalanche upconversion transition in concentrated Tm:LiYF (4) confirm that, despite the resonant nature of the excited-state optical interaction, the induced response is strongly dispersive. This surprising characteristic is shown to be a general feature of avalanche polarization, with an off-resonant process dominating the resonant response.

Mode-locking applications of nonlinear cooperative interactions

We present results on the first application of upconversion dynamics for short pulse generation in visible solid state lasers. We also describe prospects for passive mode-locking mechanisms based on cooperative nonlinearities and instabilities.