We describe the process of difference-frequency generation of short optical pulses from two-color X-ray pulses. By assuming 10¹¹ photons per X-ray pulse, we predict that the optical count rate can exceed 10⁷ photons per pulse. Similar to other effects involving nonlinear interactions of X-rays and optical radiation, the effect we describe can be used for microscopic studies of chemical bonds and as a probe for light-matter interactions on the atomic scale. Since the X-ray damage threshold is much higher than the optical damage threshold, the efficiency of difference-frequency generation from two X-ray pulses is expected to be orders of magnitude higher than the efficiency of effects such as sum/difference-frequency mixing between X-rays and optical intense short-pulse sources.
We investigate experimentally and theoretically the dynamics of polarization modes in a semiconductor laser subject to optical feedback exclusively into its dominant polarization mode. The laser, despite being edge emitting, weakly supports the orthogonally polarized mode even in a solitary configuration, i.e., without optical feedback. When subject to optical feedback, the laser displays transition behavior from correlated to anticorrelated dynamics between the polarization modes as a function of the injection current strength. We construct a theoretical model based on the Lang-Kobayashi rate equations to describe these results. We include coupling between the two polarization modes in the gain medium to reflect persistence of the second mode in both solitary configuration and under external feedback. With this coupling, the model can reproduce the observed experimental results.
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