Enhanced Four-Wave Mixing by Use of Frequency-Shifted Optical Waves in Photorefractive BaTiO3

Instability of Single-Frequency Operation in Semilinear Photorefractive Coherent Oscillators

“…It is known that for large values of the coupling strength the maxima of the phase conjugate reflectivity R pc I 3 0=I 4 0 correspond to certain frequency detuning Þ 0 while for small coupling R pc is bell-shaped with the maximum exactly at 0. This experimental observation with the passive phase conjugate mirror was supported by calculation of the spectra of phase conjugate reflectivity [13].…”

“…The underlying physical phenomenon is related to an enhancement of the phase conjugate reflectivity of the backward wave four-wave mixing phase conjugate mirror with the diffusion-driven nonlocal photorefractive nonlinearity for the signal wave with frequency detuned from that of the pump wave [13].…”

Instability of frequency degenerate operation in semilinear coherent oscillator with counterpropagating pump waves

“…8 We are searching for the threshold frequency detuning of oscillation Q and threshold coupling strength yl by solving the set of equations that includs the condition of oscillation, R.Rpc 1 and condition of maximum phase conjugate reflectivity, The onset of frequency degenerate oscillation means that the immobile photorefractive grating is replaced, above the critical r, by two photorefractive gratings with identical grating vectors but moving in opposite directions. This suggests the analogy of supercritical bifurcation in oscillation spectrum to the second order phase transition.…”

<title>Training of self-pumped phase-conjugate mirrors based on photorefractive nonlinearity</title>

“…It is quite natural therefore that, although the stationary values of the nonlinear reflection coefficient R and the overlap integral H in SPPC mirrors achieve in this case 0.8-0.9 and more than 0.9, respectively, the transition time proves to be rather long, exceeding tens of seconds (see, for example, [14]). Note that the well-known methods for increasing the writing rate of dynamic holograms in PRCs based on varying the parameters and geometry of the problem [14], an increase in the seed noise level [13,15], the use of frequency shifts [16,17], and external DC [18,19] or AC [20][21][22] electric fields prove to be inapplicable here. They either drastically reduce the SPPC mirror efficiency (R or H) or cause the development of instabilities and self-excitation resulting in the development of complicated self-oscillation lasing regimes with characteristic times up to a few hours and days [2].…”