Exact solution of a nonlinear model of four-wave mixing and phase conjugation

An exact solution of a nonlinear model of holographic four-wave mixing is derived. An expression for the reflectivity of a phase-conjugate mirror with depleted pumps is presented. We find that such a phase-conjugate mirror may exhibit bistability

Amplified reflection, transmission, and self-oscillation in real-time holography

A theory of phase conjugation in asymmetric materials that allow a phase shift between the grating and the light-interference pattern is developed. We find that when this phase is nonzero, maximum phase-conjugate reflectivity occurs for unequal pump intensities. The conditions for self-oscillation are studied

Passive (self-pumped) phase conjugate mirror: Theoretical and experimental investigation

We report the results of a theoretical and experimental investigation of a passive (self-pumped) phase conjugate mirror. This device is based on real time holography in materials which allow a spatial phase shift between the refractive index grating and the light interference pattern. An imaging experiment is reported showing the phase conjugating nature of the device. The holographic medium used was a single crystal of barium titanate

Nonlinear vectorial two-beam coupling and forward four-wave mixing in photorefractive materials

We present an exact solution of a nonlinear vector analysis of two-beam coupling and forward four-wave mixing in photorefractive media

Real-time phase conjugate window for one-way optical field imaging through a distortion

We demonstrate one-way optical field imaging through a distorting medium using a four-wave mixing implementation of real-time holography. Information can be transmitted at an arbitrarily fast rate as long as the mixing medium can respond to changes in the distortion

Theory and applications of four-wave mixing in photorefractive media

The development of a theory of four-wave mixing in photo-refractive crystals is described. This theory is solved in the undepleted pumps approximation with linear absorption and without using the undepleted pumps approximation for negligible absorption. Both the transmission and reflection gratings are treated individually. The results are used to analyze several photorefractive phase conjugate mirrors, yielding reflectivities and thresholds. The use of photorefractive crystals as optical distortion correction elements and experimental demonstrations of several of the passive phase conjugate mirrors are described

Coherent oscillation by self‐induced gratings in the photorefractive crystal BaTiO_3

We report here the demonstration of several new optical oscillator configurations including a unidirectional ring oscillator and a self‐pumped phase conjugate mirror. The gain medium is BaTiO_3, pumped by a 632.8‐nm He‐Ne laser at power levels down to 50 μW

Passive phase conjugate mirror based on self-induced oscillation in an optical ring cavity

A passive phase conjugate mirror based on four-wave mixing in an optical ring cavity is described. Unlike previously demonstrated passive phase conjugate mirrors it generates only one of its pumping beams by nonlinear optical interactions, the other being provided by feedback of the probe after transmission through the nonlinear medium. The results of a theory yielding phase conjugate reflectivity and oscillation thresholds are presented together with an experimental demonstration of phase conjugation in barium titanate and strontium barium niobate. The device is self-starting by four-wave mixing, and has an oscillation threshold lower than that of other previously demonstrated passive phase conjugate mirrors with similar ease of alignment. The operation of a device which generates nonconjugate oscillation beams is also reported

The relation of anxiety and cognition in Parkinson's disease

OBJECTIVE: Parkinson’s disease (PD) has long been conceptualized as a motor disorder, but nonmotor symptoms also manifest in the disease and significantly reduce quality of life. Anxiety and cognitive dysfunction are prevalent nonmotor symptoms, even in early disease stages, but the relation between these symptoms remains poorly understood. We examined self-reported anxiety and neurocognitive function, indexed by measures of executive function (set-shifting and phonemic fluency), categorical fluency, and attention/working memory. We hypothesized that anxiety would correlate with cognitive performance. METHOD: The Beck Anxiety Inventory and cognitive tests (Trail Making, Verbal Fluency, Digit Span) were administered to 77 nondemented adults with mild to moderate idiopathic PD (39 men, 38 women; Mage = 62.9 years). RESULTS: Higher anxiety was associated with more advanced disease stage and severity and with poorer set-shifting when using a derived metric to account for motoric slowing. Depression correlated with greater anxiety and disease severity, but not with cognitive performance. CONCLUSIONS: Our findings support the association of anxiety with a specific domain of executive function, set-shifting, in nondemented individuals with mild to moderate PD, raising the possibility that treatment of anxiety may alleviate aspects of executive dysfunction in this population.Accepted manuscrip