We report on experimental and theoretical studies of a photorefractive ring resonator pumped by a 1.06 mm beam and injected with a weak, external, seeding beam. The competition between the two dominant gratings that form inside the photorefractive crystal leads to characteristic periodic oscillations in the intensity of the resonating beam, which originate from the frequency difference between ...

this study aimed to assess changes in contrast sensitivity and aberrations in cases of myopia greater than 5.0 diopter (d) who had photorefractive keratectomy (prk). in this semi-experimental study, 20 eyes of ten patients were studied. inclusion criteria were at least 5.0 d of myopia, stable refraction in the past year, no history of refractive surgery, a minimum corneal thickness of 480 μm, a...

Photorefractive keratectomy (PRK) has long been the method of choice for refractive surgery in pilots, and was FDA approved U.S. Air Force aviators 2000. We retrospectively reviewed medical records 16 male combat pilots (mean age 25.0 ± 5.5 years) who had undergone bilateral laser with surface ablation (alcohol-assisted PRK: 81.25%, transepithelial-PRK: 18.75%), a mean baseline spherical equiva...

Objective: To compare the ocular surface changes following Femtosecond laser in situ keratomileusis (Femto-LASIK) and photorefractive keratectomy (PRK). Material Methods: TThis prospective study included 74 eyes of 37 patients: 34 were Femto-LASIK group, 40 PRK group. Schirmer test, tear break-up time, conjunctival impression cytology (CIC) used to determine before 1 month, 3 months after or Fe...

We demonstrate a self-organizing photorefractive circuit that demultiplexes a beam that has two signals imposed on separate optical carrier frequencies into two beams, each containing one of the signals on its carrier. Unlike conventional demultiplexing techniques, this method requires little a priori knowledge about the carrier frequencies. The signal channels must be spatially uncorrelated, a...

We calculate the photorefractive grating amplitude in the presence of a high-frequency applied electric field in terms of the mean-square drift length of the charge carriers. We describe how a shallow-trap level and the related long effective deep-trap recombination time are detrimental to the enhancement produced by a squarewave field. We give expressions for the shallow-trap-induced reduction...

This paper reviews our recent work on the photorefractive effect of ferroelectric liquid crystals (FLCs). The photorefractive effect is defined as the optical modulation of the refractive index of a medium as a result of a variety of processes. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon enables the creation of differ...

PURPOSE To report the effect of wavefront-guided photorefractive keratectomy and corneal collagen cross-linking (CXL) on visual problems after Ferrara ring segment placement. MATERIALS AND METHODS A 32-year-old male patient was treated with a Ferrara ring segment for keratoconus. One year later, the ring was removed due to severe glare complaints. After 6 months, wavefront-guided photorefract...

We demonstrate a photorefractive incoherent-to-coherent optical converter driven by ultraviolet light that provides a 35-mus response time and an optical resolution of 124 line pairs/mm. The device, implemented in KNbO(3) , operates with a modulating intensity of 85 mW/cm(2) , which corresponds to an optical switching energy per bit of 0.5 pJ. A conversion rate of the order of 90 Gbits/(s cm(2)...

The regularities of energy transfer between two linearly polarized light waves as their contra-directional mixing on a volume reflection holographic grating formed in photorefractive Bi12GeO20 crystal the (001)-cut are analyzed. values thickness and azimuths linear polarization waves, at which amplification object wave is achieved, determined. change direction to opposite, depending crystal, ha...