Numerical simulation of attraction of partially spatially incoherent dark solitons

We investigate numerically the interactions of partially spatially incoherent odd dark solitons in a de-focusing kerr nonlinear media based on the coherent density approach, and find that a pair of partially spatially incoherent dark solitons may be changed from repulsion to attraction with an appropriate incoherence parameter. Moreover, a pair of partially incoherent gray soliton may form under appropriate conditions. Some numerical examples are provided to illustrate their interaction behavior further.     

Spatial soliton pixels from partially incoherent light

We report what is to our knowledge the first observation of pixellike spatial solitons from partially spatially incoherent light. We created an array of as many as 32x32 soliton pixels by launching a spatially modulated incoherent light beam into a noninstantaneous self-focusing photorefraction medium. These solitons were stable and robust, forming a steady-state two-dimensional waveguide array in which optical coupling and control of local waveguide channels could be realized.     

Model for efficient simulation of spatially incoherent light using the Wiener chaos expansion method

We demonstrate a new and efficient technique for modeling and simulation of spatially incoherent sources using the Wiener chaos expansion method. By implementing this new model, we show that a practical-size photonic structure with a spatially incoherent input source can be analyzed more than 2 orders of magnitude faster compared with the conventional models without sacrificing the accuracy.     

Tomographic microscopy of three-dimensional phase objects in spatially incoherent light

The use of spatially incoherent light is proposed for raising the quality of interference projection data in tomographic microscopy of phase objects. The optical scheme of the tomographic microscope is based on the scheme of a Linnik microinterferometer with an extended source of quasi-monochromatic light. Characteristic features of the tomography of phase objects positioned near flat reflecting surfaces are considered.     

Coherence enhancement of spatially incoherent light beams through soliton interactions

We show that the spatial coherence of a partially incoherent light beam can be greatly enhanced through an energy-conserving interaction with an incoherent or a coherent dark spatial soliton. Computer simulations show that during this process a portion of the incoherent beam is trapped within the dark notch of the dark soliton, thus forming a sharp intensity spike. In this region the correlation length dramatically increases by at least 2 orders of magnitude.     

Self-deflection of partially spatially incoherent beams and solitons in photovoltaic photorefractive crystals

By considering the effect of background light and diffusion, the self-deflection process of partially spatially incoherent (PSIC) beams and photovoltaic (PV) solitons in open-circuit PV photorefractive crystals has been investigated by employing numerical method and the perturbation technique, respectively. The results from the two approaches are in good agreement: the center of PSIC PV solitons moves on a parabolic trajectory, which is similar to those of coherent solitons. In addition, we also discuss that the dependence of self-deflection effect on the coherent parameter θ₀ and find it is slight relative to θ₀ for quasi-soliton but decreases monotonously with θ₀ for PSIC beam.     

Correlated imaging with shaped spatially partially coherent light

Using a classical source generating a field with an adjustable degree of spatial coherence, we propose and demonstrate a two-photon correlated Fourier imaging scheme in which both amplitude and phase information about the spatial frequencies of an object can be obtained. The effects of the incident field's partial coherence are discussed in a geometrical optics approach.     

Pattern formation by spatially incoherent light in a nonlinear ring cavity

Modulation instability and pattern formation by spatially incoherent light is investigated experimentally in a nonlinear ring cavity using a photorefractive strontium barium niobate crystal as the nonlinear medium. A step-like threshold for the onset of pattern formation is observed experimentally for the case of high optical feedback. When compared to the case without feedback, this threshold is shifted towards smaller nonlinearities and a significant increase of the modulation degree of the obtained patterns is obtained. Our measurements also show that, above threshold, the dominating spatial frequency of the patterns decreases monotonically with both increasing nonlinearity and increasing feedback. PACS 42.65.Tg; 42.65.Sf; 89.75.Kd     

Rapid laser fabrication of microlens array using colorless liquid photopolymer for AMOLED devices

Microlens array (MLA) is microfabricated using Ultra Violet (UV) laser for display device applications. A colorless liquid photopolymer, Norland Optical Adhesive (NOA) 60, is spin-coated and pre-cured via UV light for completing the laser process. The laser energy controlled by a galvano scanner is radiated on the surface of the NOA 60. A rapid thermal volume expansion inside the material creates microlens array when the Gaussian laser energy is absorbed. The fabrication process conditions for various shapes and densities of MLA using a non-contact surface profiler are investigated. Furthermore, we analyze the optical and display characteristics for the Organic Light Emitting Diode (OLED) devices. Optimized condition furnishes the OLED with the enhancement of light emission by 15%. We show that UV laser technique, which is installed with NOA 60 MLA layer, is eligible for improving the performance of the next generation display devices.     

Propagation of spatially partially coherent emission from a vertical-cavity surface-emitting laser

Recently we observed a strong reduction of spatial coherence of the emission of large-aperture vertical-cavity surface-emitting lasers when they are driven by microsecond electrical pulses [Opt. Express 13, 9337 (2005)]. We study the influence of this partial spatial coherence on the propagation characteristics. The spatial decoherence manifests itself in the formation of a Gaussian far-field intensity distribution. We measure the transverse pulse profile from near to far field and see that the shape-invariant far-field regime starts after 140 microm in the pulsed regime as opposed to several centimeters in continuous wave operation. This value matches quantitatively calculations made with a novel partially coherent propagation model without any free fitting parameters.     

White light emission from ultraviolet laser diode

A phosphor-conversion white light using an InGaN laser diode that emits 405 nm near-ultraviolet (n-UV) light and phosphors that emit in the red/green/blue region when excited by the n-UV light was fabricated. The relationship of the luminous flux and the luminous efficacy of the white light with injection current were discussed. Based on the evaluation method for luminous efficacy of light sources established by the Commission International de I’Eclairage (CIE) and the phosphor used in this experiment, a theoretical analysis of the experiment results and the maximum luminous efficacy of this white light fabrication method were also presented.     

A partially incoherent, periodic, pulsed light source for optical flow studies

A new shadowgraph device, using a partially incoherent source generated by the sweep of a focused laser beam, is described. The exposure time is easily adjustable from a few microseconds to continuous illumination. The application of such a method on supersonic free jets is presented.     

饱和对数非线性介质中非相干孤子碰撞对相干性的改善

基于相干密度理论，数值地研究了饱和对数非线性支持的部分非相干亮孤子对的相互作用.研究表明，两个非相干亮孤子碰撞不仅能增大碰撞区的光强，还可以大大改善部分非相干光束的相干性.同时还研究了非相干性对孤子碰撞的影响，非相干性不仅抑制了孤子间的相干作用如吸引、排斥和能量交换，同时还由于非相干叠加作用而引入了弱的相互吸引. 关键词： 非相干性 饱和对数非线性 空间光孤子     

Broad band enhanced infrared light absorption of a femtosecond laser microstructured silicon

Absorptive properties of surface-structured silicon prepared by femtosecond laser pulses irradiating in SF₆ or N₂ are measured in a wide wavelength range of 0.3–16.0 μm. The SF₆-prepared surface-structured silicon shows enhanced light absorptance up to 80% or more in the entire measured wavelength range. The absorptance for N₂_prepared surface-structured silicon in the wavelength range of 9–14 µm is similar to that of a SF₆-prepared sample, although it decreases to about 30% in the wavelength range of 2–7 µm. Light absorption varies with the height and density of the spikes formed on silicon surfaces.     

Single laser exposure fabrication of diamond-like 3-dimensional photonic crystal microstructures using circularly polarized light

Phase tunable multi-level diffractive optical elements define an attractive approach for single laser exposure fabrication of 3-dimensional photonic crystal microstructures. The significant advantage of these multi-level diffractive optical elements over two-level diffractive optical elements is the flexibility of fabricating a wide range of 3-dimensional periodic structures by manipulating the relative phase of different diffracted beams. Here, phase tuning was applied to demonstrate fabrication of a hybrid 3-dimensional structure intermediate between previously reported diamond-like Woodpile-type structure of tetragonal symmetry and structure having body-centered-tetragonal lattice symmetry. Circularly polarized light was applied for the first time to balance the diffraction order efficiencies and improve the structural uniformity. Design guidelines are presented for generating diamond-like photonic crystal template that possesses complete photonic bandgap when inverted with high refractive index materials.     

Nonvolatile two-color holographic recording in near-stoichiometric lithium niobate crystals gated by incoherent ultraviolet light

Nonvolatile two-color holographic recording gated by incoherent ultraviolet （UV） light centered at 365 nm is investigated in near-stoichiometric lithium niobate crystals. The influence of thermal treatment on the two-color recording is studied. The results show that thermal reduction tends to improve the two-color recording performance, whereas thermal oxidation degrades the two-color recording. With an incoherent 0.2-W/cm2 UV gating light and a 0.25-W/cm2 semiconductor recording laser at 780 nm, a two-color recording sensitivity of 4 × 10^-3 cm/J and a recording dynamic range characterized by M/# of 0.12 are achieved in a 2.2-mm thermally reduced near-stoichiometric lithium niobate crystal. We attribute the improvement to the prolonged lifetime of small polarons and the increased absorption at the gating wavelength due to thermal reduction.     

Generation of sub-Poisson light by a single-mode two-level laser with incoherent pumping

It is found that the steady-state radiation of a single-mode two-level laser with incoherent pumping can be in a nonclassical (sub-Poisson) state if the spontaneous decay rate is less than the cavity loss rate and the pumping rate. The optimal conditions of squeezing are found. Multiple squeezing of the radiation intensity is possible in a transient lasing regime. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 755–759 (25 May 1998)     

Stimulation of E. coli growth by laser and incoherent red light

Summary The effect of low-intensity He−Ne laser radiation (λ=632.8 nm) and incoherent red light on DNA synthesis and cell division in Escherichia coli has been studied. It has been shown that the radiations of He−Ne laser (λ=632.8 nm) and filament lamp (λ=(631±4) nm) stimulate DNA synthesis and cell growth at doses of 10³ to 10⁴ J/m². The highest level of DNA synthesis is observed 10 min after irradiation and the difference in the numbers of irradiated and control cells is maximum 1 or 2 h after irradiation. The action spectrum of visible light on the growth rate of E. coli cells (from 560 nm to 640 nm) has been measured. The action spectrum has its maximum at (620±7) nm.

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Riassunto Si è studiato l'effetto della radiazione laser He−Ne a bassa intensità e della luce rossa incoerente sulla sintesi del DNA e sulla divisione della cellula in Escherichia coli. Si è mostrato che le radiazioni del laser He−Ne (λ=632.8 nm) e della lampada con filamento (λ=(631±4) nm) stimolano la sintesi del DNA e la crescita cellulare a dose di (10³⋎10⁴) J/m². Il piú alto livello di sintesi del DNA è osservato 10 min dopo l'irradiazione e la differenza nei numeri di cellule irradiate e di controllo è massima 1 o 2 ore dopo irradiazione. Si è misurato lo spettro d'azione della luce visibile sul rapporto di crescita delle cellule di E. coli (da 560 nm a 640 nm). Lo spettro d'azione ha il suo massimo a (620±7) nm.

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Резюме Изучалось влияние низконтенсивного излучения He−Ne лазэра (λ=632.8 нм) и некогерентного красного света на синтез ДНК и клеточное деление в клэтках Escherichia coli. Показано, что как излучение He−Ne лазера, так и лампьи накаливания (λ=(631±4) нм) стимулирует синтез ДНК и клетпчное леление в дозах (10⁻²⋎10⁻³) Джм². Наиболее вьисокий уровень синтеза ДНК наблюлаеттся чурез 10 минут после облучения, скорость клеточногхого делэния максимальна через (1⋎2) часа после облучения. Измерен спектр действия видимого света на скрость деления клеток E. coli от λ=560 нм до λ=640 нм. Спектр действия имеет максимум при (620±7) нм.