Modulation instability with incoherent white light in self-defocusing photorefractive crystal

We report on the first experimental observation of modulation instability and spontaneous pattern formation with incoherent white light emitted from an incandescent lamp in self-defocusing photorefractive LiNbO₃:Fe crystal. Experimental results show that the modulation instability of white light in self-defocusing medium is related to the input intensity, illumination time and the direction of the crystalline c-axis with respect to that of the lamp filament. At the illumination time t = 0 and the steady-state of MI, we give the spatial distribution of the optical Fourier power spectrum experimentally and the corresponding Fourier transformation of the output intensity numerically, and observe the emergence of the high frequency component along the c-axis.     

Spontaneous optical fractal pattern formation

We report, for the first time, spontaneous nonlinear optical spatial fractals. The proposed generic mechanism employs intrinsic nonlinear dynamics both to generate an initial pattern seed and to fill out structure across decades of spatial scale. We demonstrate this in one of the simplest of nonlinear optical systems, composed of a Kerr slice and a single-feedback mirror. In this case, the smallest pattern scales are limited by either the optical wavelength or the diffusion length of the medium photoexcitation. The dimension characteristics of these particular fractals are also derived.     

Spontaneous pattern formation in a polariton condensate

Exciton-polariton condensation can be regarded as a self-organization phenomenon, where phase ordering is established among particles in the system. In such condensed systems, further ordering can occur in the particle density distribution, under particular experimental conditions. In this work we report on spontaneous pattern formation in a polariton condensate under nonresonant optical pumping. The slightly elliptical ring-shaped excitation laser that we employ forces condensation to occur into a single-energy state with periodic boundary conditions, giving rise to a multilobe standing-wave patterned state.     

Optical correlation with totally incoherent light

An optical correlator that can operate with totally incoherent light is presented. Such a correlator can be designed to compensate completely for the inherent chromatic aberrations by resorting to elements with specialized, possibly impractical, dispersion characteristics. Nevertheless, a practical configuration that exploits available achromatic lenses and Fresnel zone plates was designed, built, and tested experimentally. The results reveal that detectable correlation peaks can be obtained with totally incoherent white light. The designs, experimental procedures, and results are presented.     

Interaction between a dark spot and a two-dimensional nonlinear photonic lattice with fully incoherent white light

We study experimentally the interaction of a dark spot with a nonlinear photonic lattice with fully incoherent white light emitted from an incandescent bulb in the self-defocussing photovoltaic media when the dark spot is aimed at different positions of lattices with different lattice spacing. In this case a host of novel phenomena is demonstrated, including dark spot induced lattice dislocation-deformation, the annihilation of the dark spot and so on. Results demonstrate that the interaction between incoherent dark spot and photonic lattice is always attraction and the large-spacing photonic lattice is analogous to the continuous medium.     

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     

Phase filters for correlators with incoherent light

Optimized phase filters can be designed and incorporated into hybrid electronic-optic correlators that exploit incoherent light. These filters lead to high optical efficiency and little, if any, loss of information that normally result from discarding amplitude data. The optimization procedure was experimentally tested by recording optimized filters in photo resist and incorporating them into the correlator. The optimization algorithm, the filter recording procedures, and the experiment correlation results demonstrating the efficacy of our design are presented. These results are superior when compared to those of correlators using holographic filters.     

量子态的非相干光时域测量

提出了利用非相干光实现对量子态的时域高分辨率测量的新方法.以测量Autler-Townes效应为例,通过对信号解析表达式的详细讨论,阐述了利用这种方法测量量子态的物理过程,揭示出被测量的演化规律及测量过程对量子态的影响.研究结果表明利用这种方法既可以有效地、高分辨地测量很小的量子态能级间距和很大的原子能级间距,同时又可以测量相干量子态的横向弛豫速率.通过对时域和频域测量方法的比较表明利用非相干光对量子态的时域测量可以全面揭示量子态演化信息. 关键词： 非相干光 量子态测量 Autler-Townes 效应     

Optical security and encryption with totally incoherent light

We present a method for securing and encrypting information optically by use of totally incoherent illumination. Encryption is performed with a multichannel optical processor working under natural (both temporal and spatially incoherent) light. In this way, the information that is to be secured can be codified by use of color signals and self-luminous displays. The encryption key is a phase-only mask, providing high security from counterfeiting. Output encrypted information is recorded as an intensity image that can be easily stored and transmitted optically or electrically. Decryption or authentication can also be performed optically or digitally. Experimental results are presented.     

Bacteriorhodopsin modules for data processing with incoherent light

Incoherent optical processing with films made from the biological photochrome bacteriorhodopsin (BR) is accomplished by use of the photoinducible anisotropy of polymeric BR films. BR has two spectrally well separated states, B and M, both of which show a high degree of optical anisotropy. Whereas with green and blue light the BR molecule can be switched between the two states, the accompanying changes in the refractive index may be nondestructively read out by wavelengths in the red, e.g., at 676nm. As the sensitivity of CCD arrays is quite high for such wavelengths, even low-power light sources are sufficient for detection. We describe a BR-based XOR computing module for incoherent optical data processing.     

Spontaneous pattern formation induced by ion bombardment of binary compounds

A theory is developed that explains the genesis of the strikingly regular hexagonal arrays of nanoscale mounds that can form when a flat surface of a binary compound is subjected to normal-incidence ion bombardment. We find that the species with the higher sputter yield is concentrated at the peaks of the nanodots and that hysteretic switching between the flat and the hexagonally ordered state can occur as the sample temperature is varied. Surface ripples are predicted to emerge for a certain range of the parameters.     

Spontaneous pattern formation in an effectively one-dimensional dielectric-barrier discharge system

In a dielectric-barrier discharge between diametrically opposite sides of a narrow tube, discharge filaments stabilize at regular intervals along the tube's length. Three types of periodic patterns are observed, as is a disordered state in which filaments fire at apparently random positions and times. Time-resolved current measurements indicate that for each spatial pattern, a particular number of discharge stages occur during the voltage half-cycle. A preliminary model of the pattern-formation dynamics is described, motivating further work on time-resolved imaging and investigations of surface charge distributions.     

Spontaneous nano pattern formation under pulsed exposure: relaxation kinetics study

Formation of spontaneous surface relief grating under pulsed exposure on the surface of an azo polymer film has been investigated. We did experiments in different repetition rates and pulse widths by use an electro mechanical chopper and a diode-pumped solid-state laser with wavelength of 532?nm as pump beam. Incidence of pump beam, has been set normal to the surface of azo-polymer film. Spontaneous surface relief grating with grating pitch of ~1,250?nm was formed. For low repetition rate, relaxation due to cis-trans isomerization becomes dominant and growth rate becomes slower. A threshold for spontaneous pattern formation was found. In addition to an increase in the diffraction intensity during illumination, anomalous variation of diffraction intensity by switching on and off the laser was observed. By switching off the recording beam sharp enhancement occurred. By switching on the recording beam, after a sharp decrease in the intensity of diffracted beam, it increased further under illumination. Anomalous variations, strongly depends on polarization of the probe beam and the irradiation time for the formation of spontaneous SRG. Sharp enhancement has been attributed to cis-trans thermal isomerization and sharp decrease has been attributed to isomeration in whole surface under illumination.     

Interferometric coherent Raman spectroscopy with incoherent light: Some applications

The theory of Interferometric Coherent Raman Scattering (ICRS) using twin broadband fields has recently been extended to include both resonant and nonresonant contributions to the signal. It is reviewed here. Valid for both ICARS and ICSRS, it is applied to new ICARS experiments on neat toluene and on alcoholic solutions of a methine dye. In each case the damped Rabi Detuning Oscillations (RDO), that are characteristic of ICRS, lead directly to vibrational frequencies and their dephasing times. The theory is also applied as a new way to determine the ratio of the nonresonant to resonant hyperpolarizabilities, accurately for toluene, and approximately for the methine dye solution whose (vibrationally) nonresonant contribution is negative.     

完全非相干白光一维光生伏打暗空间孤子

使用白炽灯作光源在LiNbO₃∶Fe晶体内实验观察到一维白光光生伏打暗空间孤 子. 由奇数 和偶数初始条件分别产生了灰孤子和灰孤子对，它们所感应的波导能导向白光和相干光. 用 相干光清楚地探测到它们内部的多模结构. 该实验证明了白光光生伏打暗空间孤子的存在， 并指出了用完全非相干的白光暗孤子控制和导向相干光的可能性. 关键词： 光生伏打效应 自陷 完全非相干孤子 波导     

Signal-to-noise ratio of lensless ghost interference with thermal incoherent light

Factors influencing the signal-to-noise ratio (SNR) of lensless ghost interference with thermal incoherent light are investigated.Our result shows that the SNR of lensless ghost interference is related to the transverse length of the object,the position of the object in the imaging system and the transverse size of the light source.Furthermore,the effects of these factors on the SNR are discussed in detail by numerical simulations.