Intensity Correlations Of Light Research Articles

Correlation Hyperspectral Imaging.

Hyperspectral imaging aims at providing information on both the spatial and the spectral distribution of light, with high resolution. However, state-of-the-art protocols are characterized by an intrinsic trade-off imposing to sacrifice either resolution or image acquisition speed. We address this limitation by exploiting light intensity correlations, which are shown to enable overcoming the typical downsides of traditional hyperspectral imaging techniques, both scanning and snapshot. The proposed approach also opens possibilities that are not otherwise achievable, such as sharper imaging and natural filtering of broadband spectral components that would otherwise hide the spectrum of interest. The enabled combination of high spatial and spectral resolution, high speed, and insensitivity to undesired spectral features shall lead to a paradigm change in hyperspectral imaging devices and open up new application scenarios.

High quality underwater computational ghost imaging based on speckle decomposition and fusion of reconstructed images

Ghost imaging (GI) is an imaging method that reconstructs object information via light-intensity correlation measurements. The unconventional imaging mechanism of GI makes it suitable for imaging in scattering medium, for instance, turbid liquid, biological tissues, etc. However, the strong background noise in the reconstructed images is still the bottleneck problems. In this paper, we focus on the improvements of the reconstructions in underwater GI and propose a speckle decomposition and fusion method for suppressing the noise. The approach utilized computational ghost imaging framework and dictionary learning to acquire high- and low-frequency components that are better suited for image feature-based reconstruction. Furthermore, once the suitable threshold has been established, the speckles captured from the reference path are decomposed using the Nonsubsampled Contourlet Transform (NSCT). The acquired high- and low-frequency are then correlated with the overall optical intensity that captured by the bucket detectors. Ultimately, a multi-scale inverse NSCT transformation is employed to produce the final fusion-reconstructed image. The quantitative evaluation of the reconstructed image quality was conducted. In contrast to previous methodologies, the proposed method offers significant enhancements of the underwater GI imaging quality.

Research and assessment of high sensitivity intensity modulation vector curvature sensor based on cascaded bamboo-joint microcavity structure

This study presents the VC-BM, a novel vector bamboo joint cascaded microcavity curvature sensor, which utilizes light intensity correlation. The device is fabricated using arc fusion, connecting a tapered seven-core optical fiber with a multi-mode and hollow-core fiber. Meanwhile, mode-coupling theory optimizes its design for high-quality transmission spectra. The feasibility and sensitivity of vector curvature sensing via intensity modulation (VC-BM) have been demonstrated through theoretical simulations and experimental validation. Building upon this foundation, a novel envelope intensity differential modulation algorithm is proposed, which maintains curvature direction recognition and enhances sensitivity, reaching up to 243.57 ± 3.63 dB/m−1. Additionally, leveraging its advantages, the successful integration of a three-layer Backpropagation (BP) neural network has enabled predictive analysis of this curvature sensing device, thereby increasing its commercial value. Furthermore, the sensor's high stability and resistance to temperature interference make it an ideal solution for wearable micro-deformation monitoring.

Omnidirectional ghost imaging system and unwrapping-free panoramic ghost imaging.

Ghost imaging (GI) is an unconventional imaging method that reconstructs the object information via light-intensity correlation measurements. However, at present, the field of view (FOV) of this method is limited to the illumination range of light patterns. To enlarge the FOV of GI efficiently, we propose an omnidirectional GI system (OGIS) that can achieve a 360° omnidirectional FOV only via the addition of a curved mirror. The OGIS features retina-like annular patterns designed as a log-polar structure and can obtain the undistorted unwrapping-free panoramic images with uniform resolution. This research presents a new, to the best of our knowledge, perspective for the applications of GI, such as pipeline detection, a panoramic situation awareness for autonomous vehicles.

Spatial coherence of light inside three-dimensional media

Speckle is maybe the most fundamental interference effect of light in disordered media, giving rise to fascinating physical phenomena and cutting edge applications. While speckle formed outside a sample is easily measured and analysed, true bulk speckle, as formed inside random media, is difficult to investigate directly due to the obvious issue of physical access. Furthermore, its proper theoretical description poses enormous challenges. Here we report on the first direct measurements of spatially resolved intensity correlations of light inside a disordered medium, using embedded DNA strings decorated with emitters separated by a controlled nanometric distance. Our method provides in situ access to fundamental properties of bulk speckles as their size and polarization degrees of freedom, both of which are found to deviate significantly from theoretical predictions. The deviations are explained, by comparison with rigorous numerical calculations, in terms of correlations among polarization components and non-universal near-field contributions at the nanoscale.

Quantum temporal imaging of antibunching

We consider transformation of quantum intensity correlations of light, observed by direct photodetection, by a single-lens temporal imaging scheme with magnification factor M . We prove that such an imaging scheme performs noiseless stretching or contraction of the second-order intensity correlation function without deteriorating such nonclassical features as antibunching and sub-Poissonian statistics of the photons. We also evaluate the photocurrent fluctuation spectrum for the photodetection of nonclassical light and show that this temporal imaging scheme performs its noiseless scaling by magnification factor M without adding any noise. We illustrate our results by two examples of nonclassical light sources: sub-Poissonian laser as a continuous-wave macroscopic nonclassical light source exhibiting antibunching and sub-Poissonian statistics of photons and single-photon source as its pulsed counterpart possessing similar nonclassical features. Our results open interesting possibilities for noiseless control of temporal and spectral characteristics of nonclassical light and can find numerous practical applications in quantum optics and quantum information.

Efficient coding of natural scene statistics predicts discrimination thresholds for grayscale textures.

Previously, in Hermundstad et al., 2014, we showed that when sampling is limiting, the efficient coding principle leads to a 'variance is salience' hypothesis, and that this hypothesis accounts for visual sensitivity to binary image statistics. Here, using extensive new psychophysical data and image analysis, we show that this hypothesis accounts for visual sensitivity to a large set of grayscale image statistics at a striking level of detail, and also identify the limits of the prediction. We define a 66-dimensional space of local grayscale light-intensity correlations, and measure the relevance of each direction to natural scenes. The 'variance is salience' hypothesis predicts that two-point correlations are most salient, and predicts their relative salience. We tested these predictions in a texture-segregation task using un-natural, synthetic textures. As predicted, correlations beyond second order are not salient, and predicted thresholds for over 300 second-order correlations match psychophysical thresholds closely (median fractional error <0.13).

Connecting field and intensity correlations: The Siegert relation and how to test it

The Siegert relation relates electric field and intensity correlations of light, under given assumptions. After a brief derivation of the relation, we present an experimental setup that can be implemented in a student laboratory: it allows measuring both field and intensity correlations at the same time, thus providing a direct test of the Siegert relation. Some experimental results are presented when the scattering medium corresponds to a cold atomic cloud. As a conclusion, we discuss typical situations where the relation fails.

Color contamination correction based on light intensity correlation in two-color, double-exposure particle tracking velocimetry

An algorithm for correcting color contamination is proposed for two-color, double-exposure particle tracking velocimetry (PTV). A two-color PTV system used in this study consists of blue and green laser diodes and a consumer digital camera, where a laser pulser with an avalanche transistor is developed for achieving optical pulses of 50 ns for application in airflows. In the PTV, the camera captures images of tracer particles illuminated by a sequence of green and blue light pulses with a certain time interval. Because of spectral characteristics of a Bayer filter, camera sensors in a blue channel respond to green light scattered by the particles. This color contamination results in pseudo-particles in the blue channel. Pixels occupied by the pseudo-particles have very high correlation of light intensity between green and blue channels. In the proposed method, the pseudo-particles caused by the color contamination are detected and removed based on the high correlation. The present color contamination correction hardly affects real particles illuminated by the blue laser diodes. Measurements of an airflow induced by DC fans confirm that the proposed system with the color contamination correction works well for PTV.

Photon bunching and N-photon interference in thermal light

Abstract We investigate the contribution of four-photon bunching term in fourth-order double-slit interference intensity correlation based on two different detection schemes with a pseudo-thermal light source. It is clearly demonstrated that the resolution of intensity correlation is significantly enhanced by using of double-slit in both fourth-order and third-order intensity correlation. Meanwhile, the visibility of fourth-order correlation can be dramatically improved in contrast to the third-order due to the four-photon bunching term by contributing in the visibility of fourth-order correlation. The position and full width at half maximum of interference peaks of fourth-order intensity correlation are same as third-order. We also use two different scanning approaches to change the resolution and visibility of interference intensity correlation. In the first detection scheme, we scan three reference detectors along the same orientation and speed. In second detection scheme we scan two of three reference detectors in the same orientation, and speed of one reference detector is twice that of the other, and simultaneously moving the other two reference detectors with opposite orientation but identical speed. Those investigations can also be promoted to high order intensity correlation of thermal light.

Measurement of the two-time intensity-correlation function of arbitrary states

For light intensity correlations measurements, different methods are used in the high photon number or high intensity regime and in the single- and two-photon regime. Hence, there is an unfortunate ...

Study of MicroMegas-based detector with ICCD imaging

Micro Pattern Gas Detector (MPGD) coupled to an optical imaging system is a good candidate for detecting polarization of X-ray, dark matter, neutron, etc. In this paper, a MicroMegas detector is designed for detecting the photoelectron track of X-ray, which working gas compose of an Ar+CF4 mixture and optical signal readout with an ICCD. The correlation of scintillation light intensity and electrical current is obtained in the varying strength of the electric field at avalanche region, and the position resolution is 385 μm. The clear track images of the 241Am alpha source and 5.9 KeV X-ray are obtained, and the X-ray imaging is achieved in the experiment.

Nonclassical storage and retrieval of a multiphoton pulse in cold Rydberg atoms

We investigate the storage and retrieval of a multiphoton probe field in cold Rydberg atoms with an effective method based on the superatom model. This probe field is found greatly attenuated in light intensity and two-photon correlation yet suffering little temporal broadening as a result of the partial dipole blockade of Rydberg excitation. In particular, the output field energy exhibits an intriguing saturation effect against the input field energy accompanied by an inhomogeneous nonclassical antibunching feature as a manifestation of the dynamic cooperative optical nonlinearity. Our numerical results are qualitatively consistent with those in a recent experiment and could be extended to pursue quantum information applications of nonclassical light fields.

Ghost Spectroscopy with Classical Thermal Light Emitted by a Superluminescent Diode

Ghost modalities are by no means ``spooky actions'', but are metrology schemes exploiting intensity correlations of light, based on the fundamentals of quantum optics. The authors demonstrate ghost spectroscopy based on classical photon correlations in the wavelength domain of broad-band light emitted by an ultraminiaturized superluminescent semiconductor diode. Comprehensive proof of principle is provided by a real-world experiment on chloroform at 1214 nm. This demonstrated analogy between ghost imaging and ghost spectroscopy is expected to further fertilize the field, to promote a deeper understanding, and to lead even to other protocols in ghost metrology.

Role of weather parameters on seasonal abundance of insects in a mangobased agroforestry in Bangladesh, with particular reference to mango hopper

Weekly sweeping was done by sweep net in order to collect insects to study the effect of weather parameters on the seasonal abundance of total insect species as well as mango hopper population in a mango-based agroforestry in Bangladesh during January to June 2013. The total insect species abundance was the highest during April to May, following the flushing of inflorescence and fruit set. At that time temperature and relative humidity were comparatively higher and there was rainfall. Mango hopper population was the highest in May and synchronized to fruit set. The abundance of total insect species and mango hopper population showed significant positive correlation with temperature, and relative humidity, while significant negative correlation with light intensity and non-significant positive correlation with rainfall. Multiple linear regression equation based on weather parameters revealed 59.2% and 61.7% role on population build up of total insect species and mango hopper, respectively. Temperature was found to be the most important effect which individually contributed 31.3% on population abundance of total insect species and 29.9% on mango hopper.Bangladesh J. Agril. Res. 42(2): 197-205, June 2017

Measuring anisotropy ellipse of atmospheric turbulence by intensity correlations of laser light.

An experimental study has been performed of a laser beam propagating horizontally through the near-ground atmosphere above a grassy field at the University of Miami (UM) Coral Gables campus. The average intensity, scintillation index, and intensity correlation function are measured in the receiver plane for three channels with different turbulent conditions and at three different heights above the ground. Our results reveal that along short links (210m) only the intensity correlation function captures the anisotropic information of turbulence, corresponding to the refractive index anisotropy ellipse of atmospheric fluctuations. In addition, we report an interesting phenomenon relating to turbulence eddy orientation near the ground. We confirmed that the experimental results are in agreement with the numerical simulations based on the multiple phase-screen method. Our findings provide an efficient method of determining the anisotropic parameters of atmospheric turbulence.

Correlation between intensity fluctuations of electromagnetic waves scattered from a spatially quasi-homogeneous, anisotropic medium.

Within the validity of the first-order Born approximation, expressions are derived for the correlation between intensity fluctuations (CIF) of an electromagnetic plane wave scattered from a spatially quasi-homogeneous (QH), anisotropic medium. Upon establishing the correlation matrix of the scattering potential of the medium, we show that the CIF is the summation of Fourier transforms of the strengths and normalized correlation coefficients (NCCs) of the scattering potential matrix. Numerical results reveal that the CIF is susceptible to the effective width and correlation length of the medium, and degree of polarization of the incident electromagnetic wave. Our study not only extends the current knowledge of the CIF of a scattered field but also provides an important reference to the study of high-order intensity correlations of light scattered from a spatially anisotropic medium.

Temporal intensity correlation of light scattered by a hot atomic vapor

We present temporal intensity correlation measurements of light scattered by a hot atomic vapor. Clear evidence of photon bunching is shown at very short time-scales (nanoseconds) imposed by the Doppler broadening of the hot vapor. Moreover, we demonstrate that relevant information about the scattering process, such as the ratio of single to multiple scattering, can be deduced from the measured intensity correlation function. These measurements confirm the interest of temporal intensity correlation to access non-trivial spectral features, with potential applications in astrophysics.

Cooperative nonlinear grating sensitive to light intensity and photon correlation.

Utilizing dipole blockade of Rydberg excitations, we study an ensemble of stationary atoms driven into the four-level N configuration for achieving a new kind of electromagnetically induced grating in the presence of a traveling-wave and a standing-wave classical control fields. This grating shows cooperative optical nonlinearities as manifested by the sensitivity of output diffraction patterns to input light intensities (photon correlations) of a quantum probe field, promising then an essential opportunity for distinguishing weaker and stronger (bunched and anti-bunched) light fields.

Pattern recognition based on the correlated intensity fluctuations of thermal light.

Here we present a pattern recognition scheme based on the intensity correlation of thermal light. We prove theoretically that under spatially incoherent illumination the matched filtering technique can be realized in the ghost imaging field. Using the matched filtering technique, it is possible to distinguish an object from a preestablished set of objects through their ghost images, which are extracted by means of intensity correlation measurement. According to the pattern recognition scheme, we present a numerical simulation in which we can easily identify the character inserted into the object arm from a set of two characters through the position of the autocorrelation peak. This pattern recognition scheme opens up the possibility of performing coherent optical processing under spatially incoherent illumination.