Pseudo-thermal Light Source Research Articles

Visibility and Resolution Enhancement of Fourth-Order Ghost Interference with Thermal Light

A scheme for fourth-order double-slit ghost interference with a pseudo-thermal light source is proposed. It is shown that not only can the visibility be dramatically enhanced compared to the third-order case, but also higher resolution is demonstrated if we scan two of three reference detectors in opposite directions with the same speed, meanwhile another two in identical directions where the speed of one reference detector is twice the other. The results show that the visibility and resolution improvement of the fourth-order ghost interference fringe can be applied to the N th-order ghost imaging.

Resolution and visibility of two-color pseudothermal lensless ghost imaging

Two-color (or nondegenerate-wavelength) lensless ghost imaging using pseudothermal light source is investigated theoretically by use of classical optical coherence theory. We find that for two-color pseudothermal lensless ghost imaging the visibility and resolution is determined by (Δ) the product of the wavelength and the corresponding path length rather than the wavelength for each path or the path length. We also confirm our theoretical conclusion by numerical simulations. The result shows we must make a trade-off between resolution and visibility in devise practical experiments, as the resolution of the imaging can be improved by decreasing Δ but with visibility getting poor, and vice versa.

Imaging through aberrating media by computational ghost imaging with incoherent light

We demonstrate a series of experiments on imaging through both stationary aberrating media and moving aberrating media by computational ghost imaging (CGI). An incoherent LED light source is used instead of the common pseudothermal light source (laser light passing through a rotating ground glass). A digital micromirror device is used as a simple spatial light modulator to perform CGI. Moreover, a digital filtering method is introduced to improve imaging quality through moving aberrating media. This imaging modality may have potential applications in medicine and astronomy.

基于不同调制方法产生赝热光源的性能比较

基于不同调制方法产生赝热光源的性能比较

Real-Time Data Acquisition for Long-Distance Reflective Ghost Imaging Experiment

We present a real-time data acquisition (DAQ) system for the long-distance reflective ghost imaging experiment which has broad application prospects in remote sensing. In the experimental setup, the light from a pseudo thermal light source is separated into signal beam and reference beam. The signal beam illuminates the target, and then the reflected light is collected by a bucket detector. In the mean time, the reference beam is directly captured by an area detector. In order to obtain the target image, the experiment requires high-speed and high-precision correlated data acquisition to collect the light intensity fluctuation in the signal beam and the reference beam. Furthermore, to reduce imaging time, real-time data acquisition is also required. The DAQ system consists of a photon-multiplier tube (PMT), a charge-coupled device (CCD) camera, a DAQ module and DAQ software. The CCD camera as the area detector connects to computer via Gigabit Ethernet. The PMT and a telescope compose the bucket detector which outputs signals to the DAQ module. The DAQ module sends acquired data to computer through universal serial bus (USB). The DAQ software collects the data and reconstructs the target image. The results of electronic tests and experiments show that the DAQ system satisfies the requirements of the experiment.

Weak localization of photon noise

We present an experimental study of coherent backscattering (CBS) of photon noise from multiple scattering media. We use a pseudothermal light source with a microsecond coherence time to produce a noise spectrum covering a continuous transition, from wave fluctuations to shot noise over several MHz. The angle-dependent Fano factor of backscattered light shows an enhancement due to CBS in the wave fluctuation regime. The CBS line shape and enhancement factor of the noise power is consistent with theory in the weak-scattering limit and for a large number of open reflection channels. These initial experiments on weakly scattering media demonstrate that sensitive noise measurements can be combined with the separation of path lengths present in CBS, opening up new experiments on noise transport in the localization regime.

Role of intensity fluctuations in third-order correlation double-slit interference of thermal light

A third-order double-slit interference experiment with a pseudothermal light source in the high-intensity limit has been performed by actually recording the intensities in three optical paths. It is shown that not only can the visibility be dramatically enhanced compared to the second-order case as previously theoretically predicted and shown experimentally, but also that the higher visibility is a consequence of the contribution of third-order correlation interaction terms, which is equal to the sum of all contributions from second-order correlation. It is interesting that, when the two reference detectors are scanned in opposite directions, negative values for the third-order correlation term of the intensity fluctuations may appear. The phenomenon can be completely explained by the theory of classical statistical optics and is the first concrete demonstration of the influence of the third-order correlation terms.

Measurement of Photon Statistics with Live Photoreceptor Cells

We analyzed the electrophysiological response of an isolated rod photoreceptor of Xenopus laevis under stimulation by coherent and pseudothermal light sources. Using the suction-electrode technique for single cell recordings and a fiber optics setup for light delivery allowed measurements of the major statistical characteristics of the rod response. The results indicate differences in average responses of rod cells to coherent and pseudothermal light of the same intensity and also differences in signal-to-noise ratios and second-order intensity correlation functions. These findings should be relevant for interdisciplinary studies seeking applications of quantum optics in biology.

Temporal correlation of photons following frequency up-conversion

We demonstrate an approach to measure temporal correlations of photons in the near infrared range using frequency up-conversion. In this approach, the near infrared signal photons are converted into the visible range, in which highly efficient silicon avalanche photodiodes are used to perform the temporal correlation measurements. A coherent light source and a pseudo-thermal light source were used in the experiment. The results are in agreement with theoretical values and those obtained from measurements directly made using superconducting nanowire single photon detectors. We conclude that the temporal correlation (up to 4th order) of photons was preserved in the frequency up-conversion process. We further theoretically and experimentally studied the influence of the dark counts on the measurement. The setup uses commercially available components and achieves high total detection efficiency (~26%).

Effects of thermal light source properties in two-photon subwavelength coincidence interference experiments

We perform two-photon coincidence subwavelength interference experiments from double slit using independent photons obtained from a pseudo-thermal light source produced by (i) slowly rotating ground glass (RGG) with turbid solution of a different density and (ii) RGG. The turbid solution is water solution containing 3 μm diameter polystyrene microspheres. It is found that the visibility of the obtained interference pattern decreases in first experiment with increasing the density of the turbid solution from N = 10 10 spheres m −3 to N = 10 14 spheres m −3. However, the results are reported here for the density of N = 10 14 spheres m −3. The visibility obtained with RGG with turbid solution having N = 10 14 spheres m −3is 23% which increases to 27% with RGG but the resolution decreases. The effect of coherence width of source in two-photon interference pattern is also studied with pseudo-thermal light obtained by RGG. It was observed that on increasing the coherence width the visibility of interference fringes increased and quality of the fringe reduced and when the coherence width was more then slit separation, in coincidence measurements, no interference pattern appeared. The results are used to explore the classical subwavelength interference nature with thermal light.

The influence of source and object characteristics on coincidence imaging

A classical coincidence imaging or ghost imaging experiment is carried out in a two-photoncounting regime using a pseudo-thermal incoherent light source. The effect of thetransverse size and transverse coherence width of the source on the visibility andthe resolution of the reconstructed ghost image is studied. It is observed thatby increasing the transverse size of the source, the resolution (quality) of thereconstructed image improves, while the visibility reduces. On the other hand, as thecoherence width of the source increases, the visibility of the image increases but theresolution becomes poor. The effect of object characteristics on the visibility ofthe ghost image is also studied and it is found that by increasing the number oftransparent features and the surface size of the object, the visibility of the imagedecreases. These experimental results validate the theoretical results published sofar.

High-order temporal coherences of chaotic and laser light

We demonstrate a new approach to measuring high-order temporal coherences that uses a four-element superconducting nanowire single-photon detector. The four independent, interleaved single-photon-sensitive elements parse a single spatial mode of an optical beam over dimensions smaller than the minimum diffraction-limited spot size. Integrating this device with four-channel time-tagging electronics to generate multi-start, multi-stop histograms enables measurement of temporal coherences up to fourth order for a continuous range of all associated time delays. We observe high-order photon bunching from a chaotic, pseudo-thermal light source, measuring maximum third- and fourth-order coherence values of 5.87 +/- 0.17 and 23.1 +/- 1.8, respectively, in agreement with the theoretically predicted values of 3! = 6 and 4! = 24. Laser light, by contrast, is confirmed to have coherence values of approximately 1 for second, third and fourth orders at all time delays.

Effects of pseudothermal light source's transverse size and coherence width in ghost-interference experiments

Ghost interference is experimentally investigated by varying the pseudothermal light source's transverse size and coherence width. Our results show that by increasing the transverse size of the source the quality of the interference pattern is improved, while the visibility is reduced. On the other hand, by increasing the coherence width of the source, the visibility of the interference pattern is improved, while the quality is reduced. These experimental results corroborate previous theoretical results.

Observation of complementarity in the macroscopic domain

Complementarity is usually considered as a phenomenon of microscopic systems. In this paper, we report an experimental observation of complementarity in correlated double-slit interference with a pseudothermal light source. The thermal light beam is divided into test and reference beams which are correlated with each other. The double slit is set in the test arm, and an interference pattern can be observed in the intensity correlation between the two arms. The experimental results show that the disappearance of the interference fringe depends on whether which-path information is gained through the reference arm. The experiment therefore shows complementarity occurring in the macroscopic domain.

Modelling of classical ghost images obtained using scattered light

The images obtained in ghost imaging with pseudo-thermal light sources are highly dependent on the spatial coherence properties of the incident light. Pseudo-thermal light is often created by reducing the coherence length of a coherent source by passing it through a turbid mixture of scattering spheres. We describe a model for simulating ghost images obtained with such partially coherent light, using a wave-transport model to calculate the influence of the scattering on initially coherent light. The model is able to predict important properties of the pseudo-thermal source, such as the coherence length and the amplitude of the residual unscattered component of the light which influence the resolution and visibility of the final ghost image. We show that the residual ballistic component introduces an additional background in the reconstructed image, and the spatial resolution obtainable depends on the size of the scattering spheres.

Photon counting statistics using a digital oscilloscope

We present a photon counting experiment designed for an undergraduate physics laboratory. The statistics of the number of photons of a pseudo-thermal light source is studied in two limiting cases: much longer and much shorter than the coherence time, giving Poisson and Bose-Einstein distributions, respectively. The experiment can be done in a reasonable time using a digital oscilloscope without the need of counting boards. The use of the oscilloscope has the advantage of allowing the storage of the data for further processing. The stochastic nature of the detection phenomena adds additional value because students are forced to do data processing and analysis.

Cross spectral purity and its influence on ghost imaging experiments

Pseudo-thermal light has been widely used in ghost imaging experiments. In order to understand the differences between the pseudo-thermal source and thermal source, we propose a method to investigate whether a light source has cross spectral purity (CSP), and experimentally measure the cross spectral properties of the pseudo-thermal light source in near-field and far-field zones. Moreover we present a theoretical analysis of the cross spectral influence on ghost imaging.

Experimental Observation of Classical Subwavelength Interference with a Pseudothermal Light Source

We report the experimental observation of classical subwavelength double slit interference with a pseudothermal light source. The experimental results are in good agreement with the theoretical simulation using the second order correlation function for the thermal light.

Photon counting statistics—Undergraduate experiment

A photon counting experiment for student physics laboratory is described. It is designed to illustrate the probabilistic nature of the photodetection process itself as well as statistical fluctuations of light. The setup enables the student to measure photon count distributions for both coherent and pseudothermal light sources yielding Poisson and Bose–Einstein distributions, respectively.

Intensity Correlations from Pseudothermal Light Sources

An experiment for observing intensity correlations from pseudothermal light sources is described. Analog rather than digital electronics is used. Results are obtained that show clearly the relation between amplitude interference and intensity interference. Gaussian, two-slit, and uniform-brightness disk sources are used. The application of this experiment to the understanding of stellar-intensity interferometry is pointed out.