Ling-An Wu

Correlated two-photon imaging with true thermal light

Received March 14, 2005; revised manuscript received May 4, 2005; accepted May 4, 2005 We report what is believed to be the first experimental demonstration of two-photon correlated imaging with true thermal light from a hollow cathode lamp. The coherence time of the source is much shorter than that of previous experiments using random scattered light from a laser. A two-pinhole mask was used as object, and the corresponding thin lens equation was well satisfied. Since thermal light sources are easier to obtain and measure than entangled light, it is conceivable that they may be used in special imaging applications.

Two-photon interference with true thermal light

The infinite-layer CaCuO2, (IL CaCuO2) was synthesized at similar to 1000 degrees C and 3 GPa, and structural and electrical properties under high-pressure were studied at room temperature using a diamond anvil cell (DAC) by in situ high-pressure energy-dispersive X-ray diffraction with synchrotron radiation and by electrical measurements, respectively. The results reveal that the primary crystal structure of IL CaCuO2 is stable under pressure up to 30 GPa. The equation of state of IL CaCuO2 was obtained from the VIVO-P relationship, which gives rise to a bulk modulus B-0 = 181 GPa for IL CaCuO2 based on the Birch-Murnaghan equation. The resistance and capacitance measurements of IL CaCuO2 UP to 20 GPa indicate that there is an abnormal hump occurring around 10 GPa with increasing pressure. Corresponding changes were also observed in the dependence of capacitance on pressure. It is considered to be related to an electronic structure transition resulting from the anisotropic compression of the IL CaCuO2 unit cell under high pressure, which can be attributed to the sudden disappearance of an X-ray diffraction peak. (c) 2005 Elsevier B.V. All rights reserved.

Lensless ghost imaging with true thermal light

We report the first (to our knowledge) experimental demonstration of lensless ghost imaging with true thermal light. Although there is no magnification, the method is suitable for all wavelengths and so may find special applications in cases where it is not possible to use lenses, such as with x rays or gamma rays. We also numerically show that some magnification may be realized away from the focal plane, but the image will always be somewhat blurred.

Adaptive compressive ghost imaging based on wavelet trees and sparse representation.

Compressed sensing is a theory which can reconstruct an image almost perfectly with only a few measurements by finding its sparsest representation. However, the computation time consumed for large images may be a few hours or more. In this work, we both theoretically and experimentally demonstrate a method that combines the advantages of both adaptive computational ghost imaging and compressed sensing, which we call adaptive compressive ghost imaging, whereby both the reconstruction time and measurements required for any image size can be significantly reduced. The technique can be used to improve the performance of all computational ghost imaging protocols, especially when measuring ultra-weak or noisy signals, and can be extended to imaging applications at any wavelength.

High-visibility, high-order lensless ghost imaging with thermal light

High-visibility Nth-order ghost imaging with thermal light has been realized by recording only the intensities in two optical paths in a lensless setup. It is shown that the visibility is dramatically enhanced as the order N increases, but longer integration times are required owing to the increased fluctuations of higher-order intensity correlation functions. It is also demonstrated that the required integration time for a good image depends on the partition ratio of the intensities on the two detectors and the complexity of the object.

Double-end-pumped 11-W Nd:YVO4 cw laser at 1342 nm

A compact, high-power, and high-stability Nd:YVO4 laser at 1342 nm has been developed. As high as 11 W cw output for 35 W of incident pump power with a slope efficiency of about 31.4% has been obtained. It has been shown that a reasonable and effective way to improve the output power is to choose a pumping scheme that can effectively extend the range of the stable resonator region by choosing the optimal dopant concentration and length of the laser rod.

Self-focusing and self-trapping in new types of Kerr media with large nonlinearities

Self-focusing and self-trapping of light in common liquid media such as Chinese tea, Chinese herbal medicine, and solutions of chlorophyll have been observed. These materials are found to be new types of natural Kerr media, and their nonlinear coefficients have been determined. Laser-heating-induced self-phase modulation in these materials has also been observed.

Lensless ghost imaging with sunlight.

An experiment demonstrating lensless ghost imaging (GI) with sunlight has been performed. A narrow spectral line is first filtered out and its intensity correlation measured. With this true thermal light source, an object consisting of two holes is imaged. The realization of lensless GI with sunlight is a step forward toward the practical application of GI with ordinary daylight as the source of illumination.

Time-correspondence differential ghost imaging

Experimental data with digital masks and a theoretical analysis are presented for an imaging scheme that we call time-correspondence differential ghost imaging (TCDGI). It is shown that by conditional averaging of the information from the reference detector but with the negative signals inverted, the quality of the reconstructed images is in general superior to all other ghost imaging (GI) methods to date. The advantages of both differential GI and time-correspondence GI are combined, plus less data manipulation and shorter computation time are required to obtain equivalent quality images under the same conditions. This TCDGI method offers a general approach applicable to all GI techniques, especially when objects with continuous gray tones are involved. DOI: 10.1103/PhysRevA.87.033813

Random number generation based on the time of arrival of single photons

We report the demonstration of a new type of true random number generator based on the random distribution of the time interval between photons from a single-photon-like source. The experimental setup is simple and robust against mechanical and temperature disturbances. With improved detector resolution and efficiency, the random number bit rate could be increased by more than an order of magnitude to satisfy practical requirements.