Xi-Hao Chen

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.

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.

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.

Single-photon level ultrafast all-optical switching

We demonstrate an approach to all-optical switching, where a weak beam controls a strong beam, based on three-wave mixing optical parametric amplification in a nonlinear crystal. Ultrafast switching within 400fs has been achieved with a 130fs single-photon level switch beam containing, on average, 0.75 photon/pulse, which can turn on/off a signal pulse containing 5.9×108 photons. The transverse patterns for the on and off states are well defined and the switch has a large bandwidth of up to 10nm.

Second-order Talbot effect with entangled photon pairs

The second-order Talbot effect is analyzed for a periodic object illuminated by entangled photon pairs in both the quantum imaging and quantum lithography configurations. The Klyshko picture is applied to describe the quantum imaging scheme, in which self-images of the object that may or may not be magnified can be observed nonlocally in the photon coincidences but not in the singles count rate. In the quantum lithography setup, we find that the second-order Talbot length is half that of the classical first-order case, thus the resolution may be improved by a factor of 2.

Two-photon interference with two independent pseudothermal sources

The nature of two-photon interference is a subject that has aroused renewed interest in recent years and is still under debate. In this paper we report the observation of two-photon interference with independent pseudothermal sources in which subwavelength interference is observed. The phenomenon may be described in terms of optical transfer functions and the classical statistical distribution of the two sources.

Absolute self-calibration of the quantum efficiency of single-photon detectors

Single-photon detectors are finding increasingly wide application in all branches of science and technology thus a precise knowledge of their quantum efficiency is an essential prerequisite. We have performed the first proof-of-principle demonstration of a means to determine the quantum efficiency by which no second detector or reference standard is required. This absolute self-calibration method is based on the time correlation of entangled photons pairs emitted in spontaneous parametric down conversion. The measured quantum efficiency of a Si avalanche photodiode single-photon detector agrees well with the product specifications.

Thermal light optical coherence tomography for transmissive objects.

We report an experimental demonstration of optical coherence tomography for transmissive objects utilizing second-order correlation ghost imaging with thermal light. To evaluate the longitudinal resolution of our system, the concept of the imaging longitudinal coherence length is introduced, which is more accurate for judging the image quality of ghost imaging with unequal optical paths than the conventional point-to-point longitudinal coherence length. Our work should help clarify our understanding of the longitudinal coherence of thermal light, as well as provide a scheme for performing optical coherence tomography on objects that are not highly reflective.