Visibility, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) are quantities that characterize the
quality of the image in ghost (or correlation) imaging. The visibility in quantum and classical ghost imaging
with scalar light is known to improve as the order of imaging increases. Recently also electromagnetic ghost
imaging has started to attract attention. In this work we analyze the effects of both the order of imaging and
the degree of polarization (P) of the illumination on the image quality parameters. The source is a classical,
partially polarized, random electromagnetic field obeying Gaussian statistics. The beam is split into several (N)
parts which are directed either into the object or reference arms and the associated intensity correlations are
calculated. When N > 2, more than one reference arm may exist which contributes to the background. We
consider two different definitions for the visibility, as well as the SNR and CNR, and examine their attainable
limiting values in second- and higher-order ghost imaging as a function of the degree of polarization. Both
expressions of the visibility behave in a similar manner; they increase with the order of imaging and the degree
of polarization. In second-order imaging the SNR decreases, due to increased noise, as P increases, while the
CNR remains essentially constant. We emphasize that the exact numerical values depend on the definitions used
and on the number of object arms in the setup.
We have developed a high-resolution, multi-color retinal imaging system using liquid crystal adaptive optics. A liquid
crystal on silicon (LCOS) spatial light modulator (SLM) is used to correct ocular aberrations. In order to compensate for
the dependency of an LCOS SLM on optical wavelength and acquire aberration-corrected images at different color, we
apply an open-loop technique. In the open-loop technique, the imaging light is separated from the sensing light and the
optimal phase modulation is applied only to the imaging light while the sensing light is not phase-modulated. With the
system, in vivo imaging of the human retina is achieved by using illumination light at wavelength of 655nm and 593nm
and sensing light at 780nm. Photoreceptors are clearly revealed at each illumination wavelength with the liquid crystal
A novel imaging system with liquid-crystal adaptive optics based on feedback interferometry is described for high-resolution retinal imaging. The performance of the system was verified by experiments using an artificial eye consisting of a lens, an aberration plate, and a resolution test target. We observed that an image of the test target (mimicking a retina) blurred by the aberration plate (mimicking ocular aberrations) was successfully restored immediately after our adaptive optics system was activated.
A novel method is described for storing and retrieving the second-order correlation function of partially coherent fields. The key element of the method is an instantaneous hologram that records the superposition of a random field whose correlation function is to be determined and the mutually incoherent reference field, taken over a time interval that is much shorter than the coherence time of the random field. The method is somewhat similar to conventional holography, but differs from it in several important respects.
A novel feedback interferometer, which consists of a polarization Sagnac interferometer and an optically- addressed phase-only spatial light modulator, is described for real-time and unambiguous visualization of the surface profile. In this system, the output intensity from the Sagnac interferometer is optically fed back to the phase modulator placed in one arm of the interferometer to produce a sawtooth fringe intensity profile which is directly and unambiguously related to the surface profile. Experimental results demonstrate the feasibility of applying this system to surface profile measurement.
It has been predicted theoretically and verified experimentally that the spectrum of light radi- ated by a partially coherent source may change on propagation, even in free space. The change depends not only on the spectrum of the source but also on its spatial coherence properties . Such correlation-induced spectral changes have become the subject of great interest in the last few years and have led to a new branch of optics, which is sometimes referred to as spatial- coherence spectroscopy.