Ghost imaging

Ghost imaging (GI) is a technique that allows a high resolution camera to produce an image of an object which the camera cannot itself see. This method reduces the number of measurements required for image reconstruction.

History

The first demonstrations of ghost imaging were based on the quantum nature of light. Specifically, quantum correlations between photon pairs were utilized to build up an image of the unseen object. When one of the photons strikes the object, the other follows a different path to the camera's lens. If the camera is constructed to only record pixels from photons that hit simultaneously at the object and the camera's image plane, an image of the object is reconstructed.

It was soon realized that the correlations between the light beam that hits the camera and the beam that hits the object can be purely classical. If quantum correlations are present, the signal-to-noise ratio of the reconstructed image can be improved. The exact role of quantum and classical correlations in ghost imaging is still controversial.

In 2009 'pseudothermal ghost imaging' and 'ghost diffraction' were demonstrated using only a single single-pixel detector. This was achieved by implementing the 'Computational ghost-imaging' scheme, relaxing the need to evoke quantum correlations arguments for the pseudothermal source case.

Recently, it was shown that the principles of 'Compressed-Sensing' can be directly utilized to reduce the number of measurements required for image reconstruction in GI. This allowed to acquire an N pixel image with much less than N measurements and may have applications in LIDAR and microscopy

External links

• Quantum camera snaps objects it cannot 'see' by Belle Dume, New Scientist, 2 May 2008. Accessed July 2008
• Air Force Demonstrates 'Ghost Imaging' By Sharon Weinberger, Wired, 3 June 2008. Accessed July 2008