Ghost imaging
Encyclopedia
Ghost imaging is a technique that allows a high resolution camera
to produce an image of an object which the camera cannot itself see. The first demonstrations of ghost imaging were based on the quantum nature of light. Specifically, quantum correlation
s 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 pixel
s 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 [4]. This was achieved by implementing the 'Computational ghost-imaging' scheme [5], 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 [6]. This allowed to acquire an N pixel image with much less than N measurements and may have applications in LIDAR
and microscopy
Camera
A camera is a device that records and stores images. These images may be still photographs or moving images such as videos or movies. The term camera comes from the camera obscura , an early mechanism for projecting images...
to produce an image of an object which the camera cannot itself see. The first demonstrations of ghost imaging were based on the quantum nature of light. Specifically, quantum correlation
Quantum correlation
In Bell test experiments the term quantum correlation has come to mean the expectation value of the product of the outcomes on the two sides. In other words, the expected change in physical characteristics as one quantum system passes through an interaction site...
s between photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
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 pixel
Pixel
In digital imaging, a pixel, or pel, is a single point in a raster image, or the smallest addressable screen element in a display device; it is the smallest unit of picture that can be represented or controlled....
s from photons that hit simultaneously at the object and the camera's image plane
Image plane
In 3D computer graphics, the image plane is that plane in the world which is identified with the plane of the monitor. If one makes the analogy of taking a photograph to rendering a 3D image, the surface of the film is the image plane. In this case, the viewing transformation is a projection that...
, an image of the object is reconstructed.
It was soon realized that the correlations between the light beam
Light beam
A light beam or beam of light is a narrow projection of light energy radiating from a source into a beam. Sunlight is a natural example of a light beam when filtered through various mediums...
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
Ratio
In mathematics, a ratio is a relationship between two numbers of the same kind , usually expressed as "a to b" or a:b, sometimes expressed arithmetically as a dimensionless quotient of the two which explicitly indicates how many times the first number contains the second In mathematics, a ratio is...
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
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
' were demonstrated using only a single single-pixel detector [4]. This was achieved by implementing the 'Computational ghost-imaging' scheme [5], relaxing the need to evoke quantum correlations arguments for the pseudothermal source case.
Recently, it was shown that the principles of 'Compressed-Sensing'
Compressed sensing
Compressed sensing, also known as compressive sensing, compressive sampling and sparse sampling, is a technique for finding sparse solutions to underdetermined linear systems...
can be directly utilized to reduce the number of measurements required for image reconstruction in GI [6]. This allowed to acquire an N pixel image with much less than N measurements and may have applications in LIDAR
LIDAR
LIDAR is an optical remote sensing technology that can measure the distance to, or other properties of a target by illuminating the target with light, often using pulses from a laser...
and microscopy
Microscopy
Microscopy is the technical field of using microscopes to view samples and objects that cannot be seen with the unaided eye...