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Correlated Photon Radiometry



Alan L. Migdall


Each of these techniques uses the process of optical parametric down-conversion (PDC) to produce correlated pairs of photons. This process employs a nonlinear medium which allows photons from a pump beam to, in effect, decay into pairs of photons under the restrictions of energy and momentum conservation. Since the two decay photons are born at the same time, the detection of one photon indicates with high certainty the existence of the other photon of the pair. In addition, the conservation of energy and momentum allow the wavelength and direction of one photon to be determined from the other. (The accompanying photo shows the broad spectral range of down-converted light produced in the nonlinear crystal.) Longer range plans include arrangements to make the absolute response/radiance methods continuously tunable, and to extend their spectral range as far into the infrared as possible.
Electronic Publication


correlated photons, metrology, photon counting, quantum efficiency, radiance, single photon


Migdall, A. (2003), Correlated Photon Radiometry, Electronic Publication, [online], internal:/None (Accessed June 21, 2024)


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Created May 1, 2003, Updated February 17, 2017