Showing papers on "Photodetection published in 1977"

Statistical Properties of Scattered Radiation

Abstract: Photomultiplier tubes which perform virtually ideal digital detection of electromagnetic radiation at visible frequencies are now widely available. The only sources of noise are a generally low dark count, typically a few counts per second, and the unavoidable shot noise due to the random (Poisson) nature of the detection process. The output of such detectors consists of a series of discrete pulses of charge, each corresponding to a single photodetection, which constitutes a Poisson process rate-modulated by variations in the incident intensity. Coincident with the development of these detectors has been the development of hardware based on integrated circuits which can perform errorless analysis of digital signals at frequencies up to about 108 Hz. Combination of these two technologies provides the techniques of photon correlation.1 (We will include the study of single-interval photon statistics in the generic term “photon correlation”.) With speed and accuracy close to the theoretical limit these techniques can be used to analyze fluctuating optical signals of any origin (provided the fluctuation time is ≳10−7 sec).

Automatic focusing apparatus

Abstract: In automatic focusing apparatus comprising a laser source, optical means for causing a light beam from the laser source to follow an information track on an information recorded medium, a photodetector which consists of quartered photodetection portions and to which a reflected light beam from the information track is guided through a cylindrical lens, and means for controlling the focusing of the light beam by the use of an error signal obtained from the shape and the intensity distribution of a light spot on the four photodetection portions, the improvement wherein a compensation signal is created from the absolute value of a difference between outputs from one set of the opposing photodetection portions and the absolute value of a difference between outputs from the other set of the opposing photodetection portions, to compensate for a disturbance ascribable to a movement of the light spot on the photodetector which arises in correspondence with the error signal.

Photodetection properties of Cu2Se‐AgInSe2 heterojunctions

Abstract: Heterojunctions were formed by vacuum evaporation of p‐type Cu2Se on n‐type AgInSe2 substrates. The photodetection characteristics of these diodes are vastly improved over those previously reported. At λ=1.05 μm, the room‐temperature quantum efficiency approaches the reflection‐limited value (∼0.7) as compared to ∼0.2 previously reported. In addition, the efficiency of the present diodes becomes greater than unity at low reverse biases. At 77 °K, even more dramatic gains can be achieved at low reverse biases. The structure appears to operate as an optically activated switch and is interpreted as a combination of photovoltaic and photoconductive mechanisms.

Comparison between the classical and quantum theories of optical coherence

Abstract: The comparison between the classical and quantum theories of optical coherence is presented by using an idea used in the problems of modulation of light beams of classical fields In such problems it is assumed that it is possible to vary the mean light intensity of a beam without changing its statistical properties defined by a set of coherence functions We generalize this idea and introduce precisely the class of optical fields which are consistent for modulation It is shown that all the quantum fields of this class have a positive $P$ representation and are strictly equivalent to classical fields Moreover, when the field is assumed to be stationary, an interpretation of this condition is given which in particular makes precise the relations between photon-counting and light-intensity measurements Finally it is shown that all the quantum fields without $P$ representation cannot be consistent for modulation, and the condition of consistency for modulation appears as a characteristic property of fields strictly equivalent to classical ones

Modulations and degrees of coherence of optical fields

Abstract: By using the concept of degree of coherence of quantum optical fields, the properties of fields which can be modulated at a complex rate are studied.