Simulation models for aerosol characterization by elastic light scattering with special emphasis on photon correlation experiments in the nano-particle size range

The input format of fast digital correlators, such as used in photon correlation or recurrence rate correlation, is often exceeded by input signals, if high count rates coincide with sample times of the order of several hundred nanoseconds or more. Clipping, random clipping, and scaling are well known methods to reduce such signals appropriately. We discuss these procedures with special attention to noise performance possible errors introduced into the correlogram. Generalizations from single to multi-bit correlators are presented with a thorough discussion of random preset scaling, a new process suitable for multi-bit correlation of signals with arbitrary statistics. Furthermore we describe a new additional preprocessor which offers significant decrease of quantization noise, if constant background contributions are present in the signal. Though demonstrated on optical measurements, the methods treated in this paper generally apply, whenever the format of digital data has to be reduced prior to correlation.

Signal preprocessing for digital correlators

In this review, the developments in the theory of photostatistics and photon correlation spectroscopy which are of particular relevance to the design and operation of digital clipping correlators are first summarised. A discussion then follows of the mathematical forms which the scattered-light signal and its autocorrelation function take, in laminar and turbulent flow, for the Doppler-difference type of laser anemometer, which represents a highly practical and efficient form of the apparatus. Various methods which have been proposed for the interpretation of the correlator output are briefly described. An analysis is also made of the information contained in the autocorrelation function resulting from a transit of the scattering region by a single particle in the presence of optical noise. Finally the properties of laser radiation which are especially important in the design of laser anemometry systems are discussed.

Theoretical Aspects of Photon Correlation Methods in Doppler-Difference Anemometry

For noiseless binary direct-detection optical channels operating with signals of classical and non-classical properties, the limits of the performance of the information at a low power level are computed. The calculations are performed and compared using two processors, the photon counter and the time intervals receiver.

Limits of the performance of the information of a direct-detection channel using classical and non-classical states of light

Error analysis of randomly clipped photo-count correlation estimator

Three models of nongaussian stationary light are studied in which the clipped photocount autocorrelation formulae at zero photon number are not simply connected to the unclipped autocorrelation intensity function of the light field.

C Bendjaballah

Papers

Analysis of clipped photocount autocorrelation formulae for nongaussian light