Photon correlation detectors

In other words, two photons can never be detected at two points separated by an odd number of X/lr 2, despite the fact that one photon can be detected anywhere. The vanishing of G 2 (Ri, t R2, f2) for two photons at widely separated points Ri and R2 is an example of quantum-mechanical nonlocality, that the outcome of a detection measurement at Ri appears to be influenced by where we have chosen to locate the R2 detector. At certain positions R2 we can never detect a photon at Ri when there is a photon detected at R2, whereas at other position R2 it is possible. The photon correlation argument shows clearly that quantum theory does not in general describe an objective physical reality independent of observation [17],... 

The problem of the detector dead time is avoided by the Hanbury-Brown-Twiss setup [215]. This setup is the basis of almost all TCSPC photon correlation experiments. 

Fig. 5.100 Dual-detector (Hanbuty-Browu Twiss) photon correlation setup...

A troublesome effect in photon correlation experiments is light emission from single photon APD detectors. When an avalanche is triggered in the APD, a small amount of light is emitted. The effect and its implications for photon correlation experiments and quantum key distribution are described in detail in [515] and [299]. If the detectors are not carefully optically decoupled, false coincidence peaks appear. An example is shown in Fig. 5.105. 

In 1953, Stockmayer and Fixman observed that the ratio, h, of hydrodynamic or Stokes radii (/ h) of the branched and linear macromolecules could also be used as a measure of branching. The relatively recent introduction of online quasielastic light scattering (QELS, also known as dynamic light scattering and as photon correlation spectroscopy) detectors for SEC permits direct determination of h by... 

For a radio astronomer, a star is a source of noise this noise can be detected and correlated from antenna to antenna in order to position precisely the source. For optical observer, the star is a source of photons, the unique photon goes through a variety of optical paths and materialize on the focal plane detector. 

T. A. Louis, G. Ripamonti and A. Lacaita, Photoluminescence lifetime microscope spectrometer based on time-correlated single-photon counting with an avalanche diode detector, Rev. Sci Instrum. 61, 11-22(1990). 

There are two ways to collect FLIM data freqnency-domain or time-domain data acqnisition (Alcala et al. 1985 Jameson et al. 1984). Briefly, in freqnency domain FLIM, the fluorescence lifetime is determined by its different phase relative to a freqnency modulated excitation signal nsing a fast Fourier transform algorithm. This method requires a frequency synthesizer phase-locked to the repetition freqnency of the laser to drive an RF power amplifier that modulates the amplification of the detector photomultiplier at the master frequency plus an additional cross-correlation freqnency. In contrast, time-domain FLIM directly measures t using a photon connting PMT and card. 

The phase-dependent directionality of photocurrents produced by such a detector entails advantageous properties of the photocurrents cross correlations in nonoverlapping time intervals or spatial regions (considered in Section 4.2.2). These directional time-dependent correlations are measured with one detector only. They involve solely terms dependent on LO phases, in contrast to similar correlations measured by conventional photocounters, which inevitably contain terms depending on photon fluxes such as the LO excess noise. Owing to these properties, the mean autocorrelation function of the SL quadrature is shown in the schemes considered here to be measurable without terms related to the LO noise. LO shot noise, which affects the degree of accuracy to which this autocorrelation is measured (i.e., its variance) is easily obtainable from zero time delay correlations because the LO excess noise is suppressed. The combined measurements of cross correlations and zero time delay correlations yield complete information on the SL in these schemes. 

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