Cornelius DPC 230 Specifications download pdf (Page 14)

8 Operation Modes

The procedure illustrated in Fig. 10 yields G(

) in equidistant

channels. The width of the

channels is equal to the time-channel width of the DPC-230, T. The algorithm is known as the

‘Linear Tau’ algorithm. The equidistant

channels result in an easily predictable statistics.

This is a benefit if a model function is to be fitted to the correlation function. Unfortunately,

for the small time-channel width of the DPC the algorithm would result in an extremely large

number of

channels in G(

), and in intolerably long calculation times.

The operating software of the DPC therefore applies binning steps to the photon data during

the correlation procedure. The general procedure is illustrated in Fig. 11.

t+T

Histogram of coincidences

photon data

shifted photon data

t+2T

shifted photon data

photon data

Binning 3:1

shifted photon data

Histogram of coincidences

photon data

n(t1)n(t2)

after

steps:

Fig. 11: Correlation procedure with progressive binning

The procedure starts with a number of shift-and-compare operations as shown in Fig. 10.

However, after a number, k

, of shift-and-compare operations the remaining photon data are

binned by a factor of three. (The factor of three is used to keep the new time intervals centred

at multiples of the original time channel width, T.) Then the shift-and-compare operation is

continued on the binned data. After every k

operations a new binning step is performed. Thus,

the width of the τ channels increases progressively. The progression is the faster the smaller

the progression parameter, k

is chosen. The procedure shown in Fig. 11 delivers similar re-

sults as the ‘multi-τ algorithm’ commonly used in conventional correlators [18].

Relative Timing Modes

In the relative timing modes reference pulses are recorded in one channel of the DPC-230. The

times of the reference pulses are recorded together with the photon times, and relative times

between the photons and the reference pulses are calculated.

Multichannel Scaler Mode

The multichannel-scaler mode records the waveform of a light signal, or, in the general case,

the density of the detected events as a function of the time within the period of a repetitive

excitation signal. In other words, the photon times are measured with reference to the pulses

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Cornelius DPC 230 Specifications Page 14

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