Cornelius DPC 230 Specifications download pdf (Page 34)

28 Typical Applications

Fig. 40: Cross-Correlation between two detector channels

Picosecond Fluorescence Correlation

Fluorescence correlation down to the picosecond range has first been described in [12]. The

authors used two bh SPC-130 modules with synchronised macro times, and included the TAC

times in the calculation. The time resolution of this system is extremely high. The time-

channel width can be as small as 820 fs; the electronic IRF width is about 5 ps FWHM. The

resolution is therefore only limited by the transit-time spread of the detector. However, be-

cause the TAC times are not synchronous with the macro time clock the approach requires

relatively complicated data analysis [13]. Of course, detector dead time and afterpulsing pre-

clude ps correlation to be obtained from a single detector. Therefore, at least two detectors

have to be used and the photon be data cross-correlated.

With the DPC-230, picosecond fluorescence correlation is merely a matter of the display scale

defined in the FCS display. A result is shown in Fig. 41. The trace parameters define two

traces, one for DPC channel 4 correlated versus channel 6, the other for channel 6 correlated

versus channel 4. The data points are shown red and black, respectively.

Fig. 41: Picosecond FCS. Left: Trace parameters. Right: FCS data. Time axis from 100 ps to 1 ms.

In contrast to classic FCS, in picosecond FCS transit time differences of the signals are no-

ticeable. The result of such differences is a shift in the curves depending on whether detector

one is correlated against detector 2 or vice versa. Therefore, make sure that the optical path

lengths and the cable lengths are the same in all detector channels.

1 2 ... 29 30 31 32 33 34 35 36 37 38 39 ... 69 70

No comments

Cornelius DPC 230 Specifications Page 34