Pulse picker

The beam was passed through a pulse picker (4). In order to compensate pulse broadening ( chirp ) introduced by the pulse picker and to precompensate that caused by other bulky optics (lenses, polarizers etc.), the beam was passed through a group velocity dispersion compensation line (5), consisting of a pair of Brewster prisms and a mirror [20], The temporal width of the pump and probe pulses was checked with a fringe-resolved... 

Bursts of pulses with a predefined number down to N= 1 were selected with a pulse picker. The focusing conditions were already described in connection with Fig. 10. Various polymer foils (250 pm thick) like polyimide (PI), polycarbonate (PC), poly(ethylene terephthalate) (PET, amorphous and crystalline), poly(tetrafluoroethylene) (PTFE), and poly(methyl methacrylate) (PMMA) were investigated (all from Goodfellow Cambridge Ltd, Huntington). These are listed together with relevant physicochemical properties in Table 1. 

The repetition rate of Ti Sapphire lasers is fixed by the resonator length. Rates from 78 to 92 MHz are common. The high repetition rate helps to minimise classic pile-up effects in TCSPC measurements. However, it can cause problems if fluorescence lifetimes longer than 3 or 4 ns have to be measured, since the fluorescence does not decay completely within the pulse period. Data analysis can account for incomplete decay to a certain degree. However, if the lifetime becomes equal to or longer than the pulse period, the accuracy of the obtained lifetime degrades. The pulse repetition rate must therefore be reduced by a pulse picker. 

The delay in the reference path is particularly important in experiments with pulse pickers or kHz lasers. With insufficient delay in the reference path it can happen that a time interval completely outside the signal is recorded. Because the signal does not wrap around a short signal period, finding the correct reference delay can be difficult. An example is shown in Fig. 7.68. 

A second strategy is, of course, to avoid the generation of synchronous noise in the system. Typical sources of coherent noise are cavity dumpers, pulse pickers, and picosecond diode lasers. For the shielding of these devices the same rules should be applied as for detector shielding. 

Pedersen T. F., Nielsen B., and Pickering M. (1991) Timing of Late Quaternary productivity pulses in the Panama Basin and implications for atmospheric CO2. Paleoceanography 6, 657-677. 

Chatterjee K, Tuli S, Pickering SO, Almond DP (2011) A comparison of the pulsed, lock-in and frequency modulated thermography nondestructive evaluation techniques. NDT E Int 44(7) 655-667 Clark MR, McCann DM, Forde MC (2003) Application of infrared thermography to the non-destructive testing of concrete and masonry bridges. NDT E International 36(4) 265-275... 

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