Pulse period jitter

The setup shown in Fig. 2.14 is based on the presumption that the period of the excitation pulses is constant and free of jitter down to the order of 1 ps. This is certainly correct for a titanium-sapphire laser or other mode-loeked laser systems using low-loss cavities. For pulsed diode lasers the pulse period jitter ean be eon-siderably higher. These lasers are eontrolled by quartz oseillators whieh ean have a pulse period jitter of the order of some 10 ps. The reversed start-stop eonfiguration can easily be made insensitive to pulse period jitter by introdueing a passive delay line in the referenee ehannel. The effeet of the delay is shown in Fig. 2.15. 

With the correct delay in the reference channel the time is measured against the laser pulse whieh released the detected photon. The influence of possible pulse period jitter is thus eliminated. 

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