Optimum Pulse Separation Time

The pulse separation time between successive light pulses is one of the important parameters during PIV measurements. For a velocity magnitude in jc-direction u, pulse separation time At, 

For small time interval, the displacement 4t varies linearly with time. At. Thus, the first term of the above equation will remain unchanged with reduction in time At. 

The error will not reduce below a certain limit due to the reduction of the pulse separation 

there is an optimum pulse separation time, Af pj, at which the combined error because of residual error magnitude and loss of image pairs is minimum. This is found iteratively by slowly increasing the pulse separation time until the number of outliers within the vector map increases. The normalized strength of displacement correlation can also be optimized with respect to pulse separation time. 

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A collinear scheme for ion- and laser beams enlarges the interaction time between the laser and the negative ions. The synchronization of the laser pulses with the pulsed ion source ensures an optimum time overlap between the ion pulses and the laser pulses. The electrons are focussed by a weak magnetic field onto the electron detector. The remaining negative ions are separated from the neutrals by a perpendicular electric field. 

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