the rotating \(E\) fields generated by \(g^{+}\) and \(T^{+}\) particles interact and give rise to the Transverse Modes in a laser.
An aperture that restrict the spread of this field in the plane perpendicular to \(OP\), prevents such interactions and "destroys" the transverse modes. A conductive wire within the resonance cavity of the laser would also short the \(E\) fields and prevent their interaction in certain directions and so produce different interference patterns.
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