May 15 2014
The Gouy phase shift is a popular axial phase shift that occurs in a converging light wave when it passes through its focus in propagating from -∞ to +∞ . The Gouy phase shift is an additional phase shift that occurs in the propagation of a Gaussian Beam.
Basic Principle
A Gaussian beam acquires a phase shift along the propagation direction; this phase shift differs from that of a plane wave propagating with the same optical frequency. This difference is known as the Gouy phase shift.
Due to the Gouy phase shift, the distance between the wave fronts is slightly increased when compared to that of a plane wave. In order to compensate for this shift the phase fronts have to propagate faster, so that the local phase velocity is increased.
The overall Gouy phase shift of a Gaussian beam for going through a focus is π. A Gaussian wave may be considered as a superposition of plane waves that are propagating in different directions. The plane waves propagating in different directions experience small phase shifts of z, the overall phase shifts is the superposition of all these waves.
The Gouy phase shift is stronger for higher-order transverse modes. For such waves, the Gouy phase shift causes resonance frequencies to be higher. The Gouy phase shift also impacts the beam quality in a laser resonator.
References