Is it referring to the speed at which a group of light pulses moves as a whole?
To understand it colloquially and visually, Group Velocity refers to the speed at which the overall envelope of a light pulse (physically called a wave packet) composed of multiple light waves of different frequencies propagates through a medium.
To understand this concept more rigorously, we can compare it with Phase Velocity:
1. Difference Between Phase Velocity and Group Velocity
- Phase Velocity (denoted as v_p): Refers to the speed at which a monochromatic simple harmonic wave of a single frequency (equiphase surface) propagates through a medium. For a monochromatic wave with angular frequency \omega and angular wavenumber k, the phase velocity is defined as:v_p = \frac{\omega}{k}
- Group Velocity (denoted as v_g): In practical engineering, absolutely monochromatic infinitely long light waves do not exist. Actual light signals (such as laser pulses) are