What is Spatial Hole Burning?
A Fabry-Perot laser is a standing wave laser. To satisfy the cavity boundary conditions for laser oscillation, any wave making a round trip back and forth between the mirrors must be in phase. This imposes the requirement that only wavelengths that are a multiple of c/2L – the possible longitudinal modes – can participate in lasing. However, since the paths in both directions are coincident, the result for any given mode will be a standing wave with peaks and valleys every 1/2 lambda. Consider a single longitudinal mode: Inside the lasing medium (e.g., HeNe gas or Nd:YAG crystal), the peaks will fully utilize the available gain but at the centers of the valleys or null points, the gain will not be used at all. In between, only a portion of the available gain will be used. This behavior is called “spatial hole burning”. In essence, periodic areas (“holes”) have been depleted (“burnt”) of gain, leaving other areas which can still contribute to lasing action if there were something to sti
A Fabry-Perot laser is a standing wave laser. To satisfy the cavity boundary conditions for laser oscillation, any wave making a round trip back and forth between the mirrors must be in phase. This imposes the requirement that only wavelengths that are a multiple of c/2L – the possible longitudinal modes – can participate in lasing. However, since the paths in both directions are coincident, the result for any given mode will be a standing wave with peaks and valleys every 1/2 lambda. Consider a single longitudinal mode: Inside the lasing medium (e.g., HeNe gas or Nd:YAG crystal), the peaks will fully utilize the available gain but at the centers of the valleys or null points, the gain will not be used at all. In between, only a portion of the available gain will be used. This behavior is called “spatial hole burning”.
