Dynamics of gas flow in hollow core photonic bandgap fibers.

The dynamics of gas flow in a hollow core photonic bandgap fiber is studied over four decades of pressure covering free molecular flow as well as hydrodynamic flow. Expressions are derived that allow for determination of the pressure inside the fiber as a function of time and position in the limits of Knudsen number Kn>>1 and Kn<<1. The expressions, which are validated by using absorption lines of acetylene as probes of the pressure inside the fiber, provide a straightforward way of predicting the temporal response for gas sensors of any fiber geometry.