By building a He&sngbnd;Xe laser within a hollow dielectric waveguide and by using a single isotope of Xe, we have been able to attain gains of 1000 dB/m. The dispersion associated with these large gains significantly modifies the ``empty‐resonator'' mode spacing when such a medium is placed within a laser resonator. We describe experiments with a short single‐frequency waveguide He&sngbnd;Xe laser in which the gain medium pulls the oscillating frequencies so that the laser always oscillates within ± (1/100) (c/2L) of the center of the Xe net‐gain curve, regardless of the physical length of the laser resonator.