Characteristics of mode-coupled lasers

The effects of mode-coupling in a gas laser resulting from a time-varying loss within the optical cavity or from the non-linear characteristics of the inverted population are investigated both theoretically and experimentally. The dominant effect resulting from this mode-coupling is that the laser operates as a pulse regenerative oscillator which produces a periodic train of subnanosecond width pulses. The exact repetition frequency is determined by the frequency of the time-varying loss, which must always be set close to a multiple of
c/2L
, i.e., the axial mode spacing, to produce sufficient coupling. To produce pulsing without a time-varying loss, it is necessary that the
Q
or loss of the cavity be judiciously adjusted. In this case the repetition frequency is very close to the axial mode spacing. A preliminary experimental investigation has verified the salient features of the analysis. The measured widths of the pulses from a 6328 Å He-Ne laser and from a 4880 Å Argon-Ion laser were 0.5 and 0.25 ns, respectively.