Dynamics and Instabilities in Homogeneously Broadened Lasers

by

Karl Koch
(1990)

This thesis describes theoretical and experimental studies of a homogeneously broadened ring dye laser. The thesis is particularly concerned with the two-frequency instability in which a bichromatic field emerges from the laser above the instability threshold. The interaction of a bichromatic field with an isolated atomic resonance is examined. The time-averaged inversion and the saturated gain exhibit structure in the form of a series of subharmonic resonances. The stability of a strong bichromatic laser field to the growth of a subharmonic probe field is examined. The gain of the subharmonic bichromatic probe field in the presence of the strong bichromatic laser field is calculated. The strong bichromatic field is stable to the growth of the subharmonic fields when the modulation frequency of the strong field coincides with the Rabi frequency of the lasing transition.

The existence of chaos in a strongly driven nonlinear system is experimentally investigated in a multimode ring dye laser. A dye laser is pumped with a modulated pump source. The response of the dye laser to commensurate and incommensurate modulations is reported. We find that for commensurate modulations, the dye laser responds in a periodic fashion and the rf spectrum of the dye laser is composed of a series of harmonics. For incommensurate modulations, the dye laser responds in a quasiperiodic fashion with a broadband rf spectrum.

The two-frequency instability in a multimode cw-pumped ring dye laser is shown to occur in a number of cavity configurations. The two-frequency instability is shown to exhibit a sensitive dependence on the cavity detuning.

The recently proposed band model of the laser is examined and theoretical predictions of the model are experimentally analyzed. Experimental evidence is presented which illustrates that conventional theories for two-, three-, and four-level lasers are inadequate to describe the excited state population dynamics of a cw dye laser. Modulation spectroscopy is used in a new signal-limited technique to measure an upper bound on the decay time of the lower levels in a rhodamine-6G dye molecule.

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