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The dependence of the parameters of the Gaussian mode in laser resonators on the properties of the medium in the cavity is studied. Experimental verification of the theoretical results is presented. It is found that the modes in a high-gain laser may differ widely from the usual free space resonator results. Also, resonator configurations which in free space are unstable may, with a suitable medium, support low-loss Gaussian modes.

Abstract-We introduce the technique of time-resolved optical gating (TROG) based on dispersive propagation (DP), a new noninterferometric method for characterizing ultrashort optical pulses in amplitude and phase without the need for a short optical gating pulse. TROG is similar to frequency-resolved optical gating except that the role of time and frequency is interchanged. For the DP-TROG geometry, we show that measurements of the autocorrelation trace of the pulse after propagation through a medium with variable dispersion together with a single measurement of its intensity spectrum contain sufficient information to reconstruct the pulse in amplitude and phase. Pulse reconstruction for this DP-TROG geometry works very well even for the case of a nonlinearly chirped double pulse. Compared with other methods, DP-TROG does not introduce an ambiguity in the direction of time for the pulse. Due to its simplicity and improved sensitivity, DP-TROG is expected to be useful in characterizing low-energy pulses.Index Terms-Optical correlators, optical fiber dispersion, optical propagation in dispersive media, optical pulse compression, optical pulse measurements, pulse characterization, time-domain measurements.

In lasers employing high-gain narrow-linewidth transitions the theory predicts major departures of the mode-splitting frequencies from their low-gain values as well as a new type of mode splitting. The first of these effects consisting of a reduction by a factor of 2.5 of the mode splitting in a xenon 3.51-μ laser is observed experimentally.