Experimental and theoretical study of noise in a dual-frequency VECSEL

We investigate, both experimentally and theoretically, the spectral behavior of the intensity noises as well as the phase noise of the radio frequency (RF) beatnote generated by optical mixing of two orthogonally polarized modes of a dual-frequency VECSEL. To be more speci c, we measure the relative intensity noises (RINs) and the correlation between the intensity noises of the two laser modes for di erent nonlinear coupling strengths between them within frequencies 10 kHz to 50 MHz. Moreover for these frequencies, we explore the spectral behavior of the phase noise of the RF beatnote generated by optical mixing of two laser modes and the dependence of this RF phase noise spectrum on the strength of non-linear coupling between the laser modes. The theoretical model considers pump intensity uctuations as the only source of noise within the considered frequency range. The pump uctuations, entering into the two spatially separated laser modes on the active medium, are measured to be white noises of identical amplitudes, partially correlated, and in phase. To model the RF phase noise, we take into account two di erent physical mechanisms: (i) the coupling of intensity noise with phase noise due to large Henry factor of the semiconductor gain medium and (ii) the thermal uctuations of the refractive index of the semiconductor active medium induced by pump intensity uctuations. For all the results, theory shows very good agreement with the experiment.