Pavel A. Khandokhin

Instabilities in a solid-state ring laser

In addition to a well-known type, two more types of relaxation oscillation are present in a solid-state ring laser. The frequencies of these specific oscillations depend on the difference in the eigenfrequencies of counterpropagating resonator modes (phase nonreciprocity). There are instability mechanisms that can convert these relaxation oscillations into undamped pulsations. The instability is responsible for the possibility of detecting low-frequency oscillation characteristic of a ring laser. In our experiment these oscillations are represented by resonant features in the intensity-fluctuation spectrum of a Nd:YAG laser operating in a stable traveling-wave regime although close to a self-modulation instability threshold.

Influence of carrier diffusion on the dynamics of a two-mode laser

The two-mode semiconductor laser rate equations are generalized to account for the diffusion of free carriers. Using the diffusion coefficient as a control parameter we analyze the competition between small-scale and large-scale gratings in the laser dynamics. Many solutions become unstable as the diffusion coefficient decreases. >

Bifurcations and chaos in the three-level model of a laser with coherent optical pumping

Abstract A three-level laser model, taking into account coherent interaction of pump and generated field, is discussed. Possible simplifications of this model are discussed for some particular cases. The characteristic features of a general model and its simplified version, a Lorentz model, are investigated using computation methods. The obtained results are compared with the known data of experimental investigations of optically pumped molecular lasers.

Low frequency relaxation oscillations in class B lasers with feedback

Relaxation oscillations have been studied both theoretically and experimentally in a multimode YAG laser in the presence of a derivative feedback. In addition to the standard relaxation oscillations, discrete low frequency components are present in the noise spectrum of each individual mode but they compensate almost exactly in the total intensity. The influence of a combined derivative feedback involving both the total intensity and that of one selected mode on the behavior of the relaxation oscillations and nonlinear dynamics of the laser is investigated. It is shown that the compensation nature of the low frequency relaxation oscillations of the multimode class B lasers can be disturbed in this case and, as a consequence, the selected relaxation oscillations appear in the noise spectrum of the total intensity. A higher feedback level can induce a destabilization of the laser and eventually chaos. An excellent qualitative agreement between experiments and theory has been obtained.

Disappearance of relaxation oscillation frequencies in a multimode solid-state laser

Abstract We study analytically the Tang, Statz and deMars rate equations describing a solid-state Fabry-Perot laser. When the modes have equal gains, there is a critical number of lasing modes, above which the low-frequency relaxation oscillations responsible for antiphase dynamics disappear. These results are generalized to include unequal modal gains resulting from a Lorentzian gain profile.

Polarization dynamics of a fibre Fabry-Perot laser with feedback

Experimental results on the low-frequency polarization dynamics of a free-running Nd-doped optical fibre laser and a fibre laser with derivative feedback are presented. It is found that the power spectrum of each polarization mode reveals three relaxation peaks. Using the combined (negative and positive) derivative feedback it is possible to suppress noise in the region of the in-phase relaxation oscillations and to excite noise in the region of one of the two antiphase relaxation oscillations. The model developed of a class B laser with two orthogonal elliptically polarized modes is checked and explains the main experimental features of relaxation oscillation peaks.

Multimode fabry-perot laser: Number of relaxation frequencies

We study analytically the Tang, Statz, and deMars equations describing a solid-state Fabry-Perot laser to determine how many relaxation oscillations it displays. When the modes have equal gains, the number of relaxation oscillations varies between zero and the mode number, depending on the laser parameters. In particular, a large number of modes or a relatively large pumping rate leads to the elimination of all relaxation oscillations except one, thereby simplifying the noise spectrum. These results are generalized to include unequal modal gains such as might result from the Lorentzian gain profile.

Dynamics of a solid-state ring laser with two-component gain line

Abstract A model of a solid-state ring laser (SSRL) with two-component gain line is discussed. It takes into account the lasing frequency detuning from the centres of both transitions and phase nonreciprocity. Laser relaxation frequencies and the conditions of instability of a unidirectional lasing are found. The comparison of theoretical and experimental results confirms the assumption that the fine structure of the 1064 nm gain line of neodymium ion in YAG is responsible for the low-frequency self-modulation of SSRL radiation. Dynamics of the counterrunning wave intensities and frequencies in our model are studied numerically. It is shown that the results are analogous to those obtained in the case of a homogeneously broadened laser with detuning.

Influence of Longitudinal Nonuniformity of Gain Distribution in Laser Medium on Low Frequency Dynamics of a Solid-State Laser

The present work repons the iesult~ of experimental and theoretical investigaliuni of the dynamic behwior of a multimode diode pumped Nd:YAG laser with a FabtyPerot cavil) The panial filling of the cavity with the laser medium. even in case of uniform pumping along the a c t i ~ e medium. leads to a atrung longitudinal nonuniformity of gain In our experiments, the cavily filling factor is wried from 0.2 l o 0.4. The resulting longitudinal gain nonuniformity causes significant changcer in the number and intensities af the lasing modes. in the ielaxatioii oscillation frequency spectrum and in the response of the laser to paramcter modulation. a? compared with the resdts far uniform gain. In particular the gain nonuniformity ma) suppress the optical modes Kith larger spectral gain in h o r of modes with lessm spectral gain. Our theoretical study of the relaxation ns~iliations demonrtratcs that these oscillations can he compenrated. manifesting themselves only in power spectra of individual modes, and non-compensated, leading to peaks in power spectrum of the total intensity as well. The exactly compensated oscillations exist only for symmetric detuning of the moder from the center of the gain line and far symmetricd loss distribution among the cavity modes. The compensated oscillations become non-compensated when these symmetries are broken. We have experimentally uncovered a hidden symmetq breaking: in the case of total symmetw of the optical spectrum, all relaxation oscillntions may appear in the transfer function of the total intensity. A possible reason is the presence of selective losses which are compensated in the experiment by detuning of the central mode from the center of gain line. We have numerically studied the conditions for the appearance of the inslahilily of stcadyst81e modal intensities caused by spatially nonuniform gain that was prediced in [I ] .

Are the sources of natural fluctuations correlated in different laser modes

The intensity fluctuations in multimode lasers with slow relaxing laser media are theoretically investigated. The power spectra corresponding to different correlation conditions between the noise sources inserted into individual modes are calculated in the framework of a two-level homogeneously broadened laser model with spatial hole burning. The comparison of calculated spectra with the experimental data allows us conclude that the noise sources are correlated.