Laser power absorbed outside the beam spot on a rippled metallic surface as determined by a matrix calorimetric method

We report first evidence in support of chaotic stimulated Brillouin scattering under cw pump conditions involving a single Stokes and pump signal. A single-mode optical fiber is used as the nonlinear medium. The inclusion of external optical feedback modifies the form of the chaotic dynamics and results in a rich variety of classifiable precursor dynamical features. PACS numbers: 42.65.Es, 05.45.+b, 42.10.Hc, Pulsating instabilities and chaos are of current interest throughout physics and, in particular, quantum optics. While observations of these phenomena are now extensive in systems with external optical feedback, notably lasers, 1 passive bistable systems, 2 and to a lesser extent systems with counterpropagating pump beams, 3 there are few if any reports 4 of such behavior in nonlinear processes for which this restriction is lifted. In this paper we consider stimulated scattering phenomena and provide, to our knowledge, first evidence indicative of chaotic dynamics in one of these basic processes, namely, stimulated Brillouin scattering (SBS). A single-mode optical fiber is used to generate SBS under cw singlemode pump conditions, 5 resulting in first-order Stokes emission only. We find both the transmitted pump and backscattered SBS to exhibit chaotic behavior under all operating conditions investigated, including those close to the threshold for SBS; the SBS exhibits massive instabilities with modulation depths -100%.The few reports to date, mainly theoretical, on the dynamics 6 " 14 of SBS principally concern the generation of instabilities, usually limit-cycle behavior, through more complex interactions involving either more than one pump beam, 12,13 external cavity feedback, 9 " 11 and/or higher-order Stokes-anti-Stokes generation. 12 Experimental findings, often in regard to plasma interaction, 10,12 have been constrained to short-pump-pulse exciposing limitations to quantitative statements tation, 7,10,13 of long-term dynamical behavior; an exception being the observation of limit-cycle behavior in fibers with external optical feedback.'' Of the theoretical contributions, an exception is the analytical findings of Blaha et al. ,4 providing evidence of unstable behavior in SBS involving a single pump and Stokes signal in a semi-infinite medium. Our experimental arrangement is schematically shown in Fig. 1. The cw emission of a single-mode argon-ion laser at 514.5 nm, with an instantaneous (:<1 msec) linewidth of -15 kHz (Coherent Innova 100) was used as a pump source providing variable output power stabilized to ±2%. Two 10 x microscope objectives L\ and Li, were used to couple the light into and out of the optical fiber, respectively. The fiber comprised a pure SiC>2 core of diameter 4.8 /xm with a B2C>3-doped SiC>2 cladding. It was optically isolated from the argon laser using a Faraday isolator (OFR Model IO-5-532) giving an isolation factor of 35 dB between them. The pump signal and backscattered signal, comprising the SBS signal together with residual scatter, were sampled via the beam splitter in ...

We show that pump-induced modifications to the gain and dispersion profiles can induce a weak sideband modulation which acts as a driving term to sustain chaotic relaxation oscillations in a single-mode, resonant, optically pumped molecular laser. Our study suggests that a careful two-or more-parameter unfolding of higher-codimension bifurcations should lead to a wealth of nonlinear dynamical behavior within easy access of current experiments.PACS numbers: 42.50.Tj, 42.55.Em Random spiking or sustained relaxation oscillations have been observed in a wide class of lasers from their very inception. However, a clear physical or mathematical explanation of these effects has, with the exception of two cases, 1,2 remained elusive despite substantial theoretical literature on the topic and recent interest in potentially chaotic laser systems. 3 In this Letter we provide a clear physical and mathematical mechanism for sustained chaotic relaxation oscillations in a single-mode, homogeneously broadened laser. Moreover, for our system, an optically pumped molecular laser, we show with a parallel bifurcation analysis that the chaotic motion is associated with a random motion on an attracting set associated with a homoclinic orbit in phase space (double saddle connection). This latter analysis allows us to establish unambiguously (i) a preturbulent regime with eventual collapse onto a stable periodic orbit or cw lasing state, (ii) a chaotic window truncated by the onset of a pump-induced stable Rabi sideband oscillation, and (iii) regimes of spontaneous pulsations from both a lasing and nonlasing state.Optically pumped molecular lasers comprise three levels with the pump and laser transitions sharing a common level, as shown in the inset in Fig. 1(a). Attempts to truncate the equations describing their dynamics to effective two-level systems of the Haken-Lorenz type 4 involves among others the assumption of a polarization decay rate for the pump transition which is considerably greater than that for the lasing transition, 5 an unrealistic condition for real molecular systems. Such unphysical truncations are reminiscent of the situation encountered in fluids where the Lorenz equations represent a severe truncation of the original Navier-Stokes equations. In the present laser context the coherent interaction between the pump and lasing emission is suppressed, eliminating the important physics associated with pumpinduced Rabi sideband oscillations. In this Letter we emphasize the unique role of the pump laser as a control parameter which, through such coherent interactions, allows one to tailor the gain profile seen by the lasing emission. This unique feature of optically pumped molecular lasers enables us to separate the dynamical features asso-ciated with the laser emission field from those of the pump field over physical parameter ranges which are well within reach of current experiments. 6 The present study suggests that much of the rich dynamical behavior of this system remains to be discovered within a careful two-or more-...

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We present a detailed analysis of the dynamical behavior of an optically pumped molecular laser. This study combines bifurcation and power spectral analysis with numerical investigation of the global features of attractor topology under control parameter variation. The special role of the pump laser in generating physically distinct periodic and chaotic dynamics is emphasized through the complementary use of laser gain and dispersion characteristics. Our main results are the following: (i) instabilities associated with the physically distinct mechanisms of relaxation and pumpinduced Rabi sideband oscillations are readily generated; (ii) the topological characteristics of both periodic and chaotic attractors reAect these physically distinct mechanisms, making it possible to discriminate between both types of behavior in heterodyne power spectra; and (iii) the ratio of deenergization to dipole-dephasing rates is central to determining the operating characteristics of the laser.