W.J. Firth

Stability of nonlinear Fabry-Perot resonators

Abstract The stability of folded Fabry-Perot resonators is investigated for the case where the resonator contains a medium with a dispersive third-order nonlinearity. Positive-branch instabilities of Ikeda type are found, with thresholds comparable to optical bistability thresholds. In the unstable region, the internal field is apparently chaotic, though oscillatory behaviour is found in a special case.

Propagation of laser beams through inhomogeneous media

Abstract The propagation of gaussian beams in media with an arbitrary gain and/or dispersion profile is discussed using a variational method. Simple analytic formulae are derived and applied to the spin-flip laser which has a gaussian gain profile. The results are a significant improvement on the quadratic-gain approximation.

Theory of Gaussian-beam optical bistability

Abstract We describe an analysis of transverse coupling effects in a plane parallel Fabry-Perot containing a medium exhibiting non-linear refraction. The method involves projection on to a set of ortho normal mode functions and numerical solution of the resulting coupled equations. We find evidence for hysteresis in the profile of the transmitted beam without accompanying power hysteresis, in first interference order.

Orthogonality properties of general optical resonator eigenmodes

Abstract We obtain biorthogonality properties for the counterpropagating (CP) modes of a very general class of optical resonators.

Nonlinear theory of self-oscillations in a phase-conjugate resonator

Abstract We present an exact, nonlinear analysis of self-oscillations in a phase-conjugate resonator. Optical bi- and multistability, as well as period doubling to chaos are predicted.

Dispersion in a cw optically pumped FIR laser

Direct frequency measurements of a13CO2/15NH3 OPFIRL output show that laser pulling effects give shifts of a few MHz, which agree well with a density matrix calculation.

Operating characterics of an optically pumped waveguide fir laser

Abstract We report measurements of the effect of resonator length changes, 13 CO 2 laser frequency and 13 CO 2 laser intensity on the FIR power emitted by an optically pumped waveguide FIR laser operating on the exceptionally strong 15 NH 3 laser line at 152.9 μm. The Doppler-splitting of the FIR output frequency shows a CO 2 power-dependent deviation from the linear dependence on 13 CO 2 laser frequency expected from rate equation theory. Similar, but weaker, effects are also reported using the less strong CH 3 OH FIR line at 118.8 μm.

Theory of tuning behaviour of the spin-flip laser

Abstract The tuning behaviour of the InSb spin-flip Raman laser is analysed using a theoretical model based on the solution of Maxwells equations. These are the first calculations to take account of finite beam size, the effects of which are found to include a marked asymmetry of the power necessary to achieve threshold and of the tuning rate across each mode. These and other predictions of the model are discussed and related to recent experimental results.

Theory of spin-flip Raman amplification in InSb

Abstract The advantages of a magneto-Raman amplifier technique for accurate study of the spin-flip Raman gain and line shape are discussed. Spin-saturation is accounted for in the theory, and found to cause anomalous line-broadening, as well as gain reduction. Related applications of the technique are outlined.

Two-Photon Light Shift in Optically Pumped FIR Lasers

We have made the first observation of a far-infrared two-photon light shift (2PLS). The 2PLS — an excess splitting of the gain peaks due to bidirectional pumping — is monitored by beating the output of two 15NH3 OPFIRL’s [1]. The effect is related to, but distinct from that observed by BIALAS, FIRTH and TOSCHEK [2], and is described by the three-level system model of FELDMAN and FELD [3].