J S Uppal

Sustained and bursting oscillations in stimulated Brillouin scattering with external feedback in optical fibre

Abstract Stimulated Brillouin scattering under cw pumping in the presence of low reflectivity feedback is shown to exhibit huge sustained or random bursts of quasi-periodic emission with an underlying weak chaotic behaviour imposed on a dc background. Theoretical analysis is in accord with these findings establishing the origin of this nonlinear dynamical behaviour to be purely deterministic and dependent on both Brillouin gain and nonlinear dispersion. No conditions have been found for stable steady state operation.

Aperiodic ruling for the measurement of Gaussian laser beam diameters

The use of an aperiodic ruling for the measurement of Gaussian laser beam diameters has been analyzed. We show that aperiodic rulings can provide spot-size measurements over a much broader range than available with Ronchi, triangular, or sinusoidal rulings used previously.

Validity of mode splitting analysis in optically pumped molecular lasers having Rabi splitting

Abstract Mode splitting analysis of three-level optically pumped molecular lasers is shown to provide both a clear physical insight and a quantitative measure of the steady state and oscillatory emission characteristics predicted from numerical analysis of these systems.

Simultaneous emission on 10P and 10R branch lines from a hybrid CO2 laser

The use of cavity length control to obtain multiline emission from a hybrid CO2 laser has been investigated. We have obtained simultaneous laser oscillation on up to four lines in the P and R branches of the 10 μm band by operating the c.w. section above the lasing threshold. For sub-threshold operation of the c.w. section the hybrid laser emission is restricted to the stronger 10P lines.

Gaussian reflectivity mirror with an absorbing lens.

A simple method for the generation of a Gaussian reflectivity mirror by using an absorbing lens is reported. The efficiency of an unstable resonator using such a Gaussian mirror as the output coupler has been analyzed.

Absorptive bistability in coherently pumped three level lasers

A resonantly pumped three level laser system has been analysed including pump depletion where it is shown that under appropriate conditions of pumping, the output emission results in a bistable action in their steady state behaviour. A combined action of nonlinear distortion of gain at pump frequency and a large amount of feedback are shown to be responsible for the absorptive bistable behaviour.

Multiline operation of a hybrid CO 2 laser

Macroscopic control of the cavity length is required, in addition to the PZT control, to obtain uniform intensity output on several rotational lines from a hybrid CO(2) laser.

Generic Instabilities and Chaos in Stimulated Scattering Phenomenon

Pulsating instabilities and deterministic chaos are known to be common features of many nonlinear processes. These implications are being strongly felt in a broad range of physical sciences. Lasers, in particular, have been found to exhibit a rich variety of nonlinear dynamical behaviour which, in addition to regular periodic oscillations, includes unstable or even chaotic solutions. The observation of deterministic instabilities in lasers is particularly significant as they provide ideal systems for quantitative investigations, owing to their simplicity and the mathematics that describe them, enriched by the possibility of a quantum description. Furthermore the timescale of these instabilities (nanosec. to microseconds) provides simplicity in maintaining stable operating conditions over many periods. From the prolific activity of this field in the area of lasers, attention is now being focussed on other important areas of nonlinear optics. In this paper, we try to explore the generic nature of nonlinear dynamical behaviour in fundamental nonlinear processes. The requirement of feedback for the emergence of instabilities is normally provided externally either by optical cavities as in the lasers or by counter-propagating beams [1–6]. There are, however, many optical phenomena in which feedback is an implicit and integral feature for their interaction. Significantly a broad range, if not the majority, of nonlinear optical interactions satisfy this criteria of which general three-wave mixing and parametric processes merit special attention as cornerstones of the field. Through recent major advances in optical fibre technology we are now able to interrogate these phenomena under ideal cw and for low power pulsed optical excitation by utilizing the long interaction length of this medium to readily induce nonlinearity under these conditions. Furthermore plane wave analysis is an excellent approximation in describing beam propagation in such media. In addition, however, fibre systems are critical components to an entire future telecommunications technology and any qualitative insight into the nonlinear dynamical behaviour of light propagation in such media has potentially important applications.

Bistable and Sustained Oscillatory Behaviour of Coherently Pumped Three Level CW Laser

Coherently pumped three level lasers are known to have a considerably rich dynamics arising due to field induced modification of the gain and dispersion of the active medium [1,2]. Here we establish analytical expressions for the output characteristics for arbitrary pump depletion and use them to describe the laser characteristics in some limiting cases. In particular we find 1) conditions for sustained Rabi oscillations and 2) bistable behaviour for both pump and generated emission for large pump depletion where both the pump and emission form a mode of the laser cavity.

Analysis of Steady State and Bistable Emission from a Three-level Laser

Abstract A resonantly pumped three-level laser is analysed in a high-Q cavity under conditions of negligible and high pump depletion to obtain expressions for the emission characteristics in analytic form. Under high pump depletion our analysis predicts bistable emission in its steady state behaviour.