A time-dependent, two-dimensional (in space) rate equation model of a transversely-pumped pulsed dye laser oscillator, which incorporates transverse pump intensity variation in the presence of intracavity dye laser radiation, is proposed to understand and predict its temporal behaviour. The model yields output pulses which agree well with experimental results using rhodamine 6G and kiton red dyes. The shape, amplitude and temporal position of the simulated pulse within the pump pulse vary dramatically across the tuning range of each dye depending on the relative gain and loss values.

Narrowband laser performances and photochemical stability of alcoholic solutions of pyrromethene 567 and rhodamine 6G dyes, under high-repetition rate copper vapour laser (at 510 nm), as well as, high-peak intensity Nd:YAG laser (at 532 nm) excitation have been investigated. We have observed that pyrromethene 567 dye solutions offer higher efficiency, wider tuning range, but lower photochemical stability and higher lasing threshold than that of rhodamine 6G dye solutions. An addition of about 100 mM DABCO, as a singlet oxygen quencher, in pyrromethene 567 dye solutions improved its photochemical stability close to that of rhodamine 6G. The observation of higher slope efficiency, in spite of higher threshold pump energy for pyrromethene 567 dye than that of rhodamine 6G dye solutions, was explained by a predictive model on gain characteristics of both dye solutions as a function of pump energy.

Nonlinear refraction in various polymethyl methacrylate (PMMA) solid hosts when doped with fluorescent organic dyes, commonly used as a laser active medium, has been studied. The observed thermal lensing effect arising from optical nonlinearity, results from non-radiative energy transfer from the dye molecules to the solid matrix and is, therefore, strongly dependent on the thermal properties and material parameters of the polymeric host. The non-linear index of refraction, n 2 , for each sample of dye doped polymeric host, has been measured employing the standard Z-scan technique. These measured values of n 2 , have been used to determine the extent of variation in the index of refraction with varying temperature, dn/dT, for the various host materials. Estimation of dn/dT is critical in determining the extent of thermal lensing in the dye doped solid-state medium, that in turn determines the spatial quality and divergence of the generated laser beam delivered by a dye doped solid-state laser system.

A saturable-absorber-based technique for spatial filtering of high-average-power laser beams is described. For a focused, radially symmetric beam having its highest intensity at the center, this saturable absorber behaves like a soft aperture with gradually increasing attenuation toward the beam edges, thus selectively transmitting the low divergence components that are confined close to the central axis of the propagating laser beam. This technique has been successfully used to reduce the divergence of a high-power, high-repetition-rate, tunable, narrowband, pulsed dye laser. Our results demonstrate how a judicious choice of operating parameters allows spatial filtering to be achieved with the introduction of a minimum absorption loss of the laser beam in the saturable absorber. Following a time-dependent analysis of a rate equation model describing the propagation and interaction of the laser beam with the saturable absorber, we have also obtained theoretical estimates for the extent of spatial filtering. Our theoretical estimates have been found to be in good agreement with our experimental observations.

Detailed experimental study of laser dye stability and the subsequent effects of photodegradation products on the operation of a Nd:YAG laser pumped Rhodamine-6G pulsed dye oscillator has been carried out. Deterioration of laser output on account of dye photodegradation resulting in the loss of active dye molecules and the generation and accumulation of reaction products that introduce a loss at the laser and pump wavelengths has been theoretically simulated in terms of a time dependent rate equation model. Our experimental observations have been found to be in good agreement with our theoretical estimates. We have also investigated the deterioration in the performance of a copper vapour laser pumped tunable dye laser with a high average power and a high repetition rate operating over an extended period of time. Our theoretical model, when suitably modified, provided useful estimates for the extent of deterioration in laser performance of such a dye laser with a high average power and a high repetition rate on account of photodegradation of the active dye molecules.

Resonant enhancement of nonlinear susceptibility in sodium vapour resulting in an intensity dependent nonlinear refractive index was investigated using the Z-scan technique. Estimates for the dipole moment obtained from the values of the near-resonant optical nonlinearity measured by us, in the vicinity of the D1 and D2 sodium resonance lines, were found to be in good quantitative agreement with the reported values. The functional dependence of the observed nonlinear susceptibility on the extent of detuning of the laser frequency with respect to the resonant atomic transition was in agreement with the adiabatic following model.

Photophysical properties of heavy-water-based rhodamine dye solutions have been investigated, with a view to assess the suitability of heavy water as a solvent for high-power, high-repetition-rate dye lasers and amplifiers. We have measured the quantum yield of fluorescence of the commonly used dyes rhodamine-6G, rhodamine-B and kiton-red, dissolved in heavy water, ethanol and normal water. The performance of a heavy-water-based pulsed rhodamine-6G dye laser has been investigated in broadband, as well as in narrowband wavelength-tunable resonator configurations, yielding laser efficiencies comparable to those achieved with ethanolic solutions of the same dye. We have also studied the thermo-optic properties of normal and heavy water, using the Z-scan technique. Finally, photodegradation rates for laser dyes have been compared in heavy water, normal water and ethanol. Our results establish heavy water as a solvent superior to both ethanol and normal water, on account of the lower thermo-optic effects and the higher photostability of rhodamine dyes when dissolved in heavy water.

The photo-stability of laser dyes, Rhodamine-6G, Rhodamine-B, and Kiton-Red, under high repetition rate (6.3 kHz) Copper-vapour-laser (CVL) irradiation has been investigated. Exhaustive photo-bleaching of these dyes in different solvents has been carried out to study the extent to which the dye photo-degraded products would interfere with the lasing process in high-power CVL-pumped dye lasers. Our results indicate that the photo-degradation of dyes occurs predominantly through excited-state intermolecular reactions, involving the singlet state, rather than the process of nonlinear optical absorption in individual molecules.

The design and the operational characteristics of a CO2 laser pumped CF4 laser developed at BARC are reported. Output energies of up to 20 mJ have been obtained at 615 cm−1 with an absorbed energy conversion efficiency of 10%.