I. Aramburu

Accurate determination of second order nonlinear optical coefficients from powder crystal monolayers

An accurate procedure for the determination of second harmonic generation (SHG) efficiency from powder crystal monolayers is proposed. The method is based on the analysis of the dependence of the SHG output on the powder particle size. Unlike with conventional powder methods, the amount of material required is very small, and the scattering of the primary beam by the powder particles is negligible, allowing for an accurate analysis of the collected data. The experimental results demonstrate that the proposed method can provide reliable values for the nonlinear optical coefficients, particularly in the case of phase-matchable uniaxial materials, for which simple analytical expressions can be derived.

Light propagation in optical crystal powders: effects of particle size and volume filling factor

In this work, we analyse the light propagation in some laser and nonlinear crystal powders. In particular, we study the dependence of the diffusive absorption lengths and the transport lengths on particle size and volume filling factor. The theoretical calculations have been made by assuming a diffusive propagation of light in these materials.

K5Nd(MoO4)4: a self-tunable laser crystal.

We report for the first time to our knowledge an experimental demonstration of wavelength self-tuning in a K5Nd(MoO4)4 broadband-emitting laser crystal (KNM), as well as a theoretical treatment of the system based on its birefringence properties. The self-frequency-tuning of the laser along the full spectral range of the KNM crystal was obtained by rotating a birefringent gain plate in its own plane. The gain plate was placed inside a resonator at Brewsters angle. The tuning characteristics of the spectral filter were obtained by use of the Jones vector formalism. The calculated wavelength-selective tuning precisely matches the experimental observations.

Characterization of light scattering in translucent ceramics

We have obtained expressions for the reflectance and transmittance of a scattering medium with weak absorption in terms of a diffusion model, where the source is an incoming beam, whose intensity exponentially decays along the propagation path. We have applied three experimental techniques, one of which is based on the developed model, to determine the transport mean-free-path in translucent samples of Nd:YAG ceramics.

Thermally induced light-scattering effects as responsible for the degradation of cholesteric liquid crystal lasers

We have studied the degradation process of the laser emission in a cholesteric liquid crystal laser. We have found that there exists a negative correlation between the laser efficiency and the amount of light scattered by the liquid-crystal sample in the illuminated area. The growth of scattering is attributed to the appearance of small imperfections generated in the sample as a result of certain thermal processes that involve the dye molecules. The scattering implies an increase of the coefficient of distributed losses, which is the main response of the rise of the laser threshold.

Role of the sample thickness on the performance of cholesteric liquid crystal lasers: Experimental, numerical, and analytical results

We have studied the performance characteristics of a dye-doped cholesteric liquid crystal (CLC) laser as a function of the sample thickness. The study has been carried out both from the experimental and theoretical points of view. The theoretical model is based on the kinetic equations for the population of the excited states of the dye and for the power of light generated within the laser cavity. From the equations, the threshold pump radiation energy Eth and the slope efficiency η are numerically calculated. Eth is rather insensitive to thickness changes, except for small thicknesses. In comparison, η shows a much more pronounced variation, exhibiting a maximum that determines the sample thickness for optimum laser performance. The predictions are in good accordance with the experimental results. Approximate analytical expressions for Eth and η as a function of the physical characteristics of the CLC laser are also proposed. These expressions present an excellent agreement with the numerical calculation...

Transport mean free path in K5Bi1- xNdx(MoO4)4 laser crystal powders

In this work, we calculate in two different ways the transport mean free paths in K5Bi1−xNdx(MoO4)4 (x = 0.05, 0.2, 1) laser crystal powders by using the diffuse spectral reflectance and transmittance of the powders and the absorption coefficient of the crystal materials. The theoretical calculations have been made by assuming a diffusive propagation of light in these materials. Similar results have been obtained from both methods.

Wavelength tuning of Titanium Sapphire Laser by its own crystal birefringence

We report for the first time to our knowledge an experimental demonstration of wavelength tuning in a broadband-emitting Ti: sapphire laser crystal based on its own birefringence properties. To investigate the tuning characteristics of the spectral filter, we have used Jones-Vector formalism. The calculated wavelength-selective tuning matches very precisely the experimental observations.

Self-frequency tuning in birefringent K5Nd(MoO4)4 laser crystal

Abstract In this paper we report an experimental demonstration of broadband wavelength self-tuning in K5Nd(MoO4)4 laser crystal (KNM) together with a theoretical treatment of the system based on its birefringence properties. The self-frequency tuning in KNM was obtained by inserting an a-cut plate inside the resonator at Brewster’s angle. At a given position of the crystal plate, when the wavelength of the oscillating mode corresponds to an integral number of full-wave retardation in the plate, the laser operates in the p polarization of the Brewster surface with no losses. The experimental self-frequency tuning of the laser emission along the free spectral range of the KNM crystal was obtained by rotating the birefringent gain plate in its own plane. To investigate the tuning characteristics of the spectral filter, we have used the Jones-vector formalism. The calculated wavelength-selective tuning matches very precisely the experimental observations. As far as we know this is the first time the grounds and operation of such a device is demonstrated.

Kinetic behavior of light emission in cholesteric liquid crystal lasers: An experimental study.

Some dynamical aspects of fluorescence and lasing have been studied in a dye-doped cholesteric liquid crystal by measuring the response of the material to nanosecond optical pumping. It has been found that as the pumping energy is increased the fluorescence pulse duration decreases, reaching a minimum at the lasing threshold. Above the threshold the temporal profiles are irregular and consist of a set of narrow pulses whose measured duration is limited by the detector risetime (1 ns). The results are interpreted in terms of a recently proposed model [JETP, 118, 822 (2014)] that makes use of rate equations to account for the laser generation in cholesteric liquid crystals. The prediction of such equations for an experimental configuration appropriate for fluorescence lifetime measurements is analyzed.