Dielectric micro-cavities are widely used as laser resonators and characterizations of their spectra are of interest for various applications. We experimentally investigate micro-lasers of simple shapes (Fabry-Perot, square, pentagon, and disk). Their lasing spectra consist mainly of almost equidistant peaks and the distance between peaks reveals the length of a quantized periodic orbit. To measure this length with a good precision, it is necessary to take into account different sources of refractive index dispersion. Our experimental and numerical results agree with the superscar model describing the formation of long-lived states in polygonal cavities. The limitations of the two-dimensional approximation are briefly discussed in connection with micro-disks.

The construction of perturbation series for slightly deformed dielectric circular cavity is discussed in details. The obtained formulae are checked on the example of cut disks. A good agreement is found with direct numerical simulations and far-field experiments.Comment: 17 pages, 12 figure

Dielectric resonators are open systems particularly interesting due to their wide range of applications in optics and photonics. In a recent paper [Phys. Rev. E 78, 056202 (2008)] the trace formula for both the smooth and the oscillating parts of the resonance density was proposed and checked for the circular cavity. The present paper deals with numerous shapes which would be integrable (square, rectangle, and ellipse), pseudointegrable (pentagon), and chaotic (stadium), if the cavities were closed (billiard case). A good agreement is found between the theoretical predictions, the numerical simulations, and experiments based on organic microlasers.

The emission from open cavities with non-integrable features remains a challenging problem of practical as well as fundamental relevance. Square-shaped dielectric microcavities provide a favorable case study with generic implications for other polygonal resonators. We report on a joint experimental and theoretical study of square-shaped organic microlasers exhibiting a far-field emission that is strongly concentrated in the directions parallel to the side walls of the cavity. A semiclassical model for the far-field distributions is developed that is in agreement with even fine features of the experimental findings. Comparison of the model calculations with the experimental data allows the precise identification of the lasing modes and their emission mechanisms, providing strong support for a physically intuitive ray-dynamical interpretation. Special attention is paid to the role of diffraction and the finite side length.

Hybrid pumping appears as a promising compromise in order to reach the much coveted goal of an electrically pumped organic laser. In such configuration the organic material is optically pumped by an electrically pumped inorganic device on chip. This engineering solution requires therefore an optimization of the organic gain medium under optical pumping. Here, we report a detailed study of the gain features of dye-doped polymer thin films. In particular we introduce the gain efficiency K, in order to facilitate comparison between different materials and experimental conditions. The gain efficiency was measured with various setups (pump-probe amplification, variable stripe length method, laser thresholds) in order to study several factors which modify the actual gain of a layer, namely the confinement factor, the pump polarization, the molecular anisotropy, and the re-absorption. For instance, for a 600 nm thick 5 wt% DCM doped PMMA layer, the different experimental approaches give a consistent value K ≃ 80 cm.MW −1 . On the contrary, the usual model predicting the gain from the characteristics of the material leads to an overestimation by two orders of magnitude, which raises a serious problem in the design of actual devices. In this context, we demonstrate the feasibility to infer the gain efficiency from the laser threshold of well-calibrated devices. Besides, temporal measurements at the picosecond scale were carried out to support the analysis.

Exciting plasmonic nanostructures by subpicosecond laser pulses can generate many interesting phenomena due to hot electrons, which can be further exploited in photonics or in chemical or biomedical applications. In order to quantitatively analyze and optimize these effects, proper evaluation of the light pulse power absorbed by the nanoparticles is highly required. However, in the literature only stationary properties are considered for that purpose.Here, we show that this may be invalid owing to the optical nonlinearity associated with the photogenerated hot electron distribution. We demonstrate through a simple optical transmission experiment the influence of hot electrons on the absorption cross section of gold nanorods, excited by subpicosecond laser pulses tuned to the longitudinal plasmon resonance spectral domain. The partial melting threshold of the nanorods is reached for a peak intensity of 5 GW cm −2 , corresponding to a volume density of energy of 2.2 aJ nm −3 . Below this threshold, the experimental results are interpreted through a model that accounts for the nonthermal nature of the electron distribution and for the multiphoton excitation. The variation of the effective optical absorption cross section, ⟨σ abs ⟩, with laser peak intensity reveals a strong and complex nonlinearity, which in addition depends on laser wavelength and nanoparticle shape, ⟨σ abs ⟩ being either larger or smaller than the stationary cross section value. Besides, we show that for a given pulse energy the shorter the pulse duration, the greater this deviation. Finally, we illustrate the consequences of this discrepancy through the evaluation of the nanoparticle temperature reached after photothermal conversion.

The far-field pattern of stadium-shaped organic microlasers is strongly modified by introducing circular air vacancies within the cavity, so as to control it in a predictive way. Experimental results are in good agreement with geometrical optics predictions whereas spectral properties of emission are investigated to improve the understanding of the lasing modes.

Polymer-based micro-lasers have recently drawn attention due to their attractive features in terms of technological potential, while providing deeper physical insights. In this perspective, we are reporting a number of advances which are related to the practical implementation of a relatively new design whereby micro-cavities are set on pedestals, in contrast with earlier architectures where the resonators were set in full contact with the substrate. Such a pedestal structure is shown to be responsible for a spectacular increase in the lasing efficiency. Depending on the cavity shape, the output power increase can reach up to 3 orders of magnitude. The emitted spectra also exhibit an enriched structure revealed by more favorable lasing and output coupling conditions. Simulations support experimental results and designate the crucial role of the cavity edges in light output coupling processes. Perspectives towards sensing applications are outlined as well as insights into fundamental issues of great practical implications such as wedge diffraction or effective index approximation.