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The mode inside a laser cavity may be understood as the interference of two counter-propagating waves, referred to as the forward and backward waves, respectively. We outline a simple experimental procedure, which does not require any additional components, to study the forward and backward propagating waves everywhere inside a laser cavity. We verify the previous theoretical-only prediction that the two fields may differ substantially in their amplitude profile, even for stable resonator systems, a result that has implications for how laser resonators are conceptualized and how the disparate traveling waves interact with nonlinear intra-cavity elements, for example, passive Qswitches and gain media. [ABSTRACT FROM AUTHOR]

In this work we propose an implementation of a new intra-cavity beam shaping technique to vary the intensity distribution of the fundamental mode in a resonator cavity while maintaining a constant intensity distribution at the output. This method can be useful for fitting a transversal intensity profile of the required mode with a pump beam profile in the region of the active medium to increase mode discrimination. [ABSTRACT FROM PUBLISHER]

Abstract: We present an efficient method to accurately calculate the reconstruction properties of a Bessel–Gauss beam after an arbitrary obstruction. Our method makes use of the well-known conical wave features of Bessel–Gauss beams, by considering the projection of the obstacle in space as a result of the travelling conical waves that produce the Bessel–Gauss beams. This approach, of projecting the obstacle boundaries rather than propagating the field itself, results in fast and accurate predictions of the field after any obstacle. We successfully predict the reconstruction properties of a Bessel–Gauss beam after three complex obstacles by calculating the boundaries of the various projected regions. This method has no restrictions regarding the geometry of the obstacle or its placement in the Bessel–Gauss field. [Copyright &y& Elsevier]

Abstract: We investigate a conventional resonator configuration, using only spherical curvature optical elements, for the generation of Bessel–Gauss beams. This is achieved through the deployment of a suitable amplitude filter at a Fourier plane create by careful selection of the geometric cavity parameters, such as mirror curvatures and resonator length. We analyze the loss behaviour of the odd and even modes, and show that the lowest Bessel–Gauss mode does not necessarily have the lowest loss. [Copyright &y& Elsevier]

Demonstration of the effect of atmospheric turbulence on the propagation of laser beams is traditionally a difficult task. This is due to the complexities of long-distance measurements and the scarcity of suitable laser wavelengths in atmospheric transmission windows. We demonstrate the simulation of atmospheric turbulence in the laboratory using a phase-only spatial light modulator. We illustrate the advantages of this approach, as well as some of the limitations, when using spatial light modulators for this application. We show experimental results demonstrating these limitations, and discuss the impact they have on the simulation of various turbulence strengths. [ABSTRACT FROM AUTHOR]

We investigate the effect of manipulating the laser quality factor and the spectral properties of the gain medium on an oligomer-based plasmonic nanolaser. We develop different designs of the oligomer resonators, decreasing the lasing threshold and increasing the mode lifetime to improve the lasing efficiency. Based on the designs we are able to decrease the lasing threshold by a factor of ten. We discuss and show numerically the influence of the oligomer geometry, the lasing mode oscillation lifetime, and the photoluminescence peak linewidth of the gain medium on the lasing efficiency of the oligomer based plasmonic nanolaser.

We investigated the selective excitation of localized surface plasmons by structured light. We derive selection rules using group theory and propose a fitting integral to quantify the contribution of the eigenmodes to the absorption spectra. Based on the result we investigate three nano oligomers of different symmetry (trimer, quadrumer, and hexamer) in detail using finite-difference time-domain simulations. We show that by controlling the incident light polarization and phase pattern we are able to control the absorption and scattering spectra. Additionally, we demonstrate that the fitting between the incident light and the oligomer modes may favor a number of modes to oscillate. Dark modes produce strong changes in the absorption spectrum and bright modes in the scattering spectrum. The experimental precision (axial shift error) may be on the same order as the oligomer diameter making the orbital angular momentum selection rules robust enough for experimental observation.

We propose a new technique for laser beam shaping into a desirable beam profile by using a laser amplifier with a pump beam that has a modified intensity profile. We developed the analytical formula, which describes the transformation of the seed beam into the desired beam profile in a four level amplifiers small signal regime. We propose a numerically method to obtain the required pump intensity profile in the case where high pump power saturated the laser crystal or for three level materials. The theory was experimentally verified by one dimensionally shaping a Gaussian shaped seed into a Flat-Top beam in a Ho:YLF amplifier pumped by a Tm:YLF laser with a HG(01) intensity profile.

Bessel beams have been extensive studied to date but are always created over a finite region inside the laboratory. Means to overcome this consider multi-element refractive designs to create beams that have a longitudinal dependent cone angle, thereby allowing for a far greater quasi non-diffracting propagation region. Here we outline a generalized approach for the creation of shape-invariant Bessel-like beams with a single phase-only element, and demonstrate it experimentally with a phase-only spatial light modulator. Our experimental results are in excellent agreement with theory, suggesting an easy-to-implement approach for long range, shape-invariant Bessel-like beams.

The self-reconstruction of superpositions of Laguerre-Gaussian (LG) beams has been observed experimentally, but the results appear anomalous and without a means to predict under what conditions this take place. In this Letter, we offer a simple equation for predicting the self-reconstruction distance of superpositions of LG beams, which we confirm by numerical propagation as well as by experiment. We explain that the self-reconstruction process is not guaranteed and predict its dependence on the obstacle location and obstacle size.

In this paper we present a general approach to determine the stability of a laser cavity which can include non-conventional phase transformation elements. We consider two pertinent examples of the detailed investigation of the stability of a laser cavity firstly with a lens with spherical aberration and thereafter a lens axicon doublet to illustrate the implementation of the given approach. In the particular case of the intra-cavity elements having parabolic surfaces, the approach comes to the well-known stability condition for conventional laser resonators namely 0 ≤ (1-z/R(1))(1-z/R(2)) ≤ 1.

We demonstrate a simple approach, using digital holograms, to perform a complete azimuthal decomposition of an optical field. Importantly, we use a set of basis functions that are not scale dependent so that unlike other methods, no knowledge of the initial field is required for the decomposition. We illustrate the power of the method by decomposing two examples: superpositions of Bessel beams and Hermite-Gaussian beams (off-axis vortex). From the measured decomposition we show reconstruction of the amplitude, phase and orbital angular momentum density of the field with a high degree of accuracy.

We study theoretically the orbital angular momentum (OAM) density in arbitrary scalar optical fields, and outline a simple approach using only a spatial light modulator to measure this density. We demonstrate the theory in the laboratory by creating superpositions of non-diffracting Bessel beams with digital holograms, and find that the OAM distribution in the superposition field matches the predicted values. Knowledge of the OAM distribution has relevance in optical trapping and tweezing, and quantum information processing.

We report on two resonator systems for producing Bessel-like beams with longitudinally dependent cone angles (LDBLBs). Such beams have extended propagation distances as compared to conventional Bessel-Gauss beams, with a far field pattern that is also Bessel-like in structure (i.e. not an annular ring). The first resonator system is based on a lens doublet with spherical aberration, while the second resonator system makes use of intra-cavity axicons and lens. In both cases we show that the LDBLB is the lowest loss fundamental mode of the cavity, and show theoretically the extended propagation distance expected from such beams.

We present the analytical and numerical analyses of two new resonator systems for generating flat-top-like beams. Both approaches lead to closed form expressions for the required cavity optics, but differ substantially in the design technique, with the first based on reverse propagation of a flattened Gaussian beam, and the second a metamorphosis of a Gaussian into a flat-top beam. We show that both have good convergence properties, and result in the desired stable mode.

A new approach to modeling the spatial intensity profile from Porro prism resonators is proposed based on rotating loss screens to mimic the apex losses of the prisms. A numerical model based on this approach is presented which correctly predicts the output transverse field distribution found experimentally from such resonators.