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Introduction to SPIE Photonics West OPTO conference 11686: Gallium Nitride Materials and Devices XVI.

Blue InGaN/GaN broad-ridge laser diodes show rich lateral mode dynamics and filamentation effects in addition to the longitudinal mode dynamics that are known from narrow-ridge laser diodes. We find a complex spectral, spatial and temporal behavior caused by the interplay between lateral and longitudinal mode competition mechanisms. In the experiment we measure the spectral-temporal dynamics with a streak camera, and the lateral resolution is achieved by scanning through a magnified near-field image. Additional time-averaged measurements with a high-resolution spectrometer indicate the presence of multiple longitudinal mode combs and the lateral scans show that there are different lateral modes in each mode comb. But also in separate regions of the laser spectrum, lateral modes of different order can be found.

Green laser diodes are being used for many applications, especially for laser projection. An important parameter for laser diodes are the internal losses. The internal losses of blue and green (Al,In)GaN laser diodes have been decreased to values significantly below αint = 10 cm-1, such enabling laser diodes with low threshold, high efficiency, and high output power. However, it is difficult to measure such low internal losses. From the slope efficiency and from Hakki-Paoli gain spectra, we derive an upper and lower limit for the internal losses of 5.4 cm-1 and 3.7 cm-1, respectively, for a specific green laser diode. Furthermore, we perform transfer matrix method simulations of the waveguide modes to simulate the dispersion of the internal losses in the wavelength range where the quantum wells are transparent. Comparing simulated and measured dependency of the internal losses on wavelength, we argue that the leakage of the waveguide mode to the p-contact and into the substrate are the main contributions to the dispersion of the internal losses.

We investigate the angularly, temporally, and spectrally resolved far-field dynamics of a single lateral mode green (Al,In)GaN laser diodes. For applications as directly modulated light source in laser projection, for AR/VR/MR, etc., a stable beam pointing angle and width of the far-field is required. Combing an angle- resolved measurement with a spectrometer and streak camera, we characterize optical intensity as function of far-field angle, wavelength, and time. Beam pointing angle and width are then calculated from the moments of the angular intensity distributions. We observe a stable far-field behavior for the narrow ridge. This is in contrast to strong variations in beam pointing direction and far-field profile during short pulses for earlier (Al,In)GaN laser diodes, where the dynamics could be tracked to heating of the waveguide. Therefore we attribute the observed stable dynamics of state-of-the-art narrow ridge laser diodes to their low internal losses, low forward voltage, and consequently low heating.

Appropriate micro-optical tools are required to exploit the key advantages of optogenetics in neuroscience, i.e. optical stimulation and inhibition of neural tissue at high spatial as well as temporal resolutions, providing cell specificity and the opportunity to simultaneously record electrophysiological signals. Besides the need for minimally invasive probes mandatory for a reduced tissue damage, highly flexible or wireless interfaces are demanded for experiments with freely behaving animals. Both these technical system requirements are achieved by integrating miniaturized waveguides for light transmission combined with bare laser diode (LD) chips integrated directly into neural probes. This paper describes a system concept using integrated, side emitting LD chips directly coupled to miniaturized waveguides implemented on silicon (Si) substrates. It details the fabrication, assembly, and optical as well as electrical characterization of waveguides (WG) made from the hybrid polymer Ormorcere. The WGs were photolithographically patterned to have a cross-section of 20x15 μm 2 . Bare LD chips are flip-chip bonded to electroplated gold (Au) pads with ±5 μm accuracy relative to the WG facets. Transmitted radiant fluxes for blue (430 nm, (Al,In)GaN) and red (650 nm, AlGaInP) LDs are measured to be 150 μW (ID = 35 mA, 5% duty cycle) and 4.35 μW (ID = 225 mA, 0.5% duty cycle), respectively. This corresponds to an efficiency of the coupled and transmitted light of 44% for the red LDs. Long term measurements for 24 h using these systems with red LDs showed a decrease of the radiant flux of about 4% caused by LD aging at stable WG transmission properties. WGs immersed into Ringer’s solution showed no significant change of their optical transmission properties after four weeks of exposure to the ionic solution.

Metallic nanostructures revealing plasmonic effects are a promising approach for improved photon management in thin solar cells. Irregular structures, as found in literature, suffer from parasitic absorption as a result of the varying dimensions of the particles. The parasitic absorption can be minimized by realising regularly ordered particles. Our fabrication process, suitable to meet these requirements, is based on interference lithography (IL), UV nanoimprint lithography (UV-NIL) and lift-off. As a process capable of large area structure origination, we use IL for the realization of master structures. Combining IL with NIL as a replication technique, the process chain is very versatile concerning nanoparticle shapes, sizes and arrangements. In the UV-NIL process, a flexible silicone stamp, which was replicated from the master structure, is pressed into a resist, which is cross-linked by UV light. A plasma etching step is applied to remove the residual resist layer. Afterwards, the substrate is coated with a thin metal layer and finally a lift-off is carried out. This results in metallic nanoparticles arranged in a regular pattern on the substrate. We show simulations and experimental results of round and elliptical disks and half spheres arranged in crossed and hexagonal gratings on glass and silicon. The elliptical particles show polarization dependent resonance effects. In a model assisted parameter study, we demonstrate the influence of various structure parameters on the absorption enhancement in silicon. Finally, optical measurements of ordered silver nanoparticles on the rear side of a silicon wafer are shown.

The possibility to increase the efficiency of solar cells by a restriction of the maximal angle of emission has been proposed for several times. Typically, this is achieved by applying a directionally selective filter on top of the solar cell. This filter leads to a reflection of emitted light under certain angles back into the cell, where it then can be reabsorbed. A system where the emission process itself is inhibited for certain angles (photonic solar cell) is in principle a better system, because then optical losses in the system can be suppressed as the emission in fact does not take place. In this contribution, we focus on a photonic solar cell, where the cell and the filter are combined in one single optoelectronic device. This means that the solar cell itself has a photonic structure or is implemented into a photonic crystal. The interesting question is how such a device could look like and how it performs. Here, design concepts for photonic solar cells are shown and simulated optically. An interesting system could be an integration of a solar cell as defect layer into a thin film stack. To get an idea of the potential of such systems, the emission out of a photonic solar cell has to be compared to the emission out of a standard solar cell. To this end, a scattering-matrix-formalism is used. First estimations of the possible system efficiencies are given as indication of the system quality.

We demonstrate pulse periods from 0:13 to 10 ns of GaN{based ridge waveguide laser diodes with monolithically integrated absorbers in the regimes of relaxation oscillations and self{Q{switching as function of gain current and absorber voltage. We introduce a simple model for the self{Q{switching regime, describing the pulse period in terms of current injection and spontaneous emission (including Auger recombination), only. At reverse voltages larger than 35V the modal absorption exceeds 500 cm-1, which cannot be explained solely by transitions of bound states in the quantum wells. Calculations based on wavefunction overlap and quantum con ned Stark e ect (QCSE) predict a decrease of absorption at such large bias. In contrast, we show experimental ndings, proving that the absorption further increases. Due to the strong tilt of the band pro le in this regime, we take into account the Franz{Keldysh e ect in the barriers and the waveguide and discuss its possible in uence on the absorption, leading to an increased absorption at large reverse bias.

The highly sensitive photoluminescence (PL) response of group III-Nitrides (III-N) nanowire heterostructures (NWHs) to hydrogen (H2) and oxygen (O2) allows for the realization of reliable gas detectors. For industrial real time gas monitoring applications, e.g. in the field of aerospace, a large scale laboratory setup was miniaturized by integrating electro-optical components and the NWHs within a robust micro optical system. As a result of the all optical addressing and read out the detection periphery can be completely isolated from the investigated environment which significantly increases the detection sensitivity. The optical design and fabrication techniques as well as an experimental investigation of the system performance are the main topics discussed in this paper.

We develop a monolithic picosecond laser pulse generator, based on the classical design of a group-III-nitride Fabry-Perot laser diode with electrically separated ridge sections. We use two different multi-section design variants, with the absorber section placed either in the center or at the end of the ridge. Profiting from the very low lateral conductivity in the p-type GaN top contact layer, we implement the multi-section concept just by etching off small sections of the top metalization on the ridge. The physical mechanism underlying short pulse generation within such system, operating in the 400 - 435nm wavelength range, strongly depends both on the reverse bias applied to the absorber and the forward current in the gain section. Varying the applied reverse bias affects both the absorption and the carrier lifetime in the absorber section through changes in the QW internal field. In consequence we can distinguish between different modes of operation. For moderately long carrier lifetimes the absorber stabilizes relaxation oscillations in the GHz frequency range and self-pulsation occurs, of relatively long duration. With increasing reverse bias, and thus decreasing carrier lifetime, we observe a transition to self-Q-switching. Finally, at large enough negative bias, the carrier life time in the absorber is so short that the laser diode operates in a passive self-mode-locking regime with a repetition rate of 87 GHz and pulse duration of 2 ps for a cavity length of 540 μm.

We demonstrate picosecond pulse generation in the blue-violet wavelength region by passive intra-cavity mode-locking in GaN-based ridge waveguide laser diodes with monolithically integrated absorbers. For cavity lengths of 1.2 and 0.6 mm we observe repetition frequencies of 40 and 90 GHz, and pulse lengths of 7 and 4 ps, respectively. The results are explained by an extremely short, tunneling dominated carrier life time in the saturable absorber at high negative bias. The fast depletion of the charge carriers in the absorber is investigated by bias-dependent life-time measurements in the absorber.

In this paper electro-optic cavity dumping of a 2 μm semiconductor disk laser is reported. Using this approach, pulsed mode operation with 3 ns pulse length, 30 W of peak power and pulse repetition frequencies between 87 kHz and 1 MHz has been achieved. For cavity dumping, a birefringent polarizer prism was inserted into the V-shaped external cavity formed by high-reflectivity mirrors, in order to establish a linear polarization of the intra-cavity field. The polarization of the intra-cavity field could be rotated by 90° when applying a voltage to a Pockels cell placed inside the cavity close to the end mirror. Photons with rotated polarization undergo then total internal reflection inside the polarizing prism and are coupled out of the cavity sideways. Furthermore, a model based on standard laser rate equations has been developed, which excellently reproduces the measured pulse shape and temporal evolution of the intracavity power. Based on this model, we have studied the pulse length and shape as well as peak power and pulse energy as a function of cavity length in order to explore routes for further increasing peak output power and pulse energy.

To achieve higher efficiencies in solar cells one possibility is to integrate angular selective filters, with the aim of decreasing losses caused by radiative recombination. In fact, thermodynamically, angular selectivity is equivalent to concentration. In both cases the Shockley-Queisser-Limit of solar cells is overcome by manipulating the ratio of incoming and outgoing radiation represented by the angles of incidence and emission. In concentrating systems the angle of incidence is increased, whereas in systems with an angular confinement the angle of emission can be decreased. Another possibility to achieve highest efficiencies is to combine both, concentration and angular confinement. Starting with a given concentrating system, photonic angularly selective filters such as thin film stacks are investigated and optimized for the use in this system. We present results of wave optical simulations of these filters and show some of their characteristics. The goal of this study is, however, not only to optimize optical filters but also to consider the whole system. One approach is to use results from optical simulations as input values for detailed balance simulations of the solar cell. So, the main advantage is, that in fact not the optical characteristics are optimized separately, but rather the whole system is taken into account, which allows predictions of theoretical efficiency enhancement.

We present a process chain to generate periodically arranged metallic nanostructures supporting plasmons for the use in solar cells. As proof-of-concept, platinum and silver nanoparticles with a period of 1 μm and a diameter of 600 nm were fabricated. For the platinum particles, an absorption enhancement for light with a wavelength of 3.6 μm was observed in silicon. By decreasing structure sizes the active spectral region can be shifted to wavelength relevant for solar cell applications. Therefore, in a second step a silver grating with a smaller period and also smaller diameter of approximately 200 nm was realized.

Picosecond (ps) lasers provide a universal tool for material processing. Due to the short pulse length material is removed by a process called "cold ablation", with minimal thermal damage to neighbouring regions. As a result, better defined structures with smother and cleaner side walls can be fabricated than with nanosecond (ns) laser pulses. This offers new possibilities for laser processing in semiconductor technology for both semiconductor materials as well as contact and bond metallizations. The fabrication of optoelectronic devices such as light-emitting diodes (LEDs) typically involves photolithography steps, requiring specific lithography masks be fabricated which, in particular for prototyping, is expensive and time consuming. Therefore it would be attractive for a range of applications to replace these steps by direct writing techniques such as laser processing, which will speed up e.g. the development and prototyping of new devices. We report on fully laser processed planar GaN-based LEDs fabricated without any photolithography steps. On the bare semiconductor wafer, isolation trenches and mesa structures are formed directly by ultraviolet ps laser pulses. For the direct deposition of patterned ohmic contact metallizations, the ps laser fabrication and subsequent use of high resolution shadow masks is presented, which exhibit a significantly reduced sidewall roughness compared to masks produced by ns laser pulses. Due to the higher precision of the laser defined masks it becomes possible to deposit multiple layers, through the use of alignment marks, similar to multiple mask level photolithography. Finally, the ps laser processed LEDs are electrically and optically characterized and their characteristic compared with that of conventionally fabricated mesa LEDs.

We develop (Al, In)GaN ridge waveguide laser diodes in the violet-blue spectral region. Varying the indium content of the InGaN quantum wells, we tailor the emission wavelength of our devices for specific applications in the range from 390 nm to 425 nm. Using different commercially available free standing GaN substrates, we adjust the epitaxial design and optimize the processing sequence for the different kinds of substrates. In particular we focus on the ridge formation. We compare different fabrication methods to obtain devices with ridge widths around ≤2 μm. So far, we have achieved threshold currents around 60 mA and slope efficiencies exceeding 1 W/A.

The resonator orientation of InGaN-based lasers on semipolar planes influences the optical polarization and the gain. We present gain measurements of semipolar (11-22) laser structures with differently oriented resonators and for various polarization states. The optical polarization state and the thresholds for lasers on different semipolar and nonpolar orientations are compared. The experimental results are accompanied by numerical calculations of the material gain as well as investigation of the surface morphology and resulting waveguide losses in dependence of the crystal orientation.

Optical polarization properties of nonpolar quantum wells and their efficiency droop at high charge carrier densities are discussed. Therefore, a photoluminescence experiment connecting both characteristics is presented. The additional property of polarization resolution provides information about the two lowest interband transitions and the occupation of holes in the two highest valence subbands. The ratio of occupation in the two subbands is a direct projection of the Fermi-Dirac statistics. Because of the carrier dependency of the Auger losses, the quantum well internal efficiency drops in the high charge carrier regime. Here, we observe that the peak of the internal quantum efficiency of the individual subband occurs at different excitation densities as a direct consequence of the Fermi-Dirac statistics.

Mobile laser projection is of great commercial interest. Today, a key parameter in embedded mobile applications is the optical output power and the wall plug efficiency of blue and green lasers. We report on improvements of the performance of true blue riedge waveguide InGaN lasers at 452nm with cw-output power up to 800mW in overstress and mono mode operation up to 500mW in a temperatures range of 20°C to 80°C. We succeeded in high and almost temperature independent wall plug efficiencies >20% at stable output power levels from 200 to 500mW in cw-operation. Due to several improvements of our blue laser diodes we now estimate life times is in the order of 40khrs for 80mW output power in cw-operation at 40°C. Additional overstress degradation tests at power levels up to 200mW show a strong dependency of lifetime with output power. Furthermore, we present pioneering results on true green InGaN laser diodes on c-plane GaN-substrates. The technological challenge is to achieve In-rich InGaN-quantum wells with sufficiently high material quality for lasing. We investigated the competing recombination processes below laser threshold like nonradiative defect recombination by electro-optical measurements, such confirming that low defect densities are essential for stimulated emission. A model for alloy fluctuations in In-rich InGaN-MQWs based on spectral and time resolved photoluminescence measurements yields potential fluctuations in the order of E0=57meV for our blue laser diodes. To get a closer insight into the physics of direct green InGaN-Laser we investigated the inhomogeneous broadening of experimentally measured gain curves via Hakki-Paoli-measurements in comparison to calculated gain spectra based on microscopic theory showing the importance of strong LO-phonon coupling in this material system. Investigations of current dependent gain measurements and calculations yield a factor of 2 higher inhomogeneous broadening for our green lasers than for our blue laser diodes on c-plane GaN. Based on the improvements of the material quality and design we demonstrate true green InGaN-Laser in cw-operation at 522nm with more than 80mW output power on c-plane GaN. The combination of low laser threshold ~60-80mA, high slope efficiency ~0.65W/A and low operating voltage 6.9-6.4V of our green monomode RWG-Laser results in a high wall plug efficiency of 5-6% in a temperature range of 20-60°C.

We present a systematic study of the dynamics of nitride laser diodes with different emission wavelengths ranging from violet (409 nm) to green (512 nm). The current-dependent relaxation behavior of the laser diodes above threshold is analyzed with high temporal and spectral resolution and electroluminescence decay measurements below threshold are employed to measure the charge carrier lifetimes at low excitation. We compare the experimental results to rate equation simulations to investigate on the origin of the differences in the dynamical behavior as function of the laser wavelength. From fitting these simulations to the experiment we extract device parameters such as the carrier lifetime at threshold and the differential gain.

For broad ridge (Al,In)GaN laser diodes, which are inevitable for high output power applications in the near-UV to blue spectral region, filaments appear, which influence the far-field beam quality. We present an extensive study of the optical mode profile of conventional c-plane LD test structures with ridge widths from 1.5 to 10 micrometers. The broad ridge samples are optimized to reach several hundred milliwatt of cw output power. Spectral and spatial resolved near- and far-field measurements show, that the characteristic lateral multi-lobed far-field pattern can be interpreted as superposition of interfering phase-locked filaments in the ridge waveguide.

Carrier lifetime and efficiency droop of green light emitting InGaN QWs in LEDs and laser diodes (LD) are discussed in term of Shockley-Read-Hall, radiative, and Auger-like recombination. The carrier lifetime, spectral shift, and carrier density as function of current density was measured by time-resolved electroluminescence with a streak camera. The current density was varied from very low for the LEDs to threshold for the LD. The transition from spontaneous emission in the low carrier density regime to stimulated emission in the high carrier regime is continuous. A comparison with Hakki-Paoli optical gain spectra provides evidence for a significant contribution of stimulated emission already at intermediate current densities. Stimulated emission is discussed as possible contribution to efficiency droop. A wavelength dependency of the lifetime is certainly caused by stimulated emission. Slope efficiency of the laser diode provides a lower limit for the injection efficiency of the LD. Time-resolved electroluminescence spectroscopy with applied bias demonstrates the variation of radiative recombination and consequently carrier lifetime with applied bias. Under certain conditions for modulated operation more light is emitted during times of zero bias than during forward bias.

For broad ridge (Al,In)GaN laser diodes, which are inevitable for high output power applications in the UV and blue spectral range, filaments or higher order lateral modes build p, which influence the far-field beam quality. We investigate the lateral profile of the optical laser mode in the waveguide experimentally by temporal and spectral resolved scanning near-field optical microscopy measurements on electrically pulsed driven laser diodes and compare these results with one-dimensional simulations of the lateral laser mode in the waveguide. We present a model that describes the optical mode profile as a superposition of different lateral modes in a refractive index profile which is modified by carrier- and thermal-induced effects. In this way the mode dynamics on a nanosecond to microsecond time scale can be explained by thermal effects.

We investigate two types of 405 nm (In, Al)GaN test laser structures (TLSs), one of them grown on SiC substrates, the other grown on low dislocation density freestanding GaN substrates. Measuring the lasing spectra of these structures, we observe an individual behavior depending on the substrate. TLSs on GaN substrates show a broad longitudinal mode spectrum above threshold, whereas TLSs on SiC are lasing only on one mode with various jumps of the laser emission at certain currents. Estimating the gain of each longitudinal mode with the Hakki-Paoli method, we find minute variations of the gain for TLSs on GaN substrate. In contrary, TLSs on SiC substrate show much larger fluctuations of the gain for individual longitudinal modes. Using a rate equation model with nonlinear gain effects, we simulate the longitudinal mode spectrum of both types of TLSs. Once we modify the gain of each longitudinal mode as observed in the gain measurements, the simulated spectra resemble the SiC or GaN substrate TLS spectra.

Photonic crystals are known to enhance the extraction efficiency of LEDs and simultaneously shaping the emission pattern. In order to determine the radiation pattern we developed a model based on coupled mode theory that takes into account the lattice pattern, etch depth and the mode distribution. From a basic geometrical consideration a fundamental limit for the directionality is predicted. The calculations fit well to experimental data obtained from green InGaN LEDs incorporating a hexagonal PhC revealing a maximum directionality of 31% within 30°. Additional FDTD simulations were performed for determining quantitatively the extraction efficiency of PhC LEDs compared to LEDs with a roughened surface. Despite its lower overall extraction efficiency, the PhC LED outperforms a standard LED with surface roughening within an acceptance angle of 34° due to the higher directionality of the extracted light.

Red, green and blue semiconductor lasers are of great interest for full color laser projection. Mobile applications require low power consumption and very small laser devices. InGaN lasers are the best choice for the blue color in applications with output power requirements below 100mW: (1) they have much higher wall plug efficiencies than conventional blue frequency doubled diode pumped solid state lasers and (2) they are more compact than semiconductor IR lasers with subsequent second harmonic generation. We present blue InGaN lasers with high efficiency at a power consumption of several 100mW. Excellent epitaxial quality permits low internal losses. Threshold current densities and slope efficiencies are further optimized by improving the facet coating. The laser threshold current is as low as 25mA and the slope efficiency reaches 1W/A. We present a wall plug efficiency of 15% at output power levels of 60mW.

We measure gain spectra for commercial (Al,In)GaN laser diodes with peak gain wavelengths of 470 nm, 440 nm,405 nm, and 375 nm, covering the spectral range accessible with electrical pumping. For this systematic study weemploy the Hakki Paoli method, i.e. the laser diodes are electrically driven and gain is measured below thresholdcurrent densities. The measured gain spectra are reasonable for a 2D carrier system and understandable whenwe take into account homogeneous and inhomogeneous broadening. While inhomogeneous broadening is almostnegligible for the near UV laser diode, it becomes the dominant broadening mechanism for the longer wavelengthlaser diodes. We compare the gain spectra with two models describing the inhomogeneous broadening. The “rstmodel assumes a constant carrier density, while the second model assumes a constant quasi Fermi level. Bothare in agreement with the experimental gain spectra, but predict very dierent carrier densities. We see ourmeasurements as providing a set of standard gain spectra for similar laser diodes covering a wide spectral rangewhich can be used to develop and calibrate theoretical manybody gain simulations.Keywords: InGaN laser diodes, optical gain, inhomogeneous broadening, localized states, Hakki Paoli method

In this contribution, substrate modes in edge-emitting lasers in the material system Gallium-Nitride are analyzed by means of comprehensive measurements and simulations. The simulations are complex vectorial optical mode calculations using a finite-element method. The simulation domain comprises the ridge waveguide and the full substrate with open boundary conditions on the sides. Therefore, the coupling mechanisms of the waveguides formed by the ridge and the substrate can be analyzed in a realistic setup. The characterization data include the optical loss spectrum obtained from Hakki-Paoli measurements, optical near field, and farfield measurements. The devices used for characterization are ridge waveguide quantum well lasers grown on GaN substrates. A comparison of the measurement data with the simulations explains the characteristics of the substrate modes in a consistent way, and shows very good agreement for the optical loss oscillations, farfield angle, and nearfield pattern. It is shown that material losses, material dispersion and optical diffraction are key ingredients for the analysis of substrate modes.

In this contribution, microscopic simulation of optical gain in GaN-based short-wavelength lasers is presented. The model is used to perform a design study of different active regions, and to discuss the impact of inhomogeneous broadening, carrier-induced screening of the piezo charges, and well thickness on material gain and laser threshold current. As a reference, the model parameters are calibrated with temperature dependent Hakki-Paoli measurements of spectral gain. Excellent agreement between measurement and simulation is achieved, which gives the design studies a quantitative character.

We combine a scanning near-field microscope (SNOM) with a time-resolved detection scheme to measure the mode dynamics of InGaN laser diodes emitting at 405 nm. Observed phenomena are filaments, mode competition, near-field phase dynamics, near-field to far-field propagation, and substrate modes. In this article we describe in detail the self-built SNOM, specialized for these studies. We also provide our recipe for SNOM tip preparation using tube etching. Then we compare the mode dynamics for a 3 μm narrow and a 10 μm wide ridge waveguide laser diode.

Ince-Gaussian modes form a complete family of exact and orthogonal solutions of the paraxial wave equation for elliptical coordinates. The transverse distribution of these fields is described by the Ince polynomials and have an inherent elliptical symmetry. These modes constitute a smooth transition from Hermite-Gaussian modes to Laguerre-Gaussian modes. We report the experimental observation of Ince-Gaussian modes directly generated in a stable resonator. By slightly breaking the symmetry of the cavity of a diode pumped Nd:YVO 4 laser and its pump beam configuration we were able to generate single high order Ince Gaussian modes with very high quality. The observed transverse modes and nodal patterns have the proposed elliptic structure and exhibit remarkable agreement with the theoretical predictions.

For blue (Al,In)GaN laser diodes we measure the evolution of the laser beam during its propagation from near-field to far-field. We reconstruct the near-field phase distribution of the waveguide mode. The dynamic behaviour is a tilting of the phase front and a far-field beam-steering on a 10 ns to 100 ns time scale. These observations are discussed in the context of the carrier induced change of the refractive index associated with the antiguiding factor and of thermal dynamics.