Antonio Lapucci

Hybrid stable-unstable resonators for diffusion-cooled CO(2) slab lasers.

We present the numerical and experimental study that we carried out to compare the performances of two hybrid stable-unstable resonators for diffusion-cooled CO(2) slab lasers. The two resonators are designed to fit a 320 mm × 60 mm ×2 mm rf-discharge channel and are both guided in the narrow transverse direction. They differ in the other transverse direction, consisting of a positive- or a negative-branch unstable resonator scheme. The two solutions have been characterized in terms of modal structure, power extraction, stability, and quality of the extracted beam.

3-D numerical simulation of Yb:YAG active slabs with longitudinal doping gradient for thermal load effects assessment.

We present a study of Yb:YAG active media slabs, based on a ceramic layered structure with different doping levels. We developed a procedure allowing 3D numerical analysis of the slab optical properties as a consequence of the thermal load induced by the pump process. The simulations are compared with a set of experimental results in order to validate the procedure. These structured ceramics appear promising in appropriate geometrical configurations, and thus are intended to be applied in the construction of High Energy Diode Pumped Solid State Laser (DPSSL) systems working in high repetition-rate pulsed regimes.

Efficiency optimization for a diode-pumped Nd:YAG ceramic slab laser

With the help of photometric calculations based on ray-tracing algorithms, we have optimized the efficiency of the optical pumping of a Nd:YAG ceramic slab laser. The slab pumping is performed by means of two horizontal diode laser array stacks. The use of two small reflecting walls allows the sort of duct coupling that is capable of significantly improving the performance of the system. Our first experiments with a simple direct coupling provided a maximum extraction of slightly more than 160 W at a 20% slope efficiency level. The use of the optimized short duct coupling leads us to the extraction of 350 W with a slope efficiency of 51%, making use of the same diode arrays. The laser design is suitable for the construction of cw sources with a power output above 1 kW.

Compact scalable diode-pumped Nd:YAG ceramic slab laser

We describe our preliminary studies of the use of neodymium-doped slab-shaped ceramic YAG media in the construction of compact, rugged, high-power diode-pumped solid-state lasers. A maximum extraction of more than 160 W at a 20% slope efficiency level, with a narrow transverse direction beam-parameter product of the order of 4 mm mrad(-1) is experimentally obtained from an extremely simple and compact (overall dimensions 160 mm x 100 mm x 60 mm) laser head in a quasi-continuous-wave regime. Experimental data together with finite-elements method simulations indicate that power extraction can be scaled up at least to 900 W cw with this laser head geometry.

Guided Talbot resonators for annular laser sources

We studied the properties of an annular waveguide laser resonator, performing a new set of numerical simulations. The existence of fractional-Talbot effects is shown and results are compared to previous free-space propagation calculations and experimental results. Our study allows us to design annular waveguide lasers efficiently extracting power into a well behaving field distribution, convertible into a high quality beam by means of simple optics.

Extraction of high-quality beams from narrow annular laser sources

We have analyzed the propagation properties of the field produced by circular arrays of coherent optical sources, obtaining the conditions for the generation of good-quality global beams. Such conditions can be obtained by the use of resonators based on the Talbot effect. This appears to be a practical method for the construction of simple, low-cost resonators for compact diffusion-cooled high-power lasers with annular format. Low-loss annular Talbot cavity configurations have also been studied.

Pulse behaviour of a compact RF discharged CO2 slab laser

Abstract We present the measurements made on a medium power, 35 cm long, radio-frequency discharge CO2 slab laser operated in a pulsed regime obtained by switching the RF discharge. In this way, pulses with peak power up to 480 W at pulse repetition frequencies in the range 1 to 10 kHz have been obtained. Pulse energy and average extracted power have been experimentally characterized with respect to the pulse repetition frequency and to the pulse duration, and the pulse shape and characteristic times have been measured. We also investigated the propagation properties of the beam emerging from our laser.

Discharge impedance variations in large area radio frequency excited CO2 lasers

Some results from a systematic study on the impedance matching conditions and on the longitudinal power distributions in planar rf discharges for CO2 lasers, are given. They show that both plasma impedance and voltage distribution are different in cw and pulsed discharge modes revealing the importance of parameters such as the interelectrode temperature distribution and the local gas density and composition. These parameters have to be taken into account when designing matching networks and voltage smoothing schemes.

Polarization state modifications in the propagation of high azimuthal order annular beams

Using a vector Fresnel diffraction propagator we investigate the far-field distributions obtained from guided annular modes with different polarization states. Furthermore we demonstrate that a pure azimuthal polarization transforms into a mainly radial one in the propagation of annular beams with azimuthal mode number higher than 0. This property could enhance the performance of a laser metal-cutting system based on these kind of beams.

Parameters affecting the power distribution in the radio frequency discharge of large-area diffusion-cooled CO/sub 2/ lasers

An efficient power extraction from radio frequency (RF) excited CO/sub 2/ lasers can only be obtained by means of a uniform discharge power distribution. This distribution is mainly determined by the line-effect produced by the discharge structure. In this paper we report on a set of measurements performed on the luminosity of a large-area discharge showing the role played by parameters such as local gas temperature, density, and composition. In particular, the existence is shown of conditions in which these parameters move distributions away from the known sheaths driven lossless line behavior.