Eichhorn M.,French German Research Institute of Saint Louis
Optics Letters | Year: 2011
First results on a diode-pumped multikilowatt-class Er3+:YAG solid-state heat-capacity laser (SSHCL) are reported. The laser achieves an output power of 4650Wand output energies in excess of 440 J. A moderate crystal temperature increase due to crystal heating of 56.7 K/s is measured at 11.3 kW of pump power and the temperature-related power drop is determined to 8.8 W/K. The presented work is believed to be the first multi-kilowatt-class resonantly diodepumped Er3+:YAG laser. © 2011 Optical Society of America.
Schellhorn M.,French German Research Institute of Saint Louis
Applied Physics B: Lasers and Optics | Year: 2011
Singly 0.5 at.% Ho doped crystals of YLiF4 (YLF) and LuLiF 4 (LLF) are studied under identical pump conditions in continuous-wave (CW) and Q-switched operation. Longitudinal end-pumped CW laser performance shows Ho:LLF to have a slightly lower threshold and a slightly higher slope efficiency with respect to absorbed pump power than Ho:YLF. Both lasers were operated on π-polarization. At a cavity output coupling of 20% and a crystal length of 30 mm, the Ho:LLF (Ho:YLF) laser yielded 18.8 W (18 W) of CW output at a wavelength of 2067.8 nm (2064.0 nm) for 41.4 W (42.2 W) of absorbed pump power with a slope efficiency of 67.1% (65.6%) and an optical-to-optical efficiency of 45.4% (42.6%) with respect to absorbed pump power. With the same output coupling and a crystal length of 40 mm, the Ho:LLF (Ho:YLF) laser yielded 20.5 W (18.1 W) of CW output at a wavelength of 2067.7 nm (2064.3 nm) for 51.5 W (50.0 W) of absorbed pump power with a slope efficiency of 58.4% (55.4%) and an optical-to-optical efficiency of 39.8 (36.1%) with respect to absorbed pump power. The influence of the temperature of the cooling mount on CW laser performance was studied and showed very similar results for both laser materials. At full pump power, a slope of-155 mW/°C (-149 mW/°C) was observed for the Ho:LLF (Ho:YLF) laser with a crystal length of 30 mm. In Q-switched operation, the Ho:LLF (Ho:YLF) laser produced 37 mJ (38.5 mJ) at a repetition rate of 100 Hz with a pulse duration of 38 ns (35 ns) at a wavelength of 2053.1 nm (2050.2 nm) with a slope efficiency of 30.3% (31%) and an optical-to-optical efficiency of 14.2% (13.9%) with respect to absorbed pump power. The beam quality was nearly diffraction limited (M2 < 1.1). © Springer-Verlag 2011.
Cheinet S.,French German Research Institute of Saint Louis
Journal of the Acoustical Society of America | Year: 2012
The present study formulates a consistent method to simulate the outdoor, near-surface sound propagation through realistic refractive conditions. The correlated atmospheric stratification and turbulence properties are derived from standard meteorological quantities through flux-profile similarity relationships. The propagation of a monochromatic sound field is simulated in presence of the turbulence and stratification effects and an impedance ground. The propagation model uses a numerical solution of a second-order moment parabolic equation, which is introduced and evaluated. The so-formed coupled atmospheric-acoustic model is used to systematically investigate the sound levels in near-surface refractive shadows. In an illustrative propagation scenario, the shadow zone sound levels are predicted to show significant variations with the meteorological conditions. Specifically, the sound levels decrease with the adverse wind, as a consequence of enhanced mean upward refraction. Conversely, they increase with the absolute value of the surface heat flux, as a consequence of enhanced turbulence scattering. Implications for the assessment of the sound levels in shadow zones are discussed. © 2012 Acoustical Society of America.
Matwyschuk A.,French German Research Institute of Saint Louis
Applied Optics | Year: 2014
An active imaging system in burst mode allows the duty cycle of laser pulses to be close to 50%. In this configuration, a visual artifact resulting from a remote zone in the scene can appear in the image of the desired visualized zone. Therefore, the elements of this remote zone will create confusion in the image with erroneous estimated distances. These misinterpretations can be very disturbing when determining the distance of a target in the scene. In order to demonstrate the occurrence of visual artifacts with an active imaging system in burst mode, the different translated signals in the time domain as well as the atmospheric attenuation and the attenuation due to the inverse square distance were included in the modeling of this mode. A graphic method, which does not take into account the different attenuations, was also proposed to give an idea of the visual artifact phenomenon. The validity of the modeling was demonstrated by comparing the results of the outdoor tests carried out with an active imaging system in burst mode. Consequently, the simulation programs can use this modeling to evaluate the visual artifact in a scene. © 2014 Optical Society of America.
Cheinet S.,French German Research Institute of Saint Louis
Journal of the Acoustical Society of America | Year: 2014
The near-surface sound levels emitted due to a point source show a large variability caused by sound propagation through changing meteorological conditions. To assess this variability, this study uses a numerical model of sound propagation which accounts for ground reflection, atmospheric refraction, and turbulence effects. The atmospheric inputs to the model - including turbulence - are calculated from Numerical Weather Prediction data. The method is used to investigate the relative sound levels at a range of 1.5km from a 40Hz sound source. The outstanding diversity of sound propagation conditions is illustrated over the globe. Over the long term, the sound propagation climates at selected sites are found to be modulated by the dominant wind regimes, the seasonal and diurnal cycles. The explored sensitivities stress the need for a careful assessment of sound scattering by turbulence and absorption by the surface. © 2014 Acoustical Society of America.