Figure - available from: Optics Letters
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Experimental setup used for the optical characterization of turbulence-induced wavefront perturbations.
Source publication
Direct laser slab face-cooling by a fluid crossing the main and pump laser beams is an important method to reach high average laser powers. However, the flow regime is usually maintained at low Reynolds numbers to prevent the onset of turbulence features in the flow that would degrade the wavefront quality. We show here how bringing the fluid tempe...
Similar publications
Direct laser slab face-cooling by a fluid crossing the main and pump laser beams is an important method to reach high average laser powers. However, the flow regime is usually maintained at low Reynolds numbers, to prevent the onset of turbulence features in the flow, that would degrade wavefront quality. We show here how bringing the fluid tempera...
Citations
... The amplifier cell was qualified at different repetition rates from one shot per few minutes to one shot per minute. Emphasis is herein placed on assessment of mid spatial scale [1 mm -10 mm] distortions in amplified wavefronts commonly observed in fluid-cooled amplifiers [25,26]. Such wavefront defects in large-aperture multi-slabs laser systems are likely to degrade the focal point quality and, in the worst case, damage optical materials due to Kerr effects and/or amplitude modulation during laser beam propagation [17,27]. ...
... We observe that increasing repetition rate from 1 shot/5 min to 1 shot/min increases frequency defects above few millimeters. Such distortions are induced by the coolant flow as reported in [24,25]. But whatever the repetition rate tested, PSD stays below the acceptable upper limit represented by the broken purple line. ...
Mid-spatial frequency wavefront deformation can be deleterious for the operation of high-energy laser systems. When fluid cooled high-repetition rate amplifiers are used, the coolant flow is likely to induce such detrimental mid-spatial frequency wavefront deformations. Here, we describe the design and performance of a 90×90 mm2 aperture, liquid-cooled Nd:phosphate split-slab laser amplifier pumped by flash lamps. The performance of the system is evaluated in terms of wavefront aberration and gain at repetition rates down to 1 shot per minute. The results show that this single cooled split-slab system exhibits low wavefront distortions in the medium to large period range, compatible with a focus on target, and despite the use of liquid coolant traversed by both pump and amplified wavelengths. This makes it a potential candidate for applications in large high-energy laser facilities.
... Mid-spatial periods are more difficult to deal with. Marion et al. evidenced that small and mid spatial striae are created by thermodynamic effects during liquid coolant flow in turbulent flow [24]. These defects degrade the focal spot quality as shown by far field measurements and stereoscopic near field images. ...
The Foucaut knife-edge test has been used as a simple and effective metrology process to characterize the transmitted wavefront of optical systems for more than a century. We apply this method to estimate the optical quality of the transmitted wavefront in the mid-spatial frequencies domain. We compare the results obtained by this approach and interferometry to estimate RMS on three calibrated reference phase plates and evidence a difference smaller than 9%. The Foucaut knife-edge method is applied to a liquid cooled Nd:phopshate split slab amplifier. This method is shown to be particularly suitable to optimize liquid cooled slab amplifiers down to the sub-nanometer RMS quality values that are generally required in high-power laser systems
