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High-power pulsed lasers are widely used in scientific and industrial applications, and control of irradiance distribution using beam shaping optics is important to increase efficiency of laser techniques. A popular approach of building optical systems is use of a refractive beam shaper and imaging optics afterwards to create resulting spot of required intensity profile and size in a working plane. Important feature of imaging optical systems is creating the image after the paraxial focal plane – this means focusing of a high energy pulse before the image plane and probable air break down disturbing the intensity distribution in image and reducing performance of entire system. This problem becomes especially actual with modern ultrashort pulse lasers which pulse energy is constantly rising. Specific requirements to beam shaping optics in these laser systems are providing variable irradiance distributions, saving of beam consistency and flatness of phase front, capability to work with TEM00 and multimode lasers, resistance to high peak power radiation. Among various refractive and diffractive beam shaping techniques only refractive field mapping beam shapers like piShaper meet these requirements. The operational principle of these devices presumes almost lossless transformation of laser beam irradiance from Gaussian to flat-top, super-Gauss or inverse-Gauss through controlled wavefront manipulation inside a beam shaper using lenses with smooth optical surfaces. To overcome the problem of eventual air break down by imaging after a beam shaper it is suggested to apply optical systems with field lenses, which main function is changing the focusing conditions without change of the system transverse magnification. This approach allows to “move” the point of pulse energy concentration from the image zone and increase the focus spot size in order to reduce probability of air break down or avoid it at all.
This paper will describe some design basics of refractive beam shapers of the field mapping type and optical layouts of their applying in optical systems of high-power lasers. Examples of real implementations and experimental results will be presented as well.
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