The native shape of the single-mode laser beam used for high power material processing applications is circular with a Gaussian intensity profile. Manufacturers are now demanding the ability to transform the intensity profile and shape to be compatible with a new generation of advanced processing applications that require much higher precision and control. We describe the design, fabrication and application of a dual-optic, beam-shaping system for single-mode laser sources, that transforms a Gaussian laser beam by remapping – hence field mapping - the intensity profile to create a wide variety of spot shapes including discs, donuts, XY separable and rotationally symmetric. The pair of optics transform the intensity distribution and subsequently flatten the phase of the beam, with spot sizes and depth of focus close to that of a diffraction limited beam. The field mapping approach to beam-shaping is a refractive solution that does not add speckle to the beam, making it ideal for use with single mode laser sources, moving beyond the limits of conventional field mapping in terms of spot size and achievable shapes. We describe a manufacturing process for refractive optics in fused silica that uses a freeform direct-write process that is especially suited for the fabrication of this type of freeform optic. The beam-shaper described above was manufactured in conventional UV-fused silica using this process. The fabrication process generates a smooth surface (<1nm RMS), leading to laser damage thresholds of greater than 100J/cm2, which is well matched to high power laser sources. Experimental verification of the dual-optic filed mapper is presented.
We report a new route to obtaining custom freeform micro-optical components that is free from symmetry restrictions,
offering drastically lower cost and delivery times than what is required by other freeform manufacturing methods. We
describe how this process can be used to realize a complex custom optic using data generated directly from a design in
Zemax. This surface is then extracted from Zemax and fabricated using the LightForge service before being measured. A
quantitative analysis of the real optic is carried out both numerically and with the design source in Zemax, and we
present a comparison between design and fabricated part performance.
High power laser beamshapers based on lens arrays are widely used to generate square, rectangular or hexagonal flat-top far-field beam profiles. These devices can provide high efficiency and excellent brightness preservation, but offer a limited range of far-field profiles and can suffer from diffraction-related artefacts when used with spatially-coherent beams. Diffractive optical elements (DOE) offer a far wider range of far-field profiles, and better speckle behavior, but bring performance trade-offs in terms of brightness, efficiency, scattered power and residual zeroth-order power. Freeform refractive optics offer additional choices in the design of high power laser beamshapers. Freeform lens arrays offer a wider range of beam profile options than that available from catalogue lens array parts. Freeform field mapping beamshapers can generate a wide range of application-specific beam profiles with high efficiency and, where required, minimal reduction in brightness. More complex quasi-random freeform surfaces can act as a pseudorandom refractive intensity mapping element (PRIME), providing a level of beamshaper design flexibility closer to that of DOEs, but without the related high-order scatter and zeroth order leakage. We describe the design and implementation of these different types of refractive beam shaper in fused silica, using PowerPhotonic’s direct-write freeform fabrication process. This is ideal for use in high-power laser systems, where high damage threshold and low loss are essential. We compare and contrast the performance, benefits and limitations of these types of beamshaper, and describe how to select the ideal beamshaper type based on source coherence properties and application beam profile requirements.
Commercially-available QCW diode laser stacks with bar pitch below 0.5mm can now deliver source power densities exceeding 10kW/cm2. An increasing number of applications for these sources also specify high brightness, with collimation requirements ranging from equalization of fast and slow axis divergence to achieving fast-axis divergence within a small multiple of the diffraction limit. While collimation can be achieved by mounting an array of rod lenses in a frame with a suitable v-groove array, the resulting optical assembly has a large number of elements and associated adhesive bonds, and the size of the mounting frame limits the density at which stacks can be packed together. We present results exploiting an alternative approach using monolithic fast-axis collimator arrays. This approach greatly reduces the component count and minimizes the number of adhesive bonds required, providing a compact and rugged assembly well-suited to demanding applications. The monolithic collimator array also simplifies package design, and maximizes the achievable device stack packing density. Lens array properties may be tailored to generate applicationspecific divergence profiles or to match the geometry of individual stacks in order to achieve low divergence. Directwrite fabrication of these components allows mass-customization, offering a scalable, low-cost route to high volume collimation for fusion applications.
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