Beam shaping of high power diode lasers benefits from asymmetrical refractive micro-lens arrays

Abstract

Micro-lens arrays are widely used for beam shaping, especially beam homogenization of various laser sources. Monolithic arrays of cylindrical lenslets made of glass, semiconductors or crystals provide great advantages in laser applications, e.g. high efficiency, intensity stability and very low absorption. However, up to now, mainly symmetrical micro-lens surfaces are utilized in most applications due to design and manufacturing restrictions. The manufacture and application benefits of asymmetrical cylindrical-like micro-lens surfaces are enabled by LIMO's unique production technology. The asymmetrical shape is defined by uneven-polynomial terms and/or an asymmetrical cut-off from an even polynomial surface. Advantages of asymmetrical micro-lenses are off-axis light propagation, the correction of aberration effects or intensity profile deformations when the illuminated surfaces are not orthogonal to the optical axis. Additionally, the opportunities in simultaneous illumination from numerous light sources to one target are extended by just geometrical arrangement without the need for collinear beam alignment. First application results of such micro-lens arrays are presented for beam shaping of high power diode lasers. The generation of a homogeneous light field by a 100 W laser with tilted illumination at an angle of 35° is shown. A multi-kW line generator based on the superposition of over 50 diode laser bars under different illumination angles is demonstrated as well. Thus, laser material processing like plastics welding, soldering or annealing becomes much more convenient and less demanding regarding beam steering.

Generation of a uniform-square focal spot by a compound lens for solar concentration applications

“…Unlike a general imaging homogenizer that uses two square-lens arrays [38][39][40][41], our design only adopts one square-lens array for simplifying the system structure, and enhancing the optical transmission efficiency. The cost of adopting such a simple structure is that the light patterns projected by the outer square concave surfaces would be distorted and extended due to their larger slanting incident angles.…”

“…A square beam cross section is widely used in laser/material processing [25][26][27][28][29][30][31][32][33][34][35], but less applied in a solar concentrator. Ryu et al [36] first proposed solar concentration optics utilizing a modularly faced Fresnel lens to achieve a square focal spot.…”

An inverse model for optimisation of laser heat flux distributions in an automated laser tape placement process for carbon-fibre/PEEK

“…Such optical systems are not only limited to uniform profiles, they can be customised with technologies such as freeform lens manufacturing [31,32]. Other methods for generating custom beam profiles include diffractive optical elements [33][34][35], geometric optics [36] or scanning mirrors [37].…”

Adjustable‐Function Beam Shaping Methods

“…To achieve this shaping, many methods of beam shaping are employed in the laser welding industry. These include diffractive optical elements (DOEs), custom fiber bundles [1] with a special arrangement [2], shaped fiber cores, multiple laser combinations where each laser is shaped individually [3], galvo-scanners [4], digital mirrors devices (DMDs), and refractive micro-optics [5].…”