Refractive statistical concave 1D diffusers for laser beam shaping

Abstract

Certain high power laser applications require thin homogeneous laser lines. A possible concept to generate the necessary flat-top profile uses multi-aperture elements followed by a lens to recombine separated beamlets. Advantages of this concept are the independence from entrance intensity profile and achromaticity. However, the periodic structure and the overlapping of beamlets produce interference effects especially when highly coherent light is used. Random optical elements that diffuse only in one direction can reduce the contrast of the interference pattern. Losses due to undesired diffusion in large angles have to be minimized to maintain a good quality and high efficiency of beam shaping. We have fabricated diffusers made of fused silica for a wide range of wavelengths that diffuse only in one direction. Structures are based on an array of concave cylindrical microlenses with locally varying size and position following a well defined statistical distribution. The scattering angle can be influenced by process parameters and is typically between 1 • and 60 • . To predict the influence of process parameters on the optical properties, a simplified model for the fabrication process and geometrical optics have been used. Characterization of the fabricated devices was done by stylus measurements for the surface shapes, microinterferometry to measure phase profiles and high resolution goniometry to obtain far field distribution of light. The simulated data compare very well to measured optical properties. Based on our simulation tool we discuss limits of our fabrication method and optimal fabrication parameters.

Femtosecond laser directed fabrication of optical diffusers

“…In addition our fabrication is very economical for scale up manufacturing, due to fast laser writing speeds, flexible and tailored pattering of glass substrates. 2 , 4 , 32 …”

Randomly varying micro-optical elements for the generation of uniform intensity profiles in coherent laser sources

“…Through this and together with the optical power of the Fourier lens, the apertures are imaged to the plane FP. With the determination that a 12 …”

“…4.4. These diffusers are generated by isotropic etching of a mask of slits of fixed width that are statistically positioned across a fused silica substrate [12]. Long etch times can be used to generate elements with large radius of curvature and consequently small angular diffusion.…”

A predictive thermal dynamic model for parameter generation in the laser assisted direct write process

“…They suggested that a shaped beam profile can improve many laser processing applications. Previous studies have shown ingenuity in both the intensity profiles created [155][156][157][158] and in the methods used for creating them [159][160][161][162].…”