Wavelength-independent laser beam shaping

This paper presents a beam shaping device namely, a Diffractive Optical Element ( DOE), which is used to change a beam having a Gaussian intensity profile into a beam with a uniform intensity profile. The DOE used in this work was fabricated from ZnSe and its performance was evaluated using a cw CO2 laser. In most cases such elements are effective only at a specific design wavelength. However, in this paper we report on the design conditions which allow for wavelength independent elements. It was found that the DOE was able to successfully transform a Gaussian beam into a flattop beam for four different wavelengths in the range 9.2 mu m to 10.6 mu m. We also present experimental results on misalignment effects and it was found that small radial offsets of the incident beam on the DOE had a significant disruptive effect on the flattop beam profile.