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 μm to 10.6 μm. 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.
Recent approaches to demonstrating adaptive optics and atmospheric turbulence have made use of spatial light
modulators (SLMs) as the active phase element. However, there are limitations in using SLMs as an accurate method of
simulating turbulence phase screens. In this work we investigate the limitation of laser beam shaping with a phase-only
spatial light modulator for the simulation of dynamic and pseudo-random turbulence in the laboratory. We find that
there are regimes where there are not sufficient pixels to resolve the phase. At the higher end of this range, at strong
turbulence levels, the zonal regions are tightly packed. This leads to two simultaneous effects: a phase screen with low
efficiency in some regions, and a modified turbulence structure due to the shifting of the zone peaks. These amplitude
and phase distortions have a deleterious effect on the accurate simulation of the turbulence. At the lower end of the
range, at weak turbulence, the phase change is too small to describe with sufficient grey scale levels, since the full 256
levels are associated with a full 2π phase shift. Further limitations include the frame rate of SLM for time-evolving
turbulence. We show experimental results demonstrating these limitations, and discuss the impact this has on
simulating turbulence with SLMs.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.