Adaptive laser systems with wave front correction and phase conjugation for fluid flow measurements compensating refractive index effects
The aim of the project is the investigation of new adaptive measurement system
concepts to compensate for distortions caused by refractive index effects. E.g. in
the case of flow measurements in a thin film flow or a droplet on an opaque surface,
the fast (up to 200 Hz) fluctuating interface significantly distorts the optical
access and increases the measurement uncertainty. Therefore, we aim to develop
modern feedback control methods, for example the Fresnel guide star technique
in combination with specialized SoC CPU & FPGA based hardware and a fast deformable
mirror to compensate the distortion. This unique SoC approach splits
the low level computational tasks e.g. the evaluation of a Hartmannogramm into
the FPGA and all the high level controlling tasks into the CPU. This enables a high
control rate of up to 1642 Hz, which is well sufficient to suppress the distortion of
a fluctuating interface of a droplet.
The technique enables for the first time turbulence investigation of film flows and
the flow inside of droplets with a free dynamic surface. It is aimed to give a contribution
to the improvement of the energy efficiency of procedural sites.
Staff: H. Radner, N. Koukourakis
Period: 07/14 – 07/19
Partner: Dr. S. Burgmann, Bergische Universität Wuppertal
PIV image, distorted and corrected by the wavefront correction system
H. Radner, L. Büttner and J. Czarske, "Interferometric velocity measurements through a fluctuating phase boundary using two Fresnel guide stars", Optics Letters 40, 2015.
N. Koukourakis, B. Fregin, J. König, L. Büttner, J. Czarske “Wavefront shaping for imaging based flow field measurements through distortions using a Fresnel guide star”, Opt. Express 24(19), 22074-22087
(2016).
F. Schmieder, L. Büttner, J. Czarske “Adaptive laser-induced ultrasound generation using a micro-mirror
array spatial light modulator”, Opt. Express 24(20), 22536-22543 (2016).
Schematic overview of the in house developed adaptive optical PIV system
M. Teich, M. Mattern, J. Sturm, L. Büttner, J. W. Czarske “Spiral phase mask shadow-imaging for 3Dmeasurement
of flow fields”, Opt. Express 24(24), 27371-27381 (2016).
H. Radner, L. Büttner and J. Czarske, "Interferometric velocity measurements through a fluctuating interface
using a Fresnel guide star based wavefront correction system", Optical Engineering, 2018.