Quantitative deflectometry is a new tool to measure specular surfaces. The spectrum of measurable surfaces ranges from flat to freeform surfaces with steep slopes, with a size ranging from millimeters to several meters. We illustrate this by several applications: eye glass measurements, measurements of big mirrors, and in-line measurements in ultra-precision manufacturing without unclamping of the sample. We describe important properties of deflectometry and compare its potentials and limitations with interferometry. We discuss which method is superior for which application and how the potential of deflectometry may be developing in the future.
Deflectometric methods that are capable of providing full-field topography data for specular freeform surfaces have been
around for more than a decade. They have proven successful in various fields of application, such as the measurement of
progressive power eyeglasses, painted car body panels, or windshields. However, up to now deflectometry has not been
considered as a viable competitor to interferometry, especially for the qualification of optical components. The reason is
that, despite the unparalleled local sensitivity provided by deflectometric methods, the global height accuracy attainable
with this measurement technique used to be limited to several microns over a field of 100 mm. Moreover, spurious
reflections at the rear surface of transparent objects could easily mess up the measured signal completely. Due to new
calibration and evaluation procedures, this situation has changed lately. We will give a comparative assessment of the
strengths and – now partly revised – weaknesses of both measurement principles from the current perspective. By
presenting recent developments and measurement examples from different applications, we will show that deflectometry
is now heading to become a serious competitor to interferometry.
Structured-illumination microscopy is an incoherent method to measure the microtopography of rough and smooth
objects. The principle: A sinusoidal fringe pattern is projected into the focal plane of a microscope. While the object is
scanned axially, the contrast evaluation of the observed pattern delivers the 3D topography with a height uncertainty of
only a few nanometers. By means of a high aperture the system can measure steep slopes: +/- 50 degrees on smooth
objects (NA=0.8) and +/- 80 degrees on rough surfaces are possible. For industrial applications a fast measurement is
one of the most desired aspects. We face this demand by exploiting the physical and information-theoretical limits of the
sensor, and giving rules for a trade-off between accuracy and efficiency. We further present a new method for data
acquisition and evaluation which allows for a fast mechanical scanning without "stop-and-go".