Infrastructure of the

In an interferometer, the light from the point light source is transformed into a plane wave using a collimator. This is reflected at the reference and test surfaces (ref1 and ref2). The two superimposed waves are then imaged on the camera, where an interference pattern is created. The different interference patterns result from optical path differences (OPD).
For example, if we investigate/analyze a tilted mirror, we can observe a pattern of light and dark stripes. If the wavelength is known, the exact tilt angle can be determined.

The interferometers can be used to measure flat, spherical and aspherical surfaces. The refractive index of lenses can also be determined - with a little extra effort. The measurement error when measuring surfaces varies from equipment to equipment and is 0.1 nm for a white light interferometer, for example.

The available interferometers are: a Zygo GPI XP, a Zygo NewView 200 microinterferometer (white light interferometer, combines microscopy & interferometry), a Zygo NewView 8300 microinterferometer and a Carl Zeiss D100.

In a vibrometer, the laser beam is first split into a reference and measurement beam. The wave reflected by the object is made up of the initial frequency and the Doppler frequency shift (change in light frequency due to displacement of the object) ( fD = 2 v / λ ). It then interferes with the reference wave. The Doppler frequency shift of the interference pattern, which is proportional to the speed of the measured object, is then determined in the equipment.

The "bragg cell" causes a frequency change of the reference beam of 70 Hz, which results in a modulation frequency of 70 Hz at the photosensor when the object is stationary. If the object now moves towards the vibrometer, the modulation frequency is increased; if the object moves away, the frequency is reduced ( fc(t) = fB + fD(t) = fB + 2 v(t) / λ ). This allows statements to be made about the direction of movement of the vibration.

The PDV 100 laser Doppler vibrometer from Polytech covers a frequency range from 0.05 Hz to 22 kHz and operates at a working distance of between 0.1 m and 30 m. The vibration velocity resolution is always better than 0.05 µm/s. The equipment can therefore be used for almost all acoustic applications. As the program is available on a laptop, on-site measurements are also possible, and the setup can be used to assess the quality of a loudspeaker, for example. Below you can see the frequency response of a loudspeaker that reproduces white noise.

In Photogrammetry, the object is first marked with various coded markers and photographed from different angles. Software then calculates the individual camera and marker positions from the images.
Furthermore, calculations can be carried out for various selected points, such as a plane fit or a distance measurement.

This School of Engineering can be used to measure large objects in particular, or to analyze deformations. For this purpose, an object is recorded before and after deformation. Both data sets are then subtracted from each other. The result is the displacement vectors.

The photogrammetry laboratory setup includes the Linearis3D software with differently coded markers on paper.

Stereometry is the measurement of objects with two cameras. These are positioned in front of the object at a constant position in relation to each other and calibrated with a defined pattern. All internal and external camera parameters are then available.

Images of the object can then be taken and its 3D coordinates extracted from the left and right images. To do this, the two images are rectified in a first step. The so-called disparity is then calculated. Using the disparity and the camera parameters, it is then possible to determine the three-dimensional coordinates.

A fringe projection system uses the eponymous fringe projection (left image) to read an object into a computer as a 3D model. To do this, images of the object are first taken with different fringe patterns.

The projected stripes show deformations that are shaped accordingly to the object. The height profile of the line can then be determined on the basis of this deformation, which is expressed as a horizontal offset in the image, and the camera parameters. The difference to laser triangulation with only one laser line is that a complete object can be recorded at once with fringe projection.

There are two different systems in our laboratory / lab. The first, the David 3D scanner, is suitable for small to medium-sized objects (everything between a contact lens and a human head). The second system is a fringe projection measuring microscope from Keyence. This can be used to measure small objects. The latter also has extensive evaluation software with which the objects can be measured and documented.

Images of the David 3D Scanner fringe projector

The Zeiss MCS 400 spectroscope can record light spectra in the field (of) 200 nm to 1010 nm. The hardware used is suitable for both reflection and transmission measurements or simply for evaluating direct light irradiation - for example that of the sun.

The Zeiss PRISMO is a high-precision coordinate measuring machine from Carl Zeiss. All solid objects that can be physically touched are suitable as measurement objects. Depending on the task and device equipment, various probes and touch probes can be used on the measuring device. The entire measuring device has active air bearings.

The core of the tactile measuring method is the probe head. It enables several measuring routines such as tactile single-point measurements, form and position measurements, as well as high-speed scanning of known and unknown contours.

The process, procedure of "Optical Coherence Tomography (OCT)" allows optical surfaces to be measured without contact - for example, subsurface damage (SSD). The advantage of OCT over conventional methods (interferometer/white light interferometer) is that surfaces can also be completely measured after the grinding process. However, OCT is still in the experimental phase.

The measuring head can be integrated, meaning that it can be used in other systems for inline measurements.

The underlying structure of the OCT is the Michelson interferometer. The resulting interference pattern is then a function of the term, period of validity, duration of the light within the sample. A three-dimensional image of scattering items can thus be recorded.

Such systems are mainly used in medical technology, for example to investigate/analyze the retina of the eye.

In laser triangulation, a line is projected onto an object using a laser. The reflected light is then recorded by a camera. The camera now has an oblique angle of view of the irradiated object. The lines, which are actually parallel, now appear distorted. The shape can then be deduced from these distortions.

Measurements are now taken at various points on the object. If the distance by which the object or the laser line has been displaced is known, a 3D model of the entire object can be created from the individual measurements (= height profile at point x).

The method therefore does not differ significantly from that of fringe projection. However, laser triangulation only uses one-dimensional illumination, whereas fringe projection uses a two-dimensional pattern. A simple line sensor can also be used for fringe projection, whereas fringe projection requires a two-dimensional sensor.

Type:

In-house development

Functions:

Deformation of mini/microdroplets by high voltage with live observation. Extensive degrees of freedom for positioning the sample or electrodes for deformation

Application:

Realization of individually deformed mini/micro-droplets as lens elements, e.g. on fibers or for adapting the radiation characteristics of LEDs

Type:

Galvo scanner Thorlabs GSM002-EC/M

Functions:

Deflection of a laser beam in X and Y direction

Application:

Curing of structures on planar and curved substrates

Type:

Extension of a Zeiss reflected light microscope

Functions:

Mask imaging for the production of masters for nanoimprint lithography

Application:

Nano-structuring of photoresists

Type:

Wintech Pro6500 with 1 µm imaged pixel size

Functions:

Structuring of photopolymers using a micromirror array

Application:

Additive manufacturing of small structures

Type:

Universal Robot 3; Vermes MDS 3280+

Functions:

Targeted deposition of individual liquid droplets

Application:

GRIN, printing on planar and non-planar surfaces

Type:

In-house development (Ricoh MH2820 print head for two materials)

Functions:

Deposition of small material droplets using the piezo-electric inkjet process, combined with robotic kinematics

Application:

Local material deposition for additive manufacturing

Type:

In-house development (Wintech Pro 4500, Hexapod HXP100P-MECA and thermographic camera Velox_1310k)

Functions:

Structuring of photopolymers using a micromirror array
Submicrometer positioning with hexapod
Analysis of the infrared radiation emitted during the process

Application:

Production of small optically functional structures with multiple structuring and thermal investigations/analyses of the curing process

Type:

DMP 2850

Functions:

Miniature clean room for and with special printing system (inkjet)

Application:

Printing of OLEDs or functional layers

Keyence Agilista 3100

Features:

Printing technology: MJM / inkjet
Min. lateral structure: 40 µm (x), 15 µm (y)
Min. layer height: 5 - 15 µm (depending on wetting)
Material: AR-M2, AR-S1

Functions:

3D printer with transparent build material and water-soluble support material

Application:

Additive manufacturing of optical elements, e.g. with monolithic design, i.e. with integrated mechanical functions (fastening)

Type:

EVG 620 (incl. coater & developer)

Functions:

Complete system for nanoimprint lithography and mask imaging

Application:

Replication of nanostructures

Type:

Lyncee DHM R2100

Functions:

Holographic topology measurement with two wavelengths

Application:

Quality control of nanostructures produced using the nanoimprint lithography system, for example.

Type:

Zygo NewView 8300 white light interferometer

Functions:

Measurement of surface profiles with high resolution

Application:

Control of manufacturing and polishing processes

ZEISS PRISMO

Type:

Tactile coordinate measuring machine

Application:

High-precision measurement of workpieces

ZEISS O-INSPECT (prototype)

Type:

Optical/tactile coordinate measuring machine

Application:

High-precision, optical measurement of workpieces

Type:

LightTec Reflet

Functions:

Angle-resolved measurement of the radiation characteristics of samples (e.g. LEDs with 3D-printed lens)

Application:

Analysis of the scattering behavior of 3D printing materials/surfaces; verification of the radiation characteristics of 3D-printed optics (comparison with simulation results)

Type:

In-house development

Functions:

Measurement of the refractive index profile of 3D-printed optics via total reflection

Application:

Characterization of the curing behavior of 3D printed materials for good process understanding and optimization