Research Directory of the Brandenburg University of Applied Sciences

these detectors respond much
faster. The detectors are connected
to a read out circuit
(ROIC) for snapshot integration.
The photocurrent generated
by the incident photon flux
will be stored in a capacitor
during a user selectable integration
time (or exposure
time). This integration time
will determine the time resolution
of the camera. For the
SC6000 variable integration
time settings from 9 μs to full
frame time are possible. For
the experiment with the falling
ball an integration time of 1
ms was used, see Fig. 3.13. No
blurring of the image of the
ball is observed and the temperature
of the ball can be correctly
determined over the
whole falling distance.
b) Spatial resolution
The spatial resolution of the thermal imaging system
determines the minimum size of objects which can be
analyzed. Fig. 3.16 demonstrates that different camera
systems lead to different results when studying miniaturized
objects. A thermal emitter with an area of 2.1
mm x 1.8 mm was analyzed with a 320 x 240 pixels MW
THV 550 camera and the 640 x 512 pixels SC6000
camera with different optics.
Obviously the SC6000 microscope
optics provides the best spatial resolution.
As will be shown below a detailed
analysis of this structure is only
possible using the SC6000 with
microscope optics.
For the determination of the spatial
resolution of the SC6000 using the
microscope objective chromium
structures on a photolithography
mask were used. The mask was heated
up and the emissivity contrast of
the mask was used for the measurement
across a 34 μm line on the
mask. Compared to the visible microscope
image (Fig. 3.17 left, top) the
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Scientific Articles – Department of Engineering
Fig. 3.16: Thermograms of a miniaturized infrared emitter (size 2.1 mm x 1.8 mm) in TO-39 housing
from
- MW camera THV 550 (320 x 240 pixels) with a 24° optics (top, left) and an additional close-up lens
(top, right)
- MW camera SC6000 (640 x 512 pixels) with a 25 mm lens (bottom, left) and microscope optics (bottom,
right)
(Region of interest is indicated in the left thermograms.)
thermogram appears blurred, see Fig. 3.17 left, bottom.
Raw signal data across the line were analyzed and a
signal plateau was observed, see Fig. 3.17, right. The
plateau is formed by about 6 pixels. If this number of
pixels is compared to the line width of 34 μm one may
conclude that resolution per pixel amounts to around 5
- 6 μm.
The spatial resolution of imaging systems is mostly
described by the modulation transfer function MTF [2 -
4]. The MTF is defined as the spatial frequency response
of an imaging system. It is the contrast of structures in
Fig. 3.17: VIS microscope image (top, left) and thermogram (bottom, left) of a line with a
width of 34 μm on a chromium mask. Raw signal profile of the line measured in the thermogram
(right) using the SC6000 camera.
Forschungsbericht Research Report 2007 – 2010 83