Low_resolution_Thesis_CDD_221009_public - Visual Optics and ...

METHODS
In both profilometers, custom algorithms were developed to extract the information
(shown in a monitor and printed in paper) to a digital format, to be processed with our
custom analysis algorithms (Section 2.2).
2.1.1.2. Non-contact profilometry
Most of the measurements of the shape of the surfaces used in this thesis (flat or
spherical, ablated or not, Chapters 4 and 5) were obtained using a non-contact
microscope profilometer (Pl, Sensofar, Terrassa, Barcelona, Spain), based at the
Visual Optics and Biophotonics Lab of the Institute of Optica, shown in Fig. 2. 4. The
confocal mode, that reconstructs the surface map from a set of images at different
planes of focus -as explained bellow-, was primarily used. The interferometric mode
of the instrument was used under certain conditions. The different measurement
modes, in combination with the corresponding microscope objectives provide different
balances between measurement precision (axial and lateral resolution) and
measurement speed. The interferometric mode was used to study ablation craters
(Chapter 4) and to locate the apex in curved surfaces (Chapter 5). White field imaging
was often used to study the sample appearance (Chapter 5).
Fig. 2. 4. Non-contact confocal microscope used for profilometry measurements (Pl,
Sensofar, Terrassa, Barcelona, Spain)
The basic setup of the illumination hardware is shown in Fig. 2. 5. The light
source is a high power LED, emitting at a peak wavelength of 480 nm with a
lambertian emission pattern. The light beam reaches a polarizing beam splitter cube
(PBS), and the resulting polarized beam strikes a microdisplay, the key active device
of the sensor head. The information transferred to the microdisplay will be imaged on
the surface of the sample by a microscope objective. In this arrangement the surface of
the illuminated sample will be also imaged on the CCD array. In order to obtain
confocal images a binary pattern is displayed in the minidisplay and imaged onto the
surface of the sample. The optical setup provides the required matching between
pixels of the microdisplay and pixels of the CCD array, which in turn behave as
confocal apertures (Artigas et al., 2004).
In our measurements, a pattern of parallel lines is projected with an infinitycorrected
microscope objective (ELWD 100X) onto each point of the surface while a
CCD camera images the reflected lines, through the same optics. The instrument scans
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