Is it possible to upgrade the EP³-BAM to an imaging ellipsometer?
Yes, as it uses the same hardware and software platform. Also an upgrade of a single wave to spectroscopic ellipsometer is possible.
Is it possible to use the imaging ellipsometer as a Brewster angle microscope?
Yes! BAM operation is a "subset" of the imaging ellipsometer. However, applicability of an imaging ellipsometer as a BAM depends on the laser power. We recommend at least 20mW, better 50mW lasers when using the imaging ellipsometer as a BAM is intended.
Why do you recommend a 50mW laser (532nm) for the Imaging Ellipsometer at the air/water interface and only 20mW for the Brewster angle microscope BAM?
In the imaging ellipsometer, the polarization state of the light beam in front of the polarizer (P) is made circular to provide constant output regardless of the P angle position. This means that ca. half of the power is lost in the polarizer for the imaging ellipsometer.
The EP³-BAM uses the near p-polarization of the laser without alteration, because for BAM operation P is always close to 0 deg. Thus, the "efficiency" in terms of laser power is twice as high compared to the imaging ellipsometer.
The EP³-BAM uses the near p-polarization of the laser without alteration, because for BAM operation P is always close to 0 deg. Thus, the "efficiency" in terms of laser power is twice as high compared to the imaging ellipsometer.
Why using Nulling Ellipsometry in the EP³?
There are many different ellipsometry methods. The idea is always the same: analyze how the state of polarization is altered due to reflection caused by the sample. Thus, this information characterizes the sample.
We use nulling ellipsometry for 3 reasons:
a) Nulling ellipsometry allows one to make the image "dark" at a certain region of the sample. If there is a difference in the optical properties of the sample, those other regions are "bright", because the nulling conditions are not fulfilled for those regions. Thus, we get a contrast that may be directly visualized by a camera. This is what we call "real-time ellipsometric contrast".
b) Nulling ellipsometry is very sensitive compared to other methods, thus giving high contrast, especially for very thin films.
c) Nulling ellipsometry offers the ability to measuring in four zones => for isotropic materials, the expected result after rotating a polarizer, compensator or analyzer 180 ° is the same as without rotation. There are four possible combinations of polarizer/compensator and compensator/analyser that give the same result. The advantage of this is that the average is, to a large extent, free of systematic errors.
In principle one could also use many other methods in an imaging system. But this would have several disadvantages: for example in "rotating analyzer" elli, one rotates the analyzer constantly. This
means that the image would be very bright most of the times, and only sometimes it gets a little darker. Thus, the sensitivity is not very high for very thin films. Also, one needs a very high dynamic range camera and very linear camera response. Several images have to be collected and then the final image is recalculated from
this by lengthy fourier transform. This is not "real-time", thus the convenience of our fast imaging is not available in such a system. This latter point is true for most non-nulling types of ellipsometers.
The disadvantage of the nulling concept is that the "measurement" of a precise ellipsometric value on one spot takes longer, because nulling requires a more complex movement of some optical components.
We use nulling ellipsometry for 3 reasons:
a) Nulling ellipsometry allows one to make the image "dark" at a certain region of the sample. If there is a difference in the optical properties of the sample, those other regions are "bright", because the nulling conditions are not fulfilled for those regions. Thus, we get a contrast that may be directly visualized by a camera. This is what we call "real-time ellipsometric contrast".
b) Nulling ellipsometry is very sensitive compared to other methods, thus giving high contrast, especially for very thin films.
c) Nulling ellipsometry offers the ability to measuring in four zones => for isotropic materials, the expected result after rotating a polarizer, compensator or analyzer 180 ° is the same as without rotation. There are four possible combinations of polarizer/compensator and compensator/analyser that give the same result. The advantage of this is that the average is, to a large extent, free of systematic errors.
In principle one could also use many other methods in an imaging system. But this would have several disadvantages: for example in "rotating analyzer" elli, one rotates the analyzer constantly. This
means that the image would be very bright most of the times, and only sometimes it gets a little darker. Thus, the sensitivity is not very high for very thin films. Also, one needs a very high dynamic range camera and very linear camera response. Several images have to be collected and then the final image is recalculated from
this by lengthy fourier transform. This is not "real-time", thus the convenience of our fast imaging is not available in such a system. This latter point is true for most non-nulling types of ellipsometers.
The disadvantage of the nulling concept is that the "measurement" of a precise ellipsometric value on one spot takes longer, because nulling requires a more complex movement of some optical components.
How large is the laser spot of the EP³?
Imaging ellipsometry, in contrast to scanning ellipsometry, is based on analyzing ellipsometric contrast micrographs at different positions of the optical components to obtain a delta and psi – map. This procedure is the reason for the unique lateral resolution of imaging ellipsometer and the short measurement time in comparison to scanning methods. The laser spot has to illuminate the complete field of view. In case of 2x objective a beam expander is needed to fulfill this requirement.
What is the number of bits for the CCD camera you use in the instrument?
The camera is digitized with 8 bits. However, sometimes less is more. The bit depth does not not limit the measurement process, nor the linearity, but it has a positive effect on the data transfer. Please note that the measurement is not "photometric" in our system in the sense that we do not use the camera signal directly. It is important to stress this because competitors use 14bit cameras in a completely different ellipsometric measurement procedure. Therefore, their data quality is not higher than ours, regardless of the camera bit depth. If you want to compare – please have a look at the results – you are invited to send us a sample for a contest!
Is it possible to enter data into the materials database?
Yes, the database may be upgraded very easily if n and k data and dispersion function, resepectivly are available. Also the results of optical modeling can be saved as a new material.