The radial and axial point spread function (PSF) and the 3D modulation transfer function (MTF) were calculated to
demonstrate the influence of phase only filters in classical optical imaging systems. The 3D line spread function (LSF)
makes it possible to discuss the influence of the degree of coherence in the optical imaging system with the phase only
filter as well. First, the phase only filter under discussion was divided in five equally area annuli. The phase variations are either
linearly increasing or decreasing with the annulus number or alternating between 0 and π. Second we have used a filter
that consists on one phase annulus with a phase shift of π in different positions over the pupil. Numerical and experimental results are shown in this paper. A spatial light modulator (SLM) was used to obtain experimentally the influence of the different phase only filters on the image of a sector star. The merit functions for filters with a phase shift of π in one annulus are also studied. These filters produce a wide variety of responses in dependence of the position of the phase shifting annulus. By studying the merit functions, a clear prediction of the imaging behaviour of an optical system is possible as well. The conclusion of our work has been that it is necessary to study the influence of the filter on the different merit functions in order to design an optimum filter for a given application.
Spatial light modulators (SLM) have found a wide range of applications in many fields of optical imaging and
measurement systems. We implement different phase only filters in the pupil plane of an imaging system. The phase
only filter is divided in five equally spaced annuli. Each annulus has a different phase transmission and inside each
annulus the phase is constant. We analyse first the influence of linear decreasing or increasing phase, second we use one
phase annulus with a phase shift of π in different positions over the pupil and finally an alternating phase between 0 and
π over the pupil.
Merit functions of the different filters are calculated. The radial and axial point spread function (PSF) or the 3D line
spread function show that in some cases these phase only filters will shift the best image plane. The experimental results
show the close correlation to the calculated shift of the best image plane.
The strong side lobes that appear in the merit functions lead to the conclusion that the image quality will be influenced
as well. This can be confirmed by the calculation and the measurement of the image intensity. So in order to get more
information about the expected image it is necessary to study the 3D modulation transfer function (MTF). With the MTF
one can see that the contrast decreases for the image obtained with each filter in comparison with the image obtained
with the clear pupil.
The conclusion of our work is, that it is necessary to study the influence of all merit functions in order to design an
optimum filter for a given application.
We are developing a new linewidth standard on the nanometre scale for use in the recently introduced new high-resolution optical microscopy techniques like deep ultraviolet microscopy (UVM) and confocal laser scanning microscopy (CLSM). Different types of high-resolution gratings, etched in amorphous silicon on quartz substrates, have been fabricated and evaluated using state-of-the-art UVM, CLSM, REM and AFM equipment. The produced linewidths range from about 80 nm to 2 μm. The contrast of the pattern in the UV region makes them suitable for transmission and reflection UV and laser scanning microscopy.
The description of the light propagation in or between planar diffractive optical elements is done with the angular spec-trum method. That means, the confinement to the paraxial approximation is removed. In addition it is not necessary to make a difference between Fraunhofer and Fresnel diffraction as usually done by the solution of the of the Rayleigh Sommerfeld formula. The diffraction properties of slits of varying width are analysed first. The transitional phenomena between Fresnel and Fraunhofer diffraction will be discussed from the view point of metrology. The transition phenomena is characterised as a problem of reduced resolution or low pass filtering in free space propagation. The light distributions produced by a plane screens, including slits, line and space structures or phase varying structures are investigated in detail.
We have studied nonuniform transmission filters to improve resolution and/or Depth of Focus in lithography. To understand the transmission behavior of these filters for periodic structures we discuss the Apparent Transfer Function in dependence on the defocus. We use the Apparent Transfer Function that is defined by the contrast of the corresponding spatial frequencies, and we analyze the behavior of the system for coherent, incoherent and partially coherent illumination.
Line widths of about 0,3 gm and focus depths of 1,3 pm are necessary for the production of 64 M DRAM's. The aim of circuit producers is to achive these parameters with i-line equipment of optical projektion lithography ( A = 365 nm, NA ek 0,5). The resolution limit w and depth of focus 4 z for lithographic systems are given by
A theory of 3D- imaging of a thick object with a depth h (Fig.l ) is developed
for vertical Illumination microscopy (Fig2). The amount as well as the phase
of the Fourier spectrum which corresponds to the 3D- object is discussed in
detaiL Fig3 shows the amount tT(01 of the Fourier spectrum for different
object depth. ii (V I has zercs In the case of planar object (h0) . As the
thickness of the object is increased an enhancement of the spatial frequencies
and a shift of the Ninhia occurs. The zeri of the planar object spectrum are
lsed.
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