Actinic patterned mask inspection (APMI) is the last major part of the infrastructure required for EUV lithography to be developed. A coherent imaging approach is proposed as a plausible solution requiring incremental improvements to available components. Diffractive optics direct a mW 13.5nm coherent beam to the mask and to interfere at the imaging detector. A motion system translates the mask between exposures. A non-iterative algorithm generates a complex reflectivity (mask image) estimate from each interferogram, in real time with GPU hardware. Realistic simulation results and requirements for the system components are presented. Except for the FEL that is likely required, many elements of the system are simpler and likely less costly than an incoherent imager. The system can be configured to image the mask through a pellicle. Of note, focus tolerance is loose as the focal distance is a software parameter.
Laser guide star wavefront sensors (WFS) using pulsed lasers can benefit from dynamic refocusing techniques which
synchronously adjust the focus of the wavefront as the light returns from the scattering layer so as to maintain a constant
axial image location. Existing techniques involve pulsating discrete mirrors and high-speed segmented MEMS in the
WFS path. A different approach is presented here, which uses a pair of rotating phase plates with cylindrical or Alvarezlens-
style tracks near the WFS pupil. Rotational speeds and disk sizes similar to that used for compact disc operation are
proposed. The plates can be manufactured by numerical machining of transparent plastic materials or as diffractive
Well-characterized test conditions are essential for validating the engineering design of an adaptive optical system. A technique for fabricating high-resolution, well- characterized pseudo-random phase plates that addresses this need is described. Among other uses, these phase plates can be used to test adaptive optics systems under controlled conditions. Machining a surface whose relief height is proportional to the desired phase forms a pixellated phase plate. Using Lexitek's Near-Index-MatchTM approach, a sandwich of two materials is formed that produces the desired phase. Phase plates with 20 micron pixels have been fabricated using a 4096 X 4096 pixel grid. Results are presented.
We describe a new high-resolution neutron-imaging detector. A neutron scintillator is imaged onto a photon-counting 2D imaging detector, with most of the scintillation used for event discrimination in this patented detector. Detection time and location are recorded, so neutron energy (time-of-flight) is measured for accelerator-based sources. We are currently fabricating a 25cmx25cm detector with 512x512 pixels and 100 ns time resolution. Results are presented for scintillator characterization measurements and imaging characteristics measured at IPNS, where the detector will reside.
A new gamma camera with intrinsically high-resolution is described. A scintillating crystal is imaged onto a photon-counting 2D imaging detector. Most of the light is directed to PMTs for energy determination in this patented detector. Detection time and position can be recorded. Time resolution is as fine as the scintillation pulse allows. Sub-millimeter resolution has been achieved and 2048 linear pixels are possible. We are fabricating a transportable detector with 25 cm sensitive diameter and 1024x1024 pixels. Results taken with a prototype detector are presented.
A method for designing and fabricating aspherical transmissive beam shaping elements for the visible and near-IR is described. Both rotationally symmetric and non-symmetric aspheres can be fabricated as Near-Index-MatchTM optics. The aspherical surface is machined or mastered using a conventional NC machine. A sandwich of two transmissive materials is formed, with the refractive phase the product of the surface relief and the index difference. Both far-field (Dickey, Romero, and Holswade) beam shapers and near-field (Rhodes and Shealy) beam shapers can be realized, as well as two-element systems with phase correction of the shaped beam. Design methodologies and results are presented.
A novel design for a zero-order achromatic diffractive optical element is presented. Applications of the optical element are discussed. Tolerances on the material properties and fabrication considerations are presented. The predicted performance characteristics, including optical efficiency and effective bandwidth, are presented.
We present the first experimental results of recovery of the 2-D spatial coherence
modulus and phase using fourth order correlation interferometry (FOCI). The technique, a
generalization of intensity interferometry and laser speckle correlography, measures the
correlation (I(x)A*(x+A)A(x+A+c)), where 1(x) and A*(x+E)A(x+A+e) are measured
with separate, unconnected apertures. The result of the measurement is t*(A)i(+c), a
cross-product of the spatial coherence factor that is analogous to the Knox-Thompson
cross-spectrum in astronomical speckle imaging. The technique has applicability when the
coherence function must be measured over distances A which are larger than the diameter
D >> XE of the largest diffraction limited optic or amplitude interferometer and the field is
a circular complex Gaussian random variable.
An experiment is described which makes the correlation measurement on a series of
laser speckle patterns. 1(x) and A*(x+A)A(x+A+e) are obtained from the focal spots of an
array of lenslets. The measured coherence function is shown to agree with the expected
value. The intensity image, given by the Fourier transform of the coherence function, is
calculated and gives good agreement with the experiment target. The usefulness of the
technique is discussed.
Knox-Thompson Speckle Imaging is studied when partial adaptive optic compensation is employed. A generalization of previous analysis allows treatment of the compensation, finite exposure time, anisoplanatism and non-zero spectral bandwidth within the extended Huygens-Fresnel framework. The compensation process is assumed statistically stationary and accounts for wavefront sensor photon noise. The effect of finite exposure time is treated assuming Taylor's hypothesis and the Bufton wind model. An innovation is a perturbation treatment of fmite spectral bandwidth effects accurate to Significant improvement results from partial compensation when 10 degrees of freedom can be corrected with < lrad2of phase error due to shot noise. The compensation also allows significantly greater spectral bandwidth for the speckle images relative to the uncompensated case. Strategies optimizing over compensation scale, spectral bandwidth, and exposure time are chosen to optimize the SNR for a fixed observation time. The results of the analysis are compared to a computer simulation with a wave-optics propagation code.
Small-scale thermal blooming is investigated with a linear theory, a fully non-linear wave
optics propagation code, and a laboratory experiment The linear theory and the wave optics code
show excellent agreement. The laboratory experiment shows excellent agreement with the modelling
for the high spatial frequency modes.