While CO2 is the main greenhouse gas responsible for climate change, it is a well-mixed gas in the atmosphere, meaning that its concentration is relatively uniform and does not vary much over short distances. This makes it difficult to monitor CO2 levels in specific regions or to detect changes in CO2 concentrations at small scales. On the other hand, NO2 is emitted from combustion sources that also emit CO2, and its concentration varies greatly depending on proximity, making it a useful tracer for identifying emissions sources. Therefore, NO2 is widely assumed to be a robust proxy for combustion CO2 and provides additional, valuable information for CO2 monitoring such as plume detection. The combination of NO2 and CO2 observations is useful in determining the exact locations and intensities of anthropogenic CO2 emissions. The idea of the present study is to design a very compact instrument for NO2 plume detection that allows easy accommodation of both CO2 and NO2 sensors on a single platform. Conceding on the need to explore internal dynamics of plumes and focusing more on the spatial evolution, NO2 detection can then rely on a relaxed set of requirements, which has a beneficial impact on instrument size, thus leading to a miniaturized instrument. In the present paper the driving requirements of such a miniaturized instrument will be introduced, and a compact design will be presented. Benefits and complexities of a compact design will be discussed.
We present a novel optical design tool that makes use of an evolutionary global optimization algorithm. The algorithm has several characteristics that make it well-suited for freeform optics design. With the design tool it is no longer necessary to make the distinction between paraxial degrees of freedom and degrees of freedom related to freeform surface description. The design process, which typically involves a multi-stage scheme consisting of finding an optimal paraxial starting layout, optimization, gradually including freeform degrees of freedom to yield an optimal nominal design, and finally a step in which the as-built design is optimized, is shortened because optimal paraxial starting point and optimal freeform shapes are combined to a single optimization step. Optionally, as-built performance can be included in this step as well. The design tool is applied to the design of a compact spectrometer.
A freeform optical surface is typically defined as any surface that does not have an axis of rotational symmetry. These surfaces provide additional degrees of freedom that can lead to improved performance compared to systems that make use solely of conventional optics.
In this paper, we discuss the two-mirror pushbroom telescope for TROPOMI. Using freeform optics, it has unprecedented resolution. The complete cycle of freeform optical design, analysis, manufacturing, metrology and functional test on a breadboard setup is described, focusing on the specific complexities concerning freeforms. The TROPOMI flight telescope will be manufactured in summer 2012.
KEYWORDS: Optical design, Actuators, Adaptive optics, Deformable mirrors, Mirrors, High power lasers, Received signal strength, Extreme ultraviolet, Spatial frequencies, Wavefronts
TNO is developing a High Power Adaptive Mirror (HPAM) to be used in the CO2 laser beam path of an Extreme Ultra- Violet (EUV) light source for next-generation lithography. In this paper we report on a developed methodology, and the necessary simulation tools, to assess the performance and associated sensitivities of this deformable mirror. Our analyses show that, given the current limited insight concerning the process window of EUV generation, the HPAM module should have an actuator pitch of ≤ 4 mm. Furthermore we have modelled the sensitivity of performance with respect to dimpling and actuator noise. For example, for a deformable mirror with an actuator pitch of 4 mm, and if the associated performance impact is to be limited to smaller than 5%, the actuator noise should be smaller than 45 nm (rms). Our tools assist in the detailed design process by assessing the performance impact of various design choices, including for example those that affect the shape and spectral content of the influence function.
The fact that every spectrometer can sort light by wavelength at the speed of light is intriguing. The field of spectrometry is a long-existing and ever-changing one. The application areas extend from optical communication to possible extraterrestrial life detection, health monitoring, environmental monitoring and quite a long list of other topics. TNO has played a role in several of these areas, always using state of the art designs and components. Some of the recent developments are described, as well as a possible path for (near) future developments. Any spectrometer consists of a telescope, slit, collimator, disperser and an imager. Each of these functions is discussed using and even pushing progress in the manufacturing and design capabilities of the industry. The progress from a two-mirror spherical telescope for a pushbroom space-based daily global coverage spectroscopy instrument OMI to a two-mirror freeform telescope for TROPOMI is described, the design and manufacturing of supergratings showing very little straylight, freeform mirrors and the use of deliberately decentered lenses is shown. A near-future small-satellite system is shown that is being built and tested as this paper was written.
TNO has developed the Optical Tube Assemblies (OTAs) for the ESO VLT Four Laser Guide Star Facility.
The OTAs are Galilean 20x beam expanders, expanding a ∅15 mm input beam (25W, 589 nm CW) to a
steerable ∅300 mm output beam. TNO has recently successfully completed acceptance testing of the four
units, showing compliance to the challenging requirements on output wavefront quality, thermally induced
defocus under operational conditions, absolute pointing accuracy and polarization extinction ratio (PER).
TNO applied its corrective polishing in combination with the NANOMEFOS measurement machine to
produce the ∅380 mm aspherical output lens, resulting in 20 nm rms output wavefront quality. The thermal
behaviour of the system has been analyzed by combining optical, lumped mass and FE analyses. A design that
is passively athermalized over a large temperature range as well as under the influence of thermal gradients
has been developed. Extensive thermal testing has shown a thermally induced defocus of less than 0.15 waves
under the operational conditions of 0-15°C and upto -0.7°C/hr gradient. A custom tip-tilt mechanism was
designed to steer the output beam over a 4.8 arcmin radius, with less than 0.1" (3σ) accuracy at 1 Hz update
rate. The PER was also measured under operational (thermal and tilt) conditions and demonstrated to be well
above 99%. This paper describes the design, modelling and analysis, and the test results of these instruments.
TNO is developing the Optical Tube Assemblies (OTAs) for the ESO VLT Four Laser Guide Star Facility. The OTAs
are Galilean 20x beam expanders, expanding a (see manuscript)15 mm input beam to a steerable (see manuscript)300 mm output beam with a
wavefront quality requirement of 50 nm rms. The allowed defocus under the influence of the changing environmental air
temperature (0-15°C, -0.7°C/hr gradient) is only 0.2 waves. An integrated model of the thermal behavior has been made,
combining optical, thermal lumped mass and FE analyses. This paper describes the athermal design and testing of the
system.
TNO is developing the Optical Tube Asssemblies (OTAs) for the ESO VLT Four Laser Guide Star Facility. The OTAs
are Galilean 20x beam expanders, expanding a Ø15 mm input beam to a steerable Ø300 mm output beam with a
wavefront quality requirement of 50 nm rms. The allowed defocus under the influence of the changing environmental air
temperature (0-15°C, -0.7°C/hr gradient) is only 0.2 waves. The thermal behaviour of the system has been analyzed by
combining optical, lumped mass and FE analyses. A design that is passively athermalized over a large temperature range
as well as under the influence of thermal gradients has been developed. Extensive thermal testing has shown the system
performs as required. This paper describes the design and test results.
A method for actinic inspection of EUV mask blanks is described, in which EUV photoresist is applied to the blank,
flood exposed with EUV, and developed. The effect of both phase and reflectivity defects on the reticle is described in
terms of a variation in intensity and phase of the standing wave in the resist. Thin film simulations are performed to
evaluate the contrast generating mechanism for various blank defects. The method was introduced earlier by others 3 and
was shown in experiments to transfer reflectivity defects on the reticle to the developed resist. We propose to reevaluate
the technique with current state-of-the-industry capabilities of resist processing, contamination control and inspection.
Various possible development directions are described.
Device shrinking combined with material manipulation under various process conditions becomes a
difficult task if specific optimization conditions should be met. Nanolithography is limited by effects
as line-edge and line-width roughness (LER and LWR respectively) and secondary electron blur
(SEB). Simulation studies could show the direction of solving design for manufacturing problems. In
the current article a simulation methodology is presented, based on the concept of stochastic modeling
of exposure, material, and process aspects of lithography and pattern transfer with plasma etching in
order to get information about the evolution of critical dimensions (CD), LER and LWR in the layout.
The study reveals that under certain process conditions, the effect of acid diffusion on LER is more
important than the one of SEB, although both deal with blurring, because acid diffusion is supposed
to extend in longer radius. However, when resists of low degree of polymerization are used, SEB
should also be considered explicitly since the deteriorations from blurring on both LER and CD are
enhanced due to the graining nature of the material. In any case, etching smoothing effects of high
frequency LER components should be considered in terms of CD loss.
The use of backscatter electron detection in a wafer alignment system has been investigated. For certain types of wafer processing such an alignment system might show improved process robustness compared to optical sensors. This expectation is based on the principle that the alignment signal generated by backscattered electrons is formed by probing the volume of the alignment mark rather than its surface. This paper presents both simulations and experiment results on the viability and potential physical limitations of this alignment method. Physical properties of the backscatter electron alignment system are discussed. The results confirm that for some semiconductor wafer processes, this concept lives up to the expectations. The impact of electron beam energy, shot noise and alignment mark surface
roughness on process-induced alignment shift and aligned position
repeatability is investigated. In addition, the sensitivity to magnetic fields and mechanical vibrations has been investigated. The theoretically predicted relation between repeatability and illumination dose, due to shot noise has been experimentally confirmed. The results show that backscatter electron alignment is a promising alignment method, although a few issues remain unresolved.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.