Mr. Erlend Leirset Profile

Erlend Leirset

Senior Research Scientist at Norsk Elektro Optikk AS

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Proceedings Article | 12 January 2023 Presentation + Paper

HYPERNOR project: high-resolution hyperspectral camera for microsatellites.

Andrei Fridman, Lars Lierstuen, Friederike Körting, Magnus Breivik, Erlend Leirset, Stephane Nicolas, Trond Løke

Proceedings Volume 12338, 123380G (2023) https://doi.org/10.1117/12.2647616

KEYWORDS: Cameras, Signal to noise ratio, Short wave infrared radiation, Satellites, Aerospace engineering, Satellite imaging, Optical design, Hyperspectral imaging, Buildings, Geology, Visible radiation

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Hyperspectral cameras are capable of obtaining highly useful data for geology, agriculture, urban planning, and many other applications. Several satellite-based hyperspectral cameras are currently operational, providing hyperspectral data to various users. Even large instruments usually have relatively large ground sampling distance (GSD): 10m or larger in 400 to 1000nm range and 30m or larger in 900 to 2500nm range. GSD is even coarser in hyperspectral cameras for microsatellites. Based on the information from PRISMA 2021 Workshop and our customer’s feedback, the most requested feature for satellite-based hyperspectral cameras is significantly improved GSD. Also, there is a strong demand for smaller microsatellite-compatible hyperspectral cameras. Due to lower mission cost, such cameras can provide hyperspectral data to more users. Additionally, microsatellite constellations could provide swath and revisit time that would be impossible for a single large satellite. Creating a hyperspectral camera with acceptable Signal-to-Noise Ratio (SNR) and small GSD, that would be still compatible with a small platform, is a big challenge. Our approach has been to create a hyperspectral camera that would surpass the current limitations of small satellite platforms, and would provide data that, for some specifications, exceed what is available for free from large instruments. Our focus has been on providing significantly improved GSD, small spatial and spectral misregistration, while keeping acceptable spectral sampling and SNR. The instrument development has been funded by the Norwegian Space Agency. One of the proposed instruments has been selected by the Norwegian Space Agency as the primary payload on an upcoming Norwegian In-Orbit Demonstrator satellite.

Proceedings Article | 27 May 2011 Paper

Optical vibration measurements of cross coupling effects in capacitive micromachined ultrasonic transducer arrays

Erlend Leirset, Astrid Aksnes

Proceedings Volume 8082, 80823N (2011) https://doi.org/10.1117/12.889835

KEYWORDS: Transducers, Interferometers, Interfaces, Phase velocity, Acoustics, Signal attenuation, Heterodyning, Silicon, Ultrasonics, Velocity measurements

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Optical vibration measurement systems are excellent tools for characterizing ultrasonic transducers. This paper presents measurements on immersed arrays of capacitive ultrasonic transducers (CMUTs) using a heterodyne interferometer. The interferometer allows measurements of vibrations from DC up to 1 GHz with a noise floor of ~1pm/√Hz. Previously CMUTs have been characterized in air. The transducer is intended for intravascular use. Therefore the CMUTs were characterized in the transparent fluids kerosene and rapeseed oil that have acoustic properties closer to blood. The optical measurements on immersed CMUTs were validated by assessing the measurement errors caused by the acousto optic effects in the fluid. When immersed there is significant cross coupling between individual CMUTs within an array. Simulations presented here indicate that this causes an acoustic wave mode that is bound to the interface between the CMUTs and the fluid. This is confirmed by measurements of the phase velocity and attenuation coefficient of this wave. The measurement results indicate that the wave exists up to a maximum frequency and that the attenuation constant increases with increasing frequency. Rapeseed oil causes a significantly larger attenuation coefficient than kerosene, which most probably is due to a considerable difference in fluid viscosities. There was a mismatch between the simulated and measured phase velocity for low frequencies. It is likely that the cause of this is coupling between the fluid CMUT interface waves and Lamb waves in the substrate of the CMUT array. Measurements performed with the heterodyne interferometer have confirmed the presence of dispersive waves bound to the surface of the transducer by directly showing their propagation along the array. The setup has also characterized the bound waves by measuring dispersion relations.

Proceedings Article | 11 August 2008 Paper

Modeling and optical characterization of vibrating micro- and nanostructures

Astrid Aksnes, Erlend Leirset, Hanne Martinussen, Helge Engan

Proceedings Volume 7063, 70630H (2008) https://doi.org/10.1117/12.795061

KEYWORDS: Heterodyning, Interferometers, Finite element methods, Electrodes, Bragg cells, Transducers, Signal detection, Nanostructures, Silicon, Interferometry

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The lack of commercial equipment for characterization of vibrating micro- and nanostructures has motivated the development of a heterodyne interferometer. The setup is designed to measure phase and absolute amplitude in the entire frequency range 0-1.2 GHz. Its transverse resolution is < 1 μm while the present sensitivity for vibrations is 3 pm/(Hz)^1/2. Capacitive micromachined ultrasonic transducers (CMUTs) are being developed for diagnostic imaging of vulnerable plaques in the coronary arteries. The CMUTs have 5.7 μm radii, 100 nm membrane thickness and ~30 MHz center frequency. Arrays of ~7500 CMUTs have been fabricated. Frequency scan measurements along a row of CMUTs reveal a variation in resonance frequency. This may be due to variations of material properties, dimensions such as thickness and transverse dimensions, and other manufacturing variance. The frequency scan revealed the fundamental mode and two closely spaced higher order modes. Modeling of individual CMUT elements was performed using the commercial program COMSOL. A finite element model (FEM) based on symmetry assumptions predicted only one higher order mode. After closer analysis it was found that the symmetry assumptions were insufficient. By using a complete physical model two higher order modes were predicted in agreement with the measurements. Simulations are able to predict transducer characteristics in great detail but are dependent on accurate input parameters. The optical measurements contribute to validate or complement simulations and assumptions they rely on. The heterodyne interferometer is therefore a valuable tool for quality control in the conception, design and manufacturing of new acoustic devices.

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