Mr. Jarmo Lehtomaa Profile

Jarmo Lehtomaa

at Specim Spectral Imaging Ltd

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Proceedings Article | 29 April 2009 Paper

Advanced pushbroom hyperspectral LWIR imagers

Hannu Holma, Timo Hyvärinen, Jarmo Lehtomaa, Harri Karjalainen, Risto Jaskari

Proceedings Volume 7319, 731907 (2009) https://doi.org/10.1117/12.818557

KEYWORDS: Long wavelength infrared, Cameras, Imaging systems, Sensors, Signal to noise ratio, Microbolometers, Calibration, Hyperspectral imaging, Black bodies, Temperature metrology

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Performance studies and instrument designs for hyperspectral pushbroom imagers in thermal wavelength region are introduced. The studies involve imaging systems based on both MCT and microbolometer detector. All the systems employ pushbroom imaging spectrograph with transmission grating and on-axis optics. The aim of the work was to design high performance instruments with good image quality and compact size for various application requirements. A big challenge in realizing these goals without considerable cooling of the whole instrument is to control the instrument radiation from all the surfaces of the instrument itself. This challenge is even bigger in hyperspectral instruments, where the optical power from the target is spread spectrally over tens of pixels, but the instrument radiation is not dispersed. Without any suppression, the instrument radiation can overwhelm the radiation from the target by 1000 times. In the first imager design, BMC-technique (background monitoring on-chip), background suppression and temperature stabilization have been combined with cryo-cooled MCT-detector. The performance of a very compact hyperspectral imager with 84 spectral bands and 384 spatial samples has been studied and NESR of 18 mW/(m²srμm) at 10 μm wavelength for 300 K target has been achieved. This leads to SNR of 580. These results are based on a simulation model. The second version of the imager with an uncooled microbolometer detector and optics in ambient temperature aims at imaging targets at higher temperatures or with illumination. Heater rods with ellipsoidal reflectors can be used to illuminate the swath line of the hyperspectral imager on a target or sample, like drill core in mineralogical analysis. Performance characteristics for microbolometer version have been experimentally verified.

Proceedings Article | 16 May 2007 Paper

Low temperature co-fired ceramics on optoelectronic sensors integration

Ville Moilanen, Kari Kautio, Pentti Karioja, Raimo Rikola, Jarmo Lehtomaa, Jouko Malinen

Proceedings Volume 6585, 658506 (2007) https://doi.org/10.1117/12.724158

KEYWORDS: Sensors, Lead, Detector arrays, Light emitting diodes, Signal detection, Chemical elements, Packaging, Assembly equipment, Infrared radiation, Ceramics

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The optical analyzers used in on-line and off-line process measurements set a large variety of special demands for optical detectors, i.e. customized detectors are needed. Both the detector (array) and its read-out circuit are affected. The typical volume for process analyzers is so low that fully customized ASICs easily become too expensive for signal recovery solutions in optical detectors. This is due to high fixed costs in ASIC development. Low Temperature Co-fired Ceramics (LTCC) substrates allow high integration grade and the smart packaging solutions needed in optical detectors. The ceramic substrate is suitable for hermetic packaging. The high integration grade is possible thanks to multilayer capability, with narrow metal strips as well as blind and buried vias which can be placed directly underneath the solder pads. Standard connection methods can be used, i.e. soldering, gluing and wire bonding for components and detector chip assembly. By using small passive components and bare chip or chip scale packaged active components, one is able to integrate the read-out functions in a small enough space. This paper briefly presents three different cases where infrared photoconductive detector arrays are attached to read-out circuitry which is made on LTCC substrate. The detector read-out hybrids are packaged in hermetic metal packages. The packages have been either non-cooled or thermoelectrically cooled. 24 element PbS, 4 by 4 element PbS and 128 element MCT cases are handled. Also an example of an integrated infrared light emitting diode array for an LED-spectrometer is presented. General feasibility analysis, including some electrical test results and the management of substrate dimensional tolerances, is given.

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