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New acousto-optic device based on calomel for hyperspectral imahining in space applications

Filter prototype compatible with imagining device on satellite

Project duration: 2010 to 2012

Project manager: Čestmír Barta

Calomel is a material with a high acousto-optic coefficient transparent in the spectral region 0,4-20 μm. Its optical and acousto-optical properties make it attractive for application in Acousto-Optical Tunable Filters (AOTFs). Calomel-based AOTF can be used as a spectral discrimination element in a compact hyperspectral imager on a small satellite. An AOTF is electronically controlled and has no moving parts.

Technology developments at BBT enabled the commercial manufacturing of Calomel crystals for AOTFs used in laser pulse shaping applications. Recent activities in BBT and FASTLITE within the framework of an ESA NAOMI project resulted in the demonstration of a Calomel-based AOTF for spectral imaging applications. The prototype AOTF has the following characteristics: spectral range 4-8 μm, spectral resolution 2 cm-1, acceptance angle ±10°, clear aperture 2 x 2,5 mm2. Other applications of calomel crystals as optical elements are currently under development.

A major difficulty with the prospect of mid-infrared acousto-optic imagers is the decrease of the efficiency of acousto-optic diffraction with increasing wavelength. Estimates indicate that radio-frequency powers of hundreds of watts would be required if standard designs of AOTF used in the visible were to be used for the mid-Infrared. This would make the use of such instruments impractical in space applications, especially in the context of small satellites. For this reason, a new imaging method (patent pending) has been introduced as the basis of the design. It allows the use of highly efficient beam-collinear configurations, which reduce the power requirement by one to two orders of magnitude and improve the spectral resolution. The results achieved are superior in terms of spectral resolution to all existing reports concerning mercurous halides or TAS devices. Potential improvements of spectral resolution and efficiency are possible through larger crystals and/or switching to other mercurous halides that have higher characteristic performance factors.

BBT - Materials Processing

The company activities follow the business and research activities of Mr Cestmir Barta, who set up the BBT - Materials Processing, Crystal Science & Technology Institute in 1991. The company studies the processes of crystal growth and solidification of melts and gases of calomel and sapphire. Apart from the research activities, the company develops and manufactures programmable crystallizers, furnaces and other devices for the material science and its’ terrestrial and space applications (MIR, Foton, ISS, drop towers, parabolic flights). The current activities are closely related to the experience gained in the programme INTERKOSMOS. BBT also deals with digital image analysis.

What would you name as main benefits of the project to you and your company?

“The project NAOMI enabled us to reach the world top level in the field of tunable acousto-optic filters. Thanks to that we got other commercial contracts, particularly exclusive OEM supplies for manufacturer of high-tech devices. Due to the good results, BBT was invited to enter the consortium of European companies developing the laser equipment for surgery in the treatment of cancer, in the frame of FP7 programme.”