An embedded control and display system for a laser-based mid-infrared hyperspectral imager

Abstract

Back-scatter absorption gas imaging (BAGI) is a powerful laser-based detection technique whereby the strong spectroscopic absorption features in the gaseous species of interest are exploited in order to provide an image of the otherwise invisible (to the naked eye) gas. Such a device had been under development at the University of St. Andrews for the past three years. This thesis is concerned with the work carried out in the design, construction and testing of an electronic supervisory system for such a device to both control the electro-mechanical image acquisition hardware and display the image data upon an LCD module via an on-board video driver. Two different LCD display technologies, super twisted nematic (STN) and thin film transistor (TFT), have been demonstrated and their suitability for use in this system is assessed. It was found that the refresh rate and contrast ratio of the TFT display was greatly superior to that of the STN. Frame rates in excess of 10 fps have been demonstrated with this module. In addition to the scanner, a laser management system (LMS) was designed, constructed and tested to control the laser illumination system, which is based on an intracavity optical parametric oscillator (ICOPO). This involved the development of a dual-channel PID temperature controller to stabilise various optical components located within the ICOPO illumination source, a digitally-controlled constant current source to drive the pump diode laser and a digitally controlled system for an associated Q-switch driver module. The LMS was developed as part of the miniaturisation process and resulted in one dedicated instrument replacing six individual devices required in the laboratory demonstrator. The BAGI device has now been commercialised with elements of this research program being part of the overall instrument.