Final Activity Report Summary - SPECTRAL MICROSCOPE (Real-time microscopic chemical imaging: The application of (...) mid-infrared sources to new techniques in spectrally-resolved microscopy) Many substances show characteristic absorption profiles for mid-infrared radiation with wavelengths between 2.5 and 10 microns. Such absorption spectra can be viewed as a 'chemical fingerprint' allowing for the identification of particular substances. For example, infrared spectra can be used to identify minute concentrations of particular gases in breath samples, opening up new possibilities in medical diagnostics. Combined with infrared microscopic imaging systems, such techniques can allow for chemical differences in apparently homogeneous samples to be observed, offering exciting possibilities for new analytical techniques in fields as diverse as medicine, forensics and art conservation. To achieve the most sensitive and fastest detection using such techniques often requires the use of tuneable laser sources. However, the availability of lasers with suitable tuning properties and sufficient power in the mid-infrared is extremely limited. The principle objective of this project was the development of such mid-infrared laser-based sources with rapid wide-range tuning characteristics and their application to spectroscopic imaging and trace-gas analysis. The results of the project included the demonstration of a mid-infrared source at three to four micron wavelengths, based on the nonlinear optical frequency conversion of a fibre laser output, and its application to the detection of methane and to the detection of ethane at trace concentrations. The source was capable of tuning over unprecedentedly wide continuous ranges in timescales of milliseconds. In an extension of this work the output was modulated in frequency and this modulation was used to investigate, for the first time with a source of this type, a range of specialised detection techniques offering extremely high sensitivity, in some cases even allowing for the detection of ethane at sub part-per-billion concentrations. In addition, a range of fast-tuning sources, having lower spectral resolutions but capable of tuning over much wider ranges, were also explored based on fibre lasers. Further source development included initial studies of a long wavelength (six to eight micron) source as a precursor to the development of advanced rapid tuning sources in this range. The work initiated within this project remained ongoing and the use of the developed sources in imaging applications was actively explored beyond the project completion.
