Improvements in chemical imaging
Exploiting the brightness of SRIR for faster chemical imaging
The ability to collect spatial and chemical information can give great insights into a range of samples from disease signatures in tissue to aging in varnishes and pigments used in frescoes. On the Multimode InfraRed Imaging And Microspectroscopy (MIRIAM) beamline (B22) the broadband infrared (IR) radiation obtained from the synchrotron is used to collect high quality spectra with better spatial resolution than is possible from a thermal IR source. At the moment these chemical maps are measured point-by-point and can take hours to collect. Advances in IR detection now allows chemical images to be collected all in one go. On B22 we are investigating how to exploit this new detector technology with the synchrotron radiation IR (SRIR) to offer chemical imaging experiments not possible with other IR sources.
The advent of focal plane array (FPA) detectors has revolutionised chemical/molecular imaging microscopy. With these detectors, IR spectra can now be collected over a large field of view simultaneously. While thermal sources are not bright enough to achieve high spatial resolution (<10 µm), SRIR is a broader and brighter source providing a much higher signal to noise. Full field IR microscopy via an FPA detector in combination with SR illumination has been experimentally proven at Diamond Light Source on the MIRIAM beamline (B22) but with some practical limitations. In order to take full advantage of the SRIR brightness the issue to be addressed is spatial structure of the SR beam (Figure 1). This structure causes artefacts in the images collected with the FPA detector, limiting the field of view which can be collected. Our aim is to implement a pair of deformable mirrors to improve the illumination of the FPA detector and eliminate the SRIR structure.
Figure 1: The adaptive optics employed at B22.
Deformable mirrors have a surface which can be manipulated and shaped; this allows the light reflected from them to be finely controlled. Deformable mirrors have been used in astronomy for many years to correct for atmospheric turbulence which can distort telescopic images. More recently these mirrors have been used in visible microscopy to correct for sample aberrations and also in super resolution techniques.
Generally deformable mirrors have been used to correct phase errors whereas the application we are implementing on B22 involves shaping the amplitude of our SRIR light source. To achieve this a new optic setup to couple the SRIR with the deformable mirrors and the microscope has been developed and built. The next step is to develop an optimisation scheme to find the mirror shapes, which produce the best illumination of the FPA detector in the IR microscope.
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