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Investigation of an Optical System using Beam Shaper for Uniform Laser Irradiation in Stigmatic Imaging Mass Spectrometry
Imaging mass spectrometry (IMS) is a developing method for visualizing the spatial distribution of chemical compositions in biotissues. However, conventional scanning IMS, in which a focused laser is irradiated one by one on the sample, has problems of low spatial resolution and long measurement time. To overcome these challenges, stigmatic IMS, in which laser is irradiated entire surface of the sample, has actively been studied in our group. However, ununiformity of ion images have been reported because of the Gaussian distribution of laser. In this study, a homogenizer was used in the optical system of stigmatic IMS to uniformize the energy distribution of laser. The sample made with crystal violet, which can be ionized without a matrix, was observed by stigmatic IMS using the homogenizer. Although the laser beam profile at the sample surface was not still completely uniform, the ion image of the crystal violet covered by a grid with a pitch of 12.7 µm was clearly observed. Therefore, the cellular scale observation would be expected by using the stigmatic IMS and the beam homogenizer. In future, to improve the uniformity of the beam profile at the sample surface, further adjustment of the optical system will be carried out.