An infrared microscope employing reflecting optics has been designed and constructed as an attachment to Perkin-Elmer single beam spectrometers. It is mounted after the exit slit of the monochromator in the dispersed beam to minimize possible heating and photochemical effects in the sample. The normal macro functions of the spectrometer are not disrupted by the addition of the microscope. Convenient macro-micro conversion is provided.
The condenser and objective pair, which are of the Schwarzschild type, operate at a numerical aperture of 0.75 with a 0.4 obscuration ratio and are designed to provide optimum imagery in the infrared region of the spectrum. The condenser forms an image of the exit slit at the sample space reduced 8.5×, and the objective provides a 25× enlarged image of the sample at an adjustable diaphragm. A viewing and manipulating system is provided to allow accurate positioning of small samples. The maximum field size is 0.650×0.220 mm. About 35 percent of the radiation available from the monochromator is conserved by minimizing the number of reflecting surfaces and by utilizing field mirrors to provide efficient energy transfer. The radiation is brought to a separate detector and preamplifier which are connected to the amplifier and recorder of the spectrometer.
The minimum sample size which can be effectively studied depends on wavelength and is primarily limited by the available energy. Minimum sample size and spectral dilution are discussed.
The infrared absorption spectra of fibers, crystals, and biological tissue sections, as well as solutions in cells, of extremely small volume, have been obtained using this instrument. Performance data are given and a figure of merit determined.
VINCENT J. COATES, ABE OFFNER, and E. H. SIEGLER, JR., "Design and Performance of an Infrared Microscope Attachment," J. Opt. Soc. Am. 43, 984-989 (1953)