Achromatization Method for Multichannel Fluorescence Imaging Systems

An achromatization method optimized for dual-channel imaging is developed. Dichroic mirrors are employed to split and recombine narrowband signals, and separation between catoptric components is used to minimize the longitudinal chromatic shift. An achromatic system based on this principle could be built from singlet lenses, since refractive element properties such as dispersion and power are not utilized to optimize wavelength-dependent performance. To demonstrate the validity of the proposed solution, a prototype miniature fluorescence microscope optimized for two emission lines of acridine orange (525 and 650 nm) is built. To reduce the cost and accelerate assembly, the system is built from commercially available optical components. The optical train consisted of two plastic singlet lenses combined with a pair of dichroic mirrors. Optical performance of the prototype is evaluated by imaging a bar line target at both design wavelengths. To demonstrate the potential of the proposed design strategy, the achromatic system prototype is used to measure a two-part white blood cells differential count on a venous blood sample. Data from the prototype fluorescence microscope are compared against results from a commercially available blood analyzer, and the difference between both instruments is within 20%. (C) 2019 Society of Photo-Optical Instrumentation Engineers (SPIE)