TITLE:
Characterization of a Multimodal and Multispectral Led Imager: Application to Organic Polymer’s Microspheres with Diameter Φ = 10.2 μm
AUTHORS:
Marcel A. Agnero, Jérémie T. Zoueu, Kouakou Konan
KEYWORDS:
Multispectral Imaging, Reference Wavelength, Correction Coefficients, Modulation Transfer Function
JOURNAL NAME:
Optics and Photonics Journal,
Vol.6 No.7,
July
21,
2016
ABSTRACT: Multispectral microscopy enables information
enhancement in the study of specimens because of the large spectral band used
in this technique. A low cost multimode multispectral microscope using a camera
and a set of quasi-monochromatic Light Emitting Diodes (LEDs) ranging from ultraviolet
to near-infrared wavelengths as illumination sources was constructed. But the
use of a large spectral band provided by non-monochromatic sources induces
variation of focal plan of the imager due to
chromatic aberration which rises up the diffraction effects and blurs the images
causing shadow around them. It results in discrepancies between standard
spectra and extracted spectra with microscope. So we need to calibrate that
instrument to be a standard one. We proceed with two types of images comparison
to choose the reference wavelength for image acquisition where diffraction
effect is more reduced. At each wavelength chosen as a reference, one image is
well contrasted. First, we compare the thirteen well contrasted images to
identify that presenting more reduced shadow. In second time, we determine the
mean of the shadow size over the images from each set. The correction of the
discrepancies required measurements on filters using a standard spectrometer
and the microscope in transmission mode and reflection mode. To evaluate the capacity of our device to transmit
information in frequency domain, its modulation transfer function is
evaluated. Multivariate analysis is used to test its capacity to recognize properties
of well-known sample. The wavelength 700 nm was chosen to be the reference for
the image acquisition, because at this wavelength the images are well
contrasted. The measurement made on the filters suggested correction
coefficients in transmission mode and reflection mode. The experimental instrument recognized the microsphere’s
properties and led to the extraction of the standard transmittance and
reflectance spectra. Therefore, this microscope is used as a conventional
instrument.