Page 361 - Fundamentals of Light Microscopy and Electronic Imaging

344 GLOSSARY

Intensity of light. Qualitatively, the brightness or flux of light energy perceived by the
eye. By universal agreement, the term intensity, meaning the flow of energy per unit
area per unit time, is being replaced by the word irradiance, a radiometric term indi-
cating the average energy (photon flux) per unit area per unit time, or watts/meter .
2
As a term describing the strength of light, intensity is proportional to the square of
the amplitude of an electromagnetic wave. 22
Interference. The sum of two or more interacting electromagnetic waves. Two waves
can interfere only if a component of the E vector of one wave vibrates in the plane of
the other wave. Resultant waves with amplitudes greater or less than the constituent
waves are said to represent constructive and destructive interference, respectively. 63
Interference color. The color that results from removal of a band of visible wavelengths
from a source of white light. 39, 141
Interference filter. A filter made from alternating layers of different dielectric materi-
als or layers of a dielectric material and thin metal film that transmits a specific band
of wavelengths. The spacings between the layers of one-quarter or one-half wave-
length allow constructive interference and reinforce propagation through the filter of
a particular wavelength λ. All other wavelengths give destructive interference and are
absorbed or reflected and do not propagate through the filter. 39
Interline transfer CCD. A form of CCD having alternate columns of pixels that func-
tion as exposed photosites and masked storage sites. During operation, the masked
pixels are read out and digitized while exposed sites simultaneously capture photo-
electrons. This double-duty action speeds up camera operation. Newer interline
CCDs contain microlenses that cover storage- and photosite-pixel pairs to increase
light-gathering efficiency. Upon completion of an exposure, the transfer of signal
charges from a photosite pixel to an adjacent storage pixel is so fast that a camera
shutter is not required. 268
Inverse transform. In image processing, the image created by a Fourier transform oper-
ation used primarily to blur and sharpen images. A Fourier transform looks like a dif-
fraction pattern and represents spatial details as spatial frequencies. After applying a
mask to select low- or high-spatial frequency information, the transform is converted
back into an image (the inverse transform). Spatial frequency masking with a Fourier
transform gives similar results as blurring and sharpening convolution filters, but can
give a more even result. 81, 299
Ion arc lamp. Lamps containing an ionized gas or plasma between two electrodes that
radiates visible wavelengths when excited by an electric current. Arc lamps used in
light microscopy usually contain mercury vapor or xenon gas. 30
Irradiance of light. The radiometrically correct term for light intensity. Irradiance is the
radiant flux incident per surface unit area and is given as watts/meter . Irradiance is
2
a measure of the concentration of power.
ISIT camera. See Intensifier silicon-intensifier target (ISIT) camera.
Isotropic. In describing the optical properties of an object or propagation medium, hav-
ing identical properties in different directions. 121
Jablonski diagram. A diagram showing the energy levels occupied by an excited elec-
tron in an atom or molecule as steps on a vertical ladder. Singlet and triplet excited
states are shown separately as ladders standing next to each other. 180
Kernel. See Convolution.
Koehler illumination. The principal method for illuminating specimens in the light
microscope, whereby a collector lens near the light source is used to focus an image
of the light source in the front aperture of the condenser. The microscope condenser