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A layer of dielectric
material, transparent in the transmission region of the filter, due
to a phase thickness of 180 degrees.
curve, absorption spectrum:
The relative tendency of a
material to absorb a specific color or energy of light, typically
plotted as intensity, transmission, or optical density versus wavelength.
The angle formed by an
incident ray of light and an imaginary line perpendicular to the
plane of the component's surface. When the ray is said to be
"normal" to the surface, the angle is 0 degrees.
Unit of length, one-tenth
of a nanometre (nm). 10-10 metres.
An optical thin-film
interference coating designed to minimise reflection that occurs when
light travels from one medium into another, typically air and glass.
AR coatings are the most common interference coatings, and are used
on such items as camera lenses and eyeglasses.
The suppression of signal
before detection in an optical system. Usually, the wavelength or
wavelength range is defined along with the degree of attenuation
expressed in relative or absolute optical density.
Transmits a band of
colour, the centre of which is the centre wavelength (CWL). The width
of the band is indicated by the full width at half maximum
transmission (FWHM), also known as the half band width (HBW). It
attenuates the light of wavelengths both longer and shorter than the passband.
The component of a fully
assembled filter that provides attenuation of a specific region of
Attenuation of light,
usually accomplished by reflection or absorption, outside the
passband. Blocking requirements are specified by wavelength range and
amount of attenuation.
Achromatic Twyman-Green (BAT) interferometer:
interferometer that uses a white (broadband) light source.
"period". The basic component of a thin-film filter
consists of two quarter-wave stack reflectors separated by a solid
dielectric spacer. As the reflectivity of each of the quarter wave
stack reflectors increases, the FWHM decreases; as the number of
cavities increases, the depth of the blocking outside the passband
increases, and the shape of the passband becomes increasingly rectangular.
Color correcting filters
modify the hue of a signal to make it more easily distinguished.
The arithmetic center of
the passband of a bandpass filter. It is not necessarily the same as
the peak wavelength.
The physical area of a
filter that performs in an optical system. The region is usually
similar, concentric, and smaller than the total region of a filter.
Unless otherwise stated, performance criteria apply throughout the
Blocking of light into the
far IR. It is a specification of blocking range, not depth. Due to a
metallic coating, the maximum transmission of a completely blocked
bandpass filter is 50-60%.
In a converging or
diverging beam of light, the full angle between the extreme off-axis rays.
The cut-on is the
wavelength of transition from attenuation to transmission, along a
continuum of increasing wavelength. The cut-off is the wavelength of
transition from transmission to reflection. Both are often given as
50% of peak transmission, but can also be given as 5% or 10% of peak transmission.
feature very steep-sided passbands with especially deep attenuation
of energy close to the band.
In reference to thin-film
interference coatings, selectively transmitting and/or reflecting
light according to its wavelength rather than its plane of polarization.
A material with both
conductive and insulative electromagnetic properties. A dielectric
thin-film material exhibits far more transmission than absorption at
the wavelength of interest.
Dichroic longpass filters
transmit a broad range of energy while efficiently reflecting shorter
wavelength energy along another channel in the optical system.
DRLP ext filters are
dichroic longpass filters enhanced to reflect an extended range of energy.
A dimensionless constant
characteristic of a coating design used to calculate the spectral
shift observed when it is used at off-normal angles of incidence.
Longpass edge filters
reflect more than 99.999% of shorter wavelength energy that is very
close to the transmitted energy.
The relative intensity of
radiation versus wavelength. In fluorescence, the radiation results
from return from the first singlet excited states to ground level.
Illumination that impinges
on the sample from the viewing direction. In microscopy, the
illuminator and the objective are common.
The relative probability
versus wavelength that will result in a fixed intensity of emission energy.
The range over which the
filter attenuates color or energy of light (light at CWL ± 1 HBW excluded).
The measurement of cell
activity on a singular basis.
A derivative of fluorescein.
An instrument for the
measurement of fluorescence.
width at half maximum transmission (FWHM):
Defines the width of the
passband of a bandpass filter. It is referenced to the points on the
cut-on and cut-off edge where the transmission is one-half of the
bandwidth (HBW or HPBW):
Same as FWHM above.
High temperature filters
protect the sample from excessive source radiation.
The quality of an optic to
transmit an unaltered wavefront.
of refraction (n):
A quantity assigned to a
light-transmitting medium that indicates the relative speed of the
light in that medium. Phenomena occuring at the interface of two
light-transmitting media, such as refraction and reflection, are
governed by the physical laws and the indices of refraction of each medium.
For example: vacuum = 1.0,
glass = 1.5, germanium = 4.0.
Light from the region of
the spectrum with wavelengths between 750nm (red) and 0.1mm (microwave).
KG is a shortpass color
absorption glass that transmits visible light while attenuating both
longer and shorter wavelenth energy.
1µ = 1000nm. 10^-6 meters.
Unit of length used to
measure wavelengths of light. 10^-9 meters.
isolate monochromatic signals from strong polychromatic illumination.
Longpass color absorption
glasses absorb more than 99.999% of shorter wavelength energy that is
very close to the transmitted energy. OG glasses absorb blue light,
RG glasses absorb blue and green light.
Original equipment manufacturer.
transmission usually in blocking regions.
Conversion: -log10(T) =
OD. For example, 1% transmission is .01 absolute, so -log10 (0.01) =
Light color or
energy-selecting device, created by depositing multiple layers of
dielectric materials such that constructive/destructive interference
reflects all light within the free spectral range except for the passband.
The feature of conserving
the most energy in the transmission band by controlling only the out-of-band
region of detector sensitivity.
The spectral region
centered at the CWL and 2 HBW in width where the interference filter
switches from reflection to non-reflection and back to reflection
(for the DF series, the absolute values are 0.99999+ to 0.1).
The portion of a periodic
function, such as a wave, which has elapsed and is measured from some
fixed origin. If the time for one period is expressed as 360 degrees
along a time axis, the phase position is called the phase angle.
When light is incident on
a thin-film coating, the component of the electric vector parallel to
the plane of incidence (P-plane) may react differently than the
perpendicular component (S-plane). The plane of incidence is defined
by the direction of the incident and reflected beams: at normal
incidence the planes of polarization are undefined. Linearly
polarized light can be either P-plane, S-plane, or a combination,
depending on the orientation of the thin-film relative to the
The system ratio of the
integrated energy within the passband envelope to the energy outside
this envelope and within the free spectral range.
The rate of transition
from attenuation (defined as 5% of peak transmission) to transmission
(defined as 80% of peak transmission). Slope = (lambda 0.80 - lambda
0.05) divided by lambda 0.05.
A layer of material which
has an optical thickness corresponding to an integral-half of the
center wavelength of the band.
A dual monochromator
instrument capable of measuring the fluorescence spectrum as a
function of an excitation wavelength.
The lower frequency of
electromagnetic energy emitted as a result of absorbed energy.
A pure SiO2 glass.
The f/#, which is the
ratio of the focal length to the aperture, of an optical system at
the location of a filter.
Light from the region of
the spectrum with wavelengths between 1nm (X-ray) and 400nm (the blue
end of the visible spectrum), approximately.
Light from the region of
the spectrum with wavelengths between 400nm (blue) and 750nm (red).
The degree of disruption
of an optical wavefront, measured by viewing the interference fringes
of a two-arm interferometer with the component at test in one arm and
a known reference in the other.
Wide band filters
combine rectangular bandshapes with broad regions of transmission.