| Term |
Symbol |
Definition
|
| Wavelength |
 |
Usually
stated in nanometers (1 nm = 10-9 m) or
microns (1 µm = 10-6 m).
|
| Wavenumber |
 |
Reciprocal
of wavelength, usually expressed in cm-1
(1 µm = 10,000 wavenumbers (cm-1)).
|
| Central
Wavelength |
CWL |
Wavelength
at the centre of the pass band measured at the half of the peak
transmittance point.
|
| Transmittance |
T |
Ratio
of the transmitted energy to the incident energy, usually expressed
in %.
|
| Peak
Transmittance |
Tpeak |
Maximum
of the transmittance.
|
| Average
Transmittance |
Tavg |
Average
of the transmittance.
|
| Peak
Wavelength |
peak |
Wavelength
at the maximum of the transmittance.
|
| Bandwidth |
HW |
Full
width of the pass band measured at half the maximum of the peak
transmittance.
|
| Blocking
Region |
|
The
region outside the pass band where the filter is designed not to
transmit light. Usually expressed as a percentage of the incident
energy, blocking is typical less than 0.1 % transmittance.
|
| Cuton
/ Cutoff Wavelength |
C |
Wavelength
at which a filter begins/ ceases to transmit.
Specified at 5% of the absolute transmittance point.
|
| Cuton
/ Cutoff Slopes |
|
A
measure of the transmittance cuton or cutoff slope.
Defined as:
|
| Band
Pass Filter, |
BP |
A
filter which transmits energy in a specified wavelength band but
rejects energy above and below.
|
| Narrow
Band Pass Filter, |
NB
|
| Broad
Band Pass Filter |
BBP
|
| Shortwave
Pass Filter |
SP |
A
filter which transmits energy at wavelengths below its cutoff point.
Sometimes called a low pass filter.
|
| Longwave
Pass Filter |
LP |
A
filter which transmits energy at wavelengths above its cuton point.
Sometimes called a high pass filter.
|
| Neutral
Density Filter |
ND |
A
filter which attenuates energy levels accurately in a defined wavelength
range.
|
