Thin Film Glossary
The following defines a number of glossary terms related to thin film optical filters and their use.
The angle at which a filter is tilted relative to the primary ray. For example, an AOI of 0° means the primary ray is perpendicular to the plane of the filter.
A filter that transmits a band of wavelengths while blocking the wavelengths on either side of the passband.
The level of rejection of light outside the passband.
Borofloat® (Borosilicate Glass)
A high temperature substrate material with high chemical resistivity against water, neutral, acidic and saline solutions.
The center of the passband for a bandpass filter. Another common definition is the average of the 50% of peak of each edge of a bandpass filter.
The range of angles of light incident on the filter about the AOI.
Average of transmission or reflection across the cone angle
A filter that transmits one band and reflects a different band
Edge Filter
A filter that transmits a band of wavelengths and blocks only low side (long wave pass) or high side (shortwave pass) of wavelengths.
Fused Silica
Substrate material composed of amorphous silicon dioxide.
An edge-type filter that transmits longer wavelengths and blocks shorter wavelengths.
A filter that blocks a narrow range while transmitting wavelengths on either side of the blocked wavelength range.
The negative logarithm (base 10) of transmittance (T). (T on a zero to unity scale)
The range of wavelengths that are desired to be transmitted.
The orientation tolerance allowed between a feature of interest and a reference datum. For plano-plano optical filters, the term describes how parallel the two main surfaces of the optic are to one another.
Variations in transmission in the passband.
An edge-type filter that transmits the shorter wavelengths and blocks higher wavelengths.
Rate of change of the spectrum from a passband to a blocking band.
Transmitted Wavefront Error (TWE)
Distortion of the wavefront of a plane wave as it transmits through a filter, generally given in units of the HeNe wavelength of 633 nm.