The vast majority of Omega Optical’s interference filters are either sputtered oxide or coatings protected with coverslips. Occasionally, Omega does produce filters that are fragile and should merely be blown off with compressed air or puffer. These filters will be marked as fragile. They are often exposed metal or other materials that are commonly used in the mid-far IR wavelengths.
CLEANING DIRECTIONS FOR DURABLE FILTERS
- Avoid depositing oil from your hands onto filters by using finger cots or gloves. Hold filters from the edges only. For smaller filters use plastic tweezers to help with handling. Metal tweezers can scratch the coatings.
- Blow loose dirt and particles from the surface of the filter using a puffer or compressed air. Do not blow air from your mouth as you may deposit small particles. Stop here if you have a fragile filter surface.
- Apply isopropyl alcohol to a lint-free cotton swab and rub the filters surface in a circular motion, working from the center to edge. Gently apply pressure. Avoid rapid side-to-side motions.
- Use the puffer to evaporate excess alcohol from filter surfaces.
- Repeat steps 3 & 4 above using a clean, lint-free cotton swab with each cleaning until all surface contamination is removed.
- To complete the cleaning process wipe filter surface using lens paper gently applying pressure.
- Return your filter to the original plastic case or envelope provided.
Note: We do not recommend the use of water, detergents or any other non-optical cleaning materials for this process.
One of the most common questions regarding completed filters is how to orient them in the optical path. Typically, our filters are labeled with an arrow on the edge indicating the direction of the light path. Place the arrow pointing away from the light source and towards the detector. When there is no arrow present, an interference filter should be placed with the most reflective, metallic looking surface towards the light source. The second surface of the filter is distinguishable by its more colored or opaque appearance. When oriented in this manner, thermal stress on the filter is minimized.
Special markings can be applied for customers who require consistency with their custom instrument design.
OPTICAL FILTER NOMENCLATURE
Omega uses a series of numbers and letters to describe its filters.
The leading number describes the most relevant spectral characteristic. For a bandpass, this would be the center wavelength (CWL). For a longpass, it would be the cut-on wavelength (where the filter goes into transmission and is transmitting 50% of the max %T) and for a shortpass, it would be the cut-off wavelength (where the filter is transitioning into reflection and is transmitting 50% of the max %T).
Letters directly following the first number are historical and relate to the filter’s design. This letter (or letters) is followed by letters that describe the filter (shortpass= SP, longpass=LP) or by numbers in the case of a bandpass filter that indicate the FWHM of the passband. FWHM is defined as the spectral bandwidth at 50% of the maximum transmission of the filter.
Some examples -
488AF40 – a bandpass filter with CWL = 488 nm and a bandwidth of 40 nm
575ABLP – a longpass filter with a cut-on wavelength of 575 nm
632AESP – a shortpass filter with a cut-off wavelength of 632 nm
505DRLP – a dichroic longpass filter with a cut-on wavelength of 505 nm (the leading D indicates this is a dichroic filter designed to work at a specific angle-of-incidence)
FLUORESCENCE MICROSCOPY SETS
All of our Fluorescence Instrumentation and Microscopy filters begin with the prefix "XF" and are distinguished between excitation, dichroic and emission filters by a subsequent 4-digit code. The excitation 4-digit code begins with the number "1" followed by any 3 other digits. For dichroics, the 4-digit code begins with the number "2" and for emission filters, the 4-digit code begins with the number "3."