Narrow Bandpass Filter Specifications

Since each narrow band filter transmits only specified wavelength ranges, the key specifications of these filters relate to the location and size of the pass band as well as the completeness of both rejection and transmission.

The center wavelength of a narrow band filter, abbreviated CWL, is the midpoint of the pass band or transmitting region. This is also the location of peak transmission.

The full-width half-max (FWHM) of the bandpass filter gives the width of the pass band at half of maximum transmission. The FWHM of a narrow band pass filter will be less than 6% of the central wavelength.

While some narrow passband filters feature a flat top, others have a peaked pass band shape. The flatness of the transmitting region in percentage points is given by the pass band ripple of the filter, and a low pass band ripple is equivalent to a flat top narrow band. Flat top filters are in especially high demand in LiDAR applications, where the filter must operate without spectral drift due to temperature cycling.

Blocking in the rejection region of a narrow band filter is described by the optical density of the filter; deep blocking density may be considered to be OD of 6.

Applications of our Ultra Narrowband Filter

Our ultra narrow band filters are designed to meet the unique requirements of sophisticated imaging setups and experimentation. The hard coating and durability of these optics means that our ultra narrowband optical filters are ideal for laser cleanup as well as for laser line and laser excitation filters. They also have applications in flow cytometry, DNA sequencing, PCR diagnostics, fluorescence microscopy, LIDAR, and Raman spectroscopy. In cytometry and fluorescence in-situ hybridization, they can be key to reducing spectral cross-talk.

Ultra Narrowband Filters at Shanghai Optics

At Shanghai Optics we take pride in manufacturing ultra narrowband filters featuring durable optical coatings. Our stock narrow bandpass filters are manufactured from UV fused silica and include options with center wavelengths from 355 to 1064 nm. The FWHM of our in-stock narrowband filters is from 1.3 (for a filter with 355 nm CWL) to 4.0 nm (for a 1064 nm CWL filter). Our filters have a surface quality of 60-40 scratch dig, and a laser damage threshold of 0.1 J/cm² @ 532 nm (10ns pulse width).

Please contact us to receive a full catalog of our in-stock narrow band filters or to discuss custom options. Our engineering team has extensive experience in designing complex optical systems for a wide variety of applications, and we have been a trusted source of custom optics for more than fifty years.