NOTCH/BANDSTOP

BACK

• Choose from 13 Center Wavelength Options
• Mounted in Ø25 mm Housing
• Peak Optical Density at Center Wavelength: >6.0 (T < 0.0001%)
• Dielectric Stack on Polished Glass Substrate
• Compatible with Thorlabs’ Filter Mounts and Filter Wheels
• Select Notch Filters Available in Custom Sizes; Contact Tech Support for Details

Notch filters, also commonly referred to as band-stop or band-rejection filters, are designed to transmit most wavelengths with little intensity loss while attenuating light within a specific wavelength range (the stop band) to a very low level. They are essentially the inverse of bandpass filters, which offer high in-band transmission and high out-of-band rejection so as to only transmit light within a small wavelength range. See the Transmission Graphs and OD Graphs tabs for the performance over the passbands and blocking region.

Notch filters are useful in applications where one needs to block light from a laser. For instance, to obtain good signal-to-noise ratios in Raman spectroscopy experiments, it is critical that light from the pump laser be blocked. This is achieved by placing a notch filter in the detection channel of the setup. In addition to spectroscopy, notch filters are commonly used in laser-based fluorescence instrumentation and biomedical laser systems.

As with all dielectric stack filters, the transmission is dependent on the angle of incidence (AOI). The central wavelength of the blocking region will shift to shorter wavelengths as the AOI is increased. The AOI Graphs tab shows the transmission of s- and p-polarized light as a function of wavelength changes for different AOI.

Thorlabs’ notch filters feature a dielectric coating on a polished glass substrate, which has excellent environmental durability. The dielectric stack provides high rejection through destructive interference and reflection in the stop band: the optical density is greater than 6.0 (corresponding to a transmission of less than 0.0001%) within the stop band. See the table below for available stop band center wavelengths. Regardless of the filter chosen, the transmitted beam’s wavefront error for light at normal incidence will be less than λ/2 at 633 nm. These filters also have an AR coating on the back surface to ensure >90% average transmission within the passbands.

Each filter is housed in a black anodized aluminum ring that is labeled with an arrow indicating the design propagation direction. The ring makes handling easier and enhances the blocking OD by limiting scattering. These filters can be mounted in our extensive line of filter mounts and wheels. As the mounts are not threaded, Ø1″ retaining rings will be required to mount the filters in one of our internally-threaded SM1 lens tubes. We do not recommend removing the filter from its mount as the risk of damaging the filter is very high. However, select filters are available unmounted as well as in custom sizes; contact Tech Support for more details.