• Peak Optical Density in Blocking Region: >6.0 (T < 0.0001%)
• Dielectric Stack on Polished Glass Substrate
• Compatible with Thorlabs’ Filter Mounts and Filter Wheels

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 basically 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.

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. The central wavelength of the blocking region will shift shorter wavelengths as the angle of incidence is increased.

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 less than 0.0001%) within the stop band. 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 passing bands.

Each filter is housed in a black anodized aluminum ring that is labeled with an arrow indicating the design propagation direction. These filters can be mounted in our extensive line of filter mounts and wheels. We do not recommend removing the filter from its mount, as the filter consists of several layers of glass that are held together with epoxy and the mounting ring. These glass layers are necessary to protect the dielectric coating from the atmosphere; exposer would significantly reduce the filter’s transmission efficiency over time.

• Transmission in Passbands: T_avg > 90%
• Peak Optical Density in Blocking Region: >6
• Clear Aperture: Ø21 mm
• Surface Quality: 60-40 Scratch-Dig
• Transmitted Wavefront Error (@633 nm):<λ/2
• Angle of Incidence: 0°
• Coating: Dielectric Stack on Front Surface
• Housing: Black-Anodized Lens Cell
• Center Wavelength: 785 ± 2 nm
• FWHM of Blocking Region: 33 nm
• Diameter: 1"
• Thickness: 1/4"
• Substrate: B270