FEL0450 In Stock

The ThorLabs FEL0450 is a highly effective longpass filter that is widely used for isolating specific regions of a spectrum. The filter is equipped with durable dielectric coatings that ensure that it can withstand regular cleaning and handling, making it a high-quality optical component. The FEL0450 filter is designed to be used in various applications, including Raman spectroscopy filters and astronomy.

One of the outstanding features of the FEL0450 filter is its film construction. It is a quarter-wave stack that is modified and instead of using absorption for the isolation of particular spectral bands, it uses interference effects. As the angle of incidence increases, the cut-on and cut-off wavelength of the filter shift to a shorter wavelength, unlike colored filter glass. This feature makes it ideal for applications where it is desirable to fine-tune the location of the cut-on or cut-off wavelength.

The FEL0450 filter is hermetically sealed to provide maximum protection against humidity, and it can be stacked to create custom bandpass filters. The filter’s housing is a black anodized aluminum ring that has an arrow that labels which the direction of the design propagation. The ring limits scattering, in turn enhancing the blocking OD, and makes handling of the filter easier. The FEL0450 filter can be mounted in an extensive line of compatible filter mounts and wheels. However, it is important to note that Ø1" retaining rings are necessary in order to mount the filter in a compatible SM1 lens tubes that are threaded internally, as the mounts are not threaded.

The FEL0450 filter is created by depositing layers of material on the surface of the substrate. The filter's dielectric stack is composed of alternating layers of low-index and high-index dielectric material, while spacer layers are placed between the dielectric stacks. The thickness of each layer in the dielectric stack is λ/4, where λ is the central wavelength of the bandpass filter. The spacer layers have a thickness of (nλ)/2, where n is an integer and can be formed from colored glass, epoxy, dyes, metallic, or dielectric layers. Each spacer layer sandwiched between dielectric stacks forms a Fabry-Perot cavity, making the FEL0450 filter highly efficient in isolating specific regions of a spectrum.