Thorlabs FEL1050 Longpass Optical Filter

The Thorlabs FEL1050 is an optical longpass filter originally manufactured by Thorlabs. It is designed to transmit wavelengths above ~1050 nm while blocking shorter wavelengths — useful for infrared (IR) applications where you need to isolate or pass only the longer-wavelength part of a light source.

🔍 Key Characteristics

• Filter Type: Soft-coated longpass optical filter — transmits longer wavelengths, rejects shorter ones.

• Cut-On Wavelength: ~1050 nm — the approximate point above which transmission begins.

• Diameter: ∼1 inch (25.4 mm) with a clear aperture of ~Ø 21 mm.

• Construction: Dielectric (soft) coating on glass, housed in a black anodized aluminum mount.

• Transmission: Good transmission above the cut-on region; strong rejection (low transmission) below it, typically <0.01 % in the rejection band.

• Compatibility: Fits standard 1″ (SM1) mounted filter holders, wheels, and tubes.

🧪 Typical Use Cases

• IR imaging and spectroscopy: to isolate near-IR signals.

• Laser systems: filter out undesired shorter wavelengths.

• Astronomy & photonics setups: reducing stray visible/near-IR light.