Notch Filters

by IDEX Health & Science

Notch Optical Filters

Notch Optical Filter Graph
Notch filters are ideal for applications that require nearly complete rejection of a laser line while passing as much non-laser light as possible. Hard-coated thin-film notch filters offer a superior solution due to their excellent transmission (> 90%), deep laser-line blocking (OD > 6) with a narrow notch bandwidth (~ 3% of the laser wavelength), environmental reliability, high laser damage threshold (> 1 J/cm2 ), and compact format with convenient back-reflection of the rejected laser light. However, until now, the main drawback of standard thin-film notch filters has been a limited passband range due to the fundamental and higher-harmonic spectral stop bands (see red curve on graph at right).

To achieve a wider passband than standard thin-film notch filters could provide, optical engineers had to turn to “holographic” or “Rugate” notch filters. Unfortunately, holographic filters suffer from lower reliability and transmission (due to the gelatin-based, laminated structure), higher cost (resulting from the sequential production process), and poorer system noise performance and/or higher system complexity. Rugate notch filters, based on a sinusoidally varying index of refraction, generally suffer from lower transmission, especially at shorter wavelengths, and less deep notches.

Semrock E-grade StopLine notch filters offer a breakthrough in optical notch filter technology, bringing together all the advantages of hard-coated standard thin-film notch filters with the ultrawide passbands that were previously possible only with holographic and Rugate notch filters. The spectral performance of the E-grade StopLine filters is virtually identical to that of Semrock’s renowned U-grade StopLine filters, but with passbands that extend from the UV (< 350 nm) to the near-IR (> 1600 nm).

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