Filter at Non Normal Angle of Incidence

Flat-top optical bandpass filters offer significant advantages over Gaussian filters when dealing with non-normal angle incidence. Their wider passband, sharper cutoff frequencies, and reduced sensitivity to polarization effects make them ideal choices for applications where precise wavelength control and high transmission efficiency are crucial, even under challenging optical conditions.

(Below is an example of flat-top bandpass filter from us)

  • Understanding Gaussian and Flat-Top Filters

    Gaussian filter: This type of filter has a Gaussian-shaped transmission profile, with a peak at the center wavelength and gradually decreasing transmission on either side.

    Flat-top filter: This filter has a relatively flat transmission profile across the passband, with sharp cutoff frequencies at the edges.

  • Why Flat-Top Filters are Better for Non-Normal Angle Incidence

    Reduced Spectral Shift: When light is incident on an optical filter at an angle other than normal, its effective wavelength shifts due to the change in optical path length. This phenomenon is known as angular dispersion. Gaussian filters, with their narrower passband, are more sensitive to this shift, leading to a potential shift in the transmitted wavelength. Flat-top filters, with their wider passband, are less affected by angular dispersion, ensuring a more stable transmitted wavelength even at non-normal angles.

    Improved Transmission Efficiency: At non-normal angles, the transmission efficiency of an optical filter can decrease due to polarization effects and increased reflection. Flat-top filters, with their sharper cutoff frequencies, can minimize these losses compared to Gaussian filters, resulting in higher overall transmission efficiency.

    Reduced Polarization Dependence: The transmission of an optical filter can vary with the polarization state of the incident light. Flat-top filters are generally less sensitive to polarization effects than Gaussian filters, especially at non-normal angles, providing a more consistent transmission response regardless of the polarization.

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