What is FWHM (for optical filters)

In the context of optical bandpass filters, FWHM stands for Full Width at Half Maximum. It refers to the bandwidth of the filter, representing the range of wavelengths over which the filter transmits light at least half of its peak intensity. In simpler terms, it tells you how "wide" the "window" of allowed wavelengths is.

Here's a breakdown of the key points about FWHM and bandpass filters:

    • Bandpass filter: Allows light within a specific range of wavelengths (passband) to pass through, while blocking other wavelengths (stopband).
    • FWHM: Measured in nanometers (nm), it indicates the width of the passband at the point where the transmittance drops to half of its peak value.
    • Narrower FWHM: More selective filter, allows a smaller range of wavelengths to pass through, but may result in lower overall signal intensity.
    • Wider FWHM: Less selective filter, allows a broader range of wavelengths to pass through, potentially offering higher signal intensity, but with less specific wavelength selection.

Choosing the right FWHM for your filter depends on your specific application:

    • High selectivity needed: Choose a narrow FWHM for precise wavelength targeting.
    • Higher signal intensity needed: Choose a wider FWHM for increased light transmission.
    • Balance between selectivity and signal: Consider your application's specific requirements and experiment with different FWHM options.

Remember, other filter characteristics like center wavelength, steepness of the stopband, and transmission efficiency also play crucial roles in filter performance.

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