Custom Optical Interference Filter For Spectral Analysis / Machine Vision

Optical interference filter introduction

Introduction to Interference Filter

Filter is a kind of optical element which can select the transmission, reflection, cut-off and attenuation of spectral wavelength. According to its function, it can be divided into band-pass filter, long wave pass filter, short wave pass filter, dichroic filter, neutral density filter, notch filter, cold mirror, hot mirror, color filter, etc. These filters are widely used in spectral analysis, biomedicine, machine vision, fluorescence microscopy, industrial automation and other industries and product fields. The band-pass filter selectively allows and blocks the transmission of a certain spectral wavelength within its spectral range; the neutral density filter reduces the luminous flux by reducing the transmittance of the specified spectral wavelength range, which is conducive to the protection of sensors / electronic components, and is widely used in the field of laser optics / optoelectronics; the cold / hot reflector It can reflect and transmit the light with longer wavelength in the spectrum range, which is widely used in the lighting system, which is beneficial to eliminate the heat generated in the lighting system. We not only provide filter standards, but also customize filters according to your needs.

Central Wavelength

Center Wavelength (CWL), used in defining bandpass filters, describes the midpoint of spectral bandwidth over which the filter transmits. Traditional Coated Optical Filters tend to achieve a maximum transmission near the center wavelength, whereas Hard Coated Optical Filters tend to have a fairly flat transmission profile over the spectral bandwidth.

Bandwidth

Bandwidth is a wavelength range used to denote a specific part of the spectrum that passes incident energy through a filter. Bandwidth is also referred to as FWHM.

Full Width-Half Maximum

Full Width-Half Maximum (FWHM) describes the spectral bandwidth over which a bandpass filter will transmit. The upper and lower limit of that bandwidth is defined at the wavelengths where the filter achieves 50% of the maximum transmission. For example, if the maximum transmission of the filter is 90%, the wavelengths at which the filter achieves 45% transmission will define the upper and lower limits of the FWHM. FWHM’s of 10nm or less are considered narrowband and often used for laser clean-up and chemical detection. FWHM’s of 25 – 50nm are often used in machine vision applications; FHWM’s of more than 50nm are considered broadband and typically used in fluorescence microscopy applications.

Blocking Range

Blocking Range is a wavelength interval used to denote a spectral region of energy that is attenuated by the filter. The degree of its blocking is typically specified in terms of optical density.

Optical Density

Optical Density (OD) describes the amount of energy blocked or rejected by a filter. A high optical density value indicates low transmission, and low optical density indicates high transmission. Optical densities of 6 or greater are used for extreme blocking needs such as Raman spectroscopy or fluorescence microscopy. Optical densities of 3.0 – 4.0 are ideal for laser separation and clean-up, machine vision, and chemical detection, while optical densities of 2.0 or less are ideal for color sorting and separating spectral orders.

Dichroic Filter

A Dichroic Filter is a type of filter used to transmit or reflect light, depending on the wavelength; light of a specific wavelength range is transmitted, while light of a different range is reflected or absorbed. Dichroic filters are commonly used for longpass and shortpass applications.

Cut-On Wavelength

Cut-On Wavelength is a term used to denote the wavelength at which the transmission increases to 50% throughput in a longpass filter. Cut-on wavelength is indicated by λcut-on

Cut-Off Wavelength

Cut-Off Wavelength is a term used to denote the wavelength at which the transmission decreases to 50% throughput in a shortpass filter. Cut-off wavelength is indicated by λcut-off.

Partial stock filter list

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