Bandpass Filters

Precision wavelength selection from 193nm to 14μm

Andover Bandpass Filters

Precision light control, from UV to IR, in one elegant solution

Bandpass filters are one of the most effective and economical solutions for isolating specific wavelengths of light while blocking all others. Like their name suggests, they act as selective gates - allowing a precise "band" of wavelengths to pass through while rejecting everything else. Each filter is defined by three key characteristics:

Center Wavelength (CWL): The central wavelength the filter is designed to transmit
Bandwidth (FWHM): The width of the transmitted band, measured at 50% of peak transmission
Peak Transmission (T): The maximum transmission level achieved

Andover Corporation offers multiple construction variations of these filters, each optimized for different applications. Using advanced thin-film technology and precision materials, we can produce bandwidths ranging from less than an Ångström to several hundred nanometers, allowing you to select the exact specifications needed for your application.

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Filter Construction Technologies

Bandpass filters are built using two distinct construction methods, each offering unique performance advantages. Understanding these differences is key to selecting the optimal filter for your application:

All-Dielectric Type

Dielectric, or bandpass filters, are a type of optical interference filter, designed to selectively transmit specific wavelength ranges while rejecting or blocking other wavelengths. They are constructed from multiple thin layers of non-conductive materials, known as dielectrics, with varying refractive indices.

Metal-Dielectric Type

Similar to all-dielectric but utilizes a metal spacer layer. Offers excellent out-of-band blocking and high passband transmission, mainly used for bandpass filters in the ultraviolet.

By partnering with Andover Corporation, you gain access to over 45 years of expertise in designing and manufacturing environmentally stable optical filters.

Emission Line Filters

Precision isolation of common spectral lines

Emission Line Filters are precision-engineered narrowband filters designed to isolate specific spectral lines emitted by gases, elements, and laser sources. These filters deliver ultra-narrow bandwidths with steep edges and high transmission, optimized for applications where selectivity and signal-to-noise ratio are critical.

Andover Corporation offers a wide range of emission line filters targeting common lines including:

H-Alpha
H-Beta
HeNe
Kr
Ar
Na
Rb
Hg
Nd:YAG
Ruby
GaAs
HeCd
N₂

Additional filters are available for specialized sources like methane, biomedical fluorescence, LED, Sapphire, and NaYAG. Each filter is manufactured in-house for precision center wavelength control, blocking, and consistent spectral performance.

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Bandpass Filter Solutions

From standard to specialized designs

Every application has unique spectral requirements. Our comprehensive range of bandpass filters spans from proven industry standards to specialized designs for demanding environments and custom specifications. Select from six distinct filter types, each optimized for specific performance characteristics.

Standard Bandpass

The mainstay of the industry for decades. With our proprietary stabilization and sealing method, these filters typically last 10-20 years in the field.

Wavelength Range
193nm - 2400nm
Bandwidths
1nm - 100nm
Construction
Soft-Coated Laminated

Low Cost
Stock Available
Long Lifetime

Semi-Custom Bandpass

Customizable filters with short lead times, offering a wide selection of wavelengths, bandwidths, and sizes to meet specific application requirements.

Wavelength Range
214nm - 2400nm
Bandwidths
0.15nm - 80nm
Construction
Soft-Coated Laminated

Quick Turnaround
Flexible Specs
Custom Sizes

Hard-Coated Broadband

This line of hard, first-surface coated filters was designed to cover the standard Raman spectroscopy lines. They feature very high transmission over a broad range about the wavelength of interest.

Wavelength Range
345nm - 1650nm
Bandwidths
80nm - 300nm
Construction
Hard First-surface

Raman Optimized
High Temp
Broad Range

High Transmitting

Andover's High-Transmitting Bandpass filters are a variant of the Standard Bandpass filter line. Designed for use with PMTs and photodiodes, they employ only dielectric coatings and have a blocking range tailored to the detector, resulting in higher transmission than their fully-blocked counterparts.

Wavelength Range
365nm - 1550nm
Bandwidths
10nm - 40nm
Blocking
OD4 UV-800nm or 1000nm

High TransmissionLong Lifetime

First Surface UV

Andover offers a first-surface variant of its standard UV bandpass filter. The coatings are deposited on a single surface of a UV-grade Fused Silica substrate and include a hard-oxide overcoat for protection, making them ideal for UV sterilization applications.

Wavelength Range
193nm - 400nm
Construction
Hard First-surface on UV-Grade Fused Silica
Operating Temperature
-50°C to +50°C

UV Optimized
Durable Design
Single Surface
Sterilization

Hard-Coated Narrowband

Our first-surface, hard-coat narrowband filters employ plasma-deposited, hard-oxide coatings on Borosilicate Glass and do not utilize any absorbing filter glasses, making them suitable for high temperature applications. They provide a steep transition from a high, peak transmission to OD4 blocking.

Wavelength Range
334nm - 1550nm
Bandwidths
10nm - 25nm
Blocking
OD4 average 200-1200nm

High Temperature
Steep Transition
Deep Blocking

Frequently Asked Questions

What are bandpass filters?

What’s the difference between a narrowband filter and a standard bandpass filter?

What is an emission line filter?

Emission Line Filters are a specialized type of bandpass filter designed to isolate extremely narrow spectral lines emitted by gases, elements, or laser sources. They're commonly used in laser-based systems, spectroscopy, fluorescence imaging, and astronomy. At Andover Corporation, we offer these filters as a dedicated subcategory of our Bandpass Filters — engineered for precision and available for many standard emission lines, including H-alpha, HeNe, Nd:YAG, and more.

What specifications define a bandpass filter?

Key specifications include:

Center Wavelength (CWL): The central point of the passband
FWHM (Bandwidth): The width of the transmission window, expressed as "full width at half-maximum"
Peak Transmission: Maximum efficiency within the passband
Blocking Range: How well the filter rejects out-of-band light

These precision optical filters are engineered for high transmission in the passband and strong attenuation elsewhere.

In what industries or systems are bandpass filters used?

Can Andover Corporation design custom bandpass filters?

What is the lead time for custom filters?

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