Optical Filters for UV to Far IR (193nm - 14μm)

Astronomy Filters from Andover Corporation

Astronomy filters are specialised optical components designed to enhance the observation and imaging of celestial objects by isolating specific wavelengths of astronomical interest while rejecting unwanted light. These precision-engineered filters enable researchers and astronomers to study specific features of stars, nebulae, galaxies and other astronomical phenomena with exceptional clarity.

Each astronomy filter is characterised by several critical parameters:

• Spectral range: the specific wavelength band optimised for different astronomical targets.
• Image quality: ultra-precise polishing and coating for minimal wavefront distortion.
• Environmental stability: designed to maintain performance in varying temperatures and conditions.
• System compatibility: engineered to work with both visual and electronic imaging systems.

Andover Corporation manufactures a comprehensive range of astronomy filters, from standard photometric systems like UBVRI (both Johnson/Bessell and Kron/Cousins sets) to specialised filters for solar observation and infrared astronomy. Using state-of-the-art thin film technology and premium optical materials, we deliver filters that meet the exacting demands of modern astronomical research, whether for ground-based observatories or space-borne instruments.

Filter Construction Technologies 

Astronomy filters require exceptional precision and optical quality to enable ground-breaking observations. Understanding the available technologies helps ensure optimal performance for your specific astronomical applications:

Standard UBVRI Systems: we offer both Johnson/Bessell and Kron/Cousins photometric systems, each optimised for different detector types. Johnson/Bessell filters are optimised for photomultiplier tubes, while Kron/Cousins variants are designed for superior performance with Silicon CCDs. All filters are precision polished with transmitted wavefront of λ/4 per inch and parallelism to 30 arc seconds or better.

Specialised Astronomical Filters:

• Sloan Digital Sky Survey (SDSS) filters with non-overlapping bands and steep transitions.
• Solar observation filters including H-alpha and CaK lines.
• Infrared astronomy filters covering J, H, K, L, M, and N bands.
• Custom solutions for space-based telescopes and observatories.

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Bandpass Filters from Andover Corporation

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:

• Centre 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 a choice of construction types for these filters, each optimised for different applications. Using advanced thin-film technology and precision materials, we can produce bandwidths ranging from less than an Ångström (0.1nm) to several hundred nanometers, allowing you to select the exact specifications needed for your application.

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. 

Dielectric 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 bandpass filters are similar to all-dielectric but utilise a metal spacer layer. They offer excellent out-of-band blocking and high passband transmission and are mainly used for bandpass filters in the ultraviolet.

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Coloured Glass Filters from Andover Corporation

Coloured glass filters provide a unique approach to wavelength selection through specially formulated glass materials which absorb unwanted light while transmitting desired wavelengths. Unlike interference-based filters, colour glass filters achieve their spectral properties through the intrinsic absorption characteristics of their constituent materials.

Each filter is characterised by three key properties:

• Transmission range: the wavelength region the glass is engineered to transmit.
• Internal transmittance: the percentage of light transmitted within the passband.
• Cut-on/cut-off points: the wavelengths where transmission rises above or falls below 50%.

Using high-quality optical filter glass that is precision polished on both surfaces, our colour glass filters deliver excellent spectral consistency and sharp contrast across ultraviolet to infrared wavelengths, providing a robust and economical solution for applications requiring broad spectral filtering.

Filter Construction Technologies

Coloured glass filters achieve their spectral control through specialised material composition and precision fabrication. Understanding these construction elements is key to selecting the optimal filter for your application:

Surface Processing: both surfaces are precision ground and polished to achieve exceptional optical quality and parallelism. This two-stage polishing process ensures transmitted wavefront quality of λ/4 per inch and parallelism to within 30 arc seconds, minimising distortion and maximizing throughput. Surface quality is maintained to 80-50 scratch-dig per MIL-M-13508 standards.

Mounting Options: filters can be provided unmounted or mounted in black anodised aluminium rings. For specific applications, threaded mounting options are available to enable direct integration into optical systems while protecting the filter edges from damage during handling and assembly.

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Dichroic Filters from Andover Corporation

Dichroic filters are sophisticated optical components that selectively transmit certain wavelengths of light while reflecting others, using interference effects rather than absorption. They consist of precision-engineered thin layers of metallic oxides that create a hard dielectric coating, making them far more durable and heat-resistant than conventional absorption filters.

Key characteristics:

• Spectral separation: sharp transition between transmitted and reflected wavelengths.
• Angular dependence: performance varies with angle of incidence.
• Temperature stability: maintains spectral properties across wide temperature ranges.
• Environmental durability: resistant to humidity and UV exposure.

Andover Corporation manufactures dichroic filters using state-of-the-art deposition technologies and quality control processes. Our filters are available in standard configurations for common colour separation needs, as well as custom designs optimised for specific applications requiring precise spectral control or unique environmental requirements.

Dichroic Filter Construction Technologies

Andover Corporation manufactures dichroic filters using two primary construction approaches to meet diverse application requirements:

Hard oxide dielectric construction: employs multiple alternating layers of high and low refractive index materials. Precision-controlled layer thicknesses give sharp spectral transitions, and these filters provide superior environmental stability and durability. Ideal for high-power applications requiring minimal absorption. Operating temperature capability up to 200°C.

Enhanced metal-dielectric hybrid construction: combines metallic and dielectric layers for specialised performance and excellent out-of-band blocking characteristics. Provides enhanced angle tolerance for non-normal incidence applications. Optimised for UV and deep blue wavelengths and provides superior polarisation properties.

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Edge Filters from Andover Corporation

Edge filters serve as highly effective optical components that provide a sharp transition between transmitting and reflecting regions of the spectrum. These filters come in two main varieties: Long Wave Pass (LWP) that transmit longer wavelengths while blocking shorter ones; and Short Wave Pass (SWP) that do the opposite. Each edge filter is characterised by three critical parameters:

• Cut-on/off wavelength: the wavelength at which transmission changes from high to low (or vice versa).
• Slope: the steepness of transition between transmission and rejection regions.
• Rejection level: the degree of attenuation in the blocking region.

Andover Corporation utilises advanced thin-film coating technologies to produce edge filters with exceptional performance characteristics. Our filters feature steep transition slopes, deep rejection, and high transmission in the pass region. By employing interference effects rather than absorption, these filters provide superior durability and thermal stability compared to traditional coloured glass alternatives. With wavelength coverage from 300nm to beyond 1000nm and the ability to fine-tune cut-on/off points through angle adjustment, we can deliver edge filters precisely matched to your application requirements.

Edge Filter Construction Technologies

Edge filters employ sophisticated thin-film coating designs that enable precise wavelength discrimination. Understanding the available options helps ensure optimal filter selection for your application:

Hard Oxide Coating Technology: our standard edge filters utilise magnetron-sputtered hard oxide coatings deposited on precision optical substrates. This construction provides excellent environmental stability and durability while delivering deep rejection (OD4 or better), sharp transition slopes (≤6% standard, ≤1% for steep-edge versions) and high transmission (>85% average in pass region).

Steep Edge Technology: for applications requiring the sharpest possible wavelength discrimination, our steep-edge filters employ specialised coating designs that achieve ultra-steep transitions (≤1% slope), exceptional transmission (≥91% average), superior blocking (OD4+) and an extended temperature range (-50°C to +200°C).

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Heat Control Filters from Andover Corporation

Heat control filters are specialised optical components designed to effectively manage infrared radiation while maintaining optimal visible light transmission. These filters work by selectively reflecting or transmitting different portions of the electromagnetic spectrum, allowing precise control over thermal energy in optical systems. Each type of heat control filter is characterised by its specific spectral response:

• Hot mirrors: transmit visible light while reflecting infrared radiation.
• Cold mirrors: reflect visible light while transmitting infrared radiation.
• UV cold mirrors: efficiently reflect UV while transmitting visible and infrared radiation.
• IR suppressing filters: provide extended blocking across the infrared spectrum.

Andover Corporation’s heat control filters utilise advanced thin-film dielectric coatings deposited on thermally-stable substrates like borosilicate glass. This construction ensures reliable performance even in high-power illumination applications. The combination of hot and cold mirrors can eliminate up to 99% of unwanted radiation, making these filters essential components in applications ranging from projection systems to medical lighting.

Heat Control Filter Technologies

Heat control filters are engineered using advanced thin-film coating technologies, each optimised for specific thermal management requirements. Understanding these options helps ensure the right solution for your application:

Hard dielectric construction: first-surface coatings composed of alternating high and low refractive index materials, creating interference effects that selectively reflect or transmit specific wavelengths. These durable coatings can achieve up to 90% transmission in the visible spectrum while providing excellent infrared reflection.

Hybrid construction: combines dielectric stacks with specialised substrate materials for enhanced performance. The IR suppressing series utilises both interference effects and absorption to achieve extended blocking ranges beyond what’s possible with standard dielectric coatings alone.

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Image-Quality Filters from Andover Corporation

Image-quality optical filters are designed for applications that demand superior resolution and imaging precision. These filters use high-purity, striation-free optical materials and advanced coatings to minimise distortion and maximise clarity.

Each image-quality filter is characterized by three essential properties:

• Transmitted Wavefront: typically λ/4 per inch or better, ensuring minimal distortion
• Parallelism: 30 arc seconds or better, maintaining precise image alignment
• Surface Quality: precision-polished surfaces with optimised AR coatings to eliminate ghosting and maximise throughput

Andover Corporation’s image-quality filters are manufactured using advanced polishing techniques and high-grade optical materials. By combining precision substrate preparation with optimised coating positions and anti-reflection treatments, we eliminate multiple reflections and fringe patterns that could compromise image quality. For applications demanding even higher performance, we can achieve transmitted wavefront quality of λ/10 and parallelism of 10 arc seconds.

Image Quality Filter Technologies

Engineered with cutting-edge polishing and coating techniques, our filters maintain strict optical tolerances for high-resolution imaging systems.

Precision Substrate Construction: our filters begin with premium-grade optical materials that are meticulously screened for freedom from striations and inclusions. Each substrate undergoes our proprietary two-stage polishing process to achieve exceptional flatness and parallelism, with surface quality up to 20-10 scratch-dig.

Advanced Coating Architecture: we employ sophisticated multi-layer coating designs optimised for imaging applications. External surfaces receive high-efficiency AR coatings to eliminate ghost images. Internal coating positions are precisely engineered to prevent interference patterns. Layer stress is carefully controlled to maintain substrate flatness. Optional enhanced durability coatings for demanding environments are available.

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Infrared Filters from Andover Corporation

Infrared filters are essential components in thermal imaging, spectroscopy, and defence applications. These specialised filters selectively transmit infrared wavelengths while blocking unwanted radiation, enabling superior optical performance. Andover Corporation designs infrared optical filters with cutting-edge thin-film coatings and premium IR-transmitting materials to ensure:

• Precise wavelength control across the near-IR (0.75–1.4µm), mid-wave IR (MWIR, 3–8µm), and longwave IR (LWIR, 8–15µm).
• Optimised transmission and blocking with high optical density (OD) for superior spectral purity.
• Custom-engineered solutions tailored to specific infrared applications.

Whether you need bandpass, longwave pass, or neutral density IR filters, Andover delivers unmatched reliability and performance.

IR Filter Construction Technologies

Environmental conditions play a crucial role in the performance and longevity of bandpass filters. Understanding these factors ensures optimal filter selection and helps maintain precise wavelength control in your application.

Magnetron sputtering: a cutting-edge method delivering highly durable and environmentally stable coatings. Providing consistent performance across batches and low water-content coatings for extended longevity. Wavelengths from UV to mid-IR (0.3–5μm. Available sizes from 2-200mm.

Resistance evaporation: a cost-effective approach offering short lead times with scalable production and versatile coating options. Providing ultra-narrowband selections (<0.1nm in visible spectrum). Wavelengths from UV to near-IR (193–2400nm). Available sizes from 5–250mm.

Diamond-like carbon (DLC) coatings: ideal for high-index infrared materials, DLC coatings provide exceptional durability for Germanium (Ge) and Silicon (Si) optics. Provide low reflectance with a refractive index ~2.0 as well as an outstanding resistance to humidity, salt fog, and abrasion. Also provides enhanced protection for outer-facing infrared lenses.

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Neutral Density Filters from Andover Corporation

Neutral Density (ND) filters are precision optical components designed to reduce light intensity uniformly across a specified wavelength range while maintaining the original spectral characteristics. Used in applications ranging from microscopy to infrared astronomy, these filters provide controlled attenuation without spectral distortion. Andover Corporation engineers ND filters using advanced thin-film technologies to ensure consistent performance across the UV-VIS-IR spectrum. The attenuation of a neutral density filter is expressed in terms of optical density (OD). Note that optical density is the logarithm of the transmittance, so a filter with 10% transmittance has an OD of 1, while a filter that transmits 1% of incident light has an OD of 2, and so on.

Each filter is characterised by:

• Optical density (OD): attenuation levels ranging from 0.1 to 4.0.

• Spectral Range: consistent attenuation across a specified wavelength region.

• Transmission uniformity: uniform light reduction across the full spectral range.

ND Filter Construction Technologies

Neutral density filters are manufactured using three distinct construction methods, each offering unique performance advantages. Understanding these differences is key to selecting the optimal filter for your application:

Metallic: utilises precision metal alloy coatings to achieve high durability and broad spectral coverage from UV through IR. These filters combine absorption and reflection mechanisms to reduce intensity while maintaining excellent environmental stability. Ideal for laser systems and broad-spectrum applications.

Absorptive: employs specialised glass substrates that absorb light uniformly across their designed spectral range. These filters minimise back reflections and are anti-reflection coated, making them perfect for imaging applications where ghost images must be eliminated.

Infrared: specifically engineered for thermal and IR applications using specialised coating materials and substrates suitable from short wave IR to thermal IR ranges. These filters maintain neutral density characteristics in the infrared region while providing the durability needed for thermal imaging and IR laser systems.

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Applications for Andover Optical Filters

Check out our blog article on the diverse applications of Andover optical filters!

Andover Corporation’s advanced optical filters are deployed wherever high performance and durability matter, from advancing the exploration of space to engineering the future of medical discovery. The main applications and markets that we serve include:

• Aerospace
• Defence 
• Astronomy & space
• LIDAR & ADAS sensors
• Biomedicine & life science
• Machine vision
• Semiconductor

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