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Stray light

Stray light refers to any unwanted light within an optical system that deviates from the intended optical path and reaches the detector or sensor, thereby interfering with the system's performance.^[1] This phenomenon occurs in both imaging and non-imaging applications, such as telescopes, cameras, spectrometers, and sensors used in automotive, aerospace, and medical fields.^[2] It can originate from the primary light source but follow unintended routes or from external sources, encompassing forms like internal reflections, scattering, and diffraction.^[3] Common causes of stray light include surface imperfections on optical components that lead to unpredictable scattering, internal reflections from elements like lens mounts or housing walls, and diffraction effects from gratings or edges in spectrometers.^[3] In array spectrometers, additional sources arise from inter-reflections between mirrors, detectors, slits, and housings, as well as interference from higher-order diffraction grating modes.^[4] External ambient light can also contribute if the system is inadequately shielded, while thermal emissions from components add to stray light in high-precision setups.^[1] The effects of stray light are significant, primarily reducing image contrast, introducing artifacts such as ghosting or veiling glare, and distorting color accuracy or measurement precision.^[2] In spectroscopy, it leads to false signals that obscure weak spectral features, particularly in ultraviolet measurements or with complex sources like halogen lamps, where stray light levels can reach 6×10^{-4}.^[4] For imaging systems, it increases background noise, impairs autofocus, and can even cause component damage in high-power applications, making it a critical concern for high-contrast scenarios like space telescopes or advanced driver-assistance systems (ADAS).^[1] Mitigation strategies involve a combination of optical design optimizations, such as using baffles to block direct stray paths, absorptive coatings to minimize reflections, and high-quality components like optimized gratings.^[4] Specialized black coatings, effective across UV to IR wavelengths and as thin as 5 microns, can suppress scattering in cleanroom environments.^[3] Additionally, mathematical corrections via stray light matrices can reduce errors by 1-2 orders of magnitude, while simulation tools like ray tracing enable proactive analysis during design.^[4]^[2]

Fundamentals

Definition and Principles

Stray light in optics refers to any unwanted radiation that reaches the detector or image plane via paths other than the designed primary optical path, often resulting from scattering, reflections, or diffraction within the system.^[5] This phenomenon degrades system performance by introducing noise that interferes with the intended signal, encompassing light from the primary source that deviates from its expected trajectory as well as extraneous radiation.^[6] In essence, stray light arises when imperfections in optical components redirect photons away from the focal plane, violating the ideal propagation defined by the system's geometry.^[7] The principles underlying stray light stem from fundamental optics, including the conservation of energy along ray paths in the absence of absorption, where total radiant power remains constant but can be redistributed into unintended directions through interactions like surface irregularities or multiple reflections.^[8] Ray tracing serves as a core method to model these deviations, simulating intended paths as straight-line propagations governed by Snell's law and refraction at interfaces, while unintended paths—such as ghost images from spurious reflections—are traced separately to quantify energy diversion.^[9] Stray light is distinguished from signal light primarily by its direction (off-axis arrival), intensity (typically lower but additive noise), and sometimes wavelength (e.g., out-of-band radiation in spectrometers), ensuring that only the primary flux contributes to the desired output.^[10] Quantitatively, stray light is often characterized by the stray light fraction (SLF), defined as the ratio of unwanted light flux to the total light flux incident on the detector, providing a measure of system purity typically expressed as a percentage.^[11] For high-performance systems, achieving an SLF below 0.1% is critical to maintain contrast and fidelity, though exact values depend on the application's tolerance for noise.^[12]

Physical Mechanisms

Stray light in optical systems arises primarily from scattering mechanisms, where incident light is redirected due to interactions with particles or inhomogeneities much smaller or comparable to the wavelength. Rayleigh scattering dominates when particles are significantly smaller than the wavelength (typically < λ/10), such as molecular-scale fluctuations in gases or dielectrics, resulting in elastic scattering with intensity inversely proportional to the fourth power of the wavelength (I ∝ 1/λ⁴), which explains phenomena like the blue sky but contributes to broadband stray light in instruments.^[13] This wavelength dependence arises from the electromagnetic theory of induced dipoles in small scatterers, where the scattered power scales with the square of the incident electric field and the fourth power of the wave number. The basic Rayleigh scattering cross-section, which quantifies the effective area for scattering per particle, is given by

\sigma = \frac{8\pi}{3} \left( k^4 \alpha^2 \right),

where k = 2\pi / \lambda is the wave number and \alpha is the particle's polarizability. This formula derives from classical electromagnetism by modeling the particle as an induced oscillating dipole that reradiates the incident field; the dipole moment \mathbf{p} = \alpha \mathbf{E} leads to scattered power P = \frac{\mu_0 \omega^4 p^2}{12\pi c} integrated over solid angle, yielding the cross-section via the optical theorem relating forward scattering to total extinction.^[14] For larger particles (size parameter x = 2\pi a / \lambda \approx 1, where a is radius), Mie scattering takes over, providing a more complex, exact solution for spherical scatterers using vector spherical harmonics and boundary conditions on Maxwell's equations, producing forward-peaked patterns without the strong λ⁴ dependence.^[15] Reflection mechanisms also generate stray light through unintended bounces off surfaces. Specular reflection occurs on smooth interfaces, following the law of reflection where angle of incidence equals angle of reflection, concentrating light like a mirror but causing ghosts if off-design paths are taken.^[16] In contrast, diffuse reflection from rough surfaces scatters light into a wide angular distribution via multiple micro-reflections, increasing veiling glare in imaging systems. Total internal reflection (TIR), governed by Snell's law when light in a higher-index medium (n₁) strikes a lower-index boundary (n₂) at angle θ > θ_c = sin⁻¹(n₂/n₁), fully reflects light back, but imperfections in prisms or fibers can leak evanescent waves, producing stray emission. Diffraction contributes to stray light by bending wavefronts around obstacles or through apertures. Edge diffraction, described by Fresnel or Fraunhofer approximations, occurs when light passes near a sharp boundary, creating interference fringes that spread energy beyond the geometric shadow, as seen in aperture stops where partial blocking diffracts rays into the focal plane.^[17] In spectrometers, diffraction gratings exhibit anomalies—abrupt efficiency changes known as Rayleigh-Wood anomalies—where diffracted order intensities vary sharply at wavelengths satisfying mλ = d sinθ (m order, d period), due to pole singularities in the grating's modal expansion, leading to enhanced or suppressed stray orders.^[18] Secondary mechanisms involve absorption followed by re-emission, such as fluorescence, where incident photons excite electrons to higher states, and subsequent relaxation emits longer-wavelength light isotropically, acting as wavelength-shifted stray that reduces signal-to-noise in detection.^[10]

Sources

Internal Sources

Internal sources of stray light in optical instruments arise primarily from imperfections and interactions within the system's components and structure, leading to unintended light paths that reach the detector. Surface roughness on lenses and mirrors scatters incident light, redirecting portions away from the intended focal plane; this scattering is particularly pronounced in high-precision optics where mid- and high-frequency surface errors contribute to wide-angle stray light distribution.^[19]^[20] Similarly, ghost images form due to multiple reflections between lens surfaces or within lens stacks, creating secondary, faint replicas of the primary image that degrade contrast.^[21]^[22] Structural elements within the instrument can also generate stray light through unintended reflections or scattering. Baffle edges and mechanical mounts, such as those supporting mirrors, may reflect light if not precisely finished, allowing off-axis rays to propagate toward sensitive areas.^[23] Adhesive residues and particulate contaminants inside housings or on internal surfaces further contribute by scattering or diffusing light, with particulates on optical surfaces acting as localized scatterers.^[24] In specialized instruments like monochromators, stray light emerges from grating-related artifacts, including inefficiencies in blaze angles that cause uneven diffraction efficiency across wavelengths and order overlaps where higher-order spectra intrude into the primary wavelength band. These effects reduce spectral purity by allowing unwanted wavelengths to reach the exit slit.^[25] In Fabry-Pérot interferometers, etalon imperfections, such as non-parallel surfaces or defects in coatings, can produce stray light, typically residual light of ~1% or more from neighboring resonance orders, manifesting as broadened resonances or excess energy in the point spread function's side lobes.^[26]^[27] A notable case in telescopes involves secondary mirror supports, where the struts or vanes diffract light from bright sources, generating characteristic spikes in the image; these diffraction patterns represent a form of structured stray light originating from the instrument's internal geometry.^[28]

External Sources

External stray light encompasses unwanted radiation entering optical systems from sources outside the instrument, influenced by environmental conditions, operational environments, and atmospheric phenomena. These intrusions often manifest as diffuse or directed light that bypasses intended apertures, reducing contrast and elevating background levels in imaging or spectroscopic data. In space-based platforms, such as satellites in low Earth orbit, external stray light can dominate the observed sky brightness, particularly from celestial and planetary reflections.^[29] Environmental sources primarily involve ambient light from natural celestial bodies leaking through seals, vents, or minor gaps in the instrument housing. Sunlight represents a dominant contributor, entering systems during orbital transitions near the day-night terminator, where its high intensity—approximating the solar constant of 1366 W/m² at Earth's distance—can scatter into the focal plane via off-axis paths. Moonlight similarly infiltrates, providing an average illuminance of about 0.2 lux on horizontal surfaces under clear skies, which can overwhelm faint target signals in nocturnal observations. In infrared optical systems, external thermal emissions from surrounding environments, such as planetary blackbody radiation, add to the stray light burden; for instance, Earth's effective temperature of approximately 255 K during shadowed orbital phases generates infrared radiance governed by Planck's law, contributing measurable flux in long-wave bands.^[30]^[31]^[24] Operational factors introduce stray light from proximate artificial or incidental sources tied to the system's deployment. In laboratory or ground-testing setups, ambient room lighting—typically fluorescent or LED sources—can penetrate enclosures, simulating unintended external illumination that mimics field conditions. In orbital contexts, glints from nearby satellites or spacecraft surfaces, produced by specular reflections of sunlight off metallic or solar panel facets, create transient bright spikes; these flashes, lasting milliseconds to seconds, have been observed to affect wide-field surveys, with rates increasing in dense satellite constellations. Such events highlight how mission geometry and proximity to other objects exacerbate external light ingress.^[32]^[33] Atmospheric contributions are particularly relevant for ground-based optical systems, where diffuse overhead emissions elevate the baseline sky brightness. Sky glow arises from scattering of incoming radiation within the atmosphere, forming a uniform veil that can exceed natural levels in non-polluted sites. Zodiacal light, originating from sunlight scattered by interplanetary dust along the ecliptic plane, appears as a faint, triangular glow extending from the horizon, with surface brightness varying by solar elongation and dust density. Auroral emissions, driven by solar wind interactions with upper atmospheric gases, produce dynamic green and red arcs or curtains in high-latitude regions, injecting variable spectral lines that interfere with broadband photometry. These phenomena collectively challenge deep-sky observations by adding photon noise comparable to or exceeding target fluxes in sensitive detectors.^[34] A key example of environmental impact in space telescopes involves Earth albedo, the fraction of incident sunlight reflected by the planet's surface, clouds, and atmosphere, averaging 0.30 globally. This reflected light scatters into instruments viewing off-nadir or limb regions, forming a persistent background; in low Earth orbit, it can dominate stray light during shadowed passes when the satellite shadows the instrument but not the viewed Earth portion. For the SeaWiFS radiometer, uncorrected stray light from high-albedo features like clouds contaminates adjacent pixels, with residuals reaching up to 0.5% of typical ocean radiances at 4–10 pixels offset, necessitating masking or algorithmic subtraction for accurate Earth observation. To contextualize interference, the full moon's 0.2 lux illuminance dwarfs darker baselines, such as starlit skies at ~0.001 lux, underscoring how external sources can swamp desired signals by orders of magnitude in low-flux regimes.^[24]^[35]^[36]

Effects in Optical Systems

In Imaging and Detection

Stray light significantly degrades imaging quality in optical systems by introducing unwanted illumination that reduces overall contrast. This occurs primarily through veiling glare, a uniform veil of light superimposed across the image plane, which diminishes the difference between bright and dark areas, making fine details less discernible.^[37] Additionally, stray light can produce halo artifacts around bright sources, manifesting as diffuse rings or glows that obscure adjacent features and alter the perceived sharpness of the image.^[38] In detection systems, stray light adversely affects sensitivity by decreasing the signal-to-noise ratio (SNR), as it contributes additional photons that mask weak signals. This effect is particularly pronounced in low-light conditions, where stray light elevates the background noise level, overwhelming faint detections and limiting the system's ability to resolve subtle variations.^[39] The degradation in SNR due to stray light can be quantified using the formula for photon-limited detection:

\text{SNR}_\text{stray} = \frac{S}{\sqrt{N_\text{signal} + N_\text{stray} + N_\text{read}}}

Here, S represents the desired signal counts, N_\text{signal} is the number of signal photons, N_\text{stray} is the number of stray light photons, and N_\text{read} accounts for readout noise (in equivalent electrons²). The total noise is the square root of the sum of these Poisson variances and readout noise. Stray light directly increases the denominator by adding N_\text{stray}, thereby reducing the SNR compared to an ideal system without stray contributions.^[40] A key quantitative metric for assessing stray light's impact on imaging contrast is the veiling glare index (VGI), defined as

\text{VGI} = \frac{L_\text{stray}}{L_\text{object}}

where L_\text{stray} is the luminance due to stray light in shadowed regions, and L_\text{object} is the luminance from the intended object or scene.^[41] Lower VGI values indicate better performance, with typical targets below 1% for high-quality systems to maintain adequate contrast.

In Spectroscopy and Measurement

Stray light in spectroscopy introduces unwanted radiation that deviates from the intended spectral band, compromising the accuracy and resolution of spectral measurements in analytical instruments such as spectrophotometers and spectrometers.^[42] This contamination primarily arises from internal reflections, diffraction inefficiencies, or scattering within the optical path, leading to spectral distortions that affect quantitative analysis.^[10] In particular, it manifests as line broadening, where spectral peaks appear wider due to the superposition of off-wavelength light, false continuum addition that elevates the baseline and obscures subtle features, and reduced dynamic range in absorbance measurements by compressing the signal scale at higher absorbances.^[42] These effects degrade the instrument's ability to resolve fine spectral details and accurately quantify analyte concentrations.^[43] In absorbance-based techniques like UV-Vis spectroscopy, stray light causes measurement errors by overestimating transmittance and underestimating concentrations, as it contributes unabsorbed light to the detected signal.^[44] According to Beer's law, true absorbance A_{\text{true}} = -\log_{10} T, where T is the true transmittance; however, with stray light fraction \text{SLF}, the measured transmittance becomes T_{\text{measured}} = \frac{T + \text{SLF}}{1 + \text{SLF}}, assuming stray light affects both reference and sample paths equally, leading to A_{\text{measured}} = -\log_{10} \left( \frac{T + \text{SLF}}{1 + \text{SLF}} \right).^[45] This results in A_{\text{measured}} < A_{\text{true}}, producing negative deviations that become pronounced at high absorbances, where the apparent absorbance plateaus near -\log_{10} (\text{SLF}).^[42] For instance, in UV-Vis spectrometers with typical stray light levels around 0.1%, linearity deviates by more than 1% at absorbances exceeding 2, limiting reliable quantification to lower concentration ranges.^[42] A notable case occurs in Raman spectroscopy, where stray light from intense Rayleigh scattering overwhelms weak inelastic Raman signals, masking low-wavenumber features critical for molecular identification.^[46] The Rayleigh line, being elastically scattered at the excitation wavelength, generates a broad stray light wing that reduces the signal-to-background ratio, often necessitating advanced suppression techniques to access transitions near the laser line.^[47] This interference particularly hinders the detection of subtle vibrational modes in dilute samples or complex mixtures.^[46]

Applications and Case Studies

In Astronomy

In astronomy, stray light significantly hampers the detection of faint celestial phenomena by increasing background noise and reducing contrast in images. A primary source is zodiacal light, the diffuse glow from sunlight scattered by interplanetary dust particles along the ecliptic plane, which creates a nearly uniform background that interferes with deep-space imaging of galaxies and other dim objects.^[48] This effect is particularly acute for infrared observations, where zodiacal emission dominates the near-infrared sky, limiting the signal-to-noise ratio for targets like distant quasars.^[49] Ground-based telescopes also contend with urban light pollution, where artificial lighting from cities scatters in the atmosphere, brightening the night sky and obscuring faint structures such as galactic halos.^[50] This skyglow can elevate surface brightness levels, effectively masking low-surface-brightness features essential for studying galaxy evolution.^[51] Space-based instruments exemplify both challenges and solutions to stray light in astronomical contexts. The Hubble Space Telescope encountered early issues with stray light leaking from Earthshine and moonlight into its optics, particularly during observations near the continuous viewing zone, where it contaminated wide-field images and raised backgrounds in the Advanced Camera for Surveys.^[52] In contrast, the James Webb Space Telescope's design incorporates a five-layer sunshield to block direct and reflected sunlight, Earth-emitted infrared, and lunar stray light, maintaining the telescope's cryogenic temperatures while suppressing off-axis illumination to levels below 10^{-6} of the primary beam.^[53] This shielding is critical for JWST's infrared sensitivity, preventing thermal stray light from overwhelming faint emissions in deep fields.^[54] Ground-based observations in the 1990s were notably affected by moonlight stray light, even during lunar eclipses, as scattered lunar illumination during partial phases increased sky backgrounds and compromised photometry of faint objects like asteroids and variable stars.^[55] Such interference reduced the effective exposure times for time-domain surveys, forcing astronomers to schedule around full moon periods to minimize scattered light impacts. Stray light sources like moonlight or zodiacal emission can degrade detection limits for faint galaxies. Historically, efforts to combat solar stray light advanced in the early 20th century with Bernard Lyot's invention of the coronagraph in the 1930s, which uses an occulting disk and Lyot stop to suppress diffracted and scattered sunlight, enabling ground-based studies of the solar corona outside of natural eclipses.^[56] This instrument reduced stray light to about 10^{-6} of the sun's intensity, revolutionizing solar astronomy by allowing routine observations of prominences and coronal structures without the logistical constraints of eclipse expeditions.^[57] Lyot's design laid the foundation for modern externally occulted coronagraphs used in missions like SOHO, prioritizing high-contrast imaging for exoplanet detection analogs.^[58]

In Remote Sensing and Photography

In remote sensing applications, stray light frequently causes sensor saturation due to sunglint in satellite imagery, where direct reflections from water surfaces overload detectors and compromise data accuracy. This phenomenon is particularly problematic for ocean color sensors, as seen in the SeaWiFS radiometer, where stray light from bright sources like glint contaminates measurements up to 10 pixels along-scan, leading to erroneous radiance values without correction.^[35] Atmospheric haze exacerbates stray light by introducing scattered light paths that add unwanted radiance to the signal, distorting surface reflectance retrievals. This scattering, often termed the adjacency effect, mixes light from adjacent areas into the sensor's field of view, impacting indices like the Normalized Difference Vegetation Index (NDVI) used for vegetation monitoring. Landsat satellites employ atmospheric correction in their processing pipeline to mitigate these effects, achieving NDVI errors below 5% in corrected imagery.^[59]^[60] In photography, stray light primarily appears as lens flare triggered by off-axis light sources, such as the sun positioned just outside the frame, which bounces internally off lens elements to create haze or ghosting artifacts that lower overall image contrast. This reduces color fidelity in portraits by veiling shadows and desaturating skin tones, making subtle details harder to discern.^[61]^[62] Smartphone cameras are especially prone to internal reflections from stray light, resulting in purple fringing along high-contrast edges, often due to interactions between infrared light and lens coatings in compact optics. The flare index in photography, defined as the veiling glare percentage—calculated as the ratio of luminance in dark regions to the uniform field luminance—helps quantify affected image area, with typical values indicating up to several percent degradation in uncorrected scenarios.^[63]^[64]

Mitigation Strategies

Design and Baffling Techniques

Baffling strategies are fundamental structural approaches to intercept and redirect unwanted light paths in optical systems, primarily by employing vane and edge baffles to block off-axis rays that could otherwise scatter into the image plane. Vane baffles consist of protruding radial structures attached to the inner walls of cylindrical or conical enclosures, designed to obstruct direct line-of-sight paths from external sources to sensitive optics while minimizing self-illumination through shadowed regions. These vanes are optimized to eliminate first-order stray light, where light reflects once off internal surfaces before reaching the detector, by ensuring that no single bounce allows illumination of subsequent elements.^[65] Edge baffles, often integrated along the rims of apertures or mirrors, further prevent peripheral light leakage by creating opaque barriers that absorb or deflect rays incident at grazing angles. In telescope designs, honeycomb structures enhance this by forming a cellular array at the baffle entrance, which fragments incoming off-axis light into multiple small apertures, suppressing transmission through geometric vignetting and reducing the effective entrance pupil for stray rays. This configuration achieves stray light suppression comparable to traditional tubular baffles but with significantly reduced overall length, as demonstrated in Cassegrain systems where point source transmittance drops below 10^{-10} for angles exceeding the rejection threshold.^[66] Aperture control complements baffling by precisely defining the beam's spatial extent, using field stops and Lyot stops to limit divergence and exclude extraneous light. A field stop, positioned at an intermediate image plane, restricts the field of view to only the desired angular range, thereby preventing off-field sources from directly projecting onto the detector and reducing the illumination of downstream surfaces.^[67] This limits the etendue of the system, confining light propagation within the intended solid angle and blocking rays from beyond the object plane's boundaries. Lyot stops, placed in planes conjugate to the entrance pupil, specifically target diffracted light by undersizing the aperture to intercept rings generated at occluder or lens edges, as seen in coronagraphs where a 4.0 cm stop blocks diffraction from a 4.7 cm entrance, reducing stray light to levels below 5 \times 10^{-6} times the solar disk brightness.^[68] Together, these stops minimize beam spread, ensuring that only on-axis light contributes to the final image while redirecting divergent rays away from critical paths. Advanced techniques refine baffle performance by addressing diffraction effects at edges, such as serrating the boundaries to disperse scattered energy away from the optical axis. Serrated or stellated edges on baffle apertures alter the diffraction pattern, redirecting forward-glancing waves into non-imaging directions and substantially lowering the stray light contribution from edge scattering, particularly in compact systems where smooth edges would otherwise produce focused ghosts.^[69] Ray-tracing optimization, conceptually implemented in software like Zemax OpticStudio's non-sequential mode, iteratively simulates light propagation to evaluate baffle placements and edge geometries, splitting rays to model scattering and convergence until stray paths are minimized without exhaustive computation.^[70] Early innovations in baffle design emerged during World War II in the 1940s within military optics for night-vision devices, where active infrared systems required enclosures to shield image converters from ambient light and backscatter, laying groundwork for modern vane-based suppression in low-light environments.^[71] Through iterative geometric refinement, these techniques target a stray light fraction below 0.1%, ensuring high-fidelity imaging by confining unwanted light to negligible levels relative to the primary signal.^[72]

Materials and Coatings

Absorptive materials play a crucial role in minimizing stray light by maximizing light absorption within optical systems. Black paints, such as Vantablack developed by Surrey NanoSystems, consist of vertically aligned carbon nanotube arrays that achieve absorptance levels up to 99.965% across the visible spectrum, effectively trapping incident photons to prevent reflection or scattering. As of 2025, sprayable variants like Vantablack 310 have been developed for enhanced durability in space applications, used in satellite optics to minimize stray light.^[73]^[74] Anodized aluminum, commonly used for baffles, provides a porous surface that enhances absorption in the visible range through diffuse scattering, though its effectiveness diminishes in the near-infrared, where it can appear reflective like polished metal.^[75] Anti-reflective (AR) coatings and specialized surface treatments further reduce stray light by suppressing surface reflections. Multilayer AR coatings, typically composed of alternating high- and low-index dielectric films, can lower reflectance to below 0.5% over targeted wavelength bands, enabling higher light transmission through optical elements while minimizing ghost images from unwanted reflections.^[76] For baffles, matte finishes—achieved via chemical etching or abrasive treatments—promote diffuse rather than specular reflection, scattering stray light away from sensitive detectors and reducing overall system noise.^[11] A notable advancement in absorptive coatings for stray light control is NASA's adoption of gold-black deposits for infrared instruments, dating back to the 1960s in early spaceflight Fourier transform spectrometers. Gold-black, a fractal-like aggregation of gold nanoparticles evaporated in a low-pressure environment, offers near-unity absorptance (over 98%) in the mid- to far-infrared, enhancing detector sensitivity by absorbing thermal radiation that could otherwise contribute to stray signals.^[77]^[78] This coating's development addressed the need for broadband absorption in cryogenic environments, where traditional paints degrade. Despite their benefits, these materials and coatings involve trade-offs related to wavelength dependence and environmental durability. For instance, many black coatings like anodized aluminum exhibit high absorptance in the visible (around 90%) but much lower in the near-infrared.^[75] Durability under space conditions, including vacuum exposure and temperature extremes from -200°C to +200°C, poses challenges; while gold-black withstands moderate thermal cycling, some nanotube-based coatings like Vantablack may suffer adhesion loss or structural degradation without protective overcoats, balancing optical performance against mechanical robustness.^[79]^[80] The fundamental principle underlying reflection in these systems is described by the Fresnel equations for a single interface between media of refractive indices n_1 and n_2, where the normal-incidence reflectance R is given by

R = \left| \frac{n_1 - n_2}{n_1 + n_2} \right|^2.

For air-glass interfaces (n_1 \approx 1, n_2 \approx 1.5), this yields R \approx 4\%, highlighting the need for AR multilayers that constructively interfere destructive waves across multiple layers to approach zero reflectance conceptually.^[81]

Analysis and Tools

Modeling Methods

Modeling stray light in optical systems relies on computational techniques that simulate the propagation and interaction of light rays or waves beyond the intended optical path. Ray-tracing models, particularly those based on Monte Carlo methods, are the cornerstone for predicting scatter and multiple reflections that contribute to stray light. In these approaches, a large number of rays are launched stochastically from sources, tracing their paths through the system while accounting for reflections, refractions, absorptions, and scattering at each surface encounter. This statistical sampling enables the estimation of irradiance distributions from unwanted light paths, providing quantitative predictions of stray light levels at detectors or image planes.^[82] To address the computational intensity of standard Monte Carlo simulations, importance sampling techniques are integrated to bias ray generation toward regions or paths likely to produce significant stray light, such as near specular reflections or high-scatter surfaces. By adjusting the probability density of ray directions and positions, these methods reduce variance in the results and accelerate convergence without sacrificing accuracy, making them suitable for complex systems with millions of rays. For instance, in baffle design evaluations, importance sampling focuses on critical zones like aperture edges, yielding reliable stray light fractions in simulations that would otherwise require prohibitive computation times.^[83] Wave-optics methods complement ray-tracing for scenarios where diffraction dominates stray light contributions, such as in systems with small apertures or periodic structures. The finite-difference time-domain (FDTD) approach discretizes Maxwell's equations on a spatiotemporal grid to simulate electromagnetic wave propagation, capturing near-field diffraction patterns and interference effects that geometric ray models overlook. FDTD is particularly valuable for modeling stray light from gratings, edges, or microlens arrays, where it predicts angular scattering distributions with high fidelity, enabling the assessment of diffracted orders that leak into the field of view. These simulations often couple with ray-tracing in hybrid frameworks to span micro- and macro-scale effects across an optical design.^[84] Specialized software tools streamline these modeling efforts by providing integrated environments for stray light analysis. TracePro, from Lambda Research Corporation, employs Monte Carlo ray tracing with support for bulk scatter, fluorescence, and polarization, allowing users to import measured bidirectional reflectance distribution function (BRDF) data as input parameters for surface scattering models. This enables detailed simulations of stray light paths in imaging and non-imaging systems, with visualization tools to identify dominant contributors like ghost images or veiling glare. Similarly, FRED Optical Engineering Software, developed by Photon Engineering, facilitates stray light predictions through non-sequential ray tracing and BRDF-based scatter, incorporating models like Harvey-Shack for rough surfaces; it handles complex geometries and thermal effects, aiding in the optimization of optomechanical layouts. Both tools require BRDF specifications, typically derived from measurements, to accurately represent material reflectance properties in the simulation.^[85]^[86] Central to scatter prediction in these models is the bidirectional reflectance distribution function (BRDF), which describes the angular distribution of reflected light from a surface. Mathematically, it is expressed as

f_r(\theta_i, \theta_s) = \frac{dL_r}{dE_i \cos \theta_i},

where dL_r represents the differential reflected radiance in the outgoing direction defined by zenith angle \theta_s, dE_i is the differential incident irradiance from the incoming direction with zenith angle \theta_i, and the cosine term normalizes for the projected area. This function allows simulations to compute the fraction of incident light scattered toward specific detectors, essential for quantifying stray light irradiance from off-specular reflections. BRDF data, often wavelength-dependent, are fitted to empirical models like Lambertian or Harvey-Shack to extrapolate measurements across untested angles, improving the fidelity of stray light forecasts in diverse optical configurations.^[84] Validation of these modeling methods involves benchmarking simulation outputs against empirical data from controlled tests, such as benchtop stray light measurements using calibrated sources and detectors. Comparisons typically demonstrate high agreement, confirming the reliability of Monte Carlo and FDTD approaches for design iteration and performance verification. Such assessments ensure that models capture real-world behaviors, including material variabilities and alignment tolerances, while guiding refinements to achieve desired suppression levels.^[87]

Measurement and Testing

Testing setups for quantifying stray light in optical systems often employ integrating spheres to provide uniform illumination across the field of view, simulating diffuse stray light sources and enabling the measurement of veiling glare under controlled conditions.^[88] The sphere's diameter should exceed 10 times the focal length of the lens under test to minimize edge effects and ensure isotropic radiance, as recommended in relevant optical testing protocols.^[88] Alternatively, point-source stray light tests use a collimated laser or monochromatic source positioned at various off-axis angles to evaluate direct and scattered light contributions, with the point source transmittance (PST) calculated as the ratio of off-axis to on-axis irradiance to assess system rejection of extraneous rays.^[89] These setups can achieve PST levels below 10^{-7} in high-performance space optics, indicating effective stray light suppression.^[89] Key metrics for stray light quantification include the veiling glare index (VGI), defined under ISO 9358 as the ratio of irradiance at the center of a small black disk image to the surrounding uniform field irradiance, providing a measure of overall image degradation from stray light. This standard outlines both integral (black patch) and analytical (glare spread function) methods for VGI determination, applicable to image-forming systems like lenses and cameras. The stray light index (SLI), often used in automotive optics, quantifies scattered light transmission through materials or assemblies by comparing luminance in clear versus obscured paths, with values below 1% indicating low degradation.^[90] For spectral stray light characterization, double monochromator configurations are employed to isolate wavelengths with minimal contamination, achieving extremely low stray light levels by sequentially filtering input and output beams to suppress higher-order diffraction and scattering.^[91] This setup is particularly effective in UV-Vis spectrophotometers, where stray light can distort absorbance readings above 2.^[91] Imaging polarimetry techniques further enable scatter characterization by resolving the polarization state of stray light paths, distinguishing between specular reflections and diffuse scattering in polarimetric cameras through Stokes parameter analysis of off-axis sources.^[92] Such methods have been applied to metasurface-based polarimeters, revealing polarization-dependent stray light contributions that vary by up to 20% across field angles.^[92] In spectrometers, the floodlight test procedure illuminates the entrance aperture uniformly across the spectrum to measure the stray light fraction (SLF), defined as the ratio of detected signal outside the nominal bandpass to the total input flux, typically using cut-off filters like sodium salicylate for UV validation.^[93] This test scans wavelengths from 200 to 800 nm, quantifying SLF variations that peak near grating blaze orders, with well-designed systems maintaining SLF below 0.01%.^[93] Modeling methods can inform pre-test predictions of these SLF profiles to optimize test parameters. Recent advancements in the 2020s include hyperspectral imaging for in-situ stray light assessment during field deployments, as demonstrated in the EnMAP satellite mission, where on-ground calibration corrects spectral stray light in push-broom imagers to achieve sub-1% error in Earth observation data.^[94] These systems use onboard uniform illumination sources to monitor SLF in real-time, enabling adaptive corrections for environmental stray light in remote sensing applications.^[94]

References

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[PDF] Overview of Stray Light Part 1
What is stray light? • Stray light refers to any unwanted light in an optical systems. Stray light is a problem in both imaging and non‐imaging systems.
[2]
What is Stray Light and How is it Analyzed? - Ansys
Stray light is the unintended, unwanted light that interferes with sensors in an optical system. Think of the sunbursts that speckle outdoor photos.
[3]
Understanding Stray Light: Impact, Causes, and Solutions in Optical ...
Feb 5, 2025 · Stray light refers to unwanted electromagnetic radiation that disrupts the intended performance of an optical system.
[4]
Stray Light Causes and Reduction Gigahertz-Optik
An overview of the causes and effects of stray light as well as ways to reduce stray light in array spectrometers/array spectroradiometers.
[5]
https://lambdares.com/news/mastering-stray-light-visualize-and-eliminate-unwanted-light-paths
[6]
Stray Light Analysis and Control - NASA ADS
Stray light is defined as unwanted light in an optical system, a familiar concept for anyone who has taken a photograph with the sun in or near their ...
[7]
[PDF] Introduction to straylight
In an optical system, straylight refers to the light redirected by the process of light scattering out of an intended path defined by the optical design.
[8]
Basic Radiometry for Stray Light Analysis - SPIE Digital Library
If absorption losses are neglected, radiance is conserved through an optical system, and thus the radiance of an image is the same as the radiance of the exit ...
[9]
[PDF] Stray Light Analysis of a Mobile Phone Camera
Note that at the specular angle the BSDF is maximum. From a conservation of energy point of view, it can be understood that energy is conserved along the ray ...
[10]
Stray Light - an overview | ScienceDirect Topics
Stray light is defined as radiation at wavelengths outside of the instrumental bandpass that unintentionally reaches the detector, caused by imperfections ...
[11]
Limits of spectral resolution in optical measurements
Aug 22, 2014 · The developments in the second half of the 19th century ... To go over this one in a million limit special care must be taken with stray light, ...<|separator|>
[12]
Optical System Optimization: Analyzing the Effects of Stray Light
Stray light can impede the performance of any optical system. With a deeper understanding of stray light, and the right tools, optical engineers can predict ...Missing: fraction SLF
[13]
[PDF] Stray Light Correction - NOAA
In UV-RSS the stray light is reduced by using dynamic range compressing fore-optics (Kiedron et al. ... Stray Light Fraction. Average. Cut-on Wavelength λc.
[14]
Rayleigh Scattering – optical fibers, propagation loss - RP Photonics
Rayleigh scattering is light scattering by centers much smaller than the wavelength. It is responsible for the phenomenon of the blue sky, for example.
[15]
[PDF] Classical, Non-Relativistic Theory of Scattering of Electromagnetic ...
We present here the theory of scattering of electromagnetic radiation from the classical, non- relativistic physics approach. A quantum-mechanical, fully- ...
[16]
Gustav Mie and the Evolving Discipline of Electromagnetic ...
The year 2008 marks the centenary of the seminal paper by Gustav Mie on electromagnetic scattering by homogeneous spherical particles.
[17]
Specular and Diffuse Reflection - Evident Scientific
Specular reflection is defined as light reflected from a smooth surface at a definite angle, and diffuse reflection, which is produced by rough surfaces.Missing: stray | Show results with:stray
[18]
Did You Know? Edge vs. Aperture Diffraction in Optics
Jul 15, 2024 · Edge and aperture diffraction occurs when light is partially blocked by an edge and is then bent or diffracted. ... TracePro can model diffraction ...
[19]
Diffraction Grating Anomalies - Newport
Diffraction Grating Anomalies. In 1902. R. W. Wood observed that the intensity of light diffracted by a grating generally changed slowly as the wavelength was ...Missing: stray | Show results with:stray
[20]
Stray light characterization with ultrafast time-of-flight imaging - PMC
May 12, 2021 · Close to 0 ps, scattering due to surface roughness of the lenses creates SL over the entire slit, with an irradiance decreasing away from y0.
[21]
[PDF] FOREOPTICS AND SLIT VIEWER OPTICAL DESIGN
Oct 15, 2010 · Stray light from surface scatter (i.e. wide angle scatter) arises from mid-frequency and high-frequency. (roughness) spatial errors of optical ...
[22]
[PDF] Ghost image analysis
This light is known as stray light, flare, veiling glare, and ghost images. Ghost images of bright objects. Ghost images of the aperture stop. Ghost pupils ...Missing: multiple | Show results with:multiple
[23]
[PDF] System Throughput Stray & Scattered Light Analysis Ghost Image ...
With refractive elements secondary reflections will cause unwanted ghost images. All combinations of two-surface ghost in the LSST optical system have been ...
[24]
Michelson Interferometer for Global High-resolution Thermospheric ...
Light from outside the FOV can only enter the optical system by reflection off of baffle structures and then onto an optical surface. ... Geometry of MIGHTI ...
[25]
[PDF] Stray Light Considerations in the Design of Near-Earth Object ...
Stray light can be caused by a wide variety of sources such as extraneous sources of light, particulate contamination on the surface of optics, and artifacts ...Missing: SLF | Show results with:SLF
[26]
On Fabry–Pérot Etalon-based Instruments. I. The Isotropic Case
Mar 7, 2019 · We find that the unavoidable presence of imperfections in the telecentrism produces a decrease of flux of photons and a shift, a broadening and ...
[27]
Moving Target Scattered Light Considerations
Dec 1, 2022 · Sources of scattered light include glints off optical mounts (including the secondary mirror struts) and diffuse scattering caused by ...
[28]
Toward a Data-driven Model of the Sky from Low Earth Orbit as ...
In this work, we quantify the impact of stray light on sky observations made by the Hubble Space Telescope (HST) Advanced Camera for Surveys. By selecting on ...Missing: albedo | Show results with:albedo
[29]
Simulation of External Stray Light for FY-3C VIRR Combined with ...
One kind of stray light, which is called the external stray light, comes from external radiation sources, which mainly include the Sun, the Moon, and ground gas ...
[30]
Analysis and Reduction of Solar Stray Light in the Nighttime Imaging ...
Mar 6, 2019 · The ground illumination of the full moon is only 0.2 lux. Compared with the typical illumination of the ground with artificial lights (from ...
[31]
Analysis and correction of stray thermal radiation in infrared optical ...
Four main types of stray-light sources are possible in an optical system. The first type is external stray light, which comes from strong external light sources ...
[32]
[2310.17322] The rate of satellite glints in ZTF and LSST sky surveys
Oct 26, 2023 · We assess the impact of satellite glints -- rapid flashes produced by reflections of a sunlight from flat surfaces of rotating satellites -- on current and ...Missing: stray light
[33]
[PDF] Dark and Quiet Skies for Science and Society - NOIRLab
Jul 8, 2020 · ... zodiacal light, auroral light, moonlight, gegen- ... parency (often known as atmospheric “windows”) that is required for ground-based observations ...
[34]
[PDF] Volume 31, Stray Light in the SeaWiFS Radiometer
ABSTRACT (Maximum 200 words). Some of the measurements from the Sea-viewing. Wide Field-of-view. Sensor (SeaWiFS) will not be useful as ocean measurements.
[35]
Variation of outdoor illumination as a function of solar elevation and ...
Jun 7, 2016 · Starlight on a clear night has a brightness of ~0.001 lux, and moonlight ~0.2 lux. In comparison, sunlight may be as intense as 100,000 lux. The ...
[36]
https://pmc.ncbi.nlm.nih.gov/articles/PMC4895134/
[37]
Stray Light Analysis – Telescope System On-Axis - Ansys Optics
Here, SNR is defined as: SNR = Signal/Noise. Signal Flux. (Imaging Path) mW. Noise Flux (Stray Light) mW ...
[38]
[PDF] Stray Light Analysis with ASAP
ASAP simulates stray light using 3D modeling and optical properties, including scatter, ghost imaging, diffraction, and thermal emission. Stray light analysis ...
[39]
[PDF] Stray light control for the space-agile optcial system with pointing ...
If the background stray light of the space optical communication system ... SNR = Nobject √Nd + Nobject + Nsun. ⁄. (15). The ...<|control11|><|separator|>
[40]
None
### Summary of Stray Light Effects in UV-Vis Spectroscopy
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Errors in Spectrophotometry and Calibration Procedures to Avoid ...
If the stray light occurs exclusively at the longwave or shortwave side, like at the ends of the spectral range, the substance may only have a longwave or ...
[42]
How does stray light influence high absorbance measurements?
Stray light photometric artifacts always yield lower than actual absorbance values. The percent error from Beer's Law linearity due to the consequences of stray ...
[43]
Simulation of Instrumental Deviation from Beer's Law
The most serious effect is caused by stray light that is not absorbed at all by the analyte at all; this is called unabsorbed stray light. This effect also ...<|control11|><|separator|>
[44]
https://www.ssi.shimadzu.com/service-support/faq/uv-vis/resolution-and-stray-light/4/index.html
[45]
Raman Spectroscopy (all content)
The chief difficulty in Raman spectroscopy is preventing overlapping of the Raman signal by stray light from the far more intense Rayleigh scattering.
[46]
[PDF] the JWST backgrounds - NASA Technical Reports Server (NTRS)
We describe the sources of stray light and thermal background that affect JWST observations; re- port actual backgrounds as measured from commissioning and ...
[47]
How Dark the Sky: The JWST Backgrounds - IOPscience
We describe the sources of stray light and thermal background that affect JWST observations, report actual backgrounds as measured from commissioning and early ...
[48]
The increasing effects of light pollution on professional and amateur ...
Jun 15, 2023 · This Review discusses how it is becoming increasingly difficult for professional and amateur astronomers to observe the night sky because of light pollution.
[49]
Light Pollution - NOIRLab
Light pollution is growing globally at an estimated rate of 2% to 6% per year and is reducing darkness everywhere, including at observatory sites.
[50]
[2205.16002] Towards a data-driven model of the sky from low Earth ...
May 31, 2022 · In this work we quantify the impact of stray light on sky observations made by the Hubble Space Telescope (HST) Advanced Camera for Surveys. By ...
[51]
James Webb Space Telescope stray light performance status update
Sep 21, 2012 · The architecture has the telescope exposed to space, with a large sun shield providing thermal isolation and protection from direct illumination ...
[52]
Stray light performance for the James Webb Space Telescope
Aug 9, 2025 · Although the sunshield would still fully protect the telescope from the Sun, there are times when the Earth and the Moon could shine on the ...
[53]
Microwave Observations and Modeling of a Lunar Eclipse
Microwave observations of the Moon during the eclipse of November 28-29, 1993, are reported. Observations were made at 1.327 mm wavelength with a 12-m-aperture ...Missing: astronomical moonlight 1990s
[54]
[PDF] Chapter 1 Solar Coronagraphs
The French astronomer Bernard Lyot invented the coronagraph in the 1930s and ... most sensitive solar coronagraphs suppress stray light to the order of 10−12 of ...
[55]
Reduction of Scattered Light in the Coronagraph
In his patient analysis of the scattering by a simple objective lens Lyot distinguished five sources of stray light which can all be seen clearly in a lens ...
[56]
Performance of the hybrid externally occulted Lyot solar coronagraph
By creating artificial eclipses, the first Lyot solar coronagraph was a breakthrough for the study of the solar corona (Lyot 1939; Dollfus 1983). The ...
[57]
[PDF] 1. lNTRODUCfION ATMOSPHERIC EFFECf ON REMOTE SENSING ...
This effect, called the adjacency' effect, is due to light renected from the ground surrounding a sensor's field-of-view and then scattered into the field·of- ...Missing: stray | Show results with:stray
[58]
[PDF] Characteristics of Landsat 8 OLI-derived NDVI by comparison with ...
Apr 23, 2015 · Atmospheric correction significantly reduced the NDVI error. At the deciduous forest site, both Landsat 7 ETM+ and Landsat. 8 OLI NDVI ...
[59]
What is Lens Flare and How to Deal with it in Photography
Apr 12, 2020 · Lens flare occurs when light from a bright source reflects off lens elements, causing haze, halos, or other artifacts in images.
[60]
(PDF) Stray light and shading reduction in digital photography
Aug 9, 2025 · Stray light reduces contrast and causes color ... Even small amounts of stray light adversely affect digital-camera color fidelity.
[61]
iPhone 5, photography, purple fringing, and what you need to know
Oct 8, 2012 · The most likely cause of the iPhone 5's purple haze is probably lens flare and internal reflections in the camera lens assembly.
[62]
Veiling Glare - Imatest
Veiling glare is measured by photographing one or more perfectly black regions inside a uniform white field that extends well beyond the image frame.Missing: L_object) | Show results with:L_object)
[63]
[PDF] Fest Chapter 9
... internal stray light path from self-emission of the housing around the detector. The design of any of these baffles should be performed as early in the optical.
[64]
Design of CASSEGRAIN telescope baffles with honeycomb entrance
The honeycomb-look front baffle guarantees a comparable performance of stray light suppression with traditional tube baffle, while reducing the size greatly.
[65]
[PDF] Stray light techniques
• A field stop limits the size of the field of view passing through the system to the sensor. • All optical systems have at least one field stop: the image ...Missing: divergence | Show results with:divergence
[66]
LASCO HANDBOOK CHAPTER 4
A field lens re- images the objective lens and its diffraction pattern, but a "Lyot stop" prevents the diffraction ring from reaching the focal plane, and a " ...
[67]
[PDF] USE OF STELLATED APERTURES TO MINIMISE INTERNAL ...
In this paper, the use of cheap and easy-to-make 3D printed baffles with stellated internal edges is demonstrated. Figure 1 shows the forward diffraction off ...
[68]
An Introduction to Stray Light Analysis Using Ansys Zemax OpticStudio
Sep 5, 2024 · Ray tracing to identify stray light paths: In non-sequential mode, Zemax OpticStudio uses ray tracing to simulate how light behaves as it ...
[69]
Seeing in the Dark: The History of Night Vision
May 19, 2017 · The history of night vision devices goes back to just before World War II, when Germany developed primitive infrared devices, and the Allies followed suit.Missing: baffle designs 1950s<|separator|>
[70]
Stray Light - Sarspec
Mar 11, 2025 · When using UV/Vis spectroscopy, stray light introduces an error in the measured absorbance value. The absorbance readings begin to decrease due ...
[71]
Vantablack | Ultra black paint
We lead in advanced nanomaterials with Vantablack®—the world's blackest coating, absorbing up to 99.965% of light. Designed to eliminate stray light and ...
[72]
[PDF] Black Coatings to Reduce Stray Light
Black anodized aluminum may be black in the visible spectrum, but is nowhere near so absorbing in the infrared spectrum. I have viewed many black anodized ...
[73]
Ultrathin Ge-YF3 antireflective coating with 0.5 % reflectivity on high ...
Aug 27, 2024 · In this study, we use discrete-to-continuous optimization to design a subwavelength-thick antireflective multilayer coating on high-refractive index Si ...
[74]
[PDF] 50 Years of Spaceflight with Fourier Transform Spectrometers (FTS ...
These were constructed of gold foil attached to p- and n-doped bismuth telluride posts, with gold-black coating to improve long-wavelength absorption. The ...
[75]
A comparative analysis of opto-thermal figures of merit for high ...
Such “space black” coatings are typically applied by vacuum deposition or spraying processes. ... For a black coating, this temperature dependence is moderate.
[76]
Black Coatings - RP Photonics
Strong absorption in the infrared and visible ranges is important, also a long lifetime and the durability at elevated temperatures.
[77]
Fresnel Equation - an overview | ScienceDirect Topics
The Fresnel equations refer to a set of mathematical formulas that describe the reflection and transmission of light at the boundary between two different ...
[78]
Optical Modeling and Performance Predictions X | (2018) - SPIE
Nov 5, 2018 · Variations of Monte Carlo ray tracing are the most popular techniques for computing stray light in optical systems. The simplest and easiest ...
[79]
Optical Systems Design 2015: Optical Design and Engineering VI
Oct 12, 2015 · In stray light calculations the concept of important sampling is used to reduce computational effort. ... Conventional Monte Carlo based non ...
[80]
https://www.rp-photonics.com/black_coatings.html
[81]
Optical and Illumination Simulation, Design & Analysis Tool. TracePro
TracePro is used to analyze non-imaging aspects of imaging systems, such as stray light, polarization effects, thermal loading, bulk scatter, and fluorescence.TracePro Applications · TracePro Support · TracePro Current Release · Free TrialMissing: BRDF | Show results with:BRDF
[82]
Effective cross sections for stray light calculations in laser ...
Jun 11, 2021 · This work describes a method used to calculate the amount of stray light able to couple to the detectors and create disturbing interference on the measurements.Missing: achieving | Show results with:achieving
[83]
https://spie.org/Publications/Proceedings/Volume/9626
[84]
https://opg.optica.org/oe/fulltext.cfm?uri=oe-29-23-37639
[85]
Stray Light Measurement for Point Source Transmittance of Space ...
The tests were performed to estimate stray light characteristics of two optical instruments. Test results demonstrated PST performance below 1×10-7 at visible ...
[86]
Characterization of the sandblasted glass degradation by light ...
It is well known that the most modern techniques use the Scattered Light Index “SLI” as a measure of windscreen degradation. In this study, we have calculated ...
[87]
Characteristics of Single and Double Monochromator UV-VIS ...
A double monochromator spectrophotometer with extremely low stray light is used for measurements of samples with high absorbance, as shown in Fig. 2. Fig. 2 ...What Is a Monochromator? · Stray Light · Configuration of Single and...
[88]
Evaluation and characterization of imaging polarimetry through ...
This work presents methods and practical considerations involved in producing accurate polarization data from a metasurface-based Stokes imaging polarimeter.
[89]
Stray Light in Monochromators and Spectrographs - Newport
Other unwanted light, called stray light, has several causes and should be minimized for both monochromators and spectrographs.Causes Of Stray Light · Designing A System To... · F/# Matching Reduces Stray...Missing: overlaps | Show results with:overlaps
[90]
(PDF) Stray Light Calibration and Correction of EnMAP's Imaging ...
Aug 6, 2025 · We report on the on-ground stray light calibration of the hyperspectral Environmental Mapping and Analysis Program (EnMAP) satellite mission ...