Apodized hollow conical occulter with gradient transmittance for stray-light suppression

To satisfy a space patrol telescope system with high angular resolution, large space area and high stray light suppression, the stray light environmental characteristics at low earth orbit are summarized. In accordance with the parameters, which diameter is 1.5m, focal length is 20m, field of view is 1.1°×1°, and the optical and mechanical structure joint-design stray light suppression is compared and analyzed for on-axis cross type, off-axis back end type and off-axis sideway type. A method of optical and mechanical structure joint-design stray light suppression is proposed to reduce the stray light suppressing angle to enhance the efficiency of the observation time and sky patrol efficiency in orbit. The detailed stray light suppression design and optimization of off-axis sideway type is given. The simulation and analysis of total optical and mechanical periodic line is presented, and the major stray ray path is simulated and analyzed.Compared with the other two types, the off-axis sideway type presents the best performance of image quality and stray light suppression. The modulation transfer functions (MTF) approach the diffraction limit at all fields. When the evadable angle out of the field is 40°, the PST is less than 10^-11 and the system can approach to the stray light suppression limitation.

The sources of stray light were briefly introduced and the necessity of stray light suppression was analyzed. Strong stray light often directly affected the performance of space debris detection camera and even invalidated it. Therefore, the application of stray light suppression in space debris detection camera was particularly important. The design of stray light suppression for space debris detection camera using baffle was proposed. On the basis of re-searching the source of stray light, the influences of the edge width of the baffle rings and the surfaces coating treatment scheme on the stray light suppression ability were finally determined. The stray light suppression ability of the baffle was greatly improved by exploring the limit of the mechanical processing of the baffle ring and optimizing the surface coating treatment method of the inner cavity of the baffle. At the same time, the stray light flow channel inside the optical system was optimized. The critical surfaces inside the optical system were found. After removing the critical surfaces, the stray light suppression design results showed the stray light rejection ratio reached 10-7 finally when off-axis angle was larger than 35°. The flares appearing on the detector disappeared completely in the experiments, and the signal-to-noise ratio was higher. The stray light suppression optimization obtained good results, which could better satisfy the requirements of space debris detection.

The stray light is one of the main factors affecting the imaging quality of optical remote sensor. The design and experimental verification of stray light suppression is also the key link in the design of aerospace optical remote sensor. This article based on the development needs of aerospace cameras in orbit, the stray light suppression analysis and product assurance of imaging remote sensing cameras with RC configuration as the optical system (or main optical system) were studied in a quantitative way. First of all, the stay light characteristics of such cameras were revealed in a quantitative way, the design and addition of the optimal stray light suppression structures were completed, and comprehensive simulation verification was carried out through the light path tracking method. Secondly, in the design stage, in strict accordance with the control requirements of the development of aerospace remote sensing camera, the necessary and reasonable product guarantee control point is set up by PDCA cycle method. Finally, through laboratory stray light qualitative tasting and on-orbit verification, the full-link verification of camera stray light suppression is completed. This paper can provide a reference for stray light suppression design and process quality control of large-caliber optical remote sensors.

The Spectral Imaging Coronagraph (SICG), deployed at Lijiang Observatory (3200m), is China’s first ground-based coronagraph and is part of the Meridian Project Phase II. It is an internal occulted coronagraph, and this paper describes its design and stray light suppression details. The SICG has a 200 mm aperture, an F-number of 6.7, and dual-channel observation capabilities at 530.3 nm (Fe XIV ) and 637.4 nm (Fe X ), with a Field of View (FOV) ranging from 1.05 to 2 R ⊙ ( R ⊙ represents the solar radius). Detailed stray light suppression methods are presented, including the use of ultra-smooth polishing techniques on the primary lens, five group of baffles and a Lyot Spot is employed to suppress corresponding stray light. A unique design was the addition of a primary lens monitoring system in the optical path, allowing the observation of dust adhesion on the lens simultaneously. Stray light measurement was conducted in the laboratory, with an inner FOV of 6 * 10 −6 B ⊙ ( B ⊙ represents the mean brightness of the solar disk) at 1.05 R ⊙ and an outer FOV of 2 * 10 −6 B ⊙ at 2 R ⊙ . These designs ensure that SICG can achieve stable and clear coronagraphic observations, and successfully captured its first image of the solar corona in 2023 October.

With the development of infrared imaging technology, especially high resolution imaging instrument for space remote sensing, the requirement of suppressing stray light the optical system is more and more high, thus suppression of stray light of IR detector module as the core device of target detection and imaging is important. The design and processing cold shield is the key of infrared focal plane detector dewar for suppressing stray light, which mainly play a role in suppressing stray light outside of field view and improving background limited detectivity of IR detector. The structure of the cold shield is mainly effect Geometry Composing Function (GCF) of the stray radiation transmission, while Black coatings of cold shield influence bidirectional reflectance distribution function (BRDF) of stray radiation transmission. This paper mainly study suppressing stray light of cold shield with black phosphating process and black nickel plating and point source transmittance (PST) is used as the evaluation index for suppression of stray light, which can be measured accurately. A PST test system in near infrared wave band has been set up for measurement of cold shield’s PST, which coupling infrared light source with light guide tube for greatly improving the uniformity of infrared light source, while the dynamic range of test system decrease slightly. After testing and verification, light source instability is less than 1% , Non uniformity of light source at the exit of the parallel light tube is 7.4%@ 87.5mm×87.5mm.and dynamic range of test system is 0～1.5×10-5, thus the test facility can satisfy PST test of stray light. The PST curve with angle for one stage cold shield with black phosphating process and black nickel plating are measured and consistent with numerical simulation, which first decrease rapidly with increase of the angle, then slowly vary after 35 angle for the structure of one stage cold shield, the results is useful for optimizing design of infrared detector modules for control of stray light.

Conference

Lund Observatory is presently designing and constructing a robotic telescope dedicated to studies of the Earth's albedo by measuring the ratio between the intensity of the dark and bright sides of the Moon. The telescope will operate both in broadband and narrow-band modes over the entire visible wavelength range and will transmit observational results back to the operation team over the Internet. Design challenges, in particular related to choice of CCD and stray light suppression, are described, together with the design of the optics, control system, and enclosure. Finally we present results from laboratory tests. The telescope will go into operation in the first half of 2011.

Stray light suppression is the main concern in designing a solar coronagraph. The main contribution to the stray light for an externally occulted space-borne solar coronagraph is the light diffracted by the occulter and scattered by the optics. It is mandatory to carefully evaluate the diffraction generated by an external occulter and the impact that it has on the stray light signal on the focal plane. The scientific need for observations to cover a large portion of the heliosphere with an inner field of view as close as possible to the photospheric limb supports the ambition of launching formation-flying giant solar coronagraphs. Their dimension prevents the possibility of replicating the flight geometry in a clean laboratory environment, and the strong need for a scaled model is thus envisaged. The problem of scaling a coronagraph has already been faced for exoplanets, for a single point source on axis at infinity. We face the problem here by adopting an original approach and by introducing the scaling of the solar disk as an extended source.

Stray light can directly influence the imaging quality and detection ability of space based detection system, and the stray light suppression of earth radiation is a key question needed to be considered by on-orbit detection system. First the basic principle and the mathematical model of stray light were analyzed here, then by using simulation analysis the requirements of stray light suppression under different imaging situations were obtained, this could be supportable for the design of space-based detection system.

Pancake virtual reality head-mounted displays (VR-HMDs) have attracted the attention of researchers in both academia and industry because of the compact size and light weight. However, owing to the use of optical path folding, there exist various stray lights in the optical system, which seriously degrades user experience. In this study, we analyze the causes and effects of multiple types of stray light systematically and design a VR-HMD with low stray light, large exit pupil diameter (EPD), compact form and light weight. Subsequently, several effective stray light suppression solutions are proposed and implemented. Finally, a prototype of a compact pancake VR-HMD system is successfully demonstrated. The prototype has stray light of less than 2.3%, a diagonal field of view (FOV) of 96° and an EPD of 10 mm at an 11 mm eye relief (ERF).

The Martin Black process has been used to coat baffles on a wide variety of visible and ultraviolet range instruments. Its infrared applications include baffles for the Infrared Astronomy Satellite and the Spacelab 2 Infrared Telescope. Because of the increased emphasis on stray light suppression in the infrared, the Martin Black process was modified with the objective of creating a better black surface for use in the near-, mid-, and far-infrared regions. These modifications resulted in the creation of an infrared absorbing surface, called Infrablack, which retains the excellent visible absorption properties of its predecessor and has increased infrared absorption. Hemispherical and specular reflectivity and bidirectional reflectance distribution function (BRDF) measurements were made on the Infra-black surface. The specular reflectance at 17° incidence ranges from less than 1% at 60 i.im to less than 15% at 450 /um. BRDF measurements made at the University of Arizona at 10.6 pm, at incidence angles of 10°, 30°, and 60°, indicate that the surface behaves in a nearly Lambertian manner at this wavelength. At 10 incidence the BRDF for Infrablack is about one-seventh that of Martin Black, and the curve is noticeably flatter.

A computer program for straylight suppression system design and analysis was developed to analyze various proposed LST straylight suppression systems. Simultaneously, experimental measurements are being made on a simplified LST straylight suppression system in a unique facility. The experimental measurements are being used to verify and improve the computer program. The facility represents the state-of-the-art in straylight suppression measurements, and transmission factors of 10 to the minus 12th power have been measured.

Within this work we propose and demonstrate a technological approach to efficiently suppress excitation laser stray-light in resonance fluorescence experiments on quantum dot micropillars. To ensure efficient stray-light suppression, their fabrication process includes a planarization step and subsequent covering with a titanium mask to fabricate self-aligned apertures at the micropillar positions. These apertures aim to limit laser stray-light in the side-excitation vertical-detection configuration, while enabling detection of the optical signal through the top facet of the micropillars. The beneficial effects of these apertures are proven and quantitatively evaluated within a statistical study in which we determine and compare the stray-light suppression of 48 micropillars with and without metal apertures. Actual resonance fluorescence experiments on single quantum dots coupled to the cavity mode prove the relevance of the proposed approach and demonstrate that it will foster further studies on cavity quantum electrodynamics phenomena under coherent optical excitation.

An optical inter-satellite communication link should be capable to operate even when the Sun comes close to the pointing direction of one terminal. Therefore straylight suppression at small Sun aspect angles is one of the topics in the Tx/Rx optics design. Each terminal should also be capable to simultaneously transmit and receive laser signals. Therefore, backreflection of transmitted laser light into the receiving channel also has to be care-fully investigated.

Ultra-high-magnification zoom electronic endoscopes are highly susceptible to stray light because compact optomechanical layouts and zoom-dependent optical reconfiguration strongly affect non-imaging light propagation. In compact systems with a small-aperture moving lens group, indiscriminate barrel blackening is not always desirable because coating degradation or peeling may compromise imaging reliability. This study presents a simulation-guided, state-dependent stray light analysis and suppression strategy for a compact ultra-high-magnification zoom endoscope. Monte Carlo ray tracing was performed at different zoom positions to identify the dominant stray light paths in the conventional, low-magnification, and high-magnification modes. The results show that the dominant sources vary significantly with zoom state; as the system moves toward near-focus and high-magnification operation, changes in group position, back focal distance, and ray geometry increase interaction with critical surfaces, leading to stronger ghosting and background stray light. Based on this analysis, targeted suppression measures were implemented at the corresponding critical locations, including reflectance optimization of key optical interfaces, selective blackening of lens edges and mechanical surfaces, and local baffling. Both simulation and experiment confirm that the proposed strategy effectively suppresses ghost artifacts and background stray light while improving image contrast, luminance uniformity, and detail visibility, especially in the high-magnification mode. This work provides a practical framework for state-dependent stray light control in compact ultra-high-magnification zoom endoscopes.