Entrance Pupil Research Articles

An improved methodology for quantifying pixel-scale entrance pupil irradiance of a Moon-based Earth radiation observatory

The establishment of a Moon-based Earth Radiation Observatory (MERO) is expected to improve current Earth radiation budget observations. In terms of the MERO instrument design, the pixel-scale entrance pupil irradiance (EPI), which acts as the true input radiation to the MERO detector unit, is essential to judge the detector optimization and systematic parameter adjustment. The primary motivation of this study is to improve the pixel-scale EPI quantification quality by proposing a modified methodology. Evaluations indicated that the new pixel ground field of view (GFOV) positioning method would bring accuracy improvements of 7.79% and 3.84% for pixel-scale shortwave (SW) EPI and longwave (LW) EPI quantifications respectively; while the accuracy enhancements result from the newly proposed Earth top of atmosphere (TOA) radiant anisotropy method in this study are about 20.67% and 12.15% for the pixel-scale SW EPI and LW EPI estimations respectively. Following this modified methodology, an 18.6-year pixel-scale EPI variability prediction was accomplished to facilitate the MERO instrument design coping with change in future decades. This prediction fully considers the influences from the MERO-Earth geometry evolution, Earth TOA radiant anisotropic factor temporal change, the Earth TOA flux temporal variation and MERO location change. Results showed that the SW EPI would vary from approximately 3.32 × 10−6 to 2.16 × 10−4 W/m2 over the future 18.6-year period (March 2019 to November 2037); while the LW EPI would change between 4.43 × 10–6 and 4.91 × 10−4 W/m2.

Michelson interferometer for phase shifting interferometry with a liquid crystal retarder

We propose an interferometric system to measure phase objects using electronic phase shifting techniques. The experimental setup is based on a polarization Michelson type interferometer, where a liquid crystal retarder is placed at the entrance pupil as a phase shifter. First, the interferometric setup is used for the calibration of a phase-shifting device. Then, the interferometer is used to measure a phase object employing generalized phase-shifting algorithms to retrieve the phase solving the nonlinear response of the liquid crystal retarder. Experimental results are presented, and the advantages and limitations of the proposed technique are also discussed.

Corneal power measurements by ray tracing in eyes after small incision lenticule extraction for myopia with a combined Scheimpflug Camera-Placido disk topographer.

To evaluate the accuracy of the measurements of corneal power obtained by ray tracing with a combined Scheimpflug camera-Placido disk corneal topographer (Sirius) in eyes after small incision lenticule extraction for myopia (SMILE). Retrospective cases study includes 50 eyes of 50 patients who underwent myopic SMILE. Mean value of simulated keratometry (Kpost), mean pupil power (MPP) (ray tracing, diameter of the entrance pupil range 3-6mm), anterior and posterior corneal radius, and corneal thickness were obtained with Sirius topographer preoperatively and three months postoperatively, as well as cycloplegic refraction. True net power, equivalent keratometry readings, and Haigis equivalent power formula were calculated, and these measurements, MPP and Kpost, were compared with the corneal power calculated with the clinical history method (CHM). Corneal power measurements obtained with all methods were significantly different from CHM (P < 0.001), except the value of MPP obtained at 5.5mm (P = 0.927). A good direct correlation was found between CHM and all measurements. The distribution of differences as compared with the CHM showed that the lowest difference corresponded to the value of MMP at 5.5mm (-0.002 ± 0.6). The Bland-Altman plots for the MPP at 5.5mm showed 95% limits of agreement between -1.1787 D and 1.1741 D. MPP obtained by ray tracing within a diameter of entrance pupil of 5.5mm could predict corrected corneal power derived from the CHM in eyes following SMILE surgery.

High-precision Shack-Hartmann wavefront sensing with a multi-focal diffraction Taiji-lenslet array

A Hartmann wavefront sensor is a type of wavefront detection instrument that has been widely used in various fields. Traditional Hartmann wavefront sensors usually comprise a monofocal refraction lenslet array to segment the wavefront at the entrance pupil. Each wavelet is focused at the focal plane along the projection of the lenslet, forming the foci array. Unlike the multifocal self-interference Taiji-lenslet array, a type of multifocal diffraction Taiji-lenslet array was proposed in this study to improve the measurement accuracy using the weighted centroid location algorithm of these multifocal spots, where the latter is more easily designed than the former. An optical experiment was implemented using the multifocal diffraction Taiji-lenslet array to verify its effectiveness. As a type of diffractive lens, a large-aperture Taiji-lenslet array can be easily fabricated via lithography, which has great potential for application in the measurement of large-scale laser beams and optical elements.

Comparison of Camera Calibration and Measurement Accuracy Techniques for Phase Measuring Deflectometry

Phase measuring deflectometry (PMD) is a competitive method for specular surface measurement that offers the advantages of a high dynamic range, non-contact process, and full field measurement; furthermore, it can also achieve high accuracy. Camera calibration is a crucial step for PMD. As a result, a method based on the calibration of the entrance pupil center is introduced in this paper. Then, our proposed approach is compared with the most popular photogrammetric method based on Zhang’s technique (PM) and Huang’s modal phase measuring deflectometry (MPMD). The calibration procedures of these three methods are described, and the measurement errors introduced by the perturbations of degrees of freedom in the PMD system are analyzed using a ray tracing technique. In the experiment, a planar window glass and an optical planar element are separately measured, and the measurement results of the use of the three methods are compared. The experimental results for the optical planar element (removing the first 6 terms of the Zernike polynomial) show that our method’s measurement accuracy reached 13.71 nm RMS and 80.50 nm PV, which is comparable to accuracy values for the interferometer.

Creating a spatial optical tube of prescribed characteristics

Based on the radiation pattern of a spatial uniform magnetic current line source (UMLS) antenna, we propose a method for creating a spatial optical tube with a variable length and arbitrary orientation for a 4π focusing system. A virtual spatial UMLS antenna situated at the foci of two high numerical aperture objectives is used to obtain the required illumination at the entrance pupil plane. Numerical results demonstrate that the length of the created optical tube is approximately equal to that of the UMLS antenna. Its orientation is consistent with that of the line source. Its polarization is pure azimuthal, and the transverse size of the optical tube shell and the dark tunnel is uniform over the entire depth of focus. This optical tube can be customized according to application requirements. The generated optical tube can be used for such applications as arbitrary orientation particle trapping and guiding, micromanipulation, and optical microscopy.

Freeform hyperspectral imager design in a CubeSat format.

A freeform pushbroom hyperspectral imager design was investigated as a combination of a freeform reflective triplet imager and a freeform reflective triplet spectrometer used in double-pass. The design operates at about F/2 with a 15-degree cross-track field-of-view and a 30 mm entrance pupil diameter. The design process led to achieving a small volume of less than 2 liters that fits comfortably within a 3U CubeSat geometry, exemplifying the compactness of this hyperspectral imager. We report the freeform sag departures and maximum slopes of the freeform surfaces, as well as the manufacturing tolerances together with an evaluation of the system stray light, all of which highlight the feasibility of a design in this class to be manufactured. This design uniquely positions itself on the landscape of compact hyperspectral imagers.

Geometric characteristics and aberration characteristics of conformal dome based on von Karman surface

In this paper, the geometry and aberration characteristics of von Karman conformal domes have been investigated. Based on the theory of differential geometry, the uniform formulas of curvature, which are suitable for von Karman surface, were deduced in the meridian plane and sagittal plane, respectively. According to the formula, the geometry characteristics were analyzed. By using ray tracing, the geometric aberrations and wave aberrations of the von Karman dome were obtained. Further, the aberration characteristics of the von Karman dome with different design parameters were analyzed in depth. The results showed that for the viewing angle changing from 0° to 15°, numerous aberrations, namely, defocus, astigmatism, coma, spherical, trefoil, and tetrafoil were introduced by the von Karman, whose law is similar to its geometric characteristics. The factors with a high impact on aberrations were the aspect ratio, material, and diameter of the entrance pupil.

General method for replacing a thin lens with a thick lens with the same value of Seidel aberration coefficient of spherical aberration or coma.

The paper deals with the problem of replacing a thin lens with a thick lens having similar third-order aberration properties as the thin lens. The equations that make possible the calculation of parameters of the thick lens, which has the same value of focal length (or transverse magnification) and one of the Seidel aberration coefficients (either Seidel aberration coefficient of spherical aberration or Seidel aberration coefficient of coma) as the thin lens for given position of the entrance pupil and object, are derived. The application of the proposed method for calculation of parameters of the thick lens is shown in examples.

Useful relations for the analysis of stellar scintillation at the entrance pupil of a telescope.

The development of new techniques for characterizing atmospheric optical turbulence (OT) has become an active topic of research again in recent years. In order to facilitate these studies, we reconsidered known theoretical results and obtained some new practically useful conclusions. We introduce a dimensionless Fresnel filter, which allows us to approximate a polychromatic weighting function (WF) by a monochromatic one with a typical precision of several percent. A so-called dimensionless WF can be easily scaled for a receiving aperture of any size. For the case of a circular aperture and monochromatic radiation, an analytical expression for the WF was found. The WFs for a square aperture and for a circular aperture match with relative difference less than 0.01 if the circular aperture diameter is 1.15 times larger than the square aperture side. A linear digital filter can be applied to the scintillation signal from an image detector. As an example of digital filtering, we considered the power law filter ∝f5/3 with the WF being constant in a wide range of altitudes. We discuss the main limitations of this approach for measuring OT integral: finite pixel size, aliasing, and finite image detector size.

Roadmap for the unobscured three-mirror freeform design space.

In rotationally symmetric lens design, there are rule-of-thumb boundaries on field-of-view and aperture for well-known design forms that provide valuable information to the designer prior to starting a design. In the design space of unobscured three-mirror imagers, freeform optics have been shown to provide a significant benefit over conventional surface shapes, but the degree to which they improve the performance for any given combination of field-of-view, entrance pupil diameter, and F-number remains unknown. Thus, designers of these systems are not afforded any pre-design information to inform their specification decisions. Here, we designed over 200 systems to establish a first-of-its-kind roadmap of specification ranges over which an unobscured three-mirror imager using freeform surfaces can achieve diffraction-limited performance in the visible spectrum. The scalability of the findings to the infrared regions of the spectrum is also addressed.

19.3: Evaluation of Entrance Pupil Location in Measuring VR\AR Eyewear Displays: Theoretical and Experimental Analyses in Field of View

The conventional display measurements are no longer satisfying the need for eyewear displays. The measurement of VR/AR type display requires light measuring devices (LMDs) to simulate the characteristics of the human eye. Factors like the position of the pupil, field of view, and the motion of the eye are often discussed. One of the factors to be considered is the choice of entrance pupil location (aperture stop setting) of the LMD. In this paper, a preliminary study was carried out to compare the deviations of FOV and luminance with the choice of entrance pupil location. The experiment demonstrated that it exists as the most accurate eye‐viewing when the entrance pupil is located at the front focal point.

REPEATABILITY OF CHOROIDAL VASCULARITY INDEX MEASUREMENTS USING DIRECTIONAL OPTICAL COHERENCE TOMOGRAPHY IMAGES.

To investigate the repeatability of choroidal vascularity index (CVI) measurements in centered and decentered (regarding pupil entry position of the beam) directional subfoveal optical coherence tomography (OCT) scans with (CVI1) and without (CVI2) brightness adjustment. Thirty-two eyes of 32 healthy volunteers were included in this prospective study. First, the fovea was evaluated by a single horizontal enhanced depth imaging OCT scan in a centered direction. Then, the same subfoveal horizontal line was scanned in a decentered direction. The agreement between CVIs obtained from these centered and decentered directional OCT scans was investigated using Bland-Altman analysis and intraclass correlation coefficient. Intraclass correlation coefficient between centered and decentered CVI1 was 0.71 (95% CI: 0.48-0.85, P value < 0.001). Intraclass correlation coefficient between centered and decentered CVI2 was 0.73 (95% CI: 0.5-0.86, P value < 0.001). The mean difference between centered and decentered directional measurements for CVI1 and CVI2 were 0.5 and 0.8, respectively. There is moderate agreement between CVIs obtained from centered and decentered directional single OCT scans of the same subfoveal area. Studies investigating choroidal vascularity should be standardized by using the same OCT beam direction in all scans.

INCREASING OF AIMING AND SEARCH SYSTEM OF LAND UNMANNED COMPLEX DURABILITY

Proposals on composition of the aiming and search system of land unmanned complex are offered. The work aims to improve one of the most important technical characteristics of land unmanned complex - survivability. Proposals are given for improving the layout of aiming and search system of land unmanned complex. Existing composition schemes have a low firing life because of the devices included in its structure have are installed into general body. Sniper impact in body makes ineffective all aiming and search system. Authors proposes to install the devices into two bodies along weapon sides. TV-sight should be installed into the first body and thermal-vision sight should be installed into the second body. Then if sniper impact is affecting one body, then the devices of the second body are able to execute a battle task with some limitations thanks to efficient sight. The issues of controlling the stability of the aiming line of the aiming and search system at the stage of bench tests using a collimation-measuring unit are considered in detail. A technique for adjusting both television and thermal imaging sights is proposed.&#x0D; In addition to increasing the survivability of the entire unmanned complex, the proposed technical solution has a number of other advantages. First, the "cold" zeroing of the combat module is greatly simplified. Instead of a system of two penta mirrors, a BS-0 ° rhombus prism can be used for this. Secondly, the proposed layout potentially simplifies the further modernization of aiming and search system, which would require the inclusion of additional units. For example, to expand the functionality of the complex by analyzing the polarization of radiation from objects and backgrounds, an additional volume is provided to accommodate polarimetric attachments. Thirdly, an even greater increase in the survivability of the complex can be achieved by increasing the secrecy of the combat mission. Usage of the base distance between the entrance pupils of the sights makes it possible to passively measure the range to the target using the internal base rangefinder instead of the laser rangefinder.

Signal of an autocorrelation low-coherence interferometer probing a layered object by a wave-field with wide angular spectrum

The effect of the width of the angular spectrum (numerical aperture) of a broadband-frequency wave-field probing a layered object on the signal of an autocorrelation low-coherence interferometer (ALCI) under spatially coherent and incoherent illumination of the entrance pupil is considered. It is found that under incoherent illumination an increase in the width of the angular spectrum of the field leads to a decrease in the amplitude, a change in the shape and position of the measuring signals of the interferometer due to decorrelation of the object field partial components which have reflected from various interlayer boundaries inside the object. In the case of coherent illumination, the ALCI signal is formed in a confocal mode, which leads to the amplitude extraction of the measurement signals are determined by the mutual correlations between a partial component reflected from the boundary on which the probing field was focused, and partial components of this field which have reflected from other boundaries within the object. This effect makes it possible to determine parameters of the internal layered structure of an object doing without apriori structure-related information. In this case, an increase in the numerical aperture of the probing light beam leads to an increase in the systematic error in determining the optical thicknesses of the layers, which can be estimated on the basis of the obtained expressions.

Human Eye Response to Pupil Size Variation Programmatically

The human eye is the best optical device in the world. The performance of this eye is influenced by optical aberrations. Several human eye models were developed to treat and correct this issue. To build and study the optimal and berated human eye, this work relies on the Liou and Brennan eye model. This model is more suitable than other models since it depends on using a gradient refractive index (n) with a spherical lens surface. The effect of entrance pupil diameter on optical aberrations were evaluated programmatically by ZEMAX , computer software (version 14) at 555 nm monochromatic light under the influence of Semi-Diameter values variation by 1.25, 1.5, 2, 3, 4 and 5 mm. The eye's performance was evaluated using the modulation transfer function (MTF), root mean square of the spot sizes (RMS), and wave front aberration. The findings showed that the best image quality acquired at 1.25 and 1.5mm Semi-diameter, which means that under monochromatic illumination, the smallest values of aberrations can be obtained by using a small pupil scale and a small field of view.

Effects of solar noise on the detection range performance of a laser spot tracker

The effects of solar spectral irradiance on the performance of laser spot tracker are analyzed. When the entrance pupil diameter of the receiver increases, the field of view decreases, but the detection range increases. If the angle between the receiver and transmitter and target increases from 0 deg to 60 deg, the detection range decreases by approximately 23%. Due to solar noise’s effects caused by solar spectral irradiance, the detection range decreases by approximately 33% during the day, more than during the night, and the laser spot tracker’s altitude decreases by approximately 13% at 2000 m, more than at 0 m. When the solar intensity’s variation increases from 1% to 5%, the detection range decreases by 54%.

Design, calibration, and application of a cryogenic low-background infrared radiometer for spectral irradiance and radiance measurements from 4 μm to 20 μm wavelength.

We have constructed, calibrated, and tested a cryogenic low-background infrared radiometer for both spectral radiance and irradiance measurements over the 4 μm to 20 μm wavelength range. The primary purpose of the Missile Defense Transfer Radiometer (MDXR) is to measure absolute irradiance or radiance from cryogenic infrared test chamber sources using a photoconductive Si:As Blocked Impurity Band (BIB) detector and a set of spectral filters. The MDXR also includes an absolute cryogenic radiometer (ACR) and a Fourier transform spectrometer (FTS). For irradiance measurements, the ACR is used to provide the primary power scale for the BIB detector in conjunction with spectral filters, while the FTS/BIB configuration derives its scale from an internal blackbody source. The two measurement scales show agreement for the irradiance of highly collimated (< 1 mrad) infrared beams from 10-13 W/μm/cm2 to 10-8 W/μm/cm2 within the combined relative uncertainties of 2.6 % (coverage factor k = 1.) We have also calibrated the radiometer for radiance measurements by using a large cavity fluid bath blackbody that overfills the spatial and angular extent of the radiometer entrance pupil. The radiometric calibration uncertainty analysis of the radiometer as well as its maintenance and stability are discussed.

Directional Reflectivity of the Ellipsoid Zone in Dry Age-Related Macular Degeneration.

Ellipsoid zone (EZ) reflectivity on optical coherence tomography (OCT) is affected by the orientation of the scanning beam. The authors sought to determine how directional reflectivity changes in dry age-related macular degeneration (AMD). Retrospective image analysis included 17 control and 20 dry AMD subjects. Directional OCT (D-OCT) was performed using multiple displaced pupil entrance positions. EZ pixel values and apparent incidence angles were measured. EZ reflectivity decreased in off-axis scans in controls (P < .001), AMD areas between drusen (P < .001), and AMD areas overlying drusen (P < .001). The magnitude of decrement in EZ reflectivity was significantly higher when incidence angles exceeded 10° in controls than in AMD areas between drusen (P = .024). EZ reflectivity in dry AMD may vary by incident angle of light less than in controls, possibly indicating alteration of photoreceptor orientation or integrity. [Ophthalmic Surg Lasers Imaging Retina. 2021;52:145-152.].

Multi-aperture system approach for snapshot multispectral imaging applications.

We present an ultra-compact system approach for snapshot, multispectral imaging. It is based on a slanted linear variable spectral filter mounted in close proximity to the entrance pupil of a micro-optical, multi-aperture imaging system. A compact demonstration setup with a size of only 60 × 60 × 28 mm3 is developed, which enables the acquisition of 66 spectral channels in a single shot and offers a linear spectral sampling of approximately six nanometers over an extended wavelength range of 450-850 nm. The spatial sampling of each channel covers up to 400 × 400 pixels. First, the concept, the optical design and the fabrication are detailed. After the optical performance characterization, a comprehensive calibration strategy is developed and applied. An experimental demonstration is performed by acquiring the spatial and the spectral information of an imaged test scene.