Stray Light Noise Research Articles

Enhancing Optical Microscopy with Quantum Entanglement

Drawing on the unique properties of entangled photons, quantum approaches can overcome the limitations of classical methods, enhance spatial resolution and reduce stray light and shot noise.

A microchip based Z-cell absorbance detector integrating micro-lenses and slits for portable liquid chromatography

A miniaturized microchip-based absorbance detector was developed for portable high-performance liquid chromatography (HPLC) to test glycated hemoglobin (HbA1c). The microchip integrating a Z-shaped cell, two collimating micro-lenses and two ink-filled optical slits is small in size (30 mm × 15 mm × 7 mm). The Z-shaped cell has a cross-sectional size of 500 μm × 500 μm and a physical optical path length of 2 mm. Two collimating micro-lenses were inserted in empty grooves on both sides of the cell, one micro-lens for collimating the initial light and the other for focusing the transmitted light. Optical slits on each end of the cell were used to block the stray light. Therefore, this detector indicated a low stray light level (0.011 %) and noise level (2.5 × 10−4 AU). This detector was applied for the commercial HPLC system to detect HbA1c level, and showed a low limit of detection (0.5 μg/mL) and excellent repeatability (≤ 2.03 %). The sensitivity was enhanced by 3.4 times when the optical path length was increased from 0.5 mm to 2 mm and the stray light was blocked by optical slits. The miniaturized microchip-based absorbance detector developed shows a great potential for application in portable and compact HPLC.

Hyperspectral screen-image-synthesis meter with scattering-noise suppression

The screen image synthesis (SIS) meter was originally proposed as a high-speed measurement tool, which fused the measured data from multiple sample-rotational angles to produce a whole-field measurement result. However, it suffered from stray light noise and lacked the capability of spectrum measurement. In this study, we propose an SIS system embedded with a snapshot hyperspectral technology, which was based on a dispersion image of the sparse sampling screen (SSS). When a photo was captured, it was transformed and calibrated to hyperspectral data at a specific sample-rotational angle. After the hyperspectral data in all sample-rotational angles were captured, an SIS image-fusion process was then applied to get the whole field hyperspectral data. By applying SSS to the SIS meter, we not only create a screen image synthesis hyperspectral meter but also effectively address the issue of stray-light noise. In the experiment, we analyze its correctness by comparing the hyperspectral value with a one-dimensional spectrum goniometer (ODSG). We also show the 2D color temperature coefficient distribution and compare it with the ODSG. Experimental results also demonstrate the feasibility in terms of both spectrum distribution meter and color coefficient temperature distribution meter.

A method of laser stripe centerline extraction based on deep learning for structured light 3D reconstruction

To overcome the stray light noise in the centerline extraction method during line structured light 3D reconstruction process, an end-to-end trainable neural network for laser stripe centerline extraction based on Convolutional Neural Network and Multi-Layer Perception is proposed. The proposed network can self-adapt to a variety of lighting (brightness) conditions and overcome the interference of different stray lights. In addition, unlike prior work on enhancing the accuracy of centerline extraction using deep learning methods that only performs it for noise reduction in pre-processing, the proposed network unifies the noise reduction and prediction processes, so that it can be optimized end-to-end directly on centerline extraction performance. The network learns an intermediate feature representation of noise reduction, which requires less complexity for data annotation, reduces the training difficulty, and has more scalability. Experiments show that the proposed method can perform centerline extraction with relatively high accuracy for laser stripes of different widths, brightness, and inclination, thus obtaining a smooth and stable reconstructed surface in the structured light 3D reconstruction process.

Scattering Model for Stray Light Calculations in Laser Interferometry Application to TianQin Science Interferometer

In the field of space optics, correct estimation of the amount of stray light is necessary to evaluate system performance and guide the selection of the correct design. Given the noise target of several picometers on distance measurements, this configuration is very sensitive to stray-light noise; thus, stray-light estimation is an important part of the design process. For complex optical systems, stray-light simulations can be performed by using specific optical analysis software (FRED, Tracepro, ASAP), which require expensive licenses and excessive computing time. Herein, we consider the effects of combined roughness, mirror contamination, and surface imperfections, construct a unified physical scattering model and simulate it. According to the analysis, the stray light of the telescope system is less than 1010 of the outgoing laser power.These considerations apply to various optical systems.

High performance telescope system design for the TianQin project

China is planning to construct a new space-borne gravitational-wave (GW) observatory, the TianQin project, in which the spaceborne telescope is an important component in laser interferometry. The telescope is aimed to transmit laser beams between the spacecrafts for the measurement of the displacements between proof-masses in long arms. The telescope should have ultra-small wavefront deviation to minimize noise caused by pointing error, ultra-stable structure to minimize optical path noise caused by temperature jitter, ultra-high stray light suppression ability to eliminate background noise. In this paper, we realize a telescope system design with ultra-stable structure as well as ultra-low wavefront distortion for the space-based GW detection mission. The design requirements demand extreme control of high image quality and extraordinary stray light suppression ability. Based on the primary aberration theory, the initial structure design of the mentioned four-mirror optical system is explored. After optimization, the maximum RMS wavefront error is less than λ/300 over the full field of view, which meets the noise budget on the telescope design. The stray light noise caused by the back reflection of the telescope is also analyzed. The noise at the position of optical bench is less than 10−10 of the transmitted power, satisfying the requirements of space GW detection. We believe that our design can be a good candidate for TianQin project, and can also be a good guide for the space telescope design in any other similar science project.

Meteoroids detection with the LUMIO lunar CubeSat

The Lunar Meteoroid Impacts Observer (LUMIO) is a CubeSat mission to observe, quantify, and characterize the meteoroid impacts on the lunar farside by detecting their flashes. This complements the knowledge gathered by Earth-based observations of the lunar nearside, thus synthesizing global information on the lunar meteoroid environment and contributing to the lunar situational awareness. The goal of LUMIO is to advance our current knowledge of meteoroid models in the solar system. In this work, we present the methodology devised to predict the scientific contribution of LUMIO. Our approach relies on combined modeling and simulation of payload, orbit, and environment. The analyses carried out have been used to drive the design of the LUMIO mission and its payload, the LUMIO-Cam. A payload radiometric model is derived and exploited to assess the quality of the scientific measurements. A dedicated study about straylight rejection is carried out to assess how straylight noise affects LUMIO-Cam measurements. Our results indicate that a 150mm baffle grants good performance when the Sun angle is between 20° and 90°. Furthermore, the present-day LUMIO mission has the potential to detect more than 6000 impact flashes during the activity peak of the Geminids in 2024 in the range of the equivalent impact kinetic energy at Earth of [10−6,10−1]kton TNT Equivalent. Compared to previous programmes, LUMIO could refine information and fill the knowledge gap about the meteoroid population in the ranges of the equivalent impact kinetic energy at Earth of [10−6,10−4]kton TNT Equivalent and [10−4,10−1]kton TNT Equivalent, respectively.

A Novel Method for Online Extraction of Small-Angle Scattering Pulse Signals from Particles Based on Variable Forgetting Factor RLS Algorithm.

The small-angle optical particle counter (OPC) can detect particles with strong light absorption. At the same time, it can ignore the properties of the detected particles and detect the particle size singly and more accurately. Reasonably improving the resolution of the low pulse signal of fine particles is key to improving the detection accuracy of the small-angle OPC. In this paper, a new adaptive filtering method for the small-angle scattering signals of particles is proposed based on the recursive least squares (RLS) algorithm. By analyzing the characteristics of the small-angle scattering signals, a variable forgetting factor (VFF) strategy is introduced to optimize the forgetting factor in the traditional RLS algorithm. It can distinguish the scattering signal from the stray light signal and dynamically adapt to the change in pulse amplitude according to different light absorptions and different particle sizes. To verify the filtering effect, small-angle scattering pulse extraction experiments were carried out in a simulated smoke box with different particle properties. The experiments show that the proposed VFF-RLS algorithm can effectively suppress system stray light and background noise. When the particle detection signal appears, the algorithm has fast convergence and tracking speed and highlights the particle pulse signal well. Compared with that of the traditional scattering pulse extraction method, the resolution of the processed scattering pulse signal of particles is greatly improved, and the extraction of weak particle scattering pulses at a small angle has a greater advantage. Finally, the effect of filter order in the algorithm on the results of extracting scattering pulses is discussed.

Stray light noise removal method of star maps based on intensity prior

Stray light noise removal method of star maps based on intensity prior

太阳杂光噪声下星敏感器星像点质心定位方法

太阳杂光噪声下星敏感器星像点质心定位方法

Data preprocessing methods for robust Fourier ptychographic microscopy

Fourier ptychographic microscopy (FPM) is a recently proposed computational imaging technique with both high resolution and wide field-of-view. In current FP experimental setup, the dark-field images with high-angle illuminations are easily submerged by stray light and background noise due to the low signal-to-noise ratio, thus significantly degrading the reconstruction quality and also imposing a major restriction on the synthetic numerical aperture (NA) of the FP approach. To this end, an overall and systematic data preprocessing scheme for noise removal from FP's raw dataset is provided, which involves sampling analysis as well as underexposed/overexposed treatments, then followed by the elimination of unknown stray light and suppression of inevitable background noise, especially Gaussian noise and CCD dark current in our experiments. The reported non-parametric scheme facilitates great enhancements of the FP's performance, which has been demonstrated experimentally that the benefits of noise removal by these methods far outweigh its defects of concomitant signal loss. In addition, it could be flexibly cooperated with the existing state-of-the-art algorithms, producing a stronger robustness of the FP approach in various applications.

IMRAN: a noise estimation method for relative radiometric calibration data

Radiometric calibration is the foundation for remote sensors to accurately record the reflected energy from targets and to also effectively display the reflectance diversity among them. As one of the calibration methods, pre-launch laboratory relative calibration is essentially a normalizing process for each detector of a sensor at different intensity levels of various radiation sources. However, interferences such as stray light, dark current, and stochastic noise will cause some deviation of the normalizing correction factor. In this article, we propose an integral noise (a combination of the aforementioned three noises) estimation method based on the correlation between the elements of the calibration data itself. Abbreviated as IMRAN (Iterative Maximal Residual As Noise), this method is an iteration procedure using least square fitting to calculate the maximum residual of the sensor pixel in question against the rest sensor pixels and to consider this value as the estimated noise. The iteration is continued after subtracting the noise from the raw data of the sensor pixel until the noise estimation gets converged and then the accumulation of the results from each round is the final estimated noise. And this procedure is applied to every sensor pixel. The verification results demonstrated the IMRAN method can effectively estimate the integral noise of pre-launch radiometric calibration data and substantially improve its precision. When the number of radiation level increases, the precision of the estimated noise will be rapidly increased, whereas the number of sensor pixels has no obvious effect. Because this IMRAN method uses the data of every sensor pixel, it is sensitive to the outlier, which can be eliminated by variance detection as part of the IMRAN method.

Development of micro-objective lens array for large field-of-view multi-optical probe confocal microscopy

We describe multi-optical probe confocal microscopy using a micro-objective lens array for large areal inspection. A microlens array with 100 µm focal length, 80 µm diameter and 90 µm pitch was designed and fabricated with an array size of 10 × 10. In order to produce the high-fidelity microlens array, a UV imprinting process was employed, and a UV transparent mold for the imprinting process was manufactured by replicating a reflow lens master. A blocking filter between the microlenses was introduced to minimize crosstalk and stray light noise for high resolution and high contrast imaging. The developed system is characterized by a 1 mm × 1 mm field of view with a nano-stage with 100 µm travel length. The lateral resolution was measured to be 0.79 µm. The method can be used for various applications such as the inspection of electric devices including display panels and large-area printed circuits with a high resolution.

The CU ground MAX-DOAS instrument: characterization of RMS noise limitations and first measurements near Pensacola, FL of BrO, IO, and CHOCHO

Abstract. We designed and assembled the University of Colorado Ground Multi AXis Differential Optical Absorption Spectroscopy (CU GMAX-DOAS) instrument to retrieve bromine oxide (BrO), iodine oxide (IO), formaldehyde (HCHO), glyoxal (CHOCHO), nitrogen dioxide (NO2) and the oxygen dimer (O4) in the coastal atmosphere of the Gulf of Mexico. The detection sensitivity of DOAS measurements is proportional to the root mean square (RMS) of the residual spectrum that remains after all absorbers have been subtracted. Here we describe the CU GMAX-DOAS instrument and demonstrate that the hardware is capable of attaining RMS of ∼6 × 10−6 from solar stray light noise tests using high photon count spectra (compatible within a factor of two with photon shot noise). Laboratory tests revealed two critical instrument properties that, in practice, can limit the RMS: (1) detector non-linearity noise, RMSNLin, and (2) temperature fluctuations that cause variations in optical resolution (full width at half the maximum, FWHM, of atomic emission lines) and give rise to optical resolution noise, RMSFWHM. The non-linearity of our detector is low (∼10−2) yet – unless actively controlled – is sufficiently large to create RMSNLin of up to 2 × 10−4. The optical resolution is sensitive to temperature changes (0.03 detector pixels °C−1 at 334 nm), and temperature variations of 0.1°C can cause RMSFWHM of ~1 × 10−4. Both factors were actively addressed in the design of the CU GMAX-DOAS instrument. With an integration time of 60 s the instrument can reach RMS noise of 3 × 10−5, and typical RMS in field measurements ranged from 6 × 10−5 to 1.4 × 10−4. The CU GMAX-DOAS was set up at a coastal site near Pensacola, Florida, where we detected BrO, IO and CHOCHO in the marine boundary layer (MBL), with daytime average tropospheric vertical column densities (average of data above the detection limit), VCDs, of ∼2 × 1013 molec cm−2, 8 × 1012 molec cm−2 and 4 × 1014 molec cm−2, respectively. HCHO and NO2 were also detected with typical MBL VCDs of 1 × 1016 and 3 × 1015 molec cm−2. These are the first measurements of BrO, IO and CHOCHO over the Gulf of Mexico. The atmospheric implications of these observations for elevated mercury wet deposition rates in this area are briefly discussed. The CU GMAX-DOAS has great potential to investigate RMS-limited problems, like the abundance and variability of trace gases in the MBL and possibly the free troposphere (FT).

Scientific objectives and specification of the SELENE Multiband Imager

The Lunar Imager/SpectroMeter (LISM) is an instrument being developed for onboarding the SELENE satellite that will be launched in 2007. The LISM consists of the three subsystems: Terrain Camera (TC), Multiband Imager (MI), and Spectral Profiler (SP). The MI is a high-resolution multiband imaging camera consisting of two visible and near infrared sensors. It takes push-broom imaging data by using selected lines of area arrays. The spectral band assignments are 415, 750, 900, 950 and 1000 nm for visible and 1000, 1050, 1250 and 1550 nm for near infrared. The spatial resolution of visible bands is 20 m, and that of near infrared bands is 62 m from the 100 km SELENE orbital altitude. We will observe globally the mineral distribution of the lunar surface in nine band images of MI. Its high spatial resolution will also enable us to investigate small but scientifically very important areas such as crater central peaks and crater walls. The advantage of MI for this aspect is that we can remove topographic effect, which causes false reflectance values seen in the crater wall and crater central peak, by photometric correction with detailed topography. Measurements of MTF, viewing vector, sensor linearity, and stray light and electrical noise level were carried out after the MI integration. Measured data indicate that MI will provide sufficient MTF, low noise and low stray light of spectral imaging data just as estimated in the MI designing phase.

Phase sensitive demodulation in multiphoton microscopy.

Multiphoton laser scanning microscopy offers advantages in depth of penetration into intact samples over other optical sectioning techniques. To achieve these advantages it is necessary to detect the emitted light without spatial filtering. In this nondescanned (nonconfocal) approach, ambient room light can easily contaminate the signal, forcing experiments to be performed in absolute darkness. For multiphoton microscope systems employing mode-locked lasers, signal processing can be used to reduce such problems by taking advantage of the pulsed characteristics of such lasers. Specifically, by recovering fluorescence generated at the mode-locked frequency, interference from stray light and other ambient noise sources can be significantly reduced. This technology can be adapted to existing microscopes by inserting demodulation circuitry between the detector and data collection system. The improvement in signal-to-noise ratio afforded by this approach yields a more robust microscope system and opens the possibility of moving multiphoton microscopy from the research lab to more demanding settings, such as the clinic.

Using the y, y-bar diagram to control stray light noise in IR systems

Stray light in an (infrared) optical system is the radiation that is incident on the detector, but does not originate from the conjugate object point. Cool stops are usually placed at strategic locations to decrease the amount of stray light noise incident into the detector plane. Contrary to the present practice, the stray light control is improved when the telescope and instrument subsystems are analyzed as a single optical system. We describe an approach to the stray light management and control that may be performed simultaneously with the first order optical system design using the y, y-bar diagram.

In-Flight Calibration of theNimbus-7Earth Radiation Budget (ERB) Sensors. Part II: Short-Term Perturbations

Abstract This paper describes the production calibration adjustment algorithms used to remove thermal perturbation and stray light noise signals from the Nimbus-7 earth radiation budget (ERB) measurements. Sunlight, both direct and scattered from the sensor baffles, contaminated the ERB measurements at satellite sunrise and sunset. The problem covered subsatellite solar zenith angles from 90° to 120° and reduced the usefulness of the longwave spectral radiation measurements. Scattered light corrections are made from 90° to 99° while orbit-by-orbit interpolation is used frown 99° to 121°. Tests indicate that in the mean the midpoint interpolation error is less than 1 W m−2 with a standard deviation of about 5 W m−2. Thermal perturbations on the total channel 12 (0.2–50 μm) appeared to be always less than 0.3%. However, the Suprasil-W domes on the otherwise similar shortwave channels 13 and 14 in some way helped produce thermal perturbations of up to 6% or more in channel 13 (0.2–3.8 μm and up to 3% or more...

Near-field scanning optical microscope with a metallic probe tip

A near-field scanning optical microscope with a metallic probe tip was developed for detecting localized photons near the surface of the fine structure of a sample. In this microscope a metallic probe is used for converting the evanescent photons localized near the sample surface to the propagating scattering light wave; the scattered light is detected in the far field with external condenser optics. During the measurement the probe tip vibrates normal to the surface with an amplitude of ~5 nm at 2.5 kHz, and the light intensity modulated with this frequency is lock-in detected. This operation permits the removal of stray-light noise contribution. Experimental results of the measurements of the exponential decay of the evanescent field produced by total internal reflection are given with and without the probe vibration. Image data of the surface profile of an optical compact disk are also shown.

Vertebrate receptor optics and orientation.

Vertebrate photoreceptors act as optical waveguides. They exhibit directionality, non-uniform distribution of energy within and immediately about the receptor, etc. Photolabile pigment absorption favors light traveling axially down the receptor. Clearly these properties influence response of the transducer. Retinal receptors, rods and cones, are aligned normally with a point approximating the center of the exit pupil of the eye. Taken together, these findings suggest that a prime role of receptor optics is to favor acceptance of the pertinent visual stimulus passing through the pupillary aperture and to inhibit stray light noise contained in the integrating sphere-like eyes. Many intriguing problems remain to be resolved. It is necessary to relate the properties of the receptor as a waveguide to determinations of directional sensitivity of the retina (Stiles-Crawford effects), and in particular, to understand mechanisms leading to fine receptor alignment. There must also be a pathology of receptor orientation--a science still in its infancy.