Stray Light Interference Research Articles

Structured illumination for two-dimensional laser induced fluorescence imaging to eliminate stray light interference

<sec>Laser sheet imaging, also called planar laser imaging, is one of the most versatile optical imaging techniques and has been frequently used in several different areas. However, when applied to the limited operating space and strong light scattering media, the light originating from indirect reflections, multiple scattering and surrounding backgrounds can produce error especially in intensity-ratio based measurements.</sec><sec>This work is motivated by these challenges, with the overall aim of making laser sheet imaging technique applicable for the study of eliminating the stray light interference. Therefore a novel two-dimensional imaging technique named structured laser illumination planar imaging (SLIPI) is developed based on planar laser imaging but uses a sophisticated illumination scheme i.e. spatial intensity modulation, to differentiate between the intensity contribution arising from useful signals and that from stray light. By recording and dealing with images, the SLIPI method can suppress the diffuse light and retain the useful signals.</sec><sec>In this paper, we first use the MATLAB software to simulate the phase-shift SLIPI method, and the results show that the stray light interference can be eliminated completely. Furthermore, the phase-shift SLIPI is combined with the liquid solution (Rhodamine B solution) laser induced fluorescence (LIF) approach to imagine the concentration distribution. By recording three images, between which this encoding is changed noticeably only for the useful LIF signals, the phase-shift SLIPI method is evidenced to be able to remove the diffuse light contribution, thus improving and enhancing the visualization quality. The instantaneous SLIPI images of rapidly moving samples, a key feature to study dynamic liquid solution diffusion behavior, are also acquired. The lock-in amplifier SLIPI technique is then experimentally studied under Rhodamine B diffused solution, and the phase-shift SLIPI method can remove the unwanted background interferences and achieve the significant improvements in terms of pronounced concentration distribution within the Rhodamine B solution.</sec><sec>The SLIPI technique is relatively inexpensive: the cost does not exceed the cost of an ordinary laser sheet arrangement noticeably, and it can combine with several other linear imaging techniques, such as Rayleigh scattering, particle image velocimetry and laser-induced phosphorescence. </sec>

An assessment of the stray light in 25 years of Dobson total ozone data at Athens, Greece

Abstract. In this study, we investigated the susceptibility of the Dobson spectrophotometer No. 118 to stray light interference. In this regard, a series of total ozone content measurements were carried out in Athens, Greece for air-mass values (μ) extending up to μ = 5. The monochromatic-heterochromatic stray light derived by Basher's model was used in order to evaluate the specific instrumental parameters which determine if this instrument suffers from this problem or not. The results obtained indicate that the measurements made by the Dobson instrument of the Athens station for air mass values up to 2.5, underestimates the total ozone content by 3.5 DU in average, or about 1 % of the station's mean total ozone content (TOC). The comparison of the values of the same parameters measured 15 years ago with the present ones indicates the good maintenance of the Dobson spectrophotometer No. 118. This fact is of crucial importance because the variability of the daily total ozone observations collected by the Athens Dobson Station since 1989 has proved to be representative to the variability of the mean total ozone observed over the whole mid-latitude zone of the Northern Hemisphere. This stresses the point that the Athens total ozone station, being the unique Dobson station in south-eastern Europe, may be assumed as a ground truth station for the reliable conversion of the satellite radiance observations to total ozone measurements.

Corrigendum to “Integrated miniature fluorescent probe to leverage the sensing potential of ZnO quantum dots for the detection of copper (II) ions” [Talanta 116 (2013) 514–519

Quantum dots are fluorescent semiconductor nanoparticles that can be utilised for sensing applications. This paper evaluates the ability to leverage their analytical potential using an integrated fluorescent sensing probe that is portable, cost effective and simple to handle. ZnO quantum dots were prepared using the simple sol-gel hydrolysis method at ambient conditions and found to be significantly and specifically quenched by copper (II) ions. This ZnO quantum dots system has been incorporated into an in-house developed miniature fluorescent probe for the detection of copper (II) ions in aqueous medium. The probe was developed using a low power handheld black light as excitation source and three photo-detectors as sensor. The sensing chamber placed between the light source and detectors was made of 4-sided clear quartz windows. The chamber was housed within a dark compartment to avoid stray light interference. The probe was operated using a microcontroller (Arduino Uno Revision 3) that has been programmed with the analytical response and the working algorithm of the electronics. The probe was sourced with a 12V rechargeable battery pack and the analytical readouts were given directly using a LCD display panel. Analytical optimisations of the ZnO quantum dots system and the probe have been performed and further described. The probe was found to have a linear response range up to 0.45mM (R(2)=0.9930) towards copper (II) ion with a limit of detection of 7.68×10(-7)M. The probe has high repeatable and reliable performance.

Integrated miniature fluorescent probe to leverage the sensing potential of ZnO quantum dots for the detection of copper (II) ions

Quantum dots are fluorescent semiconductor nanoparticles that can be utilised for sensing applications. This paper evaluates the ability to leverage their analytical potential using an integrated fluorescent sensing probe that is portable, cost effective and simple to handle. ZnO quantum dots were prepared using the simple sol–gel hydrolysis method at ambient conditions and found to be significantly and specifically quenched by copper (II) ions. This ZnO quantum dots system has been incorporated into an in-house developed miniature fluorescent probe for the detection of copper (II) ions in aqueous medium. The probe was developed using a low power handheld black light as excitation source and three photo-detectors as sensor. The sensing chamber placed between the light source and detectors was made of 4-sided clear quartz windows. The chamber was housed within a dark compartment to avoid stray light interference. The probe was operated using a microcontroller (Arduino Uno Revision 3) that has been programmed with the analytical response and the working algorithm of the electronics. The probe was sourced with a 12V rechargeable battery pack and the analytical readouts were given directly using a LCD display panel. Analytical optimisations of the ZnO quantum dots system and the probe have been performed and further described. The probe was found to have a linear response range up to 0.45mM (R2=0.9930) towards copper (II) ion with a limit of detection of 7.68×10−7M. The probe has high repeatable and reliable performance.

A liquid refractive index detect method based on negative refraction phenomenon in 2D photonic crystal structure

This paper is mainly concerned with the investigation of negative refraction phenomenon dependent on the background refractive index in 2D photonic crystal, which consists of a hexagonal lattice of circular dielectric rods with Si. The paper presents the relationship between background refractive index and negative refraction. The relationship is investigated by using the finite-difference time-domain (FDTD) method on software RSoft. The results point out that the output power is added with the increase of the background refractive index. With the research, a new fluid refractive index detection method is proposed. Compared with other normal liquid refractive index analyzer reported, this detector has advantages of faster detection, less stray light interference and miniaturization.

Effective Suppression of Stray Light in Rotational Coherent Anti-Stokes Raman Spectroscopy Using an Angle-Tuned Short-Wave-Pass Filter

Stray light interference is a common problem in spontaneous rotational Raman spectroscopy and rotational coherent anti-Stokes Raman spectropscopy (CARS). The reason is that the detected spectrum appears in the spectral vicinity of the probe beam wavelength, and stray light at this wavelength from optics and surfaces is hard to suppress. In this Note, efficient suppression of stray light is demonstrated for rotational CARS measurements using a commercially available short-wave-pass filter. By angle-tuning this filter with a specified cut-off wavelength at 561 nm, the cut-off wavelength could be tuned to a desired spectral position so that more than 80% transmission is achieved as close as 15 cm(-1) (approximately 0.4 nm) from the probe beam wavelength of 532.0 nm, while the intensity at this wavelength is suppressed by two orders of magnitude.

Application of gold quenching of luminescence to improve oxygen sensing using a ruthenium (4,7-diphenyl-1,10-phenanthroline) 3Cl 2:TEOS thin film

A new method for enhancement of luminescence from sol–gel based sensors is demonstrated, utilising the quenching effect and filtering effect of a gold film. Ruthenium (4,7-diphenyl-1,10-phenanthroline) 3Cl 2 is encapsulated in a trimethoxysilane (TEOS) xerogel and spin-coated to an approximate thickness of less than 100 nm. Using off axis illumination of the xerogel film, luminescence was collected using a photodiode below the plane of the gold and doped thin film. The gold had the effect of improving all sensor figures of merit via two mechanisms. Firstly, the transmission spectrum of the gold film peaks at 520 nm but allows poor transmission of excitation light at 450 nm reducing stray light interference in addition to a 550 nm cut-on filter. Secondly, and more, importantly relatively insensitive luminophores within approximately 10 nm of the gold film are quenched resulting in a significant noise reduction by removal of insensitive residual metal ion–ligand complex luminescence. It is questioned whether an element of radiative-decay-engineering of luminescence is occurring with luminophore emission coupling to the gold film and initiating plasmonic emission from the underside of the film, but no evidence either in terms of solely p-polarisation or increased intensity of luminescence was evidenced. This confirms that the sensor enhancement mechanism is primarily the function of metal quenching as evidenced by reduced background intensity as noise and improved response time to oxygen quenching indicating that only the most sensitive luminophores are available to be dynamically quenched by formation of the ruthenium:oxygen charge transfer complex. This simple sensor geometry improves a basic oxygen sensor luminophore:matrix combination and stands comparison with more complex combinations such as those achieved with fluorinated sol–gel matrices.

Relative performance of filled and feedhorn-coupled focal-plane architectures.

Modern far-infrared and submillimeter instruments require large-format arrays. We consider the relative performance of filled-array (bare pixel) and feedhorn-coupled architectures for bolometer focal planes. Based on typical array parameters, we quantify the relative observing speeds and comment on the merits of the different architectures. Filled arrays can provide higher mapping speed (by a factor of as much as 3.5) and simpler observing modes at the expense of reduced sensitivity for pointed observations, increased detector numbers, and greater vulnerability to stray light and electromagnetic interference. Taking advantage of the filled-array architecture requires strongly background-limited detectors. At millimeter wavelengths, filled arrays must be surrounded by a sufficiently cold enclosure to minimize the background power from the instrument itself.

Amorphous and nanocrystalline glass-covered wires

Important scientific goals of far-infrared and submillimetre astronomy include measurements of anisotropies in the cosmic background radiation, deep imaging surveys for detection of high-red-shift galaxies, and imaging and spectroscopy of star formation regions and the interstellar medium in the milky way and nearby galaxies. Use of sensitive bolometer arrays leads to very large improvements in observing speed. Recent progress in the development of bolometric detector systems for ground-based and space-borne far-infrared and submillimetre astronomical observations is reviewed, including spider-web NTD bolometers, transition-edge superconducting sensors, and micromachined planar arrays of ion-implanted silicon bolometers. Future arrays may be based on planar absorbers without feedhorns, which offer potential advantages including more efficient use of space in the focal plane and improved instantaneous sampling of the telescope point spread function, but present challenges in suppression of stray light and RF interference. FIRST and Planck Surveyor are planned satellite missions involving passively cooled (∼70 K) telescopes, and bolometer array developments for these missions are described.

Bolometers for far-infrared and submillimetre astronomy

Important scientific goals of far-infrared and submillimetre astronomy include measurements of anisotropies in the cosmic background radiation, deep imaging surveys for detection of high-red-shift galaxies, and imaging and spectroscopy of star formation regions and the interstellar medium in the milky way and nearby galaxies. Use of sensitive bolometer arrays leads to very large improvements in observing speed. Recent progress in the development of bolometric detector systems for ground-based and space-borne far-infrared and submillimetre astronomical observations is reviewed, including spider-web NTD bolometers, transition-edge superconducting sensors, and micromachined planar arrays of ion-implanted silicon bolometers. Future arrays may be based on planar absorbers without feedhorns, which offer potential advantages including more efficient use of space in the focal plane and improved instantaneous sampling of the telescope point spread function, but present challenges in suppression of stray light and RF interference. FIRST and Planck Surveyor are planned satellite missions involving passively cooled (∼70 K) telescopes, and bolometer array developments for these missions are described.

Stray light rejection in rotational coherent anti-Stokes Raman spectroscopy by use of a sodium-seeded flame

A common experimental problem with rotational coherent anti-Stokes Raman spectroscopy (CARS) is undesired spectral interference that is due to stray light from the primary laser beams. Also, for the most developed approach, dual-broadband rotational CARS, practical measurements often suffer from stray light interference from the narrow-band laser, inasmuch as the CARS signal is produced inherently in the spectral vicinity of the narrow-band laser beam. An optical filter does not provide a sufficiently sharp transmission profile, thus leading to signal loss and spectral distortion of the rotational CARS signal. An atomic filter consisting of a sodium-seeded flame is presented here as a solution to the problem, and its usefulness was demonstrated in dual-broadband rotational CARS experiments.

Technical note On the influence of stray light on total ozone measurements made with Dobson spectrophotometer no. 118 in Athens, Greece

Dobson spectrophotometer measurements are known to be subject to stray light errors. To study these errors with Dobson spectrophotometer no. 188 in Athens, Greece, a series of total ozone measurements were taken out to high airmasses extending as far as mu = 3.0. The results were compared to the simple monochromatic-heterochromatic stray light model introduced by Basher. These comparisons showed that the instrument's Ro value was between 10-3.5 and 10-3.4. These Ro values indicate that the instrument does not introduce any stray light interference for the regular observations performed at Athens. The value of the other parameter, a, of the Basher model varied between 0.6 and 0.9, having a weak dependence on the total ozone amount.

Conformational changes of bovine serum albumin upon its adsorption in dodecane-in-water emulsions as revealed by front-face steady-state fluorescence

Front-face fluorescence spectroscopy was used to characterise dodecane-in-buffer (0.1 M phosphate buffer; pH = 7.6) emulsions stabilised by bovine serum albumin (BSA). A 15-nm blue-shift of the emission maximum of the adsorbed protein and a significant increase of its fluorescence quantum yield were observed. The contribution of tyrosyl residues to total fluorescence was tentatilely evaluated from difference spectra and an R ratio talking into account the stray-light interference; R increased upon BSA adsorption but the Tyrosine contribution remained weak in all cases. Thus, conformational changes of the protein take place upon BSA adsorption onto the dodecane-water interface. They involve modifications in the environment of the protein aromatic amino acids specially of the tryptophanyl residues which are displayed to a more hydrophobic location. Moreover, the proportions of adsorbed and non-adsorbed BSA in emulsions can be estimated from the position of the emission maximum.

Applications of a d.c. plasma emission spectrometer (DCP) to the analysis of envrionmental samples

A direct current plasma spectrometer system has been used to determine specific trace elements in samples collected during several marine monitoring surveys. The data is currently being used to assess the impact on the environment of North Sea oil exploitation. The trace elements are routinely monitored in sediment and shellfish extracts and in oil terminal water effluents. The techniques used in conjunction with the d.c. plasma system are evaluated. Stray light and spectral interference problems from calcium and magnesium emissions are identified. Compensation for the interferences using simple linear corrections are described. Analysis of standard reference materials indicates that the direct current plasma system yields results comparable to other analytical techniques.

Dynamic range and stray light. An estimate of the falsifying effects of stray light in perimetry.

The role of intraocular stray light upon contrast threshold of two skilled human observers was studied by perimetric methods using the automatic perimeter Octopus. Stray light falsifies the contrast sensitivity profile of the blind spot when a critical test stimulus luminance, which differs for various targets, is exceeded. At still higher test stimulus luminance, which differs for various targets, is exceeded. At still higher luminance levels, because stray light effects increase, the blind spot shrinks and finally disappears. A series of high resolution measurements of the blind spot with the automatic perimeter Octopus provide a quantitative answer concerning the commencement and amount of this disturbance as a function of target size and target luminance. The amount of stray light, when using targets varying from 0 to 5 (Goldmann standard) is related to luminous power (target luminance x target area). Using first order assumptions about the stray light emitting characteristics of the disc and empirical data, one may conclude that an increase in luminance of target 0 from 10(3) to 10(5) asb only increases the effective dynamic range by about 2 dB (= 0.2 log units 3, the standard target as compared with target) size used in Octopus perimetry, at a luminance level of 10(3) asb. Falsification of sensitivity gradients and underestimates of depths of scotomata due to stray light effects may be an ever present danger in perimetric determinations. The useful dynamic range in perimetry appears to be limited by photon noise and noise in the neurovisual system on the one hand and by stray light interference on the other.

Einfluss des in einem Spektrallinienphotometer auftretenden Streulichtes auf die Schwärzungskurve

The paper deals with the interference effect of scattered light in a microphotometer of the type Zeiss G2 (Schnellphotometer), widely spread in Europe for several decades. The investigations are based on comparative measurements with a Joyce-Loebl MK III CS photometer. A review of the relevant literature is followed by a discussion of the linearity error of the photometer. The main substance of the paper is formed by the treatment of the mathematical relationships between the relative intensity of scattered light and the transmittance readings, the deformation of the characteristic curves, the determination of the intensity of scattered light either by calculation or graphically, and a discussion of the change in slope of the deformed characteristic curve. It was found that as a result of the straylight interference the characteristic curve is no longer linear but assumes an S-shape with saturation character. The paper further describes procedures for correcting measuring errors and is completed by conclusions.

Stray light interference in the spectrophotometric measurement of enzyme activity and determination of kinetic parameters

Adenylosuccinate synthetase (E.C. 6.3.4.4) Mg ++ was assayed spectrophotometrically at 280 nm using two double-beam instruments with different stray light specifications, and by a radioactive assay. Using the spectrophotometric assay, inhibition by high concentration of GTP and by GMP is observed; a Hill plot of the GMP inhibition data obtained with the instrument of higher stray light seems to show cooperativity in GMP binding. The radioactive assay shows no inhibition by GTP at the concentrations studied and no cooperativity in the binding of GMP. This example illustrates the care that must be exercised in the interpretation of results obtained spectrophotometrically in solution of high absorbance.