Unpolarized Intensity Research Articles

Development of a rapid polarized total synchronous fluorescence spectroscopy (pTSFS) method for protein quantification in a model bioreactor broth.

Protein quantification during bioprocess monitoring is essential for biopharmaceutical manufacturing and is complicated by the complex chemical composition of the bioreactor broth. Here we present the early-stage development and optimization of a polarized total synchronous fluorescence spectroscopy (pTSFS) method for protein quantification in a hydrolysate-protein model (mimics clarified bioreactor broth samples) using a standard benchtop laboratory fluorometer. We used UV transmitting polarizers to provide wider range pTSFS spectra for screening of the four different TSFS spectra generated by the measurement: parallel (||), perpendicular (⊥), unpolarized (T) intensity spectra and anisotropy maps. TSFS|| (parallel polarized) measurements were the best for protein quantification compared to standard unpolarized measurements and the Bradford assay. This was because TSFS|| spectra had a better analyte signal to noise ratio (SNR), due to the anisotropy of protein emission. This meant that protein signals were better resolved from the background emission of small molecule fluorophores in the cell culture media. SNR of >5000 was achieved for concentrations of bovine serum albumin/yeastolate 1.2/10 g L-1 with TSFS|| . Optimization using genetic algorithm and interval partial least squares based variable selection enabled reduction of spectral resolution and number of excitation wavelengths required without degrading performance. This enables fast (<3.5 min) online/at-line measurements, and the method had an LOD of 0.18 g L-1 and high accuracy with a predictive error of <9%.

Structured illumination Mueller matrix imaging

We perform Mueller matrix imaging (MMI) of diffusely scattering phantoms under sinusoidal irradiance of varying spatial frequency. Quantitative polarimetric sensing via MMI completely characterizes a sample's polarimetric properties, while structured illumination (SI) allows for the control of photon path length. Intralipid phantoms were measured with varying absorption and with varying depth to demonstrate photon path length control for Mueller matrix elements. We observe unpolarized intensity, linear polarization, and circular polarization to depend upon spatial frequency differently. Finally, we measured an ex vivo chicken skin sample over a bright and dark substrate to further demonstrate the sensitivity of SI-MMI to depth.

Partially polarized black-body radiation

Angular temperature fluctuations in a photon gas generate fractional polarization of the black-body spectrum. The spectral density consists of two Planckians with different temperature variables representing orthogonal polarization states. The angular-dependent fluctuating temperature variables can be inferred from the Stokes parameters which have been measured, over the full solid angle, for the cosmic microwave background (CMB) radiation. The polarization matrix of a partially polarized photon gas is obtained by way of a unitary transformation of the annihilation and creation operators. The radiation is decomposed into a totally polarized and an unpolarized intensity component, and the polarization fraction is calculated, which is very small, of order ∼10−7, for the nearly isotropic CMB radiation. Spatial energy density autocorrelations induced by polarization and temperature anisotropy are derived and isotropized by an angular average. These correlations are long-range, exhibiting power-law decay ∝1∕r6 at large distance, and much stronger than the energy density correlation of an ideal photon gas which decays ∝1∕r8. As for the CMB radiation, the spatial energy density correlations are calculated from analytic Gaussian fits to the measured temperature and polarization power spectra, including the crossover from the short-distance regime to the asymptotic power-law decay.

HAWC+/SOFIA Multiwavelength Polarimetric Observations of OMC-1

Abstract We report new polarimetric and photometric maps of the massive star-forming region OMC-1 using the HAWC+ instrument on the Stratospheric Observatory for Infrared Astronomy. We present continuum polarimetric and photometric measurements of this region at 53, 89, 154, and 214 μm at angular resolutions of 5″, 8″, 14″, and 19″ for the four bands, respectively. The photometric maps enable the computation of improved spectral energy distributions for the region. We find that at the longer wavelengths, the inferred magnetic field configuration matches the “hourglass” configuration seen in previous studies, indicating magnetically regulated star formation. The field morphology differs at the shorter wavelengths. The magnetic field inferred at these wavelengths traces the bipolar structure of the explosive Becklin–Neugebauer/Kleinman–Low outflow emerging from OMC-1 behind the Orion Nebula. Using statistical methods to estimate the field strength in the region, we find that the explosion dominates the magnetic field near the center of the feature. Farther out, the magnetic field is close to energetic equilibrium with the ejecta and may be providing confinement to the explosion. The correlation between polarization fraction and the local polarization angle dispersion indicates that the depolarization as a function of unpolarized intensity is a result of intrinsic field geometry as opposed to decreases in grain alignment efficiency in denser regions.

Radiative albedo from a linearly fibered half-space

.A growing acceptance of fiber-reinforced composite materials imparts some relevance to exploring the effects which a predominantly linear scattering lattice may have upon interior radiative transport. Indeed, a central feature of electromagnetic wave propagation within such a lattice, if sufficiently dilute, is ray confinement to cones whose half-angles are set by that between lattice and the incident ray. When such propagation is subordinated to a viewpoint of an unpolarized intensity transport, one arrives at a somewhat simplified variant of the Boltzmann equation with spherical scattering demoted to its cylindrical counterpart. With a view to initiating a hopefully wider discussion of such phenomena, we follow through in detail the half-space albedo problem. This is done first along canonical lines that harness the Wiener-Hopf technique, and then once more in a discrete ordinates setting via flux decomposition along the eigenbasis of the underlying attenuation/scattering matrix. Good agreement is seen to prevail. We further suggest that the Case singular eigenfunction apparatus could likewise be evolved here in close analogy to its original, spherical scattering model. A cursory contact with related problems in the astrophysical literature suggests, in addition, that the basic physical fidelity of our scalar radiative transfer equation (RTE) remains open to improvement by passage to a (4×1) Stokes vector, (4×4) matricial setting.

Bandpass mismatch error for satellite CMB experiments I: estimating the spurious signal

Future Cosmic Microwave Background (CMB) satellite missions aim to use the B mode polarization to measure the tensor-to-scalar ratio r with a sensitivity σr ≲ 10−3. Achieving this goal will not only require sufficient detector array sensitivity but also unprecedented control of all systematic errors inherent in CMB polarization measurements. Since polarization measurements derive from differences between observations at different times and from different sensors, detector response mismatches introduce leakages from intensity to polarization and thus lead to a spurious B mode signal. Because the expected primordial B mode polarization signal is dwarfed by the known unpolarized intensity signal, such leakages could contribute substantially to the final error budget for measuring r. Using simulations we estimate the magnitude and angular spectrum of the spurious B mode signal resulting from bandpass mismatch between different detectors. It is assumed here that the detectors are calibrated, for example using the CMB dipole, so that their sensitivity to the primordial CMB signal has been perfectly matched. Consequently the mismatch in the frequency bandpass shape between detectors introduces differences in the relative calibration of galactic emission components. We simulate this effect using a range of scanning patterns being considered for future satellite missions. We find that the spurious contribution to r from the reionization bump on large angular scales (ℓ < 10) is ≈ 10−3 assuming large detector arrays and 20 percent of the sky masked. We show how the amplitude of the leakage depends on the nonuniformity of the angular coverage in each pixel that results from the scan pattern.

Visual sensitivity and spatial resolution of the planktivorous fish, Atherinomorus forskalii (Atherinidae; Rüppell, 1838), to a polarized grating

Polarized light detection has been documented in only a small number of fish species. The benefit of polarization vision for fish is not fully understood, nor is the transduction mechanism that underlies it. Past studies proposed that one possible advantage of polarization vision is that it enhances the contrast of zooplankton targets by breaking their transparency. Here, we used an optomotor apparatus to test the responses of the planktivorous Hardyhead silverside fish Atherinomorus forskalii (Atherinidae) to vertical unpolarized (intensity) and polarized gratings. We also tested and compared the spatial and temporal resolutions of A. forskalii in the intensity and polarization domains. A. forskalii responded to the polarization pattern, but only under illumination that included ultraviolet-blue (λ>380nm) wavelengths. The spatial resolution of A. forskalii was measured as a minimum separable angle of 0.57° (a 1-mm prey viewed from 100-mm distance). The temporal resolution to unpolarized vs. polarized gratings was constant, at 33 and 10Hz respectively at most of the stripe widths tested. At the smallest stripe width tested (1mm=the minimal separable angle), which correlates with the size of prey typically consumed by these fish, the temporal resolution to the polarized grating increased to 42Hz. We conclude that A. forskalii is polarization sensitive, may use polarization vision to improve detection of its planktonic prey, and that polarization may be perceived by the fish via a separate visual pathway than intensity.

A high definition Mueller polarimetric endoscope for tissue characterisation.

The contrast mechanism of medical endoscopy is mainly based on metrics of optical intensity and wavelength. As another fundamental property of light, polarization can not only reveal tissue scattering and absorption information from a different perspective, but can also provide insight into directional tissue birefringence properties to monitor pathological changes in collagen and elastin. Here we demonstrate a low cost wide field high definition Mueller polarimetric endoscope with minimal alterations to a rigid endoscope. We show that this novel endoscopic imaging modality is able to provide a number of image contrast mechanisms besides traditional unpolarized radiation intensity, including linear depolarization, circular depolarization, cross-polarization, directional birefringence and dichroism. This enhances tissue features of interest, and additionally reveals tissue micro-structure and composition, which is of central importance for tissue diagnosis and image guidance for surgery. The potential applications of the Mueller polarimetric endoscope include wide field early epithelial cancer diagnosis, surgical margin detection and energy-based tissue fusion monitoring, and could further benefit a wide range of endoscopic investigations through intra-operative guidance.

The origins of polarimetric image contrast between healthy and cancerous human colon tissue

Experimentally measured spectral Mueller matrix images of ex vivo human colon tissue revealed the contrast enhancement between healthy and cancerous zones of colon specimen compared to unpolarized intensity images. Cancer development starts with abnormal changes which being not yet visible macroscopically may alter the polarization of reflected light. We have shown with experiments and modeling that light scattering by small (sub wavelength) scatterers and light absorption (mainly due to blood hemoglobin) are the key factors for observed polarimetric image contrast. These findings can pave the way for the alternative optical technique for the monitoring and early detection of cancer.

Detectability of tensor modes in the presence of foregrounds

In inflationary models gravitational waves are produced in the early universe and generate $B$-type polarization in the cosmic microwave background (CMB). Since $B$ polarization is only generated by gravity waves it does not suffer from the usual cosmic variance. A perfect decomposition of the CMB into $B$-modes and $E$-modes would require data from the entire sky, which in practice is not possible because of the foreground contaminants. This leads to mixing of $E$ polarization into $B$, which introduces cosmic variance contamination of $B$ polarization and reduces sensitivity to gravity wave amplitude even in absence of detector noise. We present numerical results for the uncertainty in the tensor-to-scalar ratio using the Fisher matrix formalism for various resolutions and considering several cuts of the sky, using the foreground model based on dust maps and assuming 90 GHz operating frequency. We find that the usual scaling $△(\frac{T}{S})\ensuremath{\propto}{f}_{\mathrm{sky}}^{\ensuremath{-}1/2}$ is significantly degraded and becomes $△(\frac{T}{S})\ensuremath{\propto}{f}_{\mathrm{sky}}^{\ensuremath{-}2}$ for ${f}_{\mathrm{sky}}&gt;0.7$. This dependence is affected only weakly by the choice of sky cuts. To put this into a context of what is required level of foreground cleaning, to achieve a $T/S={10}^{\ensuremath{-}3}$ detection at $3\ensuremath{\sigma}$ one needs to observe 15% of the sky as opposed to naive expectation of 0.3%. To prevent contamination over this large sky area at required level one must be able to remove polarized dust emission at or better than 0.1% of unpolarized intensity, assuming the cleanest part of the sky has been chosen. To achieve $T/S={10}^{\ensuremath{-}4}$ detection at $3\ensuremath{\sigma}$ one needs to observe 70% of the sky, which is only possible if dust emission is removed everywhere over this region at 0.01% level. Reaching $T/S={10}^{\ensuremath{-}2}$ should be easier: 1% of the sky is needed over which polarized emission needs to be removed at 1% of unpolarized intensity if the cleanest region is chosen. These results suggest that foreground contamination may make it difficult to achieve levels below $T/S={10}^{\ensuremath{-}3}$.

Systematic effects in the measurement of polarization by the PLANCK telescope

We present estimates of the response to polarized signals by the PLANCK telescope. These estimates are based on a set of simulations, using a physical optics code (GRASP8), for linearly polarized detectors at different frequencies and located in different positions of an early design of the PLANCK focal plane. We show how the optical aberration introduced by the studied focal plane configuration affects absolute and relative orientation of the sky signals polarization planes. In addition, we compute the spurious signal introduced by the telescope optics into a PLANCK-type measurement of the sky polarization. Our analysis shows that the spurious polarization expected in a PLANCK-like experiment is typically of the order of 0.2% of the unpolarized intensity.

Electron Injection Dynamics of RuII(dcbpy)2(SCN)2on Zirconia

The electron injection dynamics of RuII(4,4‘-dicarboxy-2,2‘-bipyridine)2(SCN)2 (the so-called N3-dye) adsorbed on colloidal ZrO2 particles in room-temperature solution have been studied using time-resolved absorption polarization spectroscopy. The solvents used are acetonitrile and methanol. Electron injection is evidenced by the transient absorption anisotropy and/or the wavelength-dependent unpolarized absorption intensity. The results indicate that 630 nm excitation results in no N3* to ZrO2 electron transfer in both acetonitrile and methanol solvents, 515 nm excitation results in electron injection in acetonitrile, and 495 nm excitation results in electron injection in both acetonitrile and methanol. These results may be understood in terms of simple energetic considerations: 630 nm excitation produces N3* with insufficient energy for electron injection while 495 nm excitation produces N3* with an energy just sufficient for electron injection. In all cases where electron injection is energetically fa...

Calibration and exploitation of a narrow-band imaging polarimeter

The integration and calibration of a narrow-band imaging po- larimeter is described. The system is designed to exploit subtle spectral details in visible and near-IR polarimetric images. All of the system components were commercial off the shelf. This device uses a tunable liquid crystal filter and a 16-bit cooled CCD camera. The challenges of calibrating a narrow-band imaging polarimeter are discussed. We describe examples of image data collected in the laboratory, which show that spectral polarimetric data is superior to unpolarized intensity data in facilitating the extraction of detail in shadowed regions below a vegetative canopy. In particular, we introduce a polarization-based normalized difference vegetation index (NDVI) algorithm that demonstrates significant contrast enhancement between a man-made object and a foilage background.

Near‐Infrared Polarimetric Study of Monoceros R2 IRS

We present H- and Ks-band imaging polarimetry for the star-forming region Mon R2 IRS, and spectropolarimetry from 1.2 to 4.2 μm for the infrared sources IRS 2 and IRS 3. The nebular complex in Mon R2 IRS is revealed to be composed of four domains dominated by the infrared sources IRS 1, IRS 2, IRS 3, and IRS 6. IRS 2 is the predominant illuminating source in the region and dominates the emission of the IR ring and most of the western part of the nebulosity. IRS 1 is responsible for the enhanced unpolarized intensity in the southeast part of the IR ring and inside the IR ring. IRS 3 illuminates the bright eastern nebula, and together with IRS 2 illuminates the eastern region inside the IR ring. IRS 6 illuminates a small nebula to the south of the IR ring. An arc structure of polarized intensity is observed abutting the northwest IR ring, consistent with the outflow cavity structure inferred from millimeter-wave observations. IRS 3 is associated with a disklike condensation oriented southeast-northwest, perpendicular to the elongated eastern nebula. The magnetic field in the core region exhibits an hourglass structure oriented north-south.

Morphology and movements of polarizations features on Venus as seen in the pioneer Orbiter Cloud Photopolarimeter data

Polarization observations obtained from the Orbiter Cloud Photopolarimeter (OCPP) show local, organized features whose morphology is similar to that of the ultraviolet clouds. No obvious correlation between the observed amount of polarization and relative brightness was found, suggesting that the polarization features are not due to variations in the unpolarized intensity alone, but rather to other causes such are the existence of a haze. Many of the features that can be seen even at 935 nm wavelength are believed to be signatures of local variations in the haze of submicron-size particles that have been detected from the OCCP data ( K. Kawabata, D. L/ Cooffeen, J. E. Hansen, W. A. Lane, M. Sato, and L. D. Travis (1980). J. Geophys. Res. 85, 8129–8140). Substantial variations in the structure and visibility of the polarization features that are observed suggest that the haze amount mixed with and above the main cloud layer may not be constant by varies with time. Some of these features last for least a few days thus allowing measurements of their apparent motions. The small number of measurements possible from the available data shows movements similar to those of the ultraviolet clouds in both direction and speed. According to Kawabata et al. the haze extends well above the main cloud layer to about 5 mb pressure level while the optical depth unity at 365 nm (corresponding to the level of the ultraviolet clouds tracked to infer the cloud-top level circulation) occurs at about 30 mb pressure level. Thus, the rapid retrograde circulation suggested by the movements of haze features in the polarimetry data would indicate that the layer in which such rapid circulation exists is fairly deep.

A high-purity circular polarization modulator: Application to birefringence and circular dichroism measurements on multidielectric mirrors

We present a method for producing a modulated circular polarization of high purity, i.e. whose modulation frequency allows specific discrimination against linear polarization and unpolarized intensity. We apply it to measure the circular dischroism and birefringence of high reflectivity multidielectric mirrors: no circular dichroism is observed at a level of 10 −6, but birefringence values from 3 x 10 −4 to 2 x 10 −3 radian per reflexion under normal incidence are obtained.