Spectral Polarization Measurements Research Articles

GoSPo: a goniospectropolarimeter to assess reflectance, transmittance, and surface polarization as related to leaf optical properties

Visible-near infrared (VIS-NIR) spectral data are widely used for remotely estimating a number of crop health metrics. In general, these indices and models do not explicitly account for leaf surface characteristics, which themselves can be indicators of plant status or environmental responses. To explicitly include leaf surface characteristics, data are required linking optical properties to surface characteristics. We present the design and experimental validation of a goniospectropolarimeter (GoSPo) that combines the capabilities of a spectrometer, goniometer, and polarimeter. GoSPo was designed with the objective of studying the relationships between leaf surface characteristics and the resulting light reflectance, transmission, and polarization as functions of both direction and VIS-NIR spectra. Using six motors, a pneumatic system, two spectrometers, and a combination of lenses, polarizers, and mirrors, GoSPo can examine a leaf from a particular angle, approximate hemispherical transmittance and reflectance (with root-mean-square error values of 0.0189 and 0.0216 for reflectance and transmittance, respectively, compared to a spectrophotometer and integrating sphere), and obtain spectral polarization measurements without disrupting the sample between measurements. The data collected with GoSPo will aid in model development for remote sensing applications.

EVIDENCES FOR STRONG MIXED-POLARITY MAGNETIC FIELDS IN AREA OF A SEISMIC SOURCE ASSOCIATED WITH LARGE PROTON SOLAR FLARE

We present in a concise statement the new results based on spectral-polarization measurements of magnetic fields in an extremely powerful proton solar flare on October 28, 2003 of X17.2 / 4B class. The observation material was obtained with Echelle spectrograph of HST AO KNU, which makes it possible to analyze the spectral manifestations of the Zeeman effect in very many lines of the visible region of the spectrum, including the photospheric and chromospheric lines. The I ± V and V profiles of about ten FeI and FeII lines, as well as the Hα, Hβ, Hγ, and Hδ lines were studied in a area of the seismic source of the flare, which was localized in the sunspot penumbra of S magnetic polarity. In this flare, we found an unprecedented Balmer decrement of intensities of Hα and Hβ lines which corresponds to ratio I (Hβ) / I (Hα) = 1.68. In the FeI 5434.5 line with very low Lande factor (g eff = –0.014), a reliable splitting of emission peaks was found, which could indicate superstrong magnetic fields (about 50 kG) of N polarity. Indications for magnetic fields with intensity ≈ 12 kG of S polarity were found too. These indications are based on the study of the Stokes V profile of FeII 5234.6 line. In this line, there were two positive and two negative peaks of profile V, indicating a two- component structure of the magnetic field. According to the simulation data, the small-scale component with the above-mentioned superstrong magnetic field had a filling factor about 0.1 and had narrow (about twice) the half- widths of the line profiles. The close contact of subtelescopic magnetic fields of different magnetic polarity, but of lower intensity (B ≈ 1 kG) was also indicated by the comparison of the half-widths of the FeI 5247.1 and 5250.2 lines. In general, it can be concluded that the necessary conditions for the reconnection of magnetic lines were fulfilled even at the photospheric level, rather than in the corona or chromosphere, as suggested by theoretical models of solar flares.

Vectorial Phase Retrieval for Linear Characterization of Attosecond Pulses

The waveforms of attosecond pulses produced by high-harmonic generation carry information on the electronic structure and dynamics in atomic and molecular systems. Current methods for the temporal characterization of such pulses have limited sensitivity and impose significant experimental complexity. We propose a new linear and all-optical method inspired by widely used multidimensional phase retrieval algorithms. Our new scheme is based on the spectral measurement of two attosecond sources and their interference. As an example, we focus on the case of spectral polarization measurements of attosecond pulses, relying on their most fundamental property-being well confined in time. We demonstrate this method numerically by reconstructing the temporal profiles of attosecond pulses generated from aligned CO(2) molecules.

Magnetic field in active regions of the sun at coronal heights

AbstractA method is developed for estimation of the vertical structure of the magnetic field in active regions using multi-wave spectral-polarization measurements of radio waves which gives not only the dependence of magnetic field strength on height but also determines two-dimensional form of a magnetic flux tube, emitted in the microwave range of wavelengths.

A Complete Spectral Polarimeter Design for Lightwave Communication Systems

The authors describe a fast spectral polarimeter operating in the lightwave communications band capable of measuring both state-of-polarization and degree-of-polarization of hundreds (up to thousands) of spectral components in parallel within milliseconds. In this paper, the design incorporates fast switching ferroelectric liquid crystals for polarization component selection on the 100-mus scale. Dispersion elements and an arrayed detector are used for wavelength-parallel sensing. Bandwidth of coverage can be scaled from a single wavelength-division multiplexed channel to more than 100 nm, and 256 spectral polarization measurements in under 1 ms are verified. Finally, a calibration algorithm is used to minimize measurement error. This instrument offers unprecedented sensing capability relevant to the monitoring and compensation of polarization-related impairments in high-speed lightwave communications

Monitoring PMD-induced penalty and other system performance metrics via a high-speed spectral polarimeter

We developed and tested a nonintrusive technique for estimating polarization-mode-dispersion-induced system penalties based on spectral polarization measurements. Other system characteristics such as power fluctuations and carrier-frequency drift could also be monitored simultaneously. Our spectral polarimeter works in milliseconds, and can be scaled to monitor all channels in the C-band

Broadband, high spectral resolution 2-D wavelength-parallel polarimeter for Dense WDM systems

A broadband wavelength-parallel polarimeter has been designed or polarization measurements of multiple Dense WDM channels in parallel, which is based on a 2-D spectral disperser via a diffraction grating and a virtually-imaged phased-array (VIPA). At a hyperfine 2.8 GHz sub-channel spacing, we have demonstrated spectral polarization measurements of ~1500 sub-channels (~32 nm spectral range), with a potential total measurement time of less than 5 ms.

Spectral polarization measurements by use of the grating division-of-amplitude photopolarimeter.

The grating division-of-amplitude photopolarimeter (G-DOAP) is an instrument that exploits the multiple-beam-splitting, polarizing, and dispersive properties of diffraction gratings for the time-resolved measurement of the complete state of polarization of collimated broadband incident light, as represented by the four Stokes parameters as a function of wavelength across the spectrum. It is a compact, high-speed sensor that has no moving parts and is simple to install and operate. These characteristics make the G-DOAP well suited for in situ spectroscopic ellipsometry (SE) applications for monitoring and controlling thin-film processes. The design and performance of a prototype instrument are presented. Precise SE measurements, to +/-0.04 degrees in psi and +/-0.1 degrees in delta, are demonstrated in the 550-940-nm wavelength range.

Diagnostics of the Solar Plasma Using Radio Observations with the RATAN-600

This paper summarises the methods and main results of studying physical parameters and processes in different structures of the solar atmosphere from the chromosphere to the outer corona as based on the observations with a 600-meter radio telescope the RATAN-600 (1975-1989). Diagnostics of the solar plasma have been made using the spectral-polarization measurements in the wavelength range 0.8-32 cm with high spatial resolution. The most important results concern the structure and strength of the magnetic fields at different levels of the solar atmosphere and detection of localized regions of long-lasting (several days) energy release in the lower corona.

Inversion of polarization measurements at BUV wavelengths to recover ozone and aerosol profiles

A method is proposed to recover stratospheric ozone and aerosol concentration profiles from satellite-borne polarimeter measurements of the ultraviolet light reflected from the earth’s atmosphere. A mathematical inversion is performed on simulated spectral polarization measurements demonstrating the recovery of ozone mixing ratio and aerosol scattering ratio profiles when large aerosol concentrations are present in the stratosphere.