Narrow-band Interference Filters Research Articles

Characteristic Analysis of Plasma Arc Adjusted by a Magnetic Field

The image collecting devices, which consist of optical lens, neutral density filter, narrow-band interference filter, CCD and the other equipments are set up to collect the images of plasma arc column with and without external transverse alternating magnetic field (ETAMF). On the basis of de-noising and enhancing morphological characteristics to the collected images, the characteristics of plasma arc with and without ETAMF are analyzed comparatively. The results show that the application of ETAMF is capable to get oscillation of plasma arc, and change its location, shape and heat flux density distribution, which can get efficiently control in the width of heated area and flatten heat flux density of workpiece surface.

Phase-locking of two self-seeded tapered amplifier lasers

We report on the phase-locking of two diode lasers based on self-seeded tapered amplifiers. In these lasers, a reduction of linewidth is achieved using narrow-band high-transmission interference filters for frequency selection. The lasers combine a compact design with a Lorentzian linewidth below 200 kHz at an output power of 300 mW for a wavelength of 780 nm. We characterize the phase noise of the phase-locked laser system and study its potential for coherent beam-splitting in atom interferometers.

Active and passive spectroscopic imaging in the DIII-D tokamak

Wide-angle, 2D imaging of Doppler-shifted, Balmer alpha (Dα) emission from high energy injected neutrals, charge exchange recombination (CER) emission from neutral beam interaction with thermal ions and fully stripped impurity ions and visible bremsstrahlung (VB) from the core of DIII-D plasmas has been carried out. Narrowband interference filters were used to isolate the specific wavelength ranges of visible radiation for detection by a tangentially viewing, fast-framing camera. Measurements of the Dα emission from fast neutrals injected into the plasma from the low field side reveal the vertical distribution of the beam, its divergence and the variation in its radial penetration with density. Modeling of this emission using both a full Monte Carlo collisional radiative code as well as a simple beam attenuation code coupled to Atomic Data and Analysis Structure emissivity lookup tables yields qualitative agreement, however the absolute magnitudes of the emissivities in the predicted distribution are larger than those measured. Active measurements of carbon CER brightness are in agreement with those made independently along the beam midplane using DIII-D's multichordal, CER spectrometer system, confirming the potential of this technique for obtaining 2D profiles of impurity density. Passive imaging of VB, which can be inverted to obtain local emissivity profiles, is compared with measurements from both a calibrated filter/photomultiplier array and the standard multichordal CER spectrometer system.

Voltage-controlled negative resistance and electroluminescent spectra of Al–Al2O3–Au diodes

Dielectric breakdown of metal-insulator-metal (MIM) diodes can result in the development of voltage-controlled negative resistance (VCNR) in the current-voltage (I-V) characteristics. Electroluminescence from the MIM diode appears at the same time as VCNR develops. The spectra of electroluminescence associated with VCNR of Al–Al2O3–Au diodes with anodic Al2O3 has been measured for photon energies between 1.8 eV, the lowest photon energy the photomultiplier can detect, and 3.4 eV, using narrow-band interference filters. Electroluminescent photons have maximum intensity between 1.8 and 2.4 eV with a peak at ∼2.2 eV. The voltage threshold for electroluminescence in Al–Al2O3–Au diodes, VTH, is 1.7 to 2.0 V; it is associated with an impurity band in amorphous Al2O3. Electrons injected into the impurity band can recombine with radiative centers in Al2O3 or can be emitted into vacuum. The range of values of VTH is the same as the range of values of the barrier height at the Al–Al2O3 interface measured by internal photo emission or by tunneling. The spectral data support a model of conduction and VCNR in a conducting channel. Dielectric breakdown and forming of VCNR introduce positive charge at the Al–Al2O3 interface that results in an Ohmic contact and a high field region in the conducting channel. Electrons injected into Al2O3 when the applied voltage is greater than VTH neutralize positive charge, change the Ohmic contact, and cause a decrease in current with increasing voltage. The radiative centers involved in electroluminescence are also responsible for other forms of luminescence in Al2O3.

Optical imaging and spectroscopic observation of the galactic supernova remnant G85.9-0.6

Optical CCD imaging with H$\alpha$ and [SII] filters and spectroscopic observations of the galactic supernova remnant G85.9-0.6 have been performed for the first time. The CCD image data are taken with the 1.5m Russian-Turkish Telescope (RTT150) at TUBITAK National Observatory (TUG) and spectral data are taken with the Bok 2.3 m telescope on Kitt Peak, AZ. The images are taken with narrow-band interference filters H$\alpha$, [SII] and their continuum. [SII]/H$\alpha$ ratio image is performed. The ratio obtained from [SII]/H$\alpha$ is found to be $\sim$0.42, indicating that the remnant interacts with HII regions. G85.9-0.6 shows diffuse-shell morphology. [SII]$\lambda\lambda 6716/6731$ average flux ratio is calculated from the spectra, and the electron density $N_{e}$ is obtained to be 395 $cm^{-3}$. From [OIII]/H$\beta$ ratio, shock velocity has been estimated, pre-shock density of $n_{c}=14$ $cm^{-3}$, explosion energy of $E=9.2\times10^{50}$ ergs, interstellar extinction of $E(B-V)=0.28$, and neutral hydrogen column density of $N(HI)=1.53\times10^{21}$ $cm^{-2}$ are reported.

Wide angle mirror system design for distortionless imaging of the sky

We describe a dual-mirror wide angle optical design, which removes the radial distortion associated with traditional all-sky optics for a chosen altitude. The wide angle mirror system provides a transform of the sky, for a selected altitude, as if the viewer is situated at the center of the Earth. Other advantages of the system include (1) real time achromatic transform, (2) higher optical gain compared to pure lens systems, (3) a quasi-telecentric optic capable of taking narrowband interference filters without modification, and (4) a uniform sky spatial resolution everywhere on the detector. Disadvantages include (1) cost of manufacture and (2) focusing issues, especially near the horizon.

Laser-induced breakdown spectroscopy for branching ratio and atomic lifetime measurements in singly-ionized neodymium and gallium

Precision laboratory astrophysics measurements can be made in laser-induced plasmas created for laser-induced breakdown spectroscopy. Branching ratios from highly-energetic levels in singly-ionized neodymium may be measured by observing spontaneous emission in laser-induced plasmas in an argon environment at decreased pressures (~ 7.7 mbar). Utilizing a broadband Èchelle spectrometer with a spectral range from 200–840 nm, the spontaneous emission intensities from hundreds of transitions originating in 138 energy levels in Nd I, Nd II, and Nd III have been observed simultaneously, allowing the determination of branching ratios for these energy levels for branches greater than 1% in the visible wavelength range. In this study, eight branching ratios from the 23,229.991 cm − 1 level in Nd II were measured and compared to previously determined values as a method for optimizing experimental conditions such as buffer gas pressure and observation delay time. The branching ratios of the eight branches were found to be in excellent agreement with three previously determined values from both experiment and theory. A plan to utilize this laser-induced plasma apparatus to measure the lifetime of the 4 s5 p 3 P 2 level at 118,727.89 cm − 1 in singly-ionized gallium using a cascade-photon-coincidence method is also presented. Utilizing a solid Ga target ablated in a helium environment, “start photons” at 541.6 nm from a transition into the 4 s5 p 3 P 2 level and “stop photons” at 633.4 nm from a transition out of that Ga II energy level were observed. Single-photon detection will be accomplished using avalanche photodiodes with narrowband interference filters and delay times between the detection of coincident photons from these two transitions will be measured.

Mars Reconnaissance Orbiter Mars Color Imager (MARCI): Instrument description, calibration, and performance

The Mars Color Imager (MARCI) instrument aboard the NASA Mars Reconnaissance Orbiter spacecraft is a wide‐angle, multispectral Charge‐Coupled Device (CCD) “push frame” imaging camera designed to provide frequent, synoptic‐scale color imaging of the Martian atmosphere and surface. MARCI uses a 1024 × 1024 pixel interline transfer CCD detector that has seven narrowband interference filters bonded directly to the CCD. Five of the filters are in the visible to short‐wave near‐infrared wavelength range (437, 546, 604, 653, and 718 nm) and two are in the ultraviolet range (258 and 320 nm). Here we describe the scientific objectives of the MARCI investigation and the basic characteristics, calibration, and in‐flight performance of the MARCI instrument. We include several examples of early scientific results and investigations enabled by an extensive preflight and in‐flight calibration program and by validation of the performance of the instrument in flight.

Notes on Temperature-Dependent Lidar Equations

AbstractThe temperature dependence of molecular backscatter coefficients must be taken into account when narrowband interference filters are used in lidar measurements. Thus, the spectral backscatter differential cross section of the molecules involved in the backscattering of the radiation has to be calculated or measured and the interference filter transmission efficiency must be known. The present paper is intended to describe in an easily reproducible manner the procedure involved in calculating the temperature-dependent functions introduced in the lidar equations, including the computation of the differential cross sections for air, nitrogen, and water vapor. The temperature-dependent functions are computed for the Howard University Raman lidar (HURL). The interference filter efficiencies are given by the manufacturer. Error estimates in water vapor mixing ratio and aerosol backscatter ratio involved when temperature-dependent functions are omitted are given for measurements taken with HURL. For the data analyzed, it is found that errors in estimating the water vapor mixing ratio are up to ∼6% while in estimating the aerosol backscattering ratio the errors are up to ∼1.3% in the planetary boundary layer and ∼2.2% in cirrus clouds. Theoretical computations are performed to determine temperature-dependent functions for nitrogen, water vapor, and their ratio, using simulated Gaussian-shaped filters. The goal is to find the optimum combination of different filters that will determine the ratio profiles of the temperature-dependent functions that are either the closest to unity or the least variable. The analyses reveal that quite constant profiles can be obtained for several combinations of the filters.

Accurate temperature profiling of the atmospheric boundary layer using an ultraviolet rotational Raman lidar

An ultraviolet rotational Raman lidar (RRL) system at an eye-safe wavelength of 354.7 nm is demonstrated for profiling the vertical temperature of the atmospheric layer. Two sets of narrow-band interference filters, which central wavelengths are located at 353.9 and 352.5 nm, respectively, are employed to block the elastic Mie- and Rayleigh-scattering signals and to separate two required rotational Raman signals for temperature retrieval. Experiments were carried out for verifying the feasibility of the prototype of the ultraviolet RRL from May to November in 2008, and the system calibrations were performed with the radiosonde data which were obtain from the local meteorological bureau, and good agreements were got in the experiment results. The observation results show that a statistical temperature error of less then 1 K was obtained up to the heights of 2.5 km for nighttime and 2.0 km for daytime with 300 mJ laser energy and ∼8 min observation time.

Fast ion Dα imaging in the DIII-D tokamak

Doppler shifted fast ion Dα light (FIDA) emitted by neutralized energetic ions is imaged in the DIII-D tokamak using a fast framing camera in conjunction with a narrowband interference filter. Both the 2D spatial structure and temporal evolution of the FIDA emission are in agreement with Monte Carlo simulations assuming classical energetic ion slowing down. This technique can be used to obtain 2D energetic ion profile information in fusion plasmas.

Flame Imaging for Safety Surveillance

Flame detection is important for prevention of spreading of accidental fires. When combustible gas is ignited under daylight conditions, the flame is often difficult to detect by conventional imaging because of the high background radiation. The flame can be visualized by selectively detecting the emission of the OH radical, which is present in hydrocarbon or hydrogen flames. By detecting the OH radical emission in the solar blind region of wavelength below 290 nm, the background radiation can be effectively eliminated. In this study, an experimental device for visualization of flame at wavelength 285 nm was constructed. A combination of two narrowband interference filters was found to be sufficient to eliminate background radiation and selectively image the OH emission. The device could detect butane burner flame under daylight conditions.

Structure in RF Hydrogen Plasma Induced by Magnetic Field

Images of the spatial structure of a capacitively coupled hydrogen discharge are presented for various strengths of applied magnetic field. With increasing magnetic field, we find that not only does the distribution of emission change because of the confinement of the electrons by the magnetic field, but we also find dark-bands regions that form in the discharge. By using narrowband interference filters (~10 nm bandwidth), we examine how the relative optical emission centered on Halpha and Hbeta (with respect to the total optical emission) change with the applied magnetic field.

Investigation of a Novel Large Area Dispersed Arc Plasma Source With Time-Resolved ICCD Imaging

Unsaturated time-resolved end-on images of argon arc plasma at 1 atm were captured by an intensified charge-coupled device equipped with a narrowband interference filter to evidence the homogeneity of the arc plasma dispersed by increasing the axial magnetic field. A relatively uniform diffuse current sheet was identified established between the concentric electrodes of our specified experimental geometry.

YThe Mercury sodium atmospheric spectral imager for the MMO spacecraft of Bepi-Colombo

The Mercury Sodium Atmosphere Spectral Imager (MSASI) on the Mercury Magnetospheric Orbiter (MMO) of the JAXA/ESA Bepi-Colombo (BC) Mission will address a range of fundamental scientific questions pertaining to Mercury's exosphere. The measurements will provide new information on regolith–exosphere–magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral region near the sodium D 2 emission (589 nm), a major constituent of the Mercury exosphere. A single high-resolution Fabry–Perot etalon is used in combination with a narrow-band interference filter to achieve a compact and efficient instrument design. The etalon and filter are extremely stable with respect to long-term aging and temperature variations. Full-disk images of the planet are obtained by means of a single-axis scanning mirror in combination with the spin of the MMO spacecraft. This paper presents an overview of the MSASI and the design of the Fabry–Perot interferometer used as its spectral analyser. It is concluded that: (1) The MSASI optical design is practical and can be implemented without new or critical technology developments. (2) The thermally stable etalon design is based on concepts, designs and materials that have a good space heritage. (3) The MSASI instrument will achieve a high signal-to-noise ratio (SNR) (>10) in the range of 2 K–10 M Rayleigh.

Lightning Detection by LAC Onboard the Japanese Venus Climate Orbiter, Planet-C

Lightning activity in Venus has been a mystery for a long period, although many studies based on observations both by spacecraft and by ground-based telescope have been carried out. This situation may be attributed to the ambiguity of these evidential measurements. In order to conclude this controversial subject, we are developing a new type of lightning detector, LAC (Lightning and Airglow Camera), which will be onboard Planet-C (Venus Climate Orbiter: VCO). Planet-C will be launched in 2010 by JAXA. To distinguish an optical lightning flash from other pulsing noises, high-speed sampling at 50 kHz for each pixel, that enables us to investigate the time variation of each lightning flash phenomenon, is adopted. On the other hand, spatial resolution is not the first priority. For this purpose we developed a new type of APD (avalanche photo diode) array with a format of 8×8. A narrow band interference filter at wavelength of 777.4 nm (OI), which is the expected lightning color based on laboratory discharge experiment, is chosen for lightning measurement. LAC detects lightning flash with an optical intensity of average of Earth’s lightning or less at a distance of 3 Rv. In this paper, firstly we describe the background of the Venus lightning study to locate our spacecraft project, and then introduce the mission details.

Ultraviolet B Suppresses Immunity by Inhibiting Effector and Memory T Cells

Contact hypersensitivity is a T-cell-mediated response to a hapten. Exposing C57BL/6 mice to UV B radiation systemically suppresses both primary and secondary contact hypersensitivity responses. The effects of UVB on in vivo T-cell responses during UVB-induced immunosuppression are unknown. We show here that UVB exposure, before contact sensitization, inhibits the expansion of effector CD4+ and CD8+ T cells in skin-draining lymph nodes and reduces the number of CD4+ and IFN-gamma+ CD8+ T cells infiltrating challenged ear skin. In the absence of UVB, at 10 weeks after initial hapten exposure, the ear skin of sensitized mice was infiltrated by dermal effector memory CD8+ T cells at the site of challenge. However, if mice were previously exposed to UVB, this cell population was absent, suggesting an impaired development of peripheral memory T cells. This finding occurred in the absence of UVB-induced regulatory CD4+ T cells and did not involve prostaglandin E2, suggesting that the importance of these two factors in mediating or initiating UVB-induced immunosuppression is dependent on UVB dose. Together these data indicate that in vivo T-cell responses are prone to immunoregulation by UVB, including a novel effect on both the activated T-cell pool size and the development of memory T cells in peripheral compartments.

The coronal dynamics imagers for the KuaFu mission

The Space Weather Explorer – KuaFu mission will provide simultaneous, long-term, and synoptic observations of the complete chain of disturbances from the solar atmosphere to the geospace. KuaFu-A (located at the L1 liberation point) includes Coronal Dynamics Imagers composed of a Lyman-α coronagraph (from 1.15 to 2.7 solar radii) and a white light coronagraph (out to 15 solar radii), in order to identify the initial sources of Coronal Mass Ejections (CMEs) and their acceleration profiles. The difficulty of observing the lower corona should not be underestimated since instrumental stray light remains a critical issue in the visible because of the low contrast of the corona with respect to the Sun. Observing the corona in the Lyman-α line is a valid alternative to white light observations. This approach takes advantage of both the intrinsic higher contrast of the corona with respect to the solar disk in this line compared to the visible, and the absence of F-corona at 121.6 nm. Furthermore, it has been convincingly shown that the coronal structures seen in Lyman-α correspond to those seen in the visible and which result from Thomson scattering of the coronal ionized gas. This is because the plasma is still collisional in the lower corona so that the hydrogen neutral atoms are coupled to the protons. A classical, all-reflecting internally-occulted Lyot coronagraph is required so as to preserve the image quality down to the inner limit of the field-of-view. A narrow band interference filter located in a collimated beam allows isolating the Lyman-α line. The visible coronagraph will adopt the approach of a single instrument having a large field-of-view extending from 2.5 to 15 solar radii. Such a design is based on refractive externally-occulted coronagraphs built for recent past missions, essentially the LASCO-C2 and C3 instruments and the SECCHI/COR 2 of the STEREO mission, which is itself a combination of the C2 and C3 instruments.

A Mid-IR Pyrometer Calibrated with High-Temperature Fixed Points for Improved Scale Realization to 2,500°C

Glass surface temperature can be measured using a radiation thermometer operating at a mid-IR wavelength, typically the 3–5 μm band, where the glass is opaque. For optical fiber preforms, the temperature measurement requirement may exceed 2,200°C. Scale realization at national measurement institutes at these temperatures is usually carried out at short wavelengths, typically less than 1 μm. The mismatch in wavelength can lead to significant uncertainties when calibrating a radiation thermometer working at 3–5 μm. To overcome this, a narrow band 3.95 μm radiation thermometer has been built that is designed to be used from 1,000 to 2,500°C. It is calibrated by measurement of high-temperature metal–carbon eutectic fixed-points. The instrument is based on silicon lenses, with a liquid nitrogen (LN2)-cooled InSb detector, and narrow-band interference filter. An anti-reflection coated objective lens/aperture stop focuses onto a field stop giving a 1 mm target, then a collimating lens, and glare stop. All parts visible to the detector, other than the target area, are either at LN2 temperature or are part of a temperature-stabilized housing. A relay-operated shutter that blocks the field stop is used to subtract the background. The size-of-source effect of the instrument has been measured. Gold-point measurements have been made to assess the stability. The device has been calibrated using high-temperature fixed points. A three-parameter fit has been applied and the resultant scale compared to an ITS-90 realization.

Study of the HII regions in the spiral galaxy NGC6384

The galaxy NGC6384 has been observed with an IPCS through Hα and [NII] narrow-band interference filters for direct imagery with the 2.6-m Byurakan telescope. We studied the main physical parameters of the identified 98 HII regions, their diameter and luminosity functions, as well the [NII]/Hα ratio distribution. The integrated distribution function of the HII region diameters can be well fitted by the exponential function. The characteristic diameter has the value (Do = 217 pc) predicted for a galaxy of its measured luminosity. The luminosity function of HII regions has a double power law profile with relatively shallow slope at low luminosities (α = −0.4), an abrupt turnover at logL(Hα) ≈ 38.75, and sharper slope at higher luminosities (α = −2.3). The correlation between the luminosity and diameter of HII regions confirms that in general they are constant density, radiation-bound systems. [NII]/Hα ratio data for the HII regions show that there is a negative radial gradient of [NII]/Hα. In the central region of the galaxy, nitrogen abundance is higher than in the periphery. The properties of the HII region population of this AGN galaxy do not differ significantly from the properties of the HII region population of the “normal” galaxies. Reexamining the location of the type Ia SN 1971L in the galaxy, we confirm that it lies on the spiral arm at about 8″.6 far from the closest HII region N 53 (F81). Such a location can be taken as proof that the progenitor of this SN does not belong to an old, evolved stellar population.