Optical Multichannel Analyzer System Research Articles

H α emission and target excitations in collisions ofH m+ ( m = 1, 2, 3) with Li and Na at 20–150 keV

H α line emission and target atom excitations have been observed in the collision of H +, H 2 + and H 3 + with Li and Na using an optical multichannel analysis system. The ion energy range was 20–150 keV. The emission cross sections of the observed Li I, and Na I lines, and the excitation cross sections for Li(2p) and Na(3p) have been calculated. The results show that our measurements agree well with the theoretical values.

A comparison of balmer α, β, γ emission in collisions between H1+, H2+, H3+ and He, Ne, Ar

Balmer α, β, γ emissions have been measured in collisions between H1+, H2+, H3+, and He, Ne, Ar in energy range of 50-150keV, using TN-1710 optical multichannel analysis system (OMA). The emission cross sections of Hα, Hβ, Hγ lines are given. The experimental results demonstrate that the emission cross sections of Hα,β,γ lines in H3+ +He, Ne, Ar collision systems are larger than those in H1+, H2+ +He, Ne, Ar, respectively.

He 2+ collisions with Ne and Ar atoms into excited states

The emission spectra in collisions between He 2+ and Ne and Ar have been measured by an optical multichannel analysis system (OMA). The experimental results demonstrate that there are three channels of excitation in these collision systems: (1) double-electron capture into excited states, (2) single-electron capture into excited states, and (3) direct excitation of target atoms by incident ion impact. Emission cross sections of HeI, HeII, NeI, NeII, and ArI, ArII have been obtained. Some comparisons of emission cross sections between He 2+ + Ne and He 2+ + Ar are given.

Singly and doubly charged ion collisions with neutrals into excited states

Recent experimental results on charge transfer into excited states in collisions between singly and doubly charged ions with He, Ne, Ar, H 2 and O 2 are presented, respectively. The energy range of the ion beams of He q+, Ar q+, Ne + ( q = 1,2) ions is (70–170)× q keV. The optical measurement was performed by an Optical Multichannel Analysis System (OMA). The wavelength range covered was 200–800 nm. Different processes of excitation have been observed in single and double charged ion collisions with neutrals. The dependence of emission cross sections on the potential energy defect is discussed.

Hβ‐Line Profile Measurements in Optical Discharges

AbstractIn the electrical field of a focused beam of a high‐power DC discharge multikilohertz repetition rate Q‐switched CO2 laser a so called pulsed optical discharge (POD) can be sustained. Applying laser pulses with max. 104 pulses/s, 50 mJ/pulse, pulse length 0.2 μs, average power 500 W and peak power 250 kW, the charge carrier density of a hydrogen plasma at a pressure of several MPa produced during the laser pulse is enhanced up to about the cut‐off density at λL = 10.6 μm (≃ 1025 m−3) and the electron temperature is increased to about 105 K. The non‐ideality factor reaches about 0.2. The calibrated line intensity of the Balmer Hβ was monitored by means of an optical multichannel analyzer system with spatial, frequency and time resolution. The measurements yield Stark‐broadened Hβ‐line profiles from which, assuming partial local thermal equilibrium, the electron temperature and density can be derived. The measured asymmetry of the Hβ‐line is in rough agreement with theoretical predictions available in literature.

A versatile optical multichannel analyser system for use with picosecond streak cameras

An optical multichannel analyser system has been developed which consists of a television camera linked to a microcomputer. The combination of cheaply available components and microcomputer programming capability makes this system versatile and inexpensive. The use of this system as readout for a picosecond streak camera is demonstrated.

Spectral composition of bioluminescence of epipelagic organisms from the Sargasso Sea

The spectral characteristics of single identified epipelagic sources of bioluminescence from the western Sargasso Sea were measured with an optical multichannel analyzer (OMA) system during the April, 1985, Biowatt cruise. The emission spectra of specimens representing 45 species from 8 phyla were measured. Peak bioluminescence emissions typically occurred between 440 and 500 nm, in the blue region of the visible spectrum. Three exceptions involved emission in the green, yellow, and red spectral regions. Intraspectific variability in spectra, was noted in several species. One shrimp species exhibited two modes of light emission, each with different emission spectra. Other cases involved dynamic color shifts of 10 to 14 nm; the source of the spectral variability is unknown, but may involve optical filtering or differences in the color of luminescence from multiple sites of light emission. Measurements from independent samples of unsorted plankton revealed different spectral distributions. This suggests that the spectral emissions of bioluminescence in the upper water column will vary, based on species assemblage.

Interfacing an optical multichannel analyser with a 16-bit microcomputer

The authors describe the hardware and software they have realized to control an optical multichannel analyzer (OMA) by a standard 16-bit microcomputer. The hardware consists of an interface card plugged into the microcomputer and connected to the OMA system. The software gives complete control over the OMA and adds powerful functions to the system, like various graphic representations of spectra taken by the OMA, storage of spectra on floppy disks, direct computation on the spectra, and a complete control of spectroscopy experiments.

Single and double electron capture into excited states in collisions between ions and neutrals

Recent experimental results on charge transfer into excited states in collisions between single and double charged ions with He, Ne, Ar, H2 and O2 are presented, respectively. Laboratory energy range of the ion beams of Heq+, Arq+, Ne+ (q=1,2)ions is (70-170)xq KeV. The optical measurement was performed by an optical multichannel analysis system (OMA).

EXCITED STATES IN COLLISION OF SINGLE AND DOUBLE CHARGED IONS WITH ATOMS AND COMPARISONS OF EMISSION CROSS SECTIONS

Recent experimental results on generating of excited states in collisions of single, double charged ions with He, Ne, Ar are presented. Laboratory energy range of the beams of Heq+, Arq+ (q=1,2) ions are (70-170)×q keV. The optical measurement was performed by Optical Multichannel Analysis System, the wavelength range covered was 200-800 nm. Different processes of excitation have been observed in single and double charged ions collisions with atoms. The dependence of emission cross sections on the charge number of incident ions and potential energy defect is discussed.

EXPERIMENTAL STUDIES OF EXCITED STATES IN THE COLLISIONS OF ELECTRON WITH HELIUM AND ARGON

We studied excitation processes of the targets in collisions of electron with helium and argon by optical method. Using the optical multichannel analysis system (OMA), we measured the emission spectrum of the collision systems. And the absolute emission cross sections are obtained in the electronic energy range of 200-500 eV.

Soft X-Ray Spectroscopy on the TFR Tokamak

The 2m-grating radius, extreme grazing incidence (1.5°) Schwob-Fraenkel spectrograph was developed at the Racah Institute of Physics (under CEA contract) more than 10 years ago. The first results (using photographic plates) on the TFR tokamak permitted the indentification of the spectrum of highly ionised Mo ions in the 5-50 Å spectral region /1/. Subsequently, the system was modified by J.L. Schwob into a duochromator, using two channeltron electron multipliers independently movable along the Rowland circle. It was thus possible to obtain radial profiles of the emissivities of the strongest lines of the H-and He-like isoelectronic sequences of light impurities in the 18-42 Å spectral range /2/. Recently, the duochromator has been converted into a multichannel spectrometer by equipping it with a microchannelplate (MCP) detector again movable along the Rowland circle. The detector consists of a MgF2coated, funneled MCP, associated with a phosphor screen image intensifier and coupled by a flexible fiber optic conduit to a 1024 element photodiode array (controlled and read-out by a commercially available PAR-1461 EGG Princeton Applied Research optical multichannel analyser system). The first of this type of detector was developed at Princeton for the PLT and TFTR tokamaks and was described by Schwob et al /3/. An identical system has been installed on TFR, using a 20 /μm entrance slit and a 600 groove mm−1Jobin-Yvon holographic grating. This instrument has been routinely used during the last year of TFR operation to monitor spectra of both intrinsic impurities (C, 0, Cr, Fe, and Ni, with traces of Mn, Cl, and S) and purposely injected impurity elements in the 10-330 Å spectral range. The spectrometer has been used in both the spectrographic and the polychromator modes. In the former mode, spectra of highly-ionized, unstudied, heavy elements (injected either by the laser blow-off technique or as gaseous elements) have been obtained /4,5/. In the latter utilization (in which selected individual pixels are read-out as function of time) line radiance evolutions of several different Fe ions have been simultaneously obtained on a single discharge. This has allowed the impurity transport to be modelled /6/ even though the system was not absolutely calibrated, since different ionization degrees have different time evolutions.

Noise reduction in laser photolysis studies of photolabile samples using an optical multichannel analyzer

An optical multichannel analyzer system for obtaining high-quality spectra of intermediates formed by nanosecond laser photolysis is described. The system is useful for samples which undergo irreversible photochemistry and which are available in limited amounts. Sample volumes as small as 25 μl are possible and a syringe pump driven by a linear stepper motor is used to deliver fresh sample after each photolysis pulse. The microchannel-plate intensified detector used here in gated mode can collect an entire spectrum in 5 ns, but proper synchronization of the detector scans is required to avoid severe distortion which can appear as random noise in signal averaging. Noise from various sources such as phosphor lag in the detector, time jitter, source intensity fluctuations, and the photon character of light are discussed. Experimental design for noise reduction is described including diagnostic procedures and light source filtering to produce more uniform signal-to-noise ratio throughout the spectrum. Finally, a comparison is made between the noise observed to occur between detector channels and the noise predicted to occur based on the photoelectron gain of the intensifier. The disagreement between these is discussed in terms of the spatial resolution of the detector.

EXPERIMENTAL STUDIES OF EXCITED STATES IN COLLISIONS BETWEEN He+ AND Ne

In collisions between He+ and Ne, two processes of excitation are found, one is one electron capture into excited states and another is direct excitation of projectile and target by ion impact. Optical method of measurement is performed using Optical Multichannel Analysis System (OMA), and the data of emission cross sections are obtained in the energy range of 70-150 keV.

Polarisation experiments with a Fresnel biprism

Polarisation experiments with a Fresnel biprism I S Ruddock Optical diffraction patterns displayed by microcomputer A R Allen Analogue-to-digital conversion made easy T E Jenkins and S R Goodes Microcomputer measurement of the velocity of sound in air P A Bates Using the BBC micro as a frequency meter Richard Bishop Measuring speed using a computer several techniques Jon M Pearce A versatile optical multichannel analyser system for use with picosecond streak cameras Guoguang Shen, W M Dennis and W Blau How to use your BBC computer as a cheap storage oscilloscope

Use of an optical multichannel analyzer for recording absorption spectra of short-lived transients

Characteristics of an adapted commercial optical multichannel analyzer system for recording of transient absorption spectra in single-shot pulse radiolysis and flash photolysis are described. The features discussed include temporal (2 μs) and spectral (1 nm) resolution, signal-to-noise ratio and its improvement, linearity of response, and wavelength coverage (300–650 nm). The system is intermediate in both cost and capabilities compared to two other methods: (1) recording transient spectra by repetitive pulsing and (2) using an image converter streak camera. This system is convenient for discrimination of small differences in fine structured absorption of spectra short-lived species.

Ultrafast Energy Transfer Processes In Photosynthetic Systems Probed By Picosecond Fluorescence Spectroscopy

Picosecond fluorescence spectroscopy was used to investigate the ultrafast energy transfers occurring in the light-harvesting accessory pigment complex of both photosynthetic and nonphotosynthetic leaves of the Norway maple (acer platenoides). The time-resolved fluorescence emission was measured for various wavelength regions both above and below 600 nm at room temperature and 90 K. Excitation was provided by single 6 ps pulses at 530 nm obtained from the frequency-doubled output of a Nd:glass laser, and the fluorescence emission was analyzed with the use of a streak camera optical multichannel analyzer system. Nearly identical decay kinetics were observed in both the nonphotosynthetic and photosynthetic systems. These results highlight the close relationship between the physical configuration of the carotenoid and chlorophyll accessory pigment molecules on the light-harvesting lattice and their energy transfer properties. A trapping model incorporating both photoactive and non-photoactive traps as quenchers of the absorbed excitation energy is proposed. These results question the interpretation of the in vivo fluorescence decay kinetics as being indicative of the photoactive state of the light-harvesting complex.

Irreversible loss of adatoms on Ag electrodes during potential cycling determined from surface enhanced raman intensities

Surface enhanced Raman scattering of adsorbates (Ag 0-Cl −, H 2O and pyridine) on Ag electrodes in 1M KC1 and 1M KCl+0.05M pyridine electrolytes was monitored continuously with an optical multichannel analyzer system as the electrode potential was cycled over various ranges within nonfaradaic regions of the oxidation-reduction cycle. A systematic investigation was performed of the potential dependence of SERS of pyridine in 1M KX + 0.05M pyridine electrolytes, where X = F, Cl, Br and I. Since the surface coverage of the adsorbates is reversible with potential cycling within a potential range, it was possible to determine potential dependences of the irreversible loss in the SERS enhancement factor which occurs as the electrode potential is ramped toward the potential of zero charge (PZC). The results provide strong support for the role of adatoms on the electrode surface in the overall enhancement mechanism. There is evidence that the strongly bound adsorbates immobilize the adatoms at positive potentials but allow the adatoms to migrate and become lost at surface defects as the potential approaches the PZC where the adsorbates are less tightly bound.

Enhanced HgBr(B2Σ+→X 2Σ+) emission at low pressures

Additives of N2 and I2 vapor in diffuse HgBr2 discharges have been observed to produce a large enhancement of radiated power due to B2Σ+→X2Σ+ transitions at low pressures. The integrated power in the spectral range between 374 and 543 nm was recorded by means of an optical multichannel analyzer system. Optimization of the B→X radiation was investigated, and absolute efficiency was determined over a range of ‖E‖/N.

Measurements of picosecond laser pulses from mode-locked Nd:YAG laser

This paper deals with measurements of picosecond laser pulse parameters such as temporal and spatial profile, and power. Pulseshape measurements were conducted by using the combined streak camera and optical multichannel analyzer system. The precision of measurements are discussed.