Volume 76, Issue 8, August 2005
- invited article
- optics; atoms and molecules; spectroscopy; photon detectors
- particle sources, optics and acceleration; particle detectors
- nuclear physics, fusion and plasmas
- microscopy and imaging
- condensed matter; materials
- biology and medicine
- gravity; geophysics; astronomy and astrophysics
- electronics; electromagnetic technology; microwaves
- thermometry; thermal diffusivity; acoustic; photothermal and photoacoustic
- general instruments
Index of content:
- INVITED ARTICLE
76(2005); http://dx.doi.org/10.1063/1.2001307View Description Hide Description
An area x-ray detector constructed using commercially available “off-the-shelf” parts is described and its performance is characterized. The detector consists of a charge-coupled device(CCD)camera optically coupled to x-ray sensitive phosphor screen using a standard 35 mm camera lens. The conversion efficiency, spatial nonuniformity, spatial resolution and the detective quantum efficiency of the detector have been measured. Also shown is an example of data taken with the detector. The detector is a relatively low-cost device suitable for a wide variety of quantitative x-ray experiments where the input area need not be larger than about 70 mm across.
- OPTICS; ATOMS AND MOLECULES; SPECTROSCOPY; PHOTON DETECTORS
Rocket-borne instrument for measuring vibrational-rotational temperature and density in the lower thermosphere76(2005); http://dx.doi.org/10.1063/1.1988189View Description Hide Description
We applied the electron beamfluorescence (EBF) technique to measure the vibrational temperature, rotational temperature, and number density of atmospheric molecular nitrogen in the altitude range of . The atmospheric is excited and ionized by electron beam of the energy of and the subsequent fluorescence of the first negative band is detected by a sensitive spectrometer, which covers the wavelength range. In contrast to previous rocket-borne photometric measurements using the EBF technique, the spectrometric measurement provides the above three parameters simultaneously and more accurately. Preflight laboratory experiments were carried out in order to test the spectral sensitivity over the whole spectral range, to calibrate the number density from the band intensity, and to know the accuracy of the rotational temperature measurement. Finally, we tried to calibrate the vibrational temperature measurement by using heated gas which is ejected from the small nozzle.
A high efficiency ultrahigh vacuum compatible flat field spectrometer for extreme ultraviolet wavelengths76(2005); http://dx.doi.org/10.1063/1.1988227View Description Hide Description
A custom, flat field, extreme ultravioletspectrometer built specifically for use with low power light sources that operate under ultrahigh vacuum conditions is reported. The spectral range of the spectrometer extends from 4 nm to 40 nm. The instrument optimizes the light gathering power and signal-to-noise ratio while achieving good resolution. A detailed description of the spectrometer and design considerations are presented, as well as a procedure that could be used to obtain a synthetic wavelength calibration with the aid of only a single known spectral feature. This synthetic wavelength calibration is compared to a standard wavelength calibration obtained from previously reported spectral lines of Xe, Ar, and Ne ions recorded with this spectrometer.
Broadband absolute absorption measurements of atmospheric continua with millimeter wave cavity ringdown spectroscopy76(2005); http://dx.doi.org/10.1063/1.1988027View Description Hide Description
An instrument for the measurement of continua effects in the millimeter and submillimeter (a.k.a. terahertz) spectral region for mixtures of gases is described. In addition to their scientific interest, these continua are important because they contribute more than 50% of the opacity in the atmospheric windows important in remote sensing and communications. The instrument is based upon a fast scanning cavity ringdown approach that makes possible the measurement of continua and broad line absorptions at distinct cavity frequencies from in . The instrument’s Fabry–Perot cavity is in a chamber whose temperature can be controlled between and and whose pressure can be varied between and . The scan results in statistical uncertainty in the absorptions of at each of the 6000 frequencies. From these data an uncertainty of less than 1% for the weakest atmospheric continua (the dry air continuum) can be determined. For comparison, the continuum parameters that might be considered for inclusion in atmospheric remote sensing retrievals vary over a range of 10% to more than 50%. This uncertainty significantly impacts quality and validity of atmospheric retrievals from a variety of remote sensing platforms. While much lower statistical uncertainties are achievable with modest additional observation times, it is much more important that the near simultaneous measurements at many frequencies produce a data set that contains, without the use of parameters from other experiments, all of the required experimental information. This approach significantly reduces systematic effects and makes possible more realistic assessment of uncertainties.
Full correlation from picoseconds to seconds by time-resolved and time-correlated single photon detection76(2005); http://dx.doi.org/10.1063/1.1946088View Description Hide Description
We present an advanced time-correlated single photon counting(TCSPC) technique that delivers traditional fluorescencecorrelation (FCS) or cross correlation (FCCS) and fluorescence lifetime data simultaneously. Newly developed electronics allow for detection and registration of single photon events over time periods of hours with picoseconds accuracy. Subsequent software-correlation yields correlation curves covering more than 12 orders of magnitude in time. At the same time, the original data, containing all information accessible by single photon counting techniques, can be analyzed conventionally according to common single molecule fluorescence techniques. Potential applications of the new technique using pulsed or cw laser excitation are discussed.
New target for high-intensity laser-matter interaction: Gravitational flow of micrometer-sized powders76(2005); http://dx.doi.org/10.1063/1.1988288View Description Hide Description
The design of efficient targets for high-intensity laser-matter interaction is essential to fully exploit the advantages of laser-induced photons or particles sources. We present an advantageous kind of target, consisting in a free gravitational flow of micrometer-sized powder, and describe its main technical characteristics. We demonstrate a laser-induced keV x-ray source using this target, and show that the photon flux obtained for the line of Si by irradiating different silicapowders is comparable to the one obtained with a bulk silica target.
76(2005); http://dx.doi.org/10.1063/1.1994918View Description Hide Description
This paper describes a double-cell method, which offers some advantages in image capturing and analysis of the planar laser-induced fluorescence (PLIF) experiments. Double static-cell and circulating-static designs are tested and the fluorescence results are reported. The static-static design offers some advantages when comparing the fluorescence signals for two different dyes, the effect of additives, and of oxidation, whereas the circulating-static design provides an effective method to study the thermal contributions of the measured signal, the photostability of a particular dye, the effect of adding agents, and the quenching effects on a dye under study. In this experiment Rhodamine-WT (Rh-WT) and Resorufin (RSRF) dye solutions are tested and PLIF results are reported. The photostability of both dyes is investigated and the oxidation process of fluorescent probe molecule RSRF is also demonstrated. Results obtained for these dyes are very interesting and verify that such a method can be used effectively for investigating different interesting phenomenon affecting the fluorescence emission/extinction. It is also possible to compare the fluorescence yields for different dyes in different solvents and at different molar concentrations.
High resolution time-of-flight spectrometer for crossed molecular beam study of elementary chemical reactions76(2005); http://dx.doi.org/10.1063/1.1960718View Description Hide Description
In this article, we describe an apparatus in our laboratory for investigating elementary chemical reactions using the high resolution time-of-flightRydberg tagging method. In this apparatus, we have adopted a rotating source design so that collision energy can be changed for crossed beam studies of chemical reactions. Preliminary results on the HI photodissociation and the F atom reaction with are reported here. These results suggest that the experimental apparatus is potentially a powerful tool for investigating state-to-state dynamics of elementary chemical reactions.
76(2005); http://dx.doi.org/10.1063/1.1979470View Description Hide Description
A universal method of extraction of the complex dielectric function from experimentally accessible optical quantities is developed. The central idea is that is parameterized independently at each node of a properly chosen anchor frequency mesh, while is dynamically coupled to by the Kramers–Kronig (KK) transformation. This approach can be regarded as a limiting case of the multioscillator fitting of spectra, when the number of oscillators is on the order of the number of experimental points. In the case of the normal-incidence reflectivity from a semi-infinite isotropic sample the new method gives essentially the same result as the conventional KK transformation of reflectivity. In contrast to the conventional approaches, the proposed technique is applicable, without readaptation, to virtually all types of linear-response optical measurements, or arbitrary combinations of measurements, such as reflectivity, transmission, ellipsometry, etc., done on different types of samples, including thin films and anisotropic crystals.
Calibration of second-order correlation functions for nonstationary sources with a multistart, multistop time-to-digital converter76(2005); http://dx.doi.org/10.1063/1.1986969View Description Hide Description
A novel high-throughput second-order correlation measurement system is developed that records and makes use of all the arrival times of photons detected at both start and stop detectors. This system is suitable, particularly for a light source having a high photon flux and a long coherence time, since it is more efficient than conventional methods by an amount equal to the product of the count rate and the correlation time of the light source. We have used this system in carefully investigating the dead time effects of detectors and photon counters on the second-order correlation function in the two-detector configuration. For a nonstationary light source, a distortion of the original signal was observed at high photon flux. A systematic way of calibrating the second-order correlation function has been devised by introducing the concept of an effective dead time of the entire measurement system.
76(2005); http://dx.doi.org/10.1063/1.2001670View Description Hide Description
In this paper, an electro-optically cavity-dumped, rf-excited, Z-folded waveguide laser is presented. Theoretical studies on the laser output wave form and method to control laser pulse width and output power are made. In the experiment, a pulse width of a cavity-dumped laser can be changed from 12 to 32 ns. However, the corresponding peak powers reduce from at a pulse repetition rate of . The experimental results are consistent with the theoretical analyses.
76(2005); http://dx.doi.org/10.1063/1.2001630View Description Hide Description
The erosion rate of a Hall thruster was estimated with the objective of building a real-time erosion rate monitoring system using a class anode layer type Hall thruster. This system aids the understanding of the tradeoff between lifetime and performance. To estimate the flux of the sputtered wall material, the number density of the sputterediron was measured by laser absorption spectroscopy using an absorption line from ground atomic iron at . An ultravioletdiode laser was used as the probe. The estimated number density of iron was , which is reasonable when compared with that measured by duration erosion tests. The relation between estimated erosion rate and magnetic flux density also agreed with that measured by duration erosion tests.
76(2005); http://dx.doi.org/10.1063/1.2001672View Description Hide Description
This article describes a time-of-flight sensor based on multiple pulsed laser sources which utilizes time-correlated single-photon counting. The sensor has demonstrated good performance at ranges of up to 17 km in daylight conditions. Analysis techniques were developed to examine the returns from targets containing more than one scattering surface.
76(2005); http://dx.doi.org/10.1063/1.2005407View Description Hide Description
An evaluation of two optical fiber sensing heads for measuring transversal load is presented. Their construction introduces power loss without the need of a pair of deformer plates and is based on crossing two fibers in braid-type (braid twisted), and of an optical fiber stretched out which is wrapped up by another one in spiral form (spiral twisted), respectively. For a higher sensitivity, the braid twisted configuration is preferable. Nevertheless, in both sensing heads, the sensitivity can be enhanced by decreasing the enrollment period and/or by choosing the appropriate encapsulation of the sensing head. Relative to resolution and hysteresis, the spiral twisted sensing head presented the best result. However, further work on the plasticity of the coatings is needed to decrease hysteresis. These configurations can be embedded in composite materials and used in many applications.
Diffraction-limited two-dimensional hard-x-ray focusing at the level using a Kirkpatrick-Baez mirror arrangement76(2005); http://dx.doi.org/10.1063/1.2005427View Description Hide Description
The spatial resolution of scanning x-ray microscopy depends on the beam size of focused x rays. Recently, nearly diffraction-limited line focusing has been achieved using elliptical mirroroptics at the level. To realize such focusing two-dimensionally in a Kirkpatrick-Baez system, the required accuracies of the mirror aligners in this system were estimated using optical simulators based on geometrical or wave-optical theories. A focusing unit fulfilling the required adjustment accuracies was constructed. The relationships between alignment errors and focused beam profiles were quantitatively examined at the long beamline (BL29XUL) of SPring-8 to be in good agreement with the simulation results.
76(2005); http://dx.doi.org/10.1063/1.2006671View Description Hide Description
A highly stable convection-cooled, cluster-based voltage divider chain for photomultiplier tubes has been designed and tested in single ion counting detection systems. Contrasting currently existing voltage divider chains, our unit does not require a cooling liquid to transfer the heat from the resistors and provides safer operation conditions inside ultrahigh vacuum systems utilized in the reaction dynamics community. The unit is enclosed in an air pocket inside an ultrahigh vacuum system so that outgassing of the photomultiplier tubes,resistors, and capacitors can be eliminated completely. The measured resistor chain currents of lie well within the tolerances of the resistors and power supply demonstrating that the convective cooling is actually efficient to sustain a stable signal. The monitored total ion current also depicts extremely low fluctuation of only 1.5%. The day-to-day reproducibility has been tested, too. We also demonstrate that a magnetic shielding of the photomultiplier tube and the resistor chain enhances the signal by about 15%.
Spectroscopic system for emission and absorption studies of laser produced plasmas in the extreme ultraviolet76(2005); http://dx.doi.org/10.1063/1.2008048View Description Hide Description
The experimental characterization of a stigmatic spectroscopic system for the diagnostics of laser-produced plasmas in the spectral region is presented. The instrument provides stigmatic spectra for on-axis sources and fully preserves spectral resolution also for off-axis sources. Expected theoretical performances have been compared with experimental results. Spectral and spatial resolution capabilities have been proved to match the nominal ones theoretically predicted. A laser-produced plasma experiment has been also carried out to demonstrate the instrument capabilities. The use of a stigmatic spectrometer and an image detector gives spectrally and spatially resolved images of the plasma source. The good instrumental sensitivity and high dynamic range allow to acquire complete spectra in almost single-shot experiments.
76(2005); http://dx.doi.org/10.1063/1.2008807View Description Hide Description
A normally on photomultiplier (PMT) gating strategy effectively eliminates postgate signals arising both from ion feedback after pulsing and from capacitive storage of primary photoelectrons. This approach has been applied to gating an Electron Tubes 9816B 14-stage linear focused PMT but should be applicable to a variety of other tubes. A positive potential pulse 10 V smaller than the photocathode (PC)-first dynode (D) potential difference is applied to the PC. This potential prevents ionization of residual gas, while still removing primary photoelectrons to D1. A negative pulse applied to intermediate dynodes D4/D6 increases overall attenuation to with turn-off and turn-on times of 40 ns. The system adjusts pulse amplitudes to the applied tube HV and so provides consistent gating at all PMT gains. The free-standing, independently powered pulse generators are cabled to a passive tube base and can gate essentially any PMT with a maximum high voltage of 3 kV and a maximum PC-D1 potential of 450 V. A suitable passive tube base is thus the only tube-specific requirement.
76(2005); http://dx.doi.org/10.1063/1.2008788View Description Hide Description
A new type of infrared spectrometer system working in the optical communication field has been studied and constructed. In order to achieve both high spectral resolution and fast data acquisition speed, an integrated grating with five subgratings and a set of five line-array InGaAs detectors are used to work in the wavelength range without any scanning and mechanical moving parts. The system has been calibrated with a spectral resolution of about and a fast data acquisition time of less than in the entire spectral range.
76(2005); http://dx.doi.org/10.1063/1.2010625View Description Hide Description
We present an adaptive optics (AO) system for the control of geometrical fluctuations in a laser beam based on the interferometric detection of phase front. By comparison with the usual Shack–Hartmann and phase diversity based AO systems, we show that this technique is of particular interest when high sensitivity and high bandpass are required for correction of small perturbations like, for instance, the control of the input laser beam of gravitational waves interferometric detectors.