摘要:

The temperature-dependent characteristics of fluorescence of several rare-earth-doped ceramic phosphors has made these materials the focus of a major effort in the field of noncontact thermometry over the past few decades. These “thermographic phosphors,” e.g.,Y2O3:Eu,have been used for remote measurements of the temperatures of both static and moving surfaces, and have performed many other tasks that standard sensors (thermocouples, thermistors, etc.) cannot. The range of usefulness of this class of materials extends from cryogenic temperatures to those approaching 2000 °C. The instrumentation needed for this type of thermometry has followed many different lines of development, and this evolution has produced a wide variety of both field- and laboratory-grade systems that are now described in the literature. In general, the technique offers high sensitivity(≈0.05 °C),robustness (e.g., stability of the sensor sample in harsh environments), and NIST traceability. In addition, such systems have been successfully adapted to make remotely sensed measurements of pressure, heat flux, shear stress, and strain. In this review, we summarize the physical mechanisms that form the basis for the technique, and then catalog and discuss the instrumentation-related aspects of several different remote thermometry systems that employ thermographic phosphors as the sensors. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148174

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Measurement of the lattice functions was carried out in the storage ring for the light source. The measurement includes &bgr;, dispersion functions, phase advances, tunes, momentum compaction, chromaticities, and linear coupling. Two methods were used for the &bgr; measurement; a quadrupole-tweaking method and a method using a sensitivity matrix. Using the sensitivity-matrix method gives additional information on the phase between monitors and correctors, as well as the fractional part of the tunes. The linear-coupling constant was obtained by driving the tunes across the coupling resonance and measuring the minimum tune separation. It is also shown that by using four skew-quadrupole circuits, the coupling constant can be varied arbitrarily. In this article, a detailed method for the lattice-function measurement is presented, and the result applied to the storage ring of the Pohang Light Source is given. The measured results are compared with the design values and shown to be in good agreement. ©1997 American Institute of Physics. 

ISSN:0034-6748    

DOI:10.1063/1.1148175

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A semiconductor switching power supply has been developed, in which a novel structure semiconductor device, metal-oxide-semiconductor assisted gate-triggered thyristor (MAGT) was incorporated with a single stage magnetic pulse compression circuit (MPC). The MAGT was specially designed to directly replace thyratrons in a power supply for a high repetition rate laser. Compared with conventional high power semiconductor switching devices, it was designed to enable a fast switching, retaining a high blocking voltage and to extremely reduce the transient turn-on power losses, enduring a higher peak current. A maximum peak current density of32 kA/cm2and a current density risetime ratedi/dtof142 kA/(cm2×&mgr;s)were obtained at the chip area with an applied anode voltage of 1.5 kV. A MAGT switching unit connecting 32 MAGTs in series was capable of switching on more than 25 kV–300 A at a repetition rate of 5 kHz, which, coupled with the MPC, was equivalent to the capability of a high power thyratron. A high repetition rate and high power XeCl excimer laser was excited by the power supply. The results confirmed the stable laser operation of a repetition rate of up to 5 kHz, the world record to our knowledge. An average output power of 0.56 kW was obtained at 5 kHz where the shortage of the total discharge current was subjoined by a conventional power supply with seven parallel switching thyratrons, simultaneously working, for the MAGT power supply could not switch a greater current than that switched by one thyratron. It was confirmed by those excitations that the MAGT unit with the MPC could replace a high power commercial thyratron directly for excimer lasers. The switching stability was significantly superior to that of the thyratron in a high repetition rate region, judging from the discharge current wave forms. It should be possible for the MAGT unit, in the future, to directly switch the discharge current within a rise time of 0.1 &mgr;s with a magnetic assist. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148176

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We have produced amplitude-modulated near-ultraviolet light, centered at 390 nm, using an inexpensive, commercially available blue light-emitting diode (LED). The LED was amplitude modulated with the +13 dBm ac output from a frequency generator while biased through a bias tee with 60 mA of dc current. The LED produced 45 to 54 &mgr;W of UV light over the modulation bandwidth of 0.01 to 200 MHz, when measured after optical filters to remove the residual blue output. Since the filter attenuated the UV output about 3 dB, more than 100 &mgr;W of UV light was initially produced. Modulated UV light was available to approximately 200 MHz, with a −3 dB point of 31 MHz, allowing the measurement of ns fluorescence lifetimes. The fluorescence lifetimes of standard fluorophores (9-cyanoanthracene and green fluorescent protein) were measured in the frequency domain using the phase-modulation technique, producing lifetimes that closely agree with those reported in the literature, confirming that the UV-emitting blue LED is practical for spectroscopic and sensor applications. When compared to a laser modulated with a Pockels cell, the LED was smaller, less expensive, required less power, generated less heat, and required less alignment. The ability to modulate the LED at high frequencies, along with the UV output, allows its use as an inexpensive UV light source in fluorescence lifetime optical sensors and even frequency-domain fluorometers. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148177

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new polarization modulator is presented. It uses two phase-locked identical electro-optic phase modulators at 50 kHz. Thanks to a coupling object introduced between the two phase modulators, the four Stokes parameters of the light beam are independently modulated on the basis of the first and second complex harmonics of the modulation signal. A Mueller matrix ellipsometer (MME) using this new modulation and a multichannel polarimeter are also described. The data processing and the feedback control of Pockels cells is based on a numerical Fourier transform system. It allows one to measure simultaneously, in one modulation period (20 &mgr;s), the 16 coefficients of any Mueller matrix. This MME takes advantage of an easy-to-operate calibration method. The high-frequency modulation of the four parameters of the polarization enables low-light-level measurements (without any chopper and lock-in) and presents spectroscopic capabilities. It provides a promising tool for the study of many subjects of growing interest like, for example, rough surfaces treatment or particle characterization. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148178

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Among the x-ray fluorescence techniques using energy dispersive systems, the excitation in the total reflection regime is becoming widespread. This technique may be applied to surface analysis if the fluorescent radiation emitted by the sample is measured as a function of the grazing incidence angle. The main limitation in performing this sort of analysis is the need to use a monochromator, which notably reduces the incident flux of radiation. Besides, the method requires the radiated surface to be perfectly smooth and polished and to have a total length of some centimeters. A similar technique known as grazing exit x-ray fluorescence presents certain advantages and is easier to implement. By this method, fluorescent photons in terms of the grazing exit angle are detected. In this work, a spectrometer for performing surface analysis at grazing exit is described, the different experimental situations are analyzed, and some measurements performed with this device are shown. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148179

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A photoelectron-photoelectron coincidence spectrometer, incorporating two independent toroidal analyzers, has been developed to study photodouble ionization of gas targets using synchrotron radiation. The energy-resolved and angle-dispersed electron images are recorded using two-dimensional position-sensitive detectors. The design and performance of the spectrometer is described, with particular emphasis on the electron optical properties of toroidal deflectors and their associated electrostatic lenses. The operation and calibration of the spectrometer are discussed and sample(&ggr;,2e)results of helium are presented. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148180

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

By making use of effects of the image charge on projectile trajectories in scattering of a fast beam of metastable He-atoms with keV energies from an Al (111) surface under a glancing angle of incidence, we have developed a new method to analyze fast atomic beams with respect to relative populations of excited metastable states. Based on our experimental studies we propose the construction of a corresponding detector. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148181

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Among the various possibilities for investigating the properties of ion beams, two of the most important principles for determining the beam quality are profile measurements using wires or slit apertures, and different kinds of emittance measurement devices. However, most of the commonly used systems have the disadvantage of being either destructive to the beam, or at least to have a considerable influence on the further beam propagation downstream of the point of measurement. Also, for the investigation of intense ion beams, thermal problems on the scanners themselves might arise. Observation of particles emitted from the ion beam in radial direction allow an indirect but nondestructive observation of the beam. Of the different optical methods that exist to accomplish this, we recently conducted an investigation on the possibilities to employ a charge coupled device-camera system for such nondestructive beam diagnostics in our space-charge compensation test stand. First, experimental results on optical profile measurements are presented and compared to results obtained by a slit scanner and a wire scanner. Additionally, to gain a better understanding of the measured data, optically obtained sectional profiles behind a slit and a circular aperture were analyzed. Possibilities for gaining information on the two-dimensional beam profile and the beam emittance are explored. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148182

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A new gas feeding system for an electron cyclotron resonance ion source was developed at the University of Jyva¨skyla¨. With the aid of the system, pressures of a few hundred millibars in gas lines remain constant within less than 1 mbar. Due to a very stable gas flow in the buffer and ion gas lines, the source can now deliver practically constant current beams of highly charged ions for long period runs. ©1997 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1148183

出版商:AIP    

年代:1997

数据来源: AIP