摘要:

An angle‐resolving electron energy analyzer capable of operating at an energy resolution of ≲20 meV and an angular resoltuion of ≲1/4° has been designed, constructed, and tested. A novel input lens allows independent control over both the energy and angular resolution. A series of tests has been performed which indicates that the analyzer operates at the theoretical resolution limit for the lowest values used.

ISSN:0034-6748    

DOI:10.1063/1.1137280

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A data‐acquisition system for the automatic control of photoelectron and electron energy loss spectrometers, based on a commercially available microcomputer, is presented. High versatility is achieved by the introduction of a new bus system, specially designed for laboratory applications. With this bus more than 20 external devices such as analog‐to‐digital converters, counters, digital‐to‐analog converters, and stepper‐motor interfaces can be controlled. A detailed description of the bus and the circuitry of the interfaces is given.

ISSN:0034-6748    

DOI:10.1063/1.1137281

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The electromagnetic force has been used instead of a mechanical blower to drive the gas mixtures in a closed‐circle‐type CO2laser tube for cooling and refreshment of the gas. A gas flow velocity has been obtained up to 0.8 m/s by applying a magnetic fieldB=1.67 kG externally to the discharge currentI=40 mA at a fixed gas pressureP=10 Torr. The laser output obtained by moving the gas for the gas mixture ratio of CO2:N2:He=2:1:7 is larger than that without moving the gas by a factor of 3 for up to 1 h of continuous operation.

ISSN:0034-6748    

DOI:10.1063/1.1137282

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A dc electrical discharge cell for laser optogalvanic spectroscopy has been designed and tested. Signal optimization is achieved through the use of adjustable electrode positions and an orthogonal geometry between the probe laser and the discharge axis. Results are presented for visible dye laser and infrared diode laser studies of selected neutral, radical, and ion species.

ISSN:0034-6748    

DOI:10.1063/1.1137283

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

The RCA 8850 photomultiplier has a wavelength‐dependent luminescence background when used in the UV below 320 nm. We show that this luminescence gives rise to an additional decay in the deconvoluted fluorescence and, unless corrected for, seriously interferes with the resolution of closely spaced fluorescence decays. A much lower luminescence background is found for the RCA C31000M photomultiplier, which is identical to the 8850 except that it has a fused silica rather than a Pyrex window. Use of the C31000M improves the resolution of known mixtures, but the recovered lifetimes are still somewhat in error. We believe that this residual error is due to additional low‐amplitude components in the fluorescence which cannot be resolved. An approach is presented which minimizes the effects of these contaminant decays on an analysis. Using this method, the decays of mixed compounds with lifetimes of 8.8 and 12.8 ns, of 10.1 and 12.8 ns, and of 8.8 and 10.1 ns are accurately resolved.

ISSN:0034-6748    

DOI:10.1063/1.1137284

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An alternative means of measuring fluorescence lifetimes by time correlation is described which avoids the inefficiency of direct multiplication of the high‐frequency signals. The process of sampled correlation is used, whereby samples of the input signals are gathered in pairs, the time delay between which is precisely varied. The product of the samples is computed during the long time period between the gathering of sample pairs. In this scheme, the burden of fast response is placed on the sampler while the multiplier can be a slow device of high efficiency. Furthermore, the time delay between samples can be conveniently controlled by electronic means. The sampling correlation approach to fluorescence lifetime measurements is evaluated in light of the noise power spectrum of a free‐running ion laser, used for sample excitation.

ISSN:0034-6748    

DOI:10.1063/1.1137285

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A normally on gain switch for photomultiplier tubes is described. Even using inexpensive side‐window tubes, on/off ratios exceeding 104can be obtained, with switching times of less than 50 ns. The system is used to measure weak delayed luminescences down to 200 ns after an intense actinic flash. Detectability is ultimately limited by tube afterpulsing.

ISSN:0034-6748    

DOI:10.1063/1.1137286

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

An electronic ion cyclotron resonance detection system was designed and constructed. The ions are excited by sweeping the frequency of the electric field (3–300 kHz) using a sweep frequency generator with a nonlinear sweep voltage in order to maintain an approximately constant mass resolution. Ion detection is accomplished by a bridge with a phase‐sensitive detector as a demodulator. The required reference signal for the phase‐sensitive detector is generated by a circuit with a transfer function which approximates that of the ICR signal in order to obtain an accurate phase match between the signal source and the detector. The device is capable of detecting a minimum concentration of 50 ions/cm3over a mass range of 15 to 1500 amu.

ISSN:0034-6748    

DOI:10.1063/1.1137287

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

A laboratory x‐ray absorption spectrometer is described which consists of a Johansson‐cut bent crystal, a rotating anode x‐ray generator, and a fast SSD (solid‐state detector). Because the SSD can completely discriminate the undesired reflections, contamination of the harmonics is avoided while maintaining a high‐source voltage necessary for strong x‐ray flux. Fast electronics equipment is employed to keep up with high‐x‐ray intensity. It is also possible to utilize higher‐order reflections for high resolving power. The data of quality comparable to those obtained at synchrotron radiation facilities can be obtained in a comparable period of time. In addition, the determination of the absolute absorbance as defined is possible, which makes the problem of the background subtraction in EXAFS analysis easy.

ISSN:0034-6748    

DOI:10.1063/1.1137288

出版商:AIP    

年代:1983

数据来源: AIP

摘要:

We have built a microcomputer‐controlled x‐ray absorption spectrometer which is capable of measuring 100‐&mgr;s‐resolved extended x‐ray absorption fine structure (EXAFS) of dynamic systems. The spectrometer integrates the x‐ray absorption signals over a time interval &tgr; at any timetmeasured from the time of sample excitation. A series of absorption data of differenttis measured for a given x‐ray energy. The process is repeated for as many different x‐ray energies as required. The lower limit on &tgr; is determined by the concentration of sample and the intensity of synchrotron radiation. The system was recently tested at Stanford Synchrotron Radiation Laboratory using a carboxymyoglobin sample. We present the raw data here to demonstrate the feasibility of this spectrometer.

ISSN:0034-6748    

DOI:10.1063/1.1137273

出版商:AIP    

年代:1983

数据来源: AIP