摘要:

A method is developed to detect electron paramagnetic resonance (EPR) transient signals with frequency components in the range from dc to 1 MHz and a low initial signal‐to‐noise ratio (e.g., 0.1 after one sweep). This method uses 200‐kHz magnetic field modulation on a conventional EPR spectrometer, using a modified lock‐in detector: the tuned amplifier is replaced by a broadband preamplifier with a high‐pass filter and the low‐pass filter of the lock‐in detector is replaced by a broadband amplifier. The transients are generated incoherently from the magnetic field modulation, and subsequently averaged. The function of the (removed) low‐pass filter is taken over by the averaging. An instrumental response time of less than 1 &mgr;s is obtained. This was determined by measuring the rise time of the triplet state of the photosynthetic reaction center ofRhodopseudomonassphaeroidesR‐26 at 165 K. This method, direct detection, and high‐frequency (1–2 MHz) modulation are discussed. The S/N ratio of the method described in this paper is similar to that of the other two methods. However, when large linewidths (>0.5 mT) are met, it gives a superior S/N ratio as compared to high‐frequency (1–2 MHz) modulation methods, due to the higher maximum modulation amplitude. When the transients of interest contain frequency components in the low‐frequency noise regime (dc–50 kHz), the described method is to be preferred over direct detection because of its better S/N ratio.

ISSN:0034-6748    

DOI:10.1063/1.1139624

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A transceiver which is capable of observation of spectral widths of 1.6 MHz has been constructed as an accessory to a Bruker WH‐400 NMR spectrometer. This device permits observation of the NMR resonances of solid‐state quadrupolar nuclei, which may contain frequency components more than 1 MHz away from their fundamental precession frequencies. The transceiver contains its own frequency generation section, which employs the host spectrometer’s master phase reference and synthesizer. The NMR signal undergoes image rejection mixing to an intermediate frequency above the observation band, and quadrature phase detection before final amplification with video speed operational amplifiers in the receiver section. Dual 8‐bit, video speed digitizers feed the converted data to dual 16 kword deep buffers that can accept data at a rate of 4 Msamples/s. A slower data output rate is governed by the Bruker Aspect host computer. The noise figure of the device is 1.8 dB, with a sensitivity of at least −71 dBm and a recovery time of approximately 1 &mgr;s for linear amplification to resume after an excitation pulse.

ISSN:0034-6748    

DOI:10.1063/1.1139625

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A newly designed stator assembly for cylindrical spinners used in magic‐angle spinning nuclear‐magnetic‐resonance experiments is described. Separate driving and bearing gas chambers allow variable and stable spinning speeds, and this design permits easy starting and stopping of the rotor. Isolation of the chambers is achieved with the application of pressure screws rather than O rings or glue lines to avoid leakage at high gas pressures. The overall dimensions are optimal to facilitate easy assembly. Some significant modifications have been made to an earlier spinner design. These improvements give better efficiency and concentricity of the spinner. Applications are illustrated with carbon‐13 cross polarization/magic angle spinning (CP/MAS) spectra carried out at different rotor spinning rates.

ISSN:0034-6748    

DOI:10.1063/1.1139626

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Rapid‐frequency‐scan (RAFS) dye lasers have been developed for determination of instantaneous line profiles of neutral atoms and molecules. Two types of rapid‐frequency scanners are examined and their scanning performances are compared. One scanner is an e´talon driven by a PZT piezoelectrical element, and the other is an electro‐optical (EO) filter with a KDP crystal. The PZT scanner takes 4–5 &mgr;s to scan over the free spectral range (FSR), and the EO scanner can make faster scanning. The maximum scanning range is limited by FSR, and the static bandwidth is approximately 1/100 of FSR in both cases. In fast scanning, however, the dynamic bandwidth increases. The error in the single shot measurement is evaluated, based on an experimental result of the line‐profile measurement of Fe atoms.

ISSN:0034-6748    

DOI:10.1063/1.1139627

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A simple single‐element instrument for measuring laser‐beam profiles is described. The laser beam is deflected by a self‐resonant scanner and transmitted through a pinhole or a variable slit. Correction factors for various relative sizes of pinholes and slits are also given.

ISSN:0034-6748    

DOI:10.1063/1.1139628

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We have constructed a 23‐cm‐long cell for spectroscopy of high‐pressure sodium (and sodium–mercury) vapors at high temperatures. This cell operates in contrast to a heat pipe, without buffer gas. Sodium pressures up to 100 Torr (and mercury pressures up to 3000 Torr) have been obtained at temperatures up to 1500 K.

ISSN:0034-6748    

DOI:10.1063/1.1139629

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

A Fabry–Perot interferometer constructed with a pellicle beam splitter can be used as a sensitive microphone. Pressure disturbances inside the interferometer cavity alter the mirror separation, thereby changing the optical interference pattern. The optoacoustic effect can be detected in a cell attached to the Fabry–Perot interferometer by monitoring the change in intensity of the central interference fringe.

ISSN:0034-6748    

DOI:10.1063/1.1139630

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

We describe an electron gun suitable for bremsstrahlung isochromat spectroscopy (BIS). The design is based on the Pierce geometry and especially adapted to fit a large solid angle (0.07 sr) toroidal x‐ray monochromator consisting of 54 quartz single crystals. Performance parameters, as well as some examples of BIS spectra, are presented.

ISSN:0034-6748    

DOI:10.1063/1.1139631

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

The temperature dependence of the response of piezoelectric ‘‘bimorphs’’ &squflg; (&squflg; Registered trademark of Vernitron Corp., Bedford, OH) has been studied. This response is markedly decreased as temperature is decreased. Since the bimorphs are voltage limited, the amount of motion available is thus reduced as the temperature is lowered. This effect is important in the design specifications for the use of bimorphs at low temperatures.

ISSN:0034-6748    

DOI:10.1063/1.1139632

出版商:AIP    

年代:1987

数据来源: AIP

摘要:

Two new methods for operating a time‐of‐flight mass spectrometer are suggested. The first is a beam compression method which allows separation of one kind of particle (onem/qratio) at a time, from a beam continously emitted by an ion source. Due to the continuous operation of the source a corresponding increase in signal‐to‐noise ratio is expected. The second method is based on forming a multiplex beam by modulating a continuously emitted ion beam. The use of a time array detector enables the collection of the data. The algorithm of analysis is presented. This method should have the increased throughput advantage. An improvement in signal‐to‐noise ratio need not take place.

ISSN:0034-6748    

DOI:10.1063/1.1139633

出版商:AIP    

年代:1987

数据来源: AIP