摘要:

We describe here several types of mass spectrometry in which the mass selectivity is combined with a highly selective laser ionization method to achieve both high sensitivity and very high selectivity. These methods combine the most sensitive and highly selective laser ionization methods with mass selectivity in order to improve on both the sensitivity and theZandAselectivity previously achievable in detecting atomic species. Applications of these methods include the dating of geophysical specimens, the on line analysis of rare short‐lived isotopes produced in high‐energy collisions, the detection of low levels of heavy metals or radioactive isotopes in biological samples, the detection of impurities in ultrapure materials, and a host of other applications. Because some versions of this method offer sensitivity to a hundred atoms of a particular isotope of an element in a macroscopic sample, there are new possibilities for fundamental studies of rare events. Several types of facilities for elemental and isotopic analysis will be described.

ISSN:0034-6748    

DOI:10.1063/1.1144702

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Using the stimulated Brillouin scattering phase conjugation and pulse compression technique, a conventional long pulse ruby laser was successfully converted to give 300 ps pulses at 1 J energy level. The technique allows the use of smaller amplifiers than required in a conventional short pulse laser which in turn leads to operation at increased repetition rate. The completed laser when operated at 1.5 Hz produces stable output parameters. Each laser pulse is characterized by a sharp rise and a measured pre‐pulse level of less than 10−6of the main pulse, making it suitable for LIDAR Thomson scattering measurements.

ISSN:0034-6748    

DOI:10.1063/1.1144703

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Excimer lasers are excellent sources of coherent light in the ultraviolet range of the spectrum. However, they have the drawback of requiring significant maintenance due to the corrosive gases, generation of dust, and contamination of the laser chamber optics which occur during normal operation. Improvements which are generally applicable to any excimer laser system are specifically described in terms of the two Questek (Lambda Physik, Acton, MA) model 2860 lasers in our lab. The same basic procedures are currently being implemented in two Lambda lasers in other research groups at our university. A novel gas triple filtration system, a simple cold trap with a counter‐flow heat exchanger, and a careful selection of valves have been added to minimize dust contamination of the optics, to decrease contamination and leakage of the gas fill, to provide safe and easy dust removal, and to reduce maintenance downtime.

ISSN:0034-6748    

DOI:10.1063/1.1145227

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

The performance of a simple wavemeter for measuring changes in wavelength of a pulsed dye laser is described. Details of optics and electronic circuitary used, along with the algorithm for wavelength measurement, are given. Using this instrument wavelength changes of a dye laser could be measured, as well as introduced through a user interface, with an accuracy of 1 ppm.  

ISSN:0034-6748    

DOI:10.1063/1.1144704

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A high‐voltage pulse output modulator using a step‐up transformer with two stages of magnetic pulse compression circuits has been developed as a spiker for the purpose of obtaining the breakdown of the gas mixture when using the spiker‐sustainer excitation technique for pumping XeCl discharge lasers. When the transformer input is fed by a current pulse with a peak value and a full width of 1.16 kA and 1.6 &mgr;s, respectively, formed by a discharge of an initially charged 19‐kV, 57‐nF capacitance in series in the transformer primary loop, the 2.7‐nF output capacitor bank (Cp) of the spiker can be charged up to 67 kV with a (10%–90%) rise time of 59 ns. The modulator has been tested at a repetition rate of up to 600 Hz in burst mode using a resistor in parallel withCpas the load.

ISSN:0034-6748    

DOI:10.1063/1.1144705

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A new scheme for locking an acoustic resonance of an acousto‐optic modulator to the exciting rf field applied for laser mode locking is presented. The resonance of the mode‐locking quartz prism is temperature‐tuned to match the synthesizer frequency. Deviation from perfect matching is sensed by observing the relative phase of the rf wave reflected at the device, and the error signal is fed back by a servo loop adjusting the heat delivered by a heating transistor to maintain the temperature required for exact resonance. The performance of the resonance‐tracking loop was checked on several different resonances of the modulator (used in an argon‐ion laser), because switching to another resonance is a simple and attractive way for changing the laser pulse repetition rate (or mode spacing) without replacing the mode‐locker unit. Excellent loop response was found in all cases. The new tracking principle provides a widely extended tracking range, improved tracking accuracy and laser stability, and simplifies the laser adjustment.

ISSN:0034-6748    

DOI:10.1063/1.1144706

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Optical interference fringe measurements of the thickness of weakly absorbing media can be rapid, accurate, and nondestructive. When the refractive indexnof the sample is known, it will give us the layer thicknessd. If, however,nis unknown, at least two independent spectrophotometric measurements are needed to obtain bothnandd. A statistically based scheme is proposed to analyze the interference pattern in order to determine the refractive index and the thickness of the sample. The absolute interference order is also determined with the proposed technique. The major approximation inherent in the method is that the layer must be weakly absorbing and nondispersive over the wavelength region of interest. The method is applied to determine the optical constants of a uniaxial medium with the optical axis parallel to the faces.

ISSN:0034-6748    

DOI:10.1063/1.1144707

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A small UHV chamber that fits in the sample compartment of a commercial Fourier transform infrared spectrometer (IBM‐98, Brucker) has been designed and constructed to acquire reflection/absorption spectra of species adsorbed and/or condensed on metal films vapor depositedinsituon the surface of a quartz‐crystal microbalance (QCM). The QCM is mounted on a variable‐temperature Au‐plated Cu block, which houses a second (reference) QCM, attached in turn to a liquid‐He cold finger. The unique capabilities of this apparatus make it possible to correlate quantitatively various spectral characteristics, including peak widths and intensities, with the absolute mass of adsorbed and/or condensed material per unit aream, or coverage, over a wide range ofmand temperatures. Results obtained using tetrahydrofuran (THF) condensed on freshly vapor deposited gold films have shown that the sensitivity of the instrument is sufficient to detectmTHFon the order of a single monolayer. Plots of the intensity of the most prominent THF peak at 1064 cm−1as a function ofmTHFwere found to deviate significantly from linearity in the range 0.1<mTHF<2.8 &mgr;g/cm2. In addition, the relative intensities of the most prominent THF peaks for even the largestmTHFexamined differed markedly from those of bulk‐like THF, an effect that can be attributed to a preferential orientation of THF microcrystals with respect to the underlying substrate. In the case of coverages on the order of one monolayer, such spectral behavior may arise from specific adsorbate/substrate interactions, which can cause a lowering in the molecular symmetry and/or distortions in the structure of the adsorbate. Evidence in support of a Au‐induced THF activation was obtained from independent temperature programmed desorption (TPD) measurements involving perdeuterated THF (TDF) performed in a separate UHV system. In particular, for exposures of about 1.5 L, the TPD spectra for the largestm/efeatures, i.e., 80, 48, and 30, revealed the presence of a peak centered at a higher temperature (∼180 K) than that found for much larger exposures (120 K).  

ISSN:0034-6748    

DOI:10.1063/1.1144640

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A high‐speed digitizer/averager data‐acquisition system designed and built as part of a 300‐MHz Fourier transform electron paramagnetic resonance spectrometer is described. There are two key features of the system: (1) the maximum digitizing rate is 300 Msamples/s and (2) a 256‐point free‐induction‐decay signal running summation can be updated in less than 3 &mgr;s. At the maximum digitizing rate, the system can sum 65 536 FIDs in 220 ms. The system consists of an analog‐to‐digital converter/adder unit (ADCA) and an IBM compatible personal computer. The ADCA is comprised of a digitizer, high‐speed sample buffers, high‐speed adders/memory, and control hardware. Design techniques, such as parallel processing, utilized to meet the high‐speed performance requirements are described. Trigger and timing signals for the system are derived from the spectrometer. System efficiency, synchronization, and time base stability are demonstrated in the spectrometer at a sampling frequency of 200 MHz. Signal‐to‐noise ratio enhancements are shown using a lithium phthalocyanine test sample.

ISSN:0034-6748    

DOI:10.1063/1.1145223

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A simple quantitative image processing system for pulsed soft x rays with time and spatial resolution is described. The system consists of easily obtained commercial components including a microchannel plate–phosphor screen combination, a charge coupled device camera, an image memory board, and a personal computer. To make a quantitative measurement possible, the image processing is used in conjunction with measurement of the ‘‘phosphor screen current.’’ Performance of the system is examined using a soft x‐ray source generated with a plasma focus device. The order of intensity, ∼1012photons/s mm2 mrad2 0.01% BW of ArKlines is observed for about 20 ns from the pinched plasma in which 3% of Ar is added to the 6 Torr H2.

ISSN:0034-6748    

DOI:10.1063/1.1144641

出版商:AIP    

年代:1994

数据来源: AIP