摘要:

Successful operation of a multijoule output TE CO2laser using a new magnetic‐spiker sustainer excitation circuit is reported. The use of the new excitation circuit has resulted in a significant reduction (∼90%) in the amount of sustainer pulse energy that has to pass through the magnetic switch. In addition, the new circuit technique allows operation of the discharge at reduced voltage (∼50%) and extends the range of excitation current pulse durations (up to ∼7 &mgr;s) over which arc‐free discharges can be formed. The laser has produced a typical output of 5 J at an overall efficiency of ∼13% from a helium‐free gas mixture at a pressure of 400 mbar.

ISSN:0034-6748    

DOI:10.1063/1.1144722

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Three methods are given for imposing random telegraph phase or frequency noise on a stabilized cw laser thus giving explicit control of the coherence of the laser field. In the case of phase noise, the resulting laser spectrum consists of a carrier part with nearly Lorentzian shaped noise sidebands which have full‐width at half maximum up to 14 MHz. Complete suppression of the carrier is possible if the phase is made to jump by &pgr; radians. Frequency telegraph noise results in a laser power spectrum that can be single or double peaked, depending on the relative sizes of the average dwell time and the frequency jump. The laser field has been produced for studies of noise in nonlinear spectroscopic interactions. Measurements of the resulting laser spectra are presented. As an example of the application of such a noisy laser, some results from studies of the dependence of two photon absorption on higher‐order optical coherences are given.

ISSN:0034-6748    

DOI:10.1063/1.1144723

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A multipass cell, which offers more than tenfold gain in sensitivity in ordinary and kinetic absorption spectroscopic measurements, is constructed by depositing aluminum mirrors on the flat walls of a standard fluorimetric cell, and its performance is demonstrated.

ISSN:0034-6748    

DOI:10.1063/1.1144724

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Hyper‐Rayleigh scattering has been developed as a generally applicable technique for the determination of the first hyperpolarizability &bgr; of a wide class of molecules [Clays and Persoons, Rev. Sci. Instrum.63, 3285 (1992)]. In this article, we show that it is possible to replace the low repetition rate, nanosecond pulse,Q‐switched laser source and fast gated electronics by a self‐mode‐locked, femtosecond pulse, broadly tunable continuous‐wave laser and phase‐sensitive detection. This results in a faster and much simpler measurement procedure. The accuracy of the femtosecond hyper‐Rayleigh scattering set‐up was checked by measuring the first hyperpolarizability &bgr; of the octopolar molecule crystal violet in methanol [(450±100)×10−30esu at 800 nm]. The sensitivity of the instrument allows concentration‐dependence studies, down to the pure solvent.

ISSN:0034-6748    

DOI:10.1063/1.1144725

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A cell for x‐ray diffraction studies of fluids with the energy‐dispersive technique at pressures of up to 9–10 kbar has been designed. The main advantages of the apparatus are a simple design, reliable sealing, absence of contribution from the container to the measured intensity of scattering, and high accuracy of intensity measurements achievable in a reasonable exposure time.  

ISSN:0034-6748    

DOI:10.1063/1.1144726

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

During the last decade, there has been an increasing use of synchrotron x‐ray techniques for theinsituinvestigation of the structure and composition of metal/solution interfaces under electrochemical control. While a number of experimental cell designs have been utilized in the past, every one of them has exhibited some shortcomings. This paper describes the development of a wide‐angle‐accessible, transmission‐geometry, sandwich‐type, x‐ray/electrochemical cell. From an x‐ray physics standpoint, this cell allows uninterrupted access over a 180° in‐plane angle for all incident and scattering angles between 0° and 75° with respect to the sample surface. It is especially advantageous at small scattering angles because of the uniform and insignificant background scattering. From an electrochemical standpoint, this cell provides a uniform current distribution and continuous, precise potential control of the working‐electrode surface; at the same time, it permits easy flushing of the working solution and even accommodates operating with flowing solution. Its only disadvantage is its inability to permitinsitucyclic voltammetry of only one surface of the single crystal.

ISSN:0034-6748    

DOI:10.1063/1.1144727

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

In this article, a new technique, continuous energy diffraction spectroscopy (CEDS) is described, for diffraction experiments using a synchrotron energy dispersive polychromatic beamline. This type of beamline uses a curved crystal monochromator (polychromator) to focus a range of x‐ray energies (bandwidth ∼1 keV) into a narrow (100–120 &mgr;m) line image. With a sample at this image point, using an 2D detector, we are able to measure diffracted intensities for the entire energy range of the incident beam simultaneously with limited or no motion of the sample. This method allows the collection of anomalous scattering and diffraction anomalous fine structure (DAFS) data faster and more accurately than with conventional methods. Because of the speed with which these types of diffraction experiments can be done, this method creates new options for time resolved diffraction experiments and provides new data collection strategies.

ISSN:0034-6748    

DOI:10.1063/1.1144728

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

A novel sample chamber has been developed for the study of chemical reactions involving air sensitive samples using energy‐dispersive powder diffraction. The apparatus consists of a reaction vessel, automatic reactant dispensing system, heating jacket, stirrer, and gas purge system. The use of this apparatus is illustrated with data collected on station 9.7 of the UK Synchrotron Radiation Source during a study on the intercalation of cobaltocene into tin disulfide.

ISSN:0034-6748    

DOI:10.1063/1.1144729

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

An electron momentum spectrometer has been constructed which measures electron binding energies and momenta by fully determining the kinematics of the incident, scattered, and ejected electrons resulting from (e,2e) ionizing collisions in a thin solid foil. The spectrometer operates with incident beam energies of 20–30 keV in an asymmetric, non‐coplanar scattering geometry. Bethe ridge kinematics are used which for 20 keV incident energy has scattered electron energies of 18.8 keV at a polar angle of &thgr;s=14°and azimuthal angles &fgr;sin the range from −18° to +18° and ejected electrons of 1.2 keV and &thgr;e=76°with &fgr;e=&pgr;±6°. The technique uses transmission through the target foil, but it is most sensitive to the surface from which the 1.2 keV electrons emerge, to a depth of about 2 nm. Scattered and ejected electron energies and azimuthal angles are detected in parallel using position sensitive detection, yielding true coincidence count rates of 6 Hz from a 5.5 nm thick evaporated carbon target and an incident beam current of around 100 nA. The energy resolution is approximately 1.3 eV and momentum resolution approximately 0.15a0−1. The energy resolution could readily be improved by monochromating the incident electron beam.

ISSN:0034-6748    

DOI:10.1063/1.1144730

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

After low noise FET amplifiers found widespread use in bothX‐band and low‐frequency systems, it became possible to use multidiode mixers for signal detection. Here, a novel dual diode mixer is described for use in homodyne microwave bridges for both cw and pulsed electron paramagnetic resonance spectrometers. The structure is composed of a 90° hybrid coupler and separate detectors in two arms. The device provides common mode rejection of noise‐like regular balanced mixers but, by making diode dc currents accessible, offers big advantages for tuning of the bridge when lowQsample probes are used. Although the use of this detector does not affect sensitivity directly, tuning precision and increased long‐term stability leads to unexpected improvements.

ISSN:0034-6748    

DOI:10.1063/1.1144731

出版商:AIP    

年代:1994

数据来源: AIP