摘要:

Resonant cavity techniques have been used to implement a high power source of radio frequency excitation for many parallel laser elements in a simple, compact, and low cost structure. A triode oscillator was designed capable of driving up to 48 independent and dynamic loads by utilizing the unique nature of a resonant cavity to extract multiple outputs via magnetic coupling. Over 25 kW of power has been generated at 80 MHz while driving 8 independent CO2laser slab geometry gas discharges. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147547

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Mapping of the amplification region and full characterization of a dye laser amplifier by means of a photoacoustic technique are presented. The acoustic signals generated in the pumped medium as a consequence of nonradiative transitions are gain dependent. We use the ratio between the acoustic signal measured when the oscillator beam passes through the amplifier, to the acoustic signal when it is blocked, as a figure of merit of an amplifier stage. By using the oscillator beam as a spatial probe of the amplifier gain region, it is possible to map the optically inverted medium, assigning a photoacoustic ratio to each point of the medium. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147549

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The Fabry–Perot interferometer has become a standard spectroscopic tool in scientific laboratories for the study of Brillouin scattering. This article examines some basic properties of the Fabry–Perot interferometer with the student or beginning user in mind in order to demonstrate why it is especially useful for this application. Single and complex Fabry–Perot systems in use for Brillouin scattering studies are discussed starting from elementary equations to show, in particular, how the half‐width of the transmission function depends upon the instrumental configuration. The primary results are summarized in graphical form. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147550

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

An analysis of the background at the exit of tapered borosilicate glass capillaries in synchrotron radiation scattering experiments suggests scattering due to short‐range order at larger angles while low‐angle scattering is attributed to phase separation in the glass. Background scattering can be largely suppressed by introducing a pinhole aperture at the exit of the capillary. The lowest background was obtained for a pinhole approaching the size of the exit beam. Background reduction is particularly important for wide‐ and small‐angle scattering experiments on weakly scattering samples like thin polymeric fibers. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147551

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A new improved fluorescence correlation spectroscopy method for determining motional states of particles, fluorescence correlation spectroscopy with traveling interference fringe excitation (FCSTFE), is described. With this method the modulated fluorescence signal from particles excited by an interference fringe moving at constant velocity is detected, and cosine and sine Fourier coefficients at the frequency of the traveling fringe [Fcos(t),Fsin(t)] are recorded. Autocorrelation functions ofFcos(t),Fsin(t), and the square of amplitude [A2(t)=Fcos(t)2+Fsin(t)2] were found to express the motion of the fluorescent particles. The apparatus utilizing a photon counting system was constructed, and the performance of the system was demonstrated by the determination of diffusion coefficients of dispersed fluorescent polystyrene spheres. Features of FCSTFE in particle dynamics evaluation are discussed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147552

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The design, performance, and operation of a broadband (3–26.5 GHz) high resolution microwave spectrometer is described. In comparison to previously developed molecular beam Fabry–Perot resonator spectrometers the design presented here implements some significant improvements: a coaxially oriented beam resonator arrangement (COBRA) formed by a confocal pair of mirrors incorporating an electromechanical valve and employing two pairs of microwave antennas, and a multioctave Fourier‐transform microwave (FTMW) instrument providing the pulsed excitation source with microwave pulse phase‐inversion scheme and the low‐noise receiving system employing image‐rejection downconversion with superheterodyne as well as quadrature detection. The entire apparatus, fully automated for scanning operation, covers a frequency range of more than three octaves. The novel design of the FTMW instrument does not require any changes of the spectrometer hardware in order to reach all regions of its spectral range. While operated in high resolution mode the COBRA‐FTMW spectrometer is achieving a linewidth (half‐width at half‐height, HWHH) relative to the molecular emission frequency of better than 10−7HWHH. The sensitivity and resolution of the spectrometer is demonstrated by several examples. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147553

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have developed and demonstrated a pump‐probe laser spectroscopic scheme to measure ground state vibrational population relaxation. There are two significant advantages to this technique over alternative measurement methods. The first is that the detection sensitivity of the pump‐probe method is limited by the shot noise present on the probe laser and the second is that, because of the manner in which the ground state vibration(s) are populated, it is possible to interrogateT1processes for degenerate donor–acceptor conditions. We detail in this article the form of the experimental stimulated signal, the effect of the detection scheme used, and the consequences of spontaneous (Boltzmann) population of ground state vibrations. A central conclusion of this work is that, even for small signal limit pump‐probe experiments, absorption, stimulated emission, and spontaneous emission all play important roles in collectively determining the form of the experimental signal. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147554

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A grazing‐incidence x‐ray diffraction (GIXRD) system combined with cluster formation and deposition chambers was constructed in order to study structures of clusters deposited on a low‐temperature substrate. Clusters are formed by the vapor condensation method with helium gas in the formation chamber. They are injected into the deposition chamber through a nozzle and deposited on a silicon wafer cooled down to the liquid nitrogen temperature. After deposition, GIXRD measurement is carried out without changing vacuum and temperature conditions (insitu). Using the new apparatus, GIXRD measurements were performed on two different kinds of gold cluster deposits prepared on room‐temperature and low‐temperature substrates. The size distribution of gold clusters used for both preparation conditions was measured to be 15±7.5 A˚ by the transmission electron microscope observation of gold clusters sparsely deposited on amorphous carbon film. Diffraction pattern from the room‐temperature deposit of gold clusters showed the bulk face‐centered‐cubic (fcc) structure with an average grain size of 42 A˚ estimated from a peak width, while that from the low‐temperature deposit did not exhibit the simple fcc, but probably the icosahedron‐like structure. The former result is due to coalescence growth among deposited clusters at room temperature, and the latter result suggests that the low‐temperature cluster deposition does not destroy the characteristic structure of free clusters. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147546

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A method of cathode heating using a laser was studied for an electron gun. In order to observe the practicality of the heating system, the characteristics of the laser‐heated gun with a dispenser and LaB6thermionic cathodes have been experimentally investigated. The direct laser irradiation is so efficient that the gun is equipped without heat shielding, a cooling system, or an electrical circuit in the gun chamber for cathode heating. Modeling, based on the experimental data, indicates that the cathode temperature is proportional to one‐fourth power of the laser power and that laser power loss and conduction loss of heat in the gun assembly are negligible. An electron beam current density 0.48 A/cm2was measured with 26 W laser power for a dispenser cathode of 0.06 cm2emission area. Current density 0.16 A/cm2with 25 W was recorded for a LaB6cathode of area 0.12 cm2. Electron beam emittance has been measured by using the typical pepper‐pot technique. It was observed that the growth of electron beam emittance was very small in the laser heating. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147577

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The design and operation of a simple inline optical electron polarimeter is presented. It is based on exchange excitation of ground state neon atoms. The electron polarization is determined from the degree of circular polarization of the subsequent 2p53p 3D3→2p53s 3P2(6402 A˚) fluorescence. This device can characterize both longitudinally and transversely polarized electron beams in a nondestructive fashion, and is inexpensive and easily constructed. ©1996 American Institute of Physics.

ISSN:0034-6748    

DOI:10.1063/1.1147555

出版商:AIP    

年代:1996

数据来源: AIP