摘要:

A newly designed Foucault pendulum is described in which the mechanical Charron ring, used throughout in previous designs for damping of the elliptical motion of the pendulum, is replaced by an electromagnetic eddy‐current brake, consisting of a permanent magnet attached to the bottom of the bob and a metallic ring. This damping device is very efficient, as it is self‐aligning, symmetrical in the damping effect, and never wears out. The permanent magnet is also used, together with a coil assembly and an electronic circuitry, for the dipole‐torque drive of the pendulum as well as for accurate stabilization of the amplitude of the swing. A latched time display, controlled by Hall probes activated by the magnet, is used to visualize the Foucault rotation. The pendulum system and its associated electronic circuitry are described in detail. The optimizing of the drive mode is discussed. Measurements of deviations from theoretical value of the Foucault rotation velocity made automatically in a continuous run show a reproducible accuracy of ±1% or better in individual 360° rotations during the summer months. The quality factor of the pendulum as mechanical resonator was measured as a function of the amplitude in the presence of the eddy‐current damping ring.

ISSN:0034-6748    

DOI:10.1063/1.1137615

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

This paper reports on the operation of radio frequency (rf) excited carbon dioxide waveguide lasers. An efficiency of greater than 10% has been achieved with a maximum power of 21 W. The effects of bore size, waveguide fabrication techniques, and gas mixture are discussed.

ISSN:0034-6748    

DOI:10.1063/1.1137616

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A compact externally heated discharge tube of 25‐mm internal diameter is described. The oven made of alumina tube, tungsten heater, and graphite felt insulation, takes about 45 min at 1.5‐kW heater input power to reach temperatures in excess of 1500 °C. Its use with a copper vapor laser is demonstrated. The laser gives output power of 500 mW at 500‐Hz repetition rate.

ISSN:0034-6748    

DOI:10.1063/1.1137617

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A simplified UV‐preionized long‐pulse TEA CO2‐laser amplifier is proposed, which is powered by a common Marx generator for both the preionization arc discharges and the main laser discharge. The measurements of small‐signal gain reveal that there exists an optimum capacitance for the capacitors which are provided in the preionization circuit for the control of preionization level. The physical interpretation for this is also given. A small‐signal gain higher than 3%/cm and an extraction energy of nearly 14 J/l (at the input energy level of nearly 1 J) have been achieved. It has also been demonstrated that the amplifier can amplify a long laser pulse of the order of microseconds without serious distortion of pulse waveform.

ISSN:0034-6748    

DOI:10.1063/1.1137618

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A device has been developed which offers improved performance in many applications where tubular piezoelectric elements are currently being employed. The device, called an EMT (electromechanical translator) can displace optical and small mechanical components over a range of more than 60 &mgr;m with a resolution of a few nanometers. The motion is smooth, continuous, almost tilt free (better than 50 &mgr;rad), and can be controlled in speed over a range from zero to several hundred &mgr;m per second. A self‐contained driver unit for dither stabilization schemes for laser systems has also been developed. The article describes the principle of operation of the EMT and reports various test results.

ISSN:0034-6748    

DOI:10.1063/1.1137619

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

Selective data acquisition controlled by a particle‐identification circuit is demonstrated here to improve the performance of photon‐correlation laser‐Doppler velocimetry (LDV) under unfavorable background‐light conditions (e.g., near a window surface). A gated cross‐correlation technique is used to accumulate data only when a photon‐counting particle discriminator indicates the presence of a light‐scattering particle in the LDV measurement volume. Background‐light contributions between particle transits are suppressed. The particle discriminator is also shown to facilitate measurements of temporal statistics of turbulence (e.g., time scale, energy spectrum) using particle recurrence‐rate correlation. Further applications of the particle discriminator to Rayleigh and Raman scattering are suggested, an adaptation of the circuit for higher‐velocity flows is outlined, and the relation of particle‐discriminated photon correlation to clipped correlation is discussed.

ISSN:0034-6748    

DOI:10.1063/1.1137620

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

We have constructed a circuit that permits conventional timing electronics to be used in single photon‐counting fluorimeters with high repetition rate excitation sources (synchrotrons and mode‐locked lasers). Most commercial time‐to‐amplitude and time‐to‐digital converters introduce errors when processing very short time intervals and when subjected to high‐frequency signals. This circuit reduces the frequency of signals representing the pulsed light source (stops) to the rate of detected fluorescence events (starts). Precise timing between the start/stop pair is accomplished by using the second stop pulse after a start pulse. Important features of our design are that the circuit is insensitive to the simultaneous occurrence of start and stop signals and that the reduction in the stop frequency allows the start/stop time interval to be placed in linear regions of the response functions of commercial timing electronics.

ISSN:0034-6748    

DOI:10.1063/1.1137621

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

A method for determining the refractive indices of transparent isotropic or anisotropic solids is presented. The method utilizes null position measurements of light deflected by a sample immersed in a liquid of known index. Measurements of absolute deflection angles are not involved. Natural crystal growth faces, even at right angles, can serve as prism faces, thus eliminating the need for extensive surface preparation. Consequently, this method is particularly well suited for measuring the refractive index of small samples with high indices. Using a simple refractometer, results were obtained for two biaxial and one isotropic material with high refractive indices: Ni2SiO4with the spinel structure (maximum dimension of 0.12 mm), Ni2SiO4(olivine structure), and GdAlO3(perovskite structure). Uncertainties of less than 0.1% are obtained from visual observations of the refracted light. Increased accuracy is possible by improving the calibration of the immersion liquid refractive index and the detection system.

ISSN:0034-6748    

DOI:10.1063/1.1137611

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

An instrument has been designed and built which can measure the differential scattering of circularly polarized light as a function of angle about the scattering volume. The rationale for making these measurements is to investigate the long‐range structure of large chiral, optically active molecules, or chiral aggregates of molecules. The design is based on the principle of electro‐optic modulation and synchronous demodulation to recover scattered intensities from incident left and right circularly polarized laser light. Preliminary reproducible results that have been obtained on cholesteric liquid crystals are presented.

ISSN:0034-6748    

DOI:10.1063/1.1137612

出版商:AIP    

年代:1984

数据来源: AIP

摘要:

An instrument is described which controls a two‐mirror scanning arrangement to raster a laser beam on a large‐area solar cell. The short circuit current thus produced is plotted on anX–Yrecorder, or recorded on a storage oscilloscope to study the spatial inhomogeneities of the cell.

ISSN:0034-6748    

DOI:10.1063/1.1137613

出版商:AIP    

年代:1984

数据来源: AIP