1.32 μm Nd3+∶YAG Pulse Laser

Using specially coated mirrors, an output energy of 0.97 J at 1.32 μm from a Nd3+∶YAG pulse laser is obtained with pumping energy of 66 J. The repetition rate is 1 pulse/sec and the slope efficiency is 1.7%. The repetition rate can be changed from 1 pulse/sec to 10 pulses/sec.     

1. 32μm Nd~(3 ): YAG Pulse Laser

Using specially coated mirrors, an output energy of 0.97 J at 1.32 μm from a Nd3 : YAG pulse laser is obtained with pumping energy of 66 J. The repetition rate is 1 pulse/sec and the slope efficiency is 1.7%. The repetition rate can be changed from 1 pulse/sec to 10 pulses/sec.     

Flow Characteristics in the Exhaust of a Pulsed Megawatt Gas Fed Arc

The transient flow generated by a pulsed, megawatt-level, gas-fed arc with an applied magnetic nozzle has been examined with a new design piezoelectric pressure transducer. Sensor thermal conduction and accelerations have been examined and eliminated in the 500?sec period of plasma flow. Existence of a large magnitude cold gas pressure front of 20?sec duration has been reconfirmed and its relationship to the following plasma flow of about 200?sec duration has been examined for the first time. At a point 30 cm from the arc source, initially near vacuum conditions (typically with an arc current of 11.2 kA and 1 tesla applied magnetic field), a pressure pulse of unionized gas with a magnitude of 104 N/m2 is followed by plasma flows with nearly constant impact pressure of 103 N/m2. Pressure and number density in this plasma region are seen to decrease with applied magnetic field strength. With electron density derived from Thomson scattering measurements (1020 m-3) plasma flow velocities on the order of 5 × 104 m/sec are calculated.     

Ionospheric plasma by VHF waves

The amplitude scintillations of very high frequency electromagnetic wave transmitted from geo-stationary satellite at 244.168 MHz have been recorded at Varanasi (geom. lat. 14′ 55′N) during 1991 to 1999. The data are analyzed to determine the statistical features of overhead ionospheric plasma irregularities which are mostly of small duration <30 minutes and are predominant during pre-midnight period. The increase of solar activity generally increases the depth of scintillation. The auto-correlation functions and power spectra of scintillations predict that the scale length of these irregularities varies from 200–500 m having velocity of movement between 75 m/sec to 200 m/sec. These results agree well with the results obtained by other workers.     

铁在范性形变过程中的低频内耗

在改装了的拉力试验机上测量了纯铁在范性形变过程中的内耗。研究了拉伸速率(在0.73×10^-6-50×10^-6/秒范围内)、测量频率(在0.3—3.6/秒范围内)、应变退火及含碳量等对纯铁范性形变过程中内耗的影响。所得结果表明,在屈服平台上,范性形变过程中内耗基本不变,且其值随范性形变速率的增加和测量频率倒数的增加而线性增加。将实验结果与范性形变过程内耗的位错动力学模型所得出的定量关系式进行了对比,得到了满意的符合。求得了退火纯铁在屈服平台上的位错动力学指数为10 关键词：     

On the Retrograde Motion of Arcs in Magnetic Fields

Experiments are reported which allow the determination of retrograde velocity of individual cathode spots and of the plasma flow in a pulsed discharge using various metals and carbon as cathode materials. For discharge currents from 10 to 40 amps, pressures of 3 mmHg and magnetic field strengths of 6.103G retrograde spot velocities from 30 to approximately 300 m/sec are observed and the corresponding plasma flow velocities are in the range from 4,400 to 8,600 m/sec. On cathode materials with low melting points, the splitting rate of spots and the motion of individual spots is small, whereas under identical conditions the spots on refractory materials are highly mobile, the splitting rate is large, and the lifetime of individual spots is short.     

Friction of synthetic corundum and silicon carbide on hardened ShKh15 steel

The work shows that the friction coefficient during slip of polycrystalline electrolytic corundum, single-crystal silicon carbide and sintered corundum over hardened ShKh15 steel, and the wear m in an electrolytic corundum test-piece according to slip speed have a low point at speeds close to 100 m/sec. A hypothetical explanation is given for this behavior of and m.     

Lifetime measurements of Stark states of sodium

Lifetimes of n = 17, m = 0 Stark-manifold states of Na atoms have been measured in the static electric fields ranged from 1250 to 2000 V/cm using delayed electric field ionization (DEFI). The observed lifetimes of the Stark-manifold states are of the same order of magnitude (10⁻⁶ sec). The influences of applied fields and blackbody radiation on the determination of the lifetimes were discussed.     

An interferometric velocity calibrator for73Ge Mössbauer spectrometer

A velocity calibrator based on a laser driven Michelson interferometer was designed for a⁷³Ge Mössbauer spectrometer in the range of 100 to 500 μm/sec. The conventional method of counting the interference fringes cannot be used in this case because the displacement only spans about 3 to 15 μm and only a few fringes can be observed during one velocity sweep. The velocity calibration obtained this way was compared with the calibration obtained from⁵⁷Fe measurement, and excellent agreement was found between the two methods.     

Short-term electrical relaxation in alkaline halide crystals

The temperature dependence of total conductivity in KCl and NaCl monocrystals with calcium impurity in the audio frequency range is studied, It is established that in the temperature range 50–350°C only one of the observed relaxation processes is described by the dipole relaxation mechanism with characteristic time = ₀exp (E/T); the values ₀ = 10^–14sec, E = 0.65eV, and ₀ = 10^–14sec, E = 0.7eV are obtained for KCl and NaCl respectively. Relaxations with values of ₀ and E differing from those above which were observed in the given temperature and frequency range are produced by resistance of the near electrode region.Translated from Izvestiya VUZ. Fizika, No. 6, pp. 101–106, June, 1973.     

Rapid formation kinetics of a long-lived electron-hole drop in Ge under pulsed excitation

The buildup of a large long-lived electron-hole drop in stressed Ge is studied using its Alfvén wave resonances. This microwave method permits rapid time resolution of the formation process after a short intense (100 nsec, 7 W) laser excitation pulse. A delay of about 1 μsec is observed before the drop radius rapidly increases from zero to ～ 100 μm within the next μsec. This is consistent with the interpretation that the photo-produced electron-hole pairs are quickly accelerated to the strain-induced potential minimum which is well within the crystal.     

Thermoelectric line array for spatial specification of focused laser beams

A thin-film line array of thermoelectric detectors is applied for the measurement of intensity distribution of focused laser beams. The damage threshold of these detectors is relatively high. They can tolerate 50 μsec pulses with intensities as high as 3·10⁵ W/cm². High resolutions can be achieved by fabricating line arrays having a large number of thermoelectric junctions with distances as small as 5 μm between centers.     

Ejection of uniform micrometer-sized droplets from Faraday waves on a millimeter-sized water drop

This Letter reports the first observation and theoretical analysis of a new phenomenon: one large spherical water drop ejecting simultaneously a very large number of monodisperse microdroplets. An ultrasonic nozzle with multiple-Fourier horns in resonance enables controlled excitation of megahertz Faraday waves on the free water surface. The temporal instability of such waves leads to the ejection of 3.5-4.4 μm monodisperse droplets at a high rate (>4.0×10(7) droplets/sec). This is in stark contrast to the Rayleigh-Plateau instability, which ejects one droplet at a time.     

Interface motion and nucleation of solid helium-4 induced by acoustic waves

Crystallization and melting of helium-4 was experimentally observed to be induced by acoustic radiation pressure where the liquid-solid interface is highly mobile at low temperatures. We discuss the observed anomalous reversal of this effect as a function of temperature and the nucleation by acoustic wave pulses of crystals in the liquid phase or liquid bubbles in the solid phase. A high-speed camera was used for the in situ observation of large interface velocities as high as 1 m/sec.     

Propagation of heat in anthracene crystals at helium temperatures

Measurement of temperature pulses with time resolution less than 5 nsec based, on the high-speed registration of the Debye-Waller factor in the fluourescence spectrum of an impurity layer deposited on a sample, has been achieved. In anthracene single crystals, the velocity of heat propagation was found to be equal to 0.7?1.0.10⁵ cm/sec, approaching that sound; the mean free path of phonons was found to exceed 30 μm.     

An eight-terminal fiber optics data bus using tee couplers

An analysis of the performance of a fiber optics data bus using optical Tee couplers has been carried out. Using a design based on this analysis, an eight-terminal bidirectional system was built and tested. Light-emitting diode optical sources were employed in the transmitters and silicon photodiode detectors in the receivers. The couplers, which employ a glass-mixing block with internal mirrors, have excess losses of from 1.0 to 1.8 dB. Worst-case interterminal loss for the entire bus is 45.2 dB, and the minimum signal-to-noise ratio at a 5 Mb/sec data rate is 12 dB.     

Observational Evidence for Energy Accumulation and Dissipation in Coronal Magnetic Loops

Using the Wigner-Ville transform, we study the dynamic spectra of low-frequency modulation of the intensity of microwave emission from several solar flares and detect the microwave bursts modulated by chirp signals (i.e., signals whose frequencies =₀± kt, where k is a constant and t is the time) with a positive chirp rate. Such a modulation corresponds to the process of energy accumulation in the corresponding coronal magnetic loop (CML). We also detect chirp modulation with a negative chirp rate corresponding to powerful dissipation of electric current in the CML during a solar flare. The chirp modulation of the intensity of microwave emission from a CML arises from the excitation of eigenoscillations of the loop as an equivalent electric circuit. In this case, the modulation frequency is proportional to the loop electric current and varies with the variation of the latter. The electric-current values found for a few events using the dynamic spectra of chirp signals lie in the range 10¹¹-10¹²A, and the rate of energy increase (decrease) is estimated to be 1.4·10²⁶-3·10²⁹ erg/sec for the characteristic time scale 10³-4·10⁴ sec. The events studied give evidence for the possibility of realizing the circuit model of solar flares under solar-corona conditions.     

Cryogenic microjet source for orthotropic beams of ultralarge superfluid helium droplets

Liquid 4He at pressures P(0)=0.5-30 bars and temperatures T(0)=1.5-4.2 K is discharged into vacuum through two different 2 microm nozzles. The velocities of the beam of particles obey the Bernoulli equation down to 15 m/sec. With decreasing T0 and increasing P0 the velocity and angular distributions become exceedingly narrow with Deltav/v less or similar 1% and Deltatheta less or similar 1 mrad. Optical observations indicate that the beam consists of micron-sized droplets (N greater or similar 10(9) atoms). This new droplet source provides opportunities for novel experimental studies of superfluid behavior.     

Interferenzen bei atomaren Stoßprozessen

Differential scattering cross sections for the collision partners Na-Kr and Na-Xe have been measured in the angular region of 3 to 30? for relative velocities from 670 to 1130 m/sec. Both the rainbow structures and the superimposed interference patterns, whose “wavelength” varied from 1 to 1,6?, are well resolved. The three parameters of a Lennard-Jones (n, 6) potential were determined for each system from a comparison of the experimental results with differential cross sections calculated by using the partial wave method.     

Kinetics of Formation of an Oxide Film on the Surface of the Cathode in an Atmospheric-Pressure Glow Discharge in Helium

The kinetics of formation of an oxide film on the surface of the cathode of an atmospheric-pressure glow discharge in helium has been investigated by the method of laser reflectometry. It has been established that the film is formed at a cathode temperature exceeding 550 K, and in 200 sec from the time of discharge initiation at a current of 1 A it becomes thicker than 1 m. The film consists of several concentric zones. For each of these zones, a change in time of the directional hemispherical coefficient of reflection at a wavelength of 0.63 m was determined. It is shown that the formation of an oxide film on the cathode surface leads to an increase in the cathode drop.