Transient pulse evolution of active-mode locking in an intra-cavity frequency-doubled laser

The theory of transient mode locking for an active modulator in an intracavity frequency-doubled laser is presented. The theory is applied to mode-locked and intracavity frequency-doubled Nd:YAG laser and the mode-locked pulse width is plotted as a function of number of round trips inside the cavity. It is found that the pulse compression is faster and the system takes a very short time to approach the steady state in the presence of a second harmonic generating crystal inside the laser cavity. The effect of modulation depth and the second harmonic conversion efficiency on the temporal behavior of the pulse width is discussed.

Elastic Constants of Sodium Nitrate from 77 to 300 K

The six independent elastic constants of sodium nitrate are determined using 10 MHz ultrasonic pulse echo superposition technique over the temperature interval 77 to 300 K. The values obtained at 300 K are C11 = 5.71, C12 = 2.16, C33 = 3.3, C13 = 1.66, C44 = 1.24, C14 = 0.82, and at 77 K C11 = 6.63, C12 = 2.07, C33 = 3.99, C13 = 1.67, C44 = 1.69, C14 = 1.16 all expressed in units of 1011 dyn/cm2.

Laser Raman spectra of semicarbazide hydrobromide

Semicarbazide hydrobromide which is isomorphous with SEM.HCl, was expected to belong to a new family of ferroelectrics. Dielectric, thermal and other studies on these crystals have yielded results which show many peculiarities but not confirmed ferroelectricity in the low temperature phase. As such a Laser Raman spectrosocopic study of oriented singe crystals of SEM.HBr was made at 298°K and at 253°K. The results have been correlated with structural features and compared with SEM.HCl.

Measurement of resistivity and dielectric constant of beach-sand minerals

Resistivity and dielectric constant are important parameters which influence the separation of particles in a drum-type electrostatic separator. The paper provides details of the measurement of the parameters and data on the magnitude of resistivity and dielectric constant of the minerals of beach sand.

Stability criteria for single pulse solutions of cw passive mode-locked lasers

The stability of the steady-state solutions of mode-locking of cw lasers by a fast saturable absorber is imvestigated. It is shown that the solutions are stable if the condition (Ps/Pa) = (2/3) (P0Pa) is satisfied, where (Ps/Pa) is the steady-state la ser power, (P0/Pa) is the power at mode-locking threshold, and Pa is the saturated power of the absorber.

A Microprocessor-Based Pulse-Height Analyzer

Need to analyze particles in a flow? This system takes electrical pulses from acoustical or optical sensors and groups them into bands representing ranges of particle sizes.

Studies on diglycine sulphate

Both diglycine sulphate (DGS) and diglycine sulphate monohydrate (DGS.H2O) are reported to crystallize from solution with pH < 1(1,2). DGS.H2O (point group 2/m; Z = 4) shows a dielectric anomaly at 72°C suggestive of antiferroelectric transition(1). The crystals obtained by us from solution with pH < 0.5 at 20-25°C were always DGS (point group mmm; Z = 8) as confirmed by X-ray studies. The measurement of its dielectric constant along [100], [010] and [001] did not indicate any phase transition in the range 5-400°K. Thus DGS is a normal dielectric unlike TGS. The polarized Raman spectra and the infrared spectra were recorded to examine the configuration of glycine in DGS(3). The vibration spectra reveals that both the glycines in DGS exist as NH3+CH2COOH, thus precluding the hydrogen bond of the type N+-H…O- which exists between two glycine units in TGS. This seems to be a good reason for the difference in the dielectric behaviour of these two glycine sulphates.

Non-ohmic conduction and electrical switching under pressure of the charge transfer complexo-tolidine-iodine

The current voltage characteristics ofo-tolidine-iodine, with stoichiometry 1:1 grown from benzene, have been studied under high pressures upto 6 GPa atT=300 K andT=77 K. The characteristics show a pronounced deviation from ohmicity beyond a certain current for all pressures studied. At room temperature, beyond a threshold field the system switches from a low conductingOFF state to a high conductingON state with σON/σOFF ∼ 103. TheOFF state can be restored by the application of an a.c. pulse of low frequency. The temperature dependence of the two states studied indicates that theOFF state is semiconducting while theON state, beyond a certain applied pressure is metallic. The characteristics atT=77 K do not show any switching.

Low-frequency dielectric constant measurements in the critical polar + non-polar binary liquid system: Methanol + n-heptane

The low-frequency (5–100 kHz) dielectric constant epsilon (Porson) has been measured in the temperature range 7 × 10−5 < t = (T − Tc)/Tc < 8 × 10−2. Near Tc an exponent ≈0.11 characterizes the power law behaviour of Image consistent with the theoretically predicted t−α singularity. However, over the full range of t an exponent ≈0.35 is obtained.

A simple firing delay control circuit for bridge converters

A simple ramp control firing circuit, suitable for use with fully controlled, line-commutated thyristor bridge circuits, is discussed here. This circuit uses very few components and generates the synchronized firing pulses in a simple way. It operates from a single 15 V Supply and has an inherent pulse inhibit facility. This circuit provides the synchronized firing pulses for both thyristors of the same limb in a bridge. To ensure reliability, wide triggering pulses are used, which are modulated to pass through the pulse transformers1 and demodulated before being fed to the thyristor gates. The use of throe such circuits only for a three-phase bridge is discussed.

The truncated dielectric-coated conducting sphere-radiation and gain characteristic

An exhaustive study of the radiation and gain characteristics of a truncated dielectric-coated conducting spherical antenna excited in the symmetric TM mode has been reported. The effect of the various structure parameters on the radiation and the gain characteristics for a few even and odd order TM., modes for different structures is shown. The theorctical radiation patterns and gain have been compared with experiment. It is found that there is good agreement between theory and experiment in the case of TM es and TM os,modes. A theoretical and experimental study of the radiation and gain characcteristics in the frequency range 8.0 to 12.0 GHz has been reported.

Studies on dielectric behavior of insulator-conductor composites

This paper describes the dielectric behavior of an insulator-conductor composite, namely, the wax-graphite composite. The variation of specific capacitance of these composites with parameters such as volume fraction and grain size of the conducting particles and temperature has been studied. These observed variations have been explained using the same model [C. Rajagopal and M. Satyam, J. Appl. Phys. 49, 5536 (1978)] which explains electrical conduction in composites. The specific capacitance of these materials appears to be governed by the contact capacitance between the conducting particles and the number of contacts each particle has with its neighbors. The variation of specific capacitance with temperature is attributed to the change in contact area.

Dielectric studies of As-Se glasses

Dielectric constants and loss tangents of As-Se glasses have been measured between 300 K and the respective glass transition temperatures and between 1 kHz and 20 kHz. The variation of dielectric constants has been interpreted in terms of both heteropolarity of bonds and average bond energies employing a chemically ordered network model. Various contributions to total molar polarizations have been estimated. Rapid rise of loss tangent in the vicinity of glass transitions has been interpreted in terms of rapid increase; of d.c. conductivity.

Studies on diglycine sulphate

The dielectric measurements on diglycine sulphate in the temperature range 5-400 K, show that it is a normal dielectric, unlike triglycine sulphate which is a ferroelectric. The difference in the dielectric behavior of these two glycine sulphates has been explained on the basis of certain structural features derived from a study of their vibration spectra.