Trailing Pulse Research Articles

Space–time characteristics of a SPER laser utilizing transitions in Cd, Zn, and In atoms

An experimental investigation was made of the space?time characteristics of lasers utilizing atomic transitions with a segmented plasma source of Cd, Zn, and In metal vapor. It is noted that elongation of the pump pulse trailing edge increased the output energy. Various effects were observed, confirming the recombination mechanism for pumping in an SPER (segmented plasma excitation and recombination) laser utilizing atomic transitions. These included a shift of the lasing range during cooling of the plasma, an increase in the time delay and a shift of the lasing range when the input energy was varied, and quenching of the lasing as a result of additional heating. The feasibility of pulse-periodic operation of an SPER laser was examined. It was established that the limiting pulse repetition frequency may reach 10 kHz.

Nearly free induction decay observed in picosecond pulse propagation

Coherent reshaping of resonant pulses is investigated for moderately short samples. It is shown that a trailing pulse wing develops with decay time τ < T 2/2 (dephasing time T 2). This novel phenomenon is verified experimentally for HCl: Ar at 3 bar. Ultrafast dephasing and beating of the two HCl isotopes is directly observed on time-resolved infrared spectroscopy.

Dynamic tension in water induced by the reflection of shock waves

Negative pressures were produced in distilled water by reflecting a 70-bar shock pulse off a quasi-free water-Mylar-air interface. The incident pulses, created by symmetric impact of a projectile onto a buffer, had durations of 1–2 μs. A displacement inter-ferometer measured the velocity u of the Mylar. After the pulse's trailing edge reaches the Mylar, u would tend to vanish in the absence of cavitation. If the region of tension cavitates abruptly when a tensile strength S is exceeded, the downward transition in u is terminated. The transition was observed to be terminated when u changed by Δu ≈ −4 m/s. Assuming the flow remains uniaxial, S ≈ −p0 − ρcΔu/2, where ρ, c, and p0 = 1 bar are the water's initial density, sound speed, and pressure [P. L. Marston and G. L. Pullen, Proc. of the 1981 APS Conference on Shock Waves in Condensed Matter, edited by W. J. Nellis (to be published)]. It appears that the Mylar separated from the water during pullback and the data places only a lower limit (28 bars) on S. [Work supported by ONR and the WSU Research and Arts Committee. P. Marston is an Alfred P. Sloan Research Fellow.]

Infrasonic waves from auroral arcs

The infrasonic bow wave from a traveling auroral arc of finite length is calculated, and the results of the infinite length approximation are essentially recovered. The finite length results in a distinct, separate, second trailing pulse that is weaker than, and of the opposite sign from, the main pressure wave. It is shown that the sign-reversed signatures sometimes observed may be due to arc currents that have strongly defined trailing ends and relatively diffuse frontal structures.

Pulse communication on lines

A dispersive medium, i.e. one in which the waveform of an individual pulse changes its type at successive points during propagation, is not normally appropriate for pulse communication, since greater efficiency can be achieved through it in other ways. However, conditions can arise in which it becomes desirable to employ such a link, and it is necessary to discover the restrictions imposed by the medium on multichannel pulse communication, and the steps that can be taken to minimize these limitations.The paper briefly describes a theoretical and experimental investigation by the authors into the particular problems of pulse communication over a 50-mile open-wire line of the standard Army type. The major problem, of adjacent-channel interference caused by the progressive deterioration of the individual propagated pulse waveforms to a point where they appreciably overlap, is adequately solved by adapting and extending a technique employed for wide pulses in line telegraphy to the case of narrow pulses. This is the device of reducing the interfering effect of each trailing pulse response by transmitting, instead of a simple rectangular pulse, a controllable curbed pulse, i.e. a flexible combination of contiguous pulses of opposite sign. By this means satisfactory crosstalk results are achieved for multichannel pulse operation in one direction.For two-way operation the dominant problem now becomes the near-end interference arising from the irregular sequence of pulse reflections from various inhomogeneities in the line. Unless the line is sufficiently smooth, the crosstalk so occasioned may become intolerable.