Measurement of amplified binary-modulated chirped laser pulses generated by different acousto-optic pulse shaping algorithms

The paper belongs to the field of ultrafast optics. Acousto-optic pulse shaping has been studied experimentally for binary intensity modulation in a chirped pulse amplification laser system. Direct time-domain measurement of pulse front duration with a picosecond streak camera was performed for a Ti:sapphire regenerative amplifier. It was discovered that the sign of the second order dispersion produced by the acousto-optic dispersion delay line affects the modulation rise/fall time. Two algorithms for synthesis of ultrasonic waveforms for feeding the delay line, dispersive Fourier synthesis and the Gerchberg-Saxton algorithm, were compared. Minimum pulse front duration of 3.6 ps for 3 mJ pulses with the linear chirp of 6.2 ps/nm at the wavelength of 795 nm was obtained.

Measurement of amplified binary-modulated chirped laser pulses generated by different acousto-optic pulse shaping algorithms

The paper belongs to the field of ultrafast optics. Acousto-optic pulse shaping has been studied experimentally for binary intensity modulation in a chirped pulse amplification laser system. Direct time-domain measurement of pulse front duration with a picosecond streak camera was performed for a Ti:sapphire regenerative amplifier. It was discovered that the sign of the second order dispersion produced by the acousto-optic dispersion delay line affects the modulation rise/fall time. Two algorithms for synthesis of ultrasonic waveforms for feeding the delay line, dispersive Fourier synthesis and the Gerchberg-Saxton algorithm, were compared. Minimum pulse front duration of 3.6 ps for 3 mJ pulses with the linear chirp of 6.2 ps/nm at the wavelength of 795 nm was obtained.

EXCITATION OF PLASMA BY ELECTRIC PULSES IN NEON MEDIUM

We studied characteristics of the neon plasma source excited in the atmosphere under the following conditions: gas pressure is about 2 Torr, rectangular pulses have an amplitude from 200 to 800 V, pulse duration is from 0.2 to 10 μs, repetition rate is from 0.2 up to 1 kHz. There is a mode with a stable and unstable mode of existence of the plasma when the voltage on the electrodes of the plasma source varies from 800 to 350 V and from 350 to 250 V before the extinction of the plasma. The pulse from the PMT output in a steady state plasma has a decay of about 100 μs, the duration of which does not depend on the magnitude of the voltage, frequency and pulse duration. With a decrease in the supply voltage U, the pulse front duration with a photomultiplier is increased from 74 to 450 ns. It is shown that a large neon plasma relaxation time of 100 µs compared with a beam pulse duration of 1…2 µs allows only one time to change the phase of the accelerating field.

Высоковольтные диффузионные диоды с резким восстановлением. I. Численное моделирование

The operation of diffusion step recovery diodes (dSRD) as current interrupters in high-power nanosecond pulse generators was studied in detail by the methods of numerical computer simulation for the first time. One of the necessary conditions that minimize the loss in dSRD was specified. Dependences of pre-pulse voltage, front duration, amplitude and duration of pulse formed on the active load, and the energy of switching losses in the dSRD on the device area and the break current density are obtained. It is shown that simulation results can be described by simple analytical formulas obtained in the second part of the work, with an accuracy of 10-20% if the pulse amplitude does not exceed the avalanche breakdown voltage of the dSRD. The generalized figure of merit which can be used for optimization of dSRD parameters, a mode of its operation and comparison of efficiency of current interrupters of various types was offered.

Study of the Torque Acting on the Magnetization during 90° Pulsed Reversal Process in Ferrite-Garnet Films with In-Plane Anisotropy

To calculate the torque acting on the magnetization vector during the process of 90° pulsed magnetization in real ferrite-garnet films in which, besides in-plane anisotropy, biaxial anisotropy is present, the method based on the analysis of the operating point trajectory is used. Analysis has shown that the shape of the time dependence of the torque Tφ in the time interval, within which the exciting of the magnetization oscillations occurs, is slightly dependent on the pulse front duration. As a result the magnetization oscillations (with a period of Tos ≅ 2 ns) can be observed at the pulse front duration τf ≥ 14 ns.

A Comparative Study on the Positive Lightning Return Stroke Electric Fields in Different Meteorological Conditions

Positive cloud-ground lightning is considerably more complex and less studied compared to the negative lightning. This paper aims to measure and characterize the significant parameters of positive return strokes electric field, namely, the zero-to-peak rise time, 10–90% rise time, slow front duration, fast transition rise time (10–90%), zero-crossing time, and opposite polarity overshoot relative to peak. To the best of the authors’ knowledge, this is the first time such detailed characteristics of positive lightning in Malaysia are thoroughly analyzed. A total of 41 positive lightning flashes containing 48 return strokes were analyzed. The average multiplicity is 1.2 strokes per flash. The majority of positive lightning was initiated from the primary positive charge rather than as a byproduct of in-cloud discharges. The cumulative probability distribution of rise time parameters, opposite polarity overshoot relative to peak, and slow front amplitude relative to peak are presented. A comparison between studies in four countries representing tropic, subtropic, and temperate regions was also carried out. Measured parameters in Florida, Sweden, and Japan are generally lower than those in Malaysia. Positive lightning occurrences in tropical regions should be further studied and analyzed to improve our current understanding on positive return strokes.