Pulse duration

About: Pulse duration is a research topic. Over the lifetime, 19429 publications have been published within this topic receiving 286507 citations.

Non-equilibrium plasma in liquid water: dynamics of generation and quenching

Abstract: In most cases, the electric breakdown of liquids is initiated by the application of high electric field on the electrode, followed by rapid propagation and branching of plasma channels. Typically plasmas are only considered to exist through the ionization of gases and typical production of plasmas in liquids generates bubbles through heating or via cavitation and sustains the plasmas within those bubbles. The question arises: is it possible to ionize the liquid without cracking and void formation?To answer this question we used a pulsed power system with 32–220 kV pulse amplitude, 0.5–12 ns pulse duration, 150 ps rise time. The discharge cell had a point-to-plate geometry with a tip diameter of 100 µm. These parameters allowed us to observe non-equilibrium plasma generation. The measurements were performed with the help of a 4Picos ICCD camera. It was found that the discharge in liquid water forms on a picosecond time scale. The increase of emission intensity and plasma formation took 200–300 ps. The diameter of the excited region near the tip of the high-voltage electrode was ~1 mm. After this initial stage emission rapidly decreased and the plasma region became almost invisible after 500 ps. The absence of emission during the rest of the pulse is explained by a decrease of the electrical field on the boundary of the conductive zone.Thus we have demonstrated the possibility of formation of non-equilibrium plasma in the liquid phase and investigated the dynamics of excitation and quenching of non-equilibrium plasma in liquid water.

Nonlinear refraction in CS 2

Abstract: The nonlinear refractive index (γ) of CS2 was measured using the Z-scan technique and laser radiation of various (femto-, pico-, and nano-second) pulse durations. We observed the growth of γ with the increase of the pulse duration (from (3±0.6)×10-15 cm2 W-1 at 110 fs to (4±2)×10-14 cm2 W-1 at 75 ns) due to the additional influence of the molecular reorientational Kerr effect in the case of longer (picosecond and nanosecond) pulses. Acoustic wave induced negative nonlinear refraction was observed using wavefront analysis. We analyzed the simultaneous influence of both electronic and molecular processes leading to the positive nonlinear refraction and acoustic processes leading to the negative nonlinear refraction in carbon disulfide. Variations of the refractive index due to the thermal effect at high pulse repetition rates were also investigated.

Tissue Damage by Pulsed Electrical Stimulation

Abstract: Repeated pulsed electrical stimulation is used in a multitude of neural interfaces; damage resulting from such stimulation was studied as a function of pulse duration, electrode size, and number of pulses using a fluorescent assay on chick chorioallontoic membrane (CAM) in vivo and chick retina in vitro. Data from the chick model were verified by repeating some measurements on porcine retina in-vitro. The electrode size varied from 100 mum to 1 mm, pulse duration from 6 mus to 6 ms, and the number of pulses from 1 to 7500. The threshold current density for damage was independent of electrode size for diameters greater than 300 mum, and scaled as 1/r2 for electrodes smaller than 200 mum. Damage threshold decreased with the number of pulses, dropping by a factor of 14 on the CAM and 7 on the retina as the number of pulses increased from 1 to 50, and remained constant for a higher numbers of pulses. The damage threshold current density on large electrodes scaled with pulse duration as approximately 1/t0.5, characteristic of electroporation. The threshold current density for repeated exposure on the retina varied between 0.061 A/cm2 at 6 ms to 1.3 A/cm2 at 6 mus. The highest ratio of the damage threshold to the stimulation threshold in retinal ganglion cells occurred at pulse durations near chronaxie - around 1.3 ms.

Shielding properties of laser-induced breakdown in water for pulse durations from 5 ns to 125 fs

Abstract: The shielding effectiveness of laser-induced breakdown from focused, visible laser pulses from 5 ns to 125 fs is determined from measurements of transmission of energy through the focal volume. The shielding efficiency decreases as a function of pulse duration from 5 ns to 300 fs and increases from 300 fs to 125 fs. The results are compared with past studies at similar pulse durations. The results of the measurements support laser-induced breakdown models and may lead to an optimization of laser-induced breakdown in ophthalmic surgery by reduction of collateral effects.