Expansion of laser sparks produced by a mode-locked Nd: Glass-laser

Shock waves and ionizing radiation plasmas produced by a mode-locked laser

“…In a second build-up the plasma was imaged onto the slit of a streak camera. This arrangement is described in detail by Meyer and Stritzke (1976). The streak camera had a time resolution of 0.2 ns.…”

“…Photos taken with the streak camera demonstrate that the plasma zone €3 is created some distance from the plasma A (see e.g. the paper of Meyer and Stritzke 1976). The figure 3(a) shows furthermore that after 11 ns, when the second plasma zone B is created by the laser, neither the shock wave nor the plasma edge of the first plasma A has reached the position at which the creation of the plasma B starts.…”

“…A second plasma zone is then created at that point, where the density of free electrons, generated by the ionizing radiation, is sufficient for the following laser pulse to increase it to the density of a visible plasma. If one calculates this process (Meyer and Stritzke 1976) one finds a complex dependence of the expansion velocity U from the gas pressure p and the focal lengthf of the lens in the form where a is the divergence of the laser beam and A its cross-section, ncr is the amplification factor for the first electron in the focus volume to create a visible plasma, E ( T ) is the emission coefficient of the continuum in a frequency interval AV around the ionizing frequency of the gas, p is the absorption coefficient of the ionizing radiation, and Eion is the ionization energy of the gas.…”

“…They found that the plasma grows, starting in the focus of the focusing lens, in several steps towards the lens under the action of the laser pulses. Further experiments by Kaitmazov et al (1968) and Meyer and Stritzke (1976) showed that the plasma consists of discrete layers and that each laser pulse in the pulse train generates one layer, each nearer to the lens than the one before. Figure 1 (plate) shows a typical photo of a mode-locked spark.…”

Spatial and temporal dynamics of light attenuation and transmission by plasmas induced in liquids by nanosecond Nd:YAG laser pulses

“…Plasma expansion models based on the interaction of the incoming light pulse with expanding shockwaves [9,10] or with diffusing ions [11] have been proposed. It was shown [3] that, for nanosecond pulses, the expansion velocity of shock waves or ionized particles was lower than the apparent expansion of the plasma streack, calculated as dz(t)/dt, at least in the early part of the plasma growth.…”