Langmuir Probe and Microwave Measurements of the Properties of Streaming Plasmas Generated by Focused Laser Pulses

Measurements have been made on density, velocity, electron temperature, and ion temperature in streaming plasmas generated by allowing the high‐density, high‐temperature material formed by a $Q$ ‐switched laser pulse focused on a solid target to expand into vacuum. Langmuir probe and Lecher‐wire microwave systems for this application have been developed and their reliable operation has been verified. Typical conditions at distances 15‐50 cm from the target are found to be: $T_e{\text{≃1‐12\hspace{0.17em}eV,\hspace{0.17em}n}}_e{\mathrm{\hspace{0.17em}=\hspace{0.17em}\Sigma n}}_i{Z}_i{\text{≃10}}^{10}{\text{‐10}}^{12}/{\mathrm{cm}}^3{\mathrm{,\hspace{0.17em}T}}_i\text{\hspace{0.17em}<\hspace{0.17em}10\hspace{0.17em}eV}$ , peak flow velocity $\text{U\hspace{0.17em}≃\hspace{0.17em}10‐20\hspace{0.17em}}\mathrm{cm}\mathrm{/\mu }\sec$ , the exact values depending on target materials, laser power, and position. Photoionization and charge exchange in a low‐density background gas have been observed.