Generation of Uniform Plasmas for Beat Wave Experiments

The laser plasma "beat wave" mechanism for the generation of ultrahigh electric fields requires plasmas of several meters length with density uniformity of about 1 percent. Multiphoton ionization of molecular hydrogen gas at a pressure of a few torr provides a scalable mechanism for generating these plasmas using the same laser beams that drive the beat wave. We describe measurements of electron density, temperature, and uniformity of plasmas generated by a frequency doubled Neodymium glass laser, at an irradiance of about 1014 W · cm-2. The plasma density corresponds to 100-percent ionization and is measured to be uniform to within the measurement errors over a length of 8 mm.