Generation of uniform plasmas for beat wave experiments

The laser plasma ‘‘beat wave’’ mechanism for the generation of ultra‐high electric fields requires plasmas of several metres length with density uniformity of about 1%. Multiphoton ionization of molecular hydrogen gas at a pressure of a few torr provides a scaleable mechanism for generating these plasmas. We describe measurements of electron density, temperature and uniformity of plasmas generated by a frequency doubled Neodymium glass laser, at an irradiance of about 1014Wcm−2. The plasma density corresponds to 100% ionization and is measured to be uniform to within the measurement errors over a length of 8mm.