Experimental studies of laser guiding and wake excitation in plasma channels
- Massachusetts Inst. of Tech., Cambridge, MA (United States). Dept. of Physics
This thesis presents results of experimental investigations of laser guiding in plasma channels. A new technique for plasma channel creation, the Ignitor-Heater scheme was proposed and experimentally tested in hydrogen and nitrogen. It made use of two laser pulses. The Ignitor, an ultrashort (< 100 fs) laser pulse, was brought to a line focus using a cylindrical lens to ionize the gas. The Heater pulse (100--200 ps long) was used subsequently to heat the existing spark via inverse Bremsstrahlung. The hydrodynamic shock expansion created a partially evacuated plasma channel with a density minimum on axis. Such a channel has properties of an optical waveguide. This technique allowed, for the first time, creation of plasma channels in low atomic number gases, such as hydrogen, which is of importance for guiding of highly intense laser pulses. The channel density was diagnosed with time resolved longitudinal interferometry. From these measurements the plasma temperature was inferred. The guiding properties of the channels were tested by injecting a 5 {times} 10{sup 17} W/cm{sup 2}, 75fs laser pulse. The guiding properties and transmission and coupling efficiency were studied as a function of relative position of the channel and the injection pulse focus. Whereas entrance coupling efficiency into the channel was lower than expected, channel coupling to continuum losses were found to be in good agreement with analytical predictions. The authors speculate that increased coupling efficiency can be achieved through better mode matching into the channel. Analytic and numerical one dimensional (1-D), nonrelativistic theory of laser pulse propagation in underdense plasma was presented, in the context of laser wakefield acceleration. The relation between the laser pulse energy depletion, longitudinal laser pulse shape distortion, and changes in the group velocity and center wavelength was explored. 1-D theory was extended to treat the case of a laser exciting a wake in a hollow plasma channel, by making use of an energy conservation argument. Based on the results of this theory, a laser wakefield diagnostic was proposed where, by measuring the changes in phase or spectrum of the driving laser pulse, it is possible to infer the amplitude of the plasma wake.
- Research Organization:
- Lawrence Berkeley National Lab., Accelerator and Fusion Research Div., CA (United States)
- Sponsoring Organization:
- USDOE Office of Energy Research, Washington, DC (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 335554
- Report Number(s):
- LBNL-41892; TRN: 99:005024
- Resource Relation:
- Other Information: DN: Thesis submitted to Massachusetts Inst. of Tech., Dept. of Physics, Cambridge, MA (US); TH: Thesis (Ph.D.); PBD: Jun 1998
- Country of Publication:
- United States
- Language:
- English
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Guiding of high intensity ultrashort laser pulses in plasma channels produced with the dual laser pulse Ignitor-Heater technique.
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