Nonlinear processes in laser-produced dense plasma (observation of the fractional harmonics)
One of the main issues of laser plasma physics interactions is harmonic generation. The harmonic emission spectrum provides clues as to which non-linear processes take place in the plasma. Several effects contribute to a given line as judged from the complexity of the actual spectra. Unfolding of them has not been done satisfactorily yet. Harmonic lines with half integer or integer orders have been observed, but the physics are far from complete. In this dissertation research, we observed the usual second harmonic generation and a set of fractional harmonics which we believe have been observed for the first time in plasma physics. The plasma was produced by a high power laser and we have characterized its properties from the analysis of the radiation spectra, including the harmonic lines, as measured using the methods of transient spectroscopy. We produced the plasma with a Nd:glass laser which had a 65 nsec pulse width (FWHM) with a total energy of up to 6 Joules. The targets were steel alloys, copper, and aluminum. The harmonic generation from the plasma with a planar metal target was not strong. But, it became stronger when we made a dead hole (cavity) at the laser spot on the target surface. The second harmonic line appears first before the time of the peak of laser pulse. The fractional harmonics, which are related to the laser wavelength by rational number other than integers or half integers, appear near or after the time of the laser peak and weaker in UV wavelength range but stronger if some atomic emission line are near by. To understand the plasma evolution better, we developed computer simulation codes. The codes contain all relevant processes necessary to compute the plasma evolution.
- Research Organization:
- Lehigh Univ., Bethlehem, PA (USA)
- OSTI ID:
- 6894487
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
LASER-PRODUCED PLASMA
NONLINEAR PROBLEMS
ALLOYS
ALUMINIUM
COMPUTERIZED SIMULATION
COPPER
DATA ANALYSIS
EXPERIMENTAL DATA
HARMONIC GENERATION
HARMONICS
MEASURING INSTRUMENTS
MEASURING METHODS
NEODYMIUM LASERS
DATA
ELEMENTS
FREQUENCY MIXING
INFORMATION
LASERS
METALS
NUMERICAL DATA
OSCILLATIONS
PLASMA
SIMULATION
SOLID STATE LASERS
TRANSITION ELEMENTS
700101* - Fusion Energy- Plasma Research- Confinement
Heating
& Production
656000 - Condensed Matter Physics