Laser Pulse Formatting to Reduce Thermal Blooming by Aerosol Vaporization
Abstract
Propagation of ground-based, high-energy laser (HEL) beams through the atmosphere at a laser wavelength of lambda(L) = 1.06 microns is limited by thermal blooming due to aerosol absorption. The scaling of critical laser power with beam diameter requires that the aperture size exceed 20 m for average laser powers of 100 MW. SRL has shown that this problem may be resolved by vaporizing the aerosols with a laser for aerosol vaporization (LAV). The dependence of vaporization on fluence and wavelength has been determined. In particular, it is shown that a LAV wavelength lambda(nu) = 1.06 microns and intensity of 10 MW/sq cm yields a reduction by a factor of 5 at 2 microsec, corresponding to 20 J/sq cm of laser fluence per pulse. The best LAV wavelength appears to be that of a KrF laser, lambda(nu) = 0.248 microns. For this wavelength, an intensity of 3 MW/sq cm and a pulse duration of 1 microsec, corresponding to a fluence of 3 J/sq cm per pulse, reduces aerosol absorption by a factor of 50. The dependence of the critical HEL power on the beam aperture diameter d has been determined in the presence and absence of LAV, assuming no wind shear. Without vaporization the scaling law is pessimistic - on can propagate less than 10 MW average power at d = 10 m. If one uses a KrF LAV at an average power of 2 MW, a pulsewidth of 1 microsec, and a pulse repetition frequency of 10 Hz, the critical power at d = 5 m is 100 MW. This greatly alleviates the thermal blooming problem.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 17, 1989
- Accession Number
- ADA351546
Entities
People
- Allen Flusberg
- Vladimir Krapchev