LASER PULSE FORMATTING TO REDUCE THERMAL BLOOMING BY AEROSOL VAPORIZATION

THE PROPAGATION OF A GROUND BASED LASER BEAM TO A RELAY MIRROR IN SPACE REQUIRES COMPENSATION FOR THE DELETERIOUS EFFECTS OF ATMOSPHERICTURBULENCE AND THERMAL BLOOMING TO ACHIEVE NEAR DIFFRACTION LIMITED PERFORMANCE. THE EFFECTS OF PULSE FORMATTING ON THE UPLINK PROPAGATION OF HIGH POWER LASER BEAMS THROUGH THE ATMOSPHERE NEEDS TO BE DETERMINED. FOR A LASER WAVELENGTH OF 1 MICROMETER, THE ABSORPTION WILLLIKELY BE DOMINATED BY AEROSOLS SINCE MOLECULAR ABSORPTION OF 2-3% LEADS TO INEFFICIENT BEAM PROPAGATION FROM THE GROUND TO A RELAY MIRROR OR A TARGET IN SPACE. A PULSE FORMAT FOR THE HIGH POWER UPLINKBEAM IS BEING DEVELOPED CONSISTING OF A BURST OF PULSES AT A PULSE RE-PETITION FREQUENCY GREATER THAN OR EQUAL TO 1 MHZ FORMING A MACROPULSE OF LENGTH 100-200 MICROSECONDS. DURING A SINGLE MACROPULSE, THEAERISIKS ARE EXPECTED TO BE VAPORIZED AND THE BEAM PATH CLEARED. SUB-SEQUENT PULSES WOULD BE EXPECTED TO EXPERIENCE SIGNIFICANTLY REDUCED THERMAL BLOOMING. THIS CONCEPT OF PULSE FORMATTING FOR AEROSOL VAPORIZATION FOR REDUCING THERMAL BLOOMING IS BEING MODELED. A LABORATORY SCALE EXPERIMENT IS BEING DESIGNED TO MEASURE THERMAL BLOOMING BY AEROSOLS. DEVELOPMENT OF PULSE FORMATTING TO REDUCE AEROSOL ABSORPTION, WHEN SUCCESSFUL, WOULD RESOLVE A DIFFICULT PROBLEMASSOCIATED WITH THE UPLINK PROPAGATION OF HIGH POWER GROUND BASED LASERS FOR BALLISTIC MISSILE DEFENSE APPLICATIONS.