2.09-micron laser propagation at 1-km range through diverse atmospheric conditions

The effects of dynamic weather on the transmission of a pulsed 2.09-μm laser beam across a 1-km coastal channel are presented. Tests were conducted at the University of Central Florida's Townes Institute Science &#38; Technology Experimentation Facility (TISTEF). By collecting data before, during, and after the morning quiescent period, diverse atmospheric conditions are explored, including periods of clear and cloudy skies and calm and turbulent optical paths. Spatial variations of the laser beam in response to temperature fluctuations and atmospheric turbulence were captured by an infrared camera positioned at the target site. Recorded data were analyzed to assess changes in beam diameter and beam wander relative to range conditions. A suite of weather sensors provided air temperature, wind speed, and solar irradiance. A line-of-sight scintillometer quantified optical turbulence by providing estimates of the refractive-index structure parameter (C<i>_n²</i>), ranging from 2×10^–15 m^–2/3 to 4×10^–13 m^–2/3. Data obtained from range sensors provided inputs for new split-step wave-optics simulations. This work presents the first known comparison of 2-μm laser propagation with the simulation software “High Energy Laser - Performance Estimation Test Technology (HEL-PETT)” developed by Coherent Aerospace &#38; Defense. Experimental results agree well with simulations. Data also revealed the quantitative effects of small, dense cloud cover on range conditions: one-minute cloud cover had no effect on range temperature, optical turbulence, or laser beam properties, whereas four-minute cloud cover generated distinct changes in these properties.