Stellar scintillation in the near-IR

dThe Starfire Optical Range (SOR) has measured stellar scintillation at 0.9 to 1.7 microns over a wide range of elevation angles. The telescope pupil was imaged onto a mask with four circular apertures of scaled diameters 0.1, 0.2, 0.75 and 1.5 m. These smaller pupils were then re-imaged onto InGaAs photodiodes operating at 10 kHz. The entire 3.5 m pupil was also imaged onto a fifth photodiode. Since all five signals were recorded simultaneously, the influence of aperture diameter on scintillation statistics can be readily seen. The detectors were located at pupil planes; no fluctuations due to atmospheric tilt were measured. Comparisons of power spectral densities, signal variances and other fluctuation statistics have been made as functions of the aperture diameter and elevation angle. Experimental results and theoretical expectations reveal widespread agreement. Within experimental error, log-normal statistics are followed. High spatial frequency content increased with elevation angle. Aperture averaging of scintillation variance followed a 7/6(th) dependence. Increasing the aperture dimensions had an even larger effect on the number of fluctuations below a given threshold. Scintillation in the near-IR has been shown to produce consistent results with previous studies performed at visible wavelengths.