ABSTRACT
High abundances of iodine monoxide (IO) are known to exist and to participate in local photochemistry of the marine boundary layer. Of particular interest are the roles IO plays in the formation of new particles in coastal marine environments and in depletion episodes of ozone and mercury in the Arctic polar spring. This paper describes a ground-based instrument that measures IO at mixing ratios less than one part in 10(12). The IO radical is measured by detecting laser-induced fluorescence at wavelengths longer that 500 nm. Tunable visible light is used to pump the A(2)Π3/2 (v(') = 2) â X(2)Π3/2 (v(â³) = 0) transition of IO near 445 nm. The laser light is produced by a solid-state, Nd:YAG-pumped Ti:Sapphire laser at 5 kHz repetition rate. The laser-induced fluorescence instrument performs reliably with very high signal-to-noise ratios (>10) achieved in short integration times (<1 min). The observations from a validation deployment to the Shoals Marine Lab on Appledore Island, ME are presented and are broadly consistent with in situ observations from European Coastal Sites. Mixing ratios ranged from the instrumental detection limit (<1 pptv) to 10 pptv. These data represent the first in situ point measurements of IO in North America.
Subject(s)
Fluorescence , Free Radicals/analysis , Iodine Compounds/analysis , Lasers , Oxides/analysisABSTRACT
The detection efficiencies of channel electron multipliers with opaque MgF(2) photocathodes have been measured at wavelengths between 44 A and 900 A. Efficiencies a factor of 2 greater than those of uncoated channel electron multipliers were obtained over the wavelength range from 50 A to 350 A. The absolute detection efficiencies were greater than 10% in the range from 67 A to 990 A for photocathodes illuminated at an angle of incidence of 45 degrees , with additional increases in sensitivity being obtained at short wavelengths using higher angles of incidence. Following an initial aging period, the photocathodes showed no degradation of response during storage under vacuum or in air.
ABSTRACT
The procedures available for photometric calibration at extreme ultraviolet (EUV) wavelengths are outlined and the requirements for a secondary standard EUV photomultiplier defined. The performance of a number of commercially available channel electron multipliers over the 304-1350-A wavelength range is described and their suitability for use as secondary standards discussed in detail. Although none of the multipliers evaluated fully met the requirements for a secondary standard it proved possible to calibrate absolutely a Mullard cone channel over the required wavelength range to an accuracy of +/-9% and to employ it as a secondary standard in the calibration of a series of sounding rocket spectrometers.
ABSTRACT
The photoelectric yields of 2000-A thick samples of MgF(2) and LiF have been measured at wavelengths in the range 1216-461 A. Peak values of 43% and 34%, respectively, were obtained at wavelengths around 550 A at 45 degrees incidence. Coating the cathode of a channel electron multiplier with 3000 A of MgF(2) produced no significant deterioration in the electrical properties and increased the sensitivity by factors of 1.62, 2.76, and 2.60 at wavelengths of 742 A, 584 A, and 461 A, respectively. Since the stability of response of the MgF(2) photocathodes appears to be equal to that of conventional metallic and semiconducting cathodes, it is concluded that MgF(2) would be a practical, high-efficiency photocathode for use in the extreme uv.
ABSTRACT
The design and performance characteristics of a prototype cloud physics laser nephelometer are described. The instrument measures radiation scattered from individual cloud droplets, determining droplet concentrations from scattered light-pulse count rates and size distributions from pulse amplitudes.
