Lee C. Bradley

Phase Compensation for Thermal Blooming

Appropriate correction of the initial phase of a laser beam is shown by numerical computation to be capable of appreciably reducing thermal blooming for a cw beam.

Atmospheric-turbulence measurements using a synthetic beacon in the mesospheric sodium layer

We have performed what are, to our knowledge, the first measurements of wave fronts propagated through atmospheric turbulence with the use of a synthetic beacon in the mesospheric sodium layer. The synthetic-beacon wave fronts showed reasonable agreement with those from reference stars. The sodium-layer beacon performance was also compared with that of beacons produced by Rayleigh backscatter in the 6-20-km altitude range.

Hyperfine Structure and Isotope Shift in the 7 2 S 1/2 –6 2 P 1/2 Transition of Natural Thallium by Atomic Beam Absorption*

The isotope shift in the 72S12−62P12 transition (3776 A) and the hyperfine-structure separations of Tl203 and Tl205 in the 72S12 state have been determined spectroscopically by atomic beam absorption with the use of a Fabry–Perot interferometer crossed with a 10-in. diffraction grating. Our results are: 0.0554 ± 0.0012 cm−1 for the isotope shift in the 3776 A line; −0.0405 ± 0.0013 cm−1 in the 62P12 level; and Δν(72S12)=0.4078±0.0014cm−1 and 0.4109 ± 0.0012 cm−1 for the hyperfine-structure separation in Tl203 and Tl205, respectively.

Dispersion in the Vicinity of an Optical Resonance

The optical dispersion in the vicinity of the 3P1–1S0 transition in mercury has been examined in high resolution by a novel method employing a variable frequency light source and a Mach-Zehnder interferometer. The enhancement of instrument sensitivity through lock-in synchronous detection, particularly for small negative dispersion measurements, was demonstrated. In some cases fringe shifts as small as one ten-thousandth of a fringe could be observed. The large Faraday rotation expected near resonance was also observed and the feasibility of using it as a narrow band modulatable filter demonstrated. A derivation of the refractive index in the vicinity of the resonance using the Kramers-Kronig relations is given, and the theory is shown to be consistent with experiment. The generalization of these techniques to laser work is briefly discussed.

Measurement of Absorption-Line Profiles with a Fabry–Perot Interferometer*

We have calculated the line profiles to be expected when a Fabry–Perot interferometer is used to measure absorption lines. We have shown that large errors may be introduced in the measurement of the integrated absorption, even when an interferometer of high finesse is used. Curves and tables are given for finding the true absorption width and the true peak absorption from the apparent values observed under different operating conditions of the emission light source and the interferometer. We show qualitatively that the distortions are partially due to the presence of nonzero wings in the instrument-bandpass function. Finally, we show a Fourier series expansion of the integral giving the transmittance of the Fabry-Perot interferometer when absorbing atoms are in the light path.

The absence of circular dichroism in16O2 and a resultant upper limit for parity nonconservation

SummaryBy a study to determine the preferential absorption of one component of circularly polarized light in a molecular magnetic dipole transition in16O2 we have determined an upper limit to the parity impurity of the states involved in the transition. We find the amplitude of the PNC part of the states are less than or equal to 3·10−8 from a measurement of the circular polarization that is less than or equal to 6·10−4.RiassuntoCon uno studio per determinare l’assorbimento preferenziale di una componente della luce polarizzata circolarmente in una transizione molecolare di dipolo magnetico nel16O2, abbiamo stabilito un limite superiore alla impurezza della parità degli stati coinvolti nella transizione. Troviamo che le ampiezze della parte PNC degli stati sono minori od uguali a 3·10−8 in base a misure della polarizzazione circolare che è minore od uguale a 6·10−4.