Analytical description of a Fabry-Perot spectrometer 6: minimum number of samples required in the determination of Doppler widths and shifts

The minimum number of samples required to obtain the least uncertainties of determination for measurements of temperature and winds with a Fabry-Perot photoelectric spectrometer are derived. The specific cases for a spectrometer optimized for Doppler width (temperature) and Doppler shift (winds) determinations are treated where the minimum (critical) number of equidistant samples per free spectral range is found to be equal to 14 and 8, respectively. An approximate empirical criterion to derive the number of samples in terms of effective finesse N(e) has been obtained and is equal to approximately 4N(e) for practical spectrometer and source widths.

Analytical description of a Fabry-Perot spectrometer. 7: TESS, a high-luminosity high-resolution twin-etalon scanning spectrometer

The analytical description of the twin-etalon scanning spectrometer (TESS), i.e., an enhanced Fabry-Perot spectrometer, is presented in detail. Practical gains of >100 are attainable with this device, and it is also shown that this instrument is competitive with the spherical Fabry-Perot but with the ability to change the resolution at will. The spectral properties of the TESS are investigated for the determination of Doppler widths and shifts to emphasize the similarities and slight differences between this instrument and the single-etalon single-aperture Fabry-Perot. Practical considerations and tolerances required for operation of the TESS are discussed.

Analytical description of a Fabry-Perot spectrometer. 5: Optimization for minimum uncertainties in the determination of Doppler widths and shifts

Based on the statistical criterion of least uncertainty, it has been found that there exists an optimum combination of source and instrumental parameters, which lead to the most efficient use of a Fabry-Perot spectrometer in the measurement and determination of either line profile position or temperature. Results are given in order to optimize the design of a spectrometer and/or quantitatively deduce the uncertainties of determination from measurements. Comparisons between the present results, the luminosity-resolution product method, and the usual method to determine line positions show the present quantitative method to give the most efficient spectrometer and the best estimates of uncertainty. A useful result of this investigation shows that a low reflective finesse etalon provides the optimum spectrometer. The implicit relaxation of the surface quality of the flats and precision of etalon adjustment deduced from this result lead not only to simplified operation but to lower instrumental costs as well.

Thermospheric dynamics investigations with very high resolution spectrometers

Since 1972 high resolution Fabry-Perot spectrometers have been used at Fritz Peak Observatory (39.9 degrees N, 105.5 degrees W), Colorado to measure the nighttime variation of thermospheric temperatures and winds from the line profiles and Doppler shifts of the OI 15,867 K (630.0-nm) line emission in the nightglow. With the aid of these measurements we have defined the nighttime variation of winds and temperatures at F-layer heights for the various seasons of the year during geomagnetic quiet periods. During geomagnetic storm periods deviation in the nighttime variation of the winds and temperatures from those determined during geomagnetic quiet conditions have been shown to occur. In addition, measurements made during geomagnetic disturbed conditions have shown the existence of large-scale thermospheric waves generated at high latitudes by impulsive auroral heating events that are observed to propagate equatorward. The nighttime winds and temperatures measured from Fritz Peak Observatory have been used in various heoretical models of global thermospheric dynamics to infer the global circulation patterns, temperature structure, and thermospheric response to geomagnetic activity. By requiring agreement between the calculated and measured winds and temperatures over Fritz Peak Observatory, the over-all magnitude of the thermospheric high latitude heat source due to auroral processes has been inferred for both geomagnetic quiet and disturbed conditions. This energy source has been shown to be related to dissipation of the ring current energy in the high latitude ionosphere. The results of various geophysical studies using Fritz Peak Observatory data and theoretical model calculation are summarized.

Atmospheric spectroscopy: an introduction

The summer 1978 Optical Society of America Topical Meeting on Atmospheric Spectroscopy is briefly reviewed in this introduction to a set of representative papers presented at the Topical Meeting held at keystone, Colorado.

Piezoelectric scanning of Fabry-Perot spectrometers: nonlinearities

Piezoelectric materials used in mechanical scanning of Fabry-Perot spectrometers are found to have measurable nonlinearities. Dynamic scanning has been used in the present investigation in order to decrease the effects of some of the variables, such as creep, of the piezoelectric material in static operation. The results show mainly a decrease in the distance between corresponding maxima, or apparent free spectral range, as the driving voltage increases to higher values. A relationship between this voltage and displacement (in terms of orders) has been derived, and it is given by v(i) = In {1 - (x(i) - x(0))/[a/(1 - b) - x(0)]}/In b, where v(i) is the displacement in orders from an arbitrary starting point, x(i) is a quantity directly proportional to the voltage, while x(0) is also a quantity proportional to the voltage at the arbitrary reference point, a is the distance between the arbitrary reference point and the next order, and b is the nonlinearity constant for a given piezoelectric material. Examples are given for emission and absorption measurements where the usually large effects of the piezoelectric material nonlinearities are derived, as well as schemes to minimize or altogether remove the effects by suitable handling of the data or by changing the experiment such that the scanning is forced to be linear.

Analytical description of a Fabry-Perot spectrometer. 4: Signal noise limitations in data retrieval; winds, temperature, and emission rate

A quantitative investigation of the effects of noise inherent in the signal received by the detector of a Fabry-Perot spectrometer has been carried out in detail. The study also includes the effects of the instrumental profile width and the presence of unwanted continuum radiation in the signal, such as background radiation and detector dark current. The results show the spectrum of the noise in the transform plane to have a quantitative description in terms of the instrumental and line shapes as well as the signal strength, or emission rate, of both the line profile and the unwanted radiation. The magnitude and shape of this noise spectrum not only limits in a known quantitative manner the amount of useful information available from a given measured profile, but it also provides information on the profile itself, thus allowing for more information to be obtained from the measurement than would otherwise be possible. A detailed example is given for the retrieval of winds, temperature, and emission rate from line profile measurements, and it is quantitatively shown how the (noise) limited information available from a measured profile appears as uncertainties of determination. These uncertainties are shown to be dependent on the signal strength, more correctly the noise inherent in this signal, as well as the shapes and relative widths of the line and instrumental profiles, with the temperature uncertainty showing the most sensitivity to these factors. Although in some cases the results are qualitatively obvious, their quantitative nature allows the design of experiments for least uncertainty and/or define the limitations inherent in such experiments.

Endemoepidemic non-parenteral type B hepatitis in Costa Rica

In an endemic area of Costa Rica nonparenteral type B hepatitis occurs at a yearly rate of 160/100,000, in an endemoepidemic pattern with periodic localized outbreaks. In a recent episode in the village of San Rafael, 23 clinical and 67 subclinical cases, all subtype adw, originated from two carriers living in opposite ends of the village. Contact transmission was identified as the mode of spread. In a coincidental outbreak in another village, San Juan, 17 clinical and 40 subclinical cases were observed. Thirty-seven cases of HBs Ag/ayw positive hepatitis occurred in the Western sector of the village, apparently originating from contact with three HBs Ag/ayw carriers found in that area. There were also 20 cases of HBs Ag/adw positive hepatitis, but these occurred almost exclusively in the Eastern sector, where subtype adw disease has been prevalent in previous years. The geographic distribution of antibody subtypes found in the two separated sectors of the village coincided fully with that of the antigen subtypes. These observations show that personal contact is definitely a mode of transmission of hepatitis B.

The preparation and properties of factor V from bovine plasma

1. A procedure for the purification of factor V from bovine plasma with a good yield and in a high state of purity is described. The isolation procedure involves BaSO4, adsorption, chromatography of the absorbed plasma on DEAE-Sephadex A-50, activation with thrombin of the A-50 eluate, chromatography on Amberlite CG-50 and precipitation with (NH4)2SO4. Factor V is obtained with a 160% yield and 5000-fold purification. 2. Some of the physico-chemical properties of Ac-globulin have been measured. The molecular weight was determined by electrophoresis is SDS-polyacrylamide gel and found to be 30 000. The studies employing disc electrophoresis and immunoelectrophoresis suggest the existence of several active isoforms of factor V.

Analytical description of a fabry-perot spectrometer. 3: off-axis behavior and interference filters

A general expression is derived for a Fabry-Perot spectrometer when one or more of the functions entering into its description lack the inherent radial symmetry of the fringe pattern about the etalon optical axis. Calculations of the effects of these asymmetric functions applicable to densitometry of photographic fringe records and vidicon scanning of fringe patterns are given. The theory is also applied to interference filters in order to quantitatively explain their behavior as they are tilted in order to scan a spectrum. Rather simple approximations to the theory are also derived for interference filters that show that both the inverse of the peak transmission and the square of the width (normalized to the unbroadened filter) are proportional to the square of the product of the tilt and field of view angles over the width, in excellent agreement with experimental measurements.

Chorioallantoic membrane measles: development and clinical evaluation of a new further attenuated measles vaccine

A new, further attenuated measles vaccine, developed by propagation of Edmonston B measles virus in the chorioallantoic membrane in ovo, has been clinically evaluated in children and found to compare favorably with a commercially available product. The vaccine is prepared in chick embryo tissue culture and appears to possess noteworthy stability at 4 C.

Feedback stabilized fabry-perot interferometer

A method of stabilizing a Fabry-Perot interferometer with respect to a reference wavelength, while simultaneously stabilizing the parallelism of the flats, is described. The method consists of creating correcting signals proportional to the displacement of the fringe maxima of three auxiliary spectral sources with respect to a fixed reference point and feeding these signals back to the interferometer piezoelectric drive so that the correcting signals become time invariant, and the interferometer is stabilized. The stability of the finished instrument with respect to the reference wavelength and parallelism is near lambda/1000, at 546 nm, for a 6-h period; however, the actual parallelism of the etalon is limited by the surface defects of the flats. The method, as described, allows simultaneous stabilization and data taking, since the instrument is continuously updating itself.

Analytical description of a fabry-perot photoelectric spectrometer. 2: numerical results

Quantitative tabulations of the properties of a Fabry-Perot spectrometer are presented using the analytical expression previously derived. These tabulations are given in terms of measurable instrumental parameters in a nondimensional scheme, hence of wide application.

Analytical description of a Fabry-Perot photoelectric spectrometer

An analytical expression for the response of a complete Fabry-Perot photoelectric spectrometer to a line profile is derived. The case of a doppler-broadened Lorentzian profile examined by a spectrometer comprised of an etalon of variable thickness and reflectivity, with surface defects consisting of spherical curvature, as well as microscopic flatness imperfections, a finite exploring slit in front of the photodetector, and bandwidth limiting circuits is considered. Some of the properties and uses of the expression obtained are discussed.