We describe an image scanning method which samples the Fourier Transform of the image at points l... more We describe an image scanning method which samples the Fourier Transform of the image at points lying on a circle in Fourier space. It works by transmitting the image through a rotating grating. Reconstructions of point and continuous images are illustrated. A system using two rotating gratings is proposed to improve the performance for continuous images.
Experimental measurements of infra-red transmittance are reported, which show that the computer c... more Experimental measurements of infra-red transmittance are reported, which show that the computer code LOWTRAN-4 predicts too high a transmittance in the region 4.3-5.5 micron, and that the discrepancy is dependent on the water vapor content. We have carried out experiments at various ranges up to 45 km in order to vary the precipitable water amount over a wide range, and from the results we have deduced that the anomalous transmittance results from an incorrect estimate of the continuous absorption, while the spectral component is substantially correct.
We first present some results of experiments performed on the morphology of dendritic crystals gr... more We first present some results of experiments performed on the morphology of dendritic crystals growing from a supersaturated solution during free fall. Then we show an quantitative investigation of the diffusion field around growing dendritic tips as observed in an interference microscope. The results give a picture of some aspects of the kinetic growth effects at the crystal-fluid interface.
A method of calculating the self-radiance of the sky based on the LOWTRAN-4 computer code is desc... more A method of calculating the self-radiance of the sky based on the LOWTRAN-4 computer code is described. The method is a significant improvement on that included as an option in LOWTRAN-4 itself as a result of two modifications: a) Our method, unlike the one included in LOWTRAN-4, takes into account the radiance scattered into the line of sight. b) The model of the atmosphere in the computer code must be divided into a certain number of layers, each one having approximately uniform conditions. Our method uses a correct optimal division. Consequently, our method gives a better agreement with the experimental data, especially for long optical paths in the lower layers of the atmosphere.
A method of calculating 2×2 reflection and transmission-coefficient matrices for a multilayer bir... more A method of calculating 2×2 reflection and transmission-coefficient matrices for a multilayer birefringent system, developed for use in a plane stratified magnetoplasma, is applied to an optical system. The diagonal matrix elements refer to the direct reflection and transmission coefficients of the two characteristic or normal modes, and off-diagonal elements refer to inter-mode coupling between them. For waves normally incident on the plane stratified system, in the positive or negative z directions, corresponding reflection and transmission-coefficient matrices, R± and T±, are defined in terms of suitably normalized wave fields. A reciprocity theorem is established wherein it is shown that the matrices R+ and R− are symmetric, and the matrix T+ is the transpose of T−, provided that the dielectric tensors of the layers composing the system are either (a) all symmetric, or (b) all gyrotropic (magnetoactive), having a common principal axis that is generally the external magnetic-field direction. Optically inactive, isotropic layers may be included in either class, but care must be taken in defining characteristic modes for such layers. Some applications are discussed, including the feasibility of constructing light valves.
The shape of a crystal growing from a supercooled pure melt is influenced by the temperature-depe... more The shape of a crystal growing from a supercooled pure melt is influenced by the temperature-dependent kinetics of the nucleation on the interface. In the course of this growth, heat is released from the interface, thus feeding back on the temperature field. In this intrinsically nonlinear process, the three-dimensional temperature field in the fluid is a vital dynamic parameter which has not been previously measured. This can be done with the aid of multi-directional interferometry, using the temperature dependence of the refractive index of the melt. If the growth regime lies in the path of one of the interferometer beams, a phase shift, proportional to the integrated refractive index change, is observed. To measure the three-dimensional field of the refractive index requires some form of tomographic reconstruction. We built an apparatus that includes a crystal growing cell which is viewed by four Mach-Zehnder interferometers. The interferograms are analyzed by Fourier fringe anal...
Pentane drops on a water surface are predicted to have contact angles of the order of 1 degree or... more Pentane drops on a water surface are predicted to have contact angles of the order of 1 degree or less in the phase of frustrated complete wetting. We have developed an optical method of measuring such small contact angles, applicable to cases where the refractive indices of the substrate and adsorbate are very similar and the fluid dynamics do not allow delay between image acquisitions, by using phase retrieval to map the surface profile of the drops. It is empirically shown that, with our method, a difference of nanometer order can be achieved for the phase-retrieved dimensions relative to their expected value. Results agree with numerical predictions by Weiss and Widom [Physica A292, 137 (2001)PHYADX0378-437110.1016/S0378-4371(00)00619-1].
With an optical technique it is found that the equilibrium interface between superfluid and hcp 4... more With an optical technique it is found that the equilibrium interface between superfluid and hcp 4He is partially faceted, showing that at least some of it is atomically smooth. This conclusion is also consistent with the behavior of the crystal during melting and growth. The surface tension alphaLS on the rounded part of the interface is found to be independent
Experimental measurements of infrared transmittance are reported, which show that the computer co... more Experimental measurements of infrared transmittance are reported, which show that the computer code LOWTRAN-4 predicts too high a transmittance in the region 4.3 to 5.5 microns, and that the discrepancy is dependent on the water-vapor content. We have carried out experiments at various ranges up to 45 km in order to vary the precipitable water amount over a wide range, and, from the results, we have deduced that the anomalous transmittance results from an incorrect estimate of the continuum absorption, while the spectral component is substantially correct.
During the last two decades, optical stellar interferometry has become an important tool in astro... more During the last two decades, optical stellar interferometry has become an important tool in astronomical investigations requiring spatial resolution well beyond that of traditional telescopes. This book, first published in 2006, was the first to be written on the subject. The authors provide an extended introduction discussing basic physical and atmospheric optics, which establishes the framework necessary to present the ideas and practice of interferometry as applied to the astronomical scene. They follow with an overview of historical, operational and planned interferometric observatories, and a selection of important astrophysical discoveries made with them. Finally, they present some as-yet untested ideas for instruments both on the ground and in space which may allow us to image details of planetary systems beyond our own.
Publisher Summary This chapter reviews various experiments that have been performed on the helium... more Publisher Summary This chapter reviews various experiments that have been performed on the helium surface and indicates their significance in terms of simple theoretical models. The helium surface is unique in being the only solid–liquid interface that exists over a wide continuous range of temperatures, so that the physical mechanisms of crystal growth and equilibrium can be investigated as a function of temperature. In any other material the temperature range over which this is possible is limited by the triple point on one side and the steepness of the melting curve on the other. Other significant factors contributing to the importance of the 4He surface are in particular the high inherent purity of the system and the fact that, at temperatures below 1.8 K, the fluid phase is superfluid. The mechanisms involved in atomic movements in solid helium have been reviewed. The dominant process of atomic motion appears to be quantum tunneling into vacancies. This process is temperature independent and so the time constants for structural changes in helium do not become asymptotically infinite as the temperature falls.
Page 1. JOSA COMMUNICATIONS Communications are short papers. Appropriate material for this sectio... more Page 1. JOSA COMMUNICATIONS Communications are short papers. Appropriate material for this section includes reports of incidental research results, comments on papers previously published, and short descriptions of theoretical and experimental techniques. ...
A mechanical manostat is described which enables the forced evaporation rate from a helium cryost... more A mechanical manostat is described which enables the forced evaporation rate from a helium cryostat to be controlled by the pressure measured immediately over the helium rather than at some remote point outside the cryostat. A temperature stability somewhat better than that of conventional designs has been achieved, particularly when the gas flow rate is not too small.
We describe an image scanning method which samples the Fourier Transform of the image at points l... more We describe an image scanning method which samples the Fourier Transform of the image at points lying on a circle in Fourier space. It works by transmitting the image through a rotating grating. Reconstructions of point and continuous images are illustrated. A system using two rotating gratings is proposed to improve the performance for continuous images.
Experimental measurements of infra-red transmittance are reported, which show that the computer c... more Experimental measurements of infra-red transmittance are reported, which show that the computer code LOWTRAN-4 predicts too high a transmittance in the region 4.3-5.5 micron, and that the discrepancy is dependent on the water vapor content. We have carried out experiments at various ranges up to 45 km in order to vary the precipitable water amount over a wide range, and from the results we have deduced that the anomalous transmittance results from an incorrect estimate of the continuous absorption, while the spectral component is substantially correct.
We first present some results of experiments performed on the morphology of dendritic crystals gr... more We first present some results of experiments performed on the morphology of dendritic crystals growing from a supersaturated solution during free fall. Then we show an quantitative investigation of the diffusion field around growing dendritic tips as observed in an interference microscope. The results give a picture of some aspects of the kinetic growth effects at the crystal-fluid interface.
A method of calculating the self-radiance of the sky based on the LOWTRAN-4 computer code is desc... more A method of calculating the self-radiance of the sky based on the LOWTRAN-4 computer code is described. The method is a significant improvement on that included as an option in LOWTRAN-4 itself as a result of two modifications: a) Our method, unlike the one included in LOWTRAN-4, takes into account the radiance scattered into the line of sight. b) The model of the atmosphere in the computer code must be divided into a certain number of layers, each one having approximately uniform conditions. Our method uses a correct optimal division. Consequently, our method gives a better agreement with the experimental data, especially for long optical paths in the lower layers of the atmosphere.
A method of calculating 2×2 reflection and transmission-coefficient matrices for a multilayer bir... more A method of calculating 2×2 reflection and transmission-coefficient matrices for a multilayer birefringent system, developed for use in a plane stratified magnetoplasma, is applied to an optical system. The diagonal matrix elements refer to the direct reflection and transmission coefficients of the two characteristic or normal modes, and off-diagonal elements refer to inter-mode coupling between them. For waves normally incident on the plane stratified system, in the positive or negative z directions, corresponding reflection and transmission-coefficient matrices, R± and T±, are defined in terms of suitably normalized wave fields. A reciprocity theorem is established wherein it is shown that the matrices R+ and R− are symmetric, and the matrix T+ is the transpose of T−, provided that the dielectric tensors of the layers composing the system are either (a) all symmetric, or (b) all gyrotropic (magnetoactive), having a common principal axis that is generally the external magnetic-field direction. Optically inactive, isotropic layers may be included in either class, but care must be taken in defining characteristic modes for such layers. Some applications are discussed, including the feasibility of constructing light valves.
The shape of a crystal growing from a supercooled pure melt is influenced by the temperature-depe... more The shape of a crystal growing from a supercooled pure melt is influenced by the temperature-dependent kinetics of the nucleation on the interface. In the course of this growth, heat is released from the interface, thus feeding back on the temperature field. In this intrinsically nonlinear process, the three-dimensional temperature field in the fluid is a vital dynamic parameter which has not been previously measured. This can be done with the aid of multi-directional interferometry, using the temperature dependence of the refractive index of the melt. If the growth regime lies in the path of one of the interferometer beams, a phase shift, proportional to the integrated refractive index change, is observed. To measure the three-dimensional field of the refractive index requires some form of tomographic reconstruction. We built an apparatus that includes a crystal growing cell which is viewed by four Mach-Zehnder interferometers. The interferograms are analyzed by Fourier fringe anal...
Pentane drops on a water surface are predicted to have contact angles of the order of 1 degree or... more Pentane drops on a water surface are predicted to have contact angles of the order of 1 degree or less in the phase of frustrated complete wetting. We have developed an optical method of measuring such small contact angles, applicable to cases where the refractive indices of the substrate and adsorbate are very similar and the fluid dynamics do not allow delay between image acquisitions, by using phase retrieval to map the surface profile of the drops. It is empirically shown that, with our method, a difference of nanometer order can be achieved for the phase-retrieved dimensions relative to their expected value. Results agree with numerical predictions by Weiss and Widom [Physica A292, 137 (2001)PHYADX0378-437110.1016/S0378-4371(00)00619-1].
With an optical technique it is found that the equilibrium interface between superfluid and hcp 4... more With an optical technique it is found that the equilibrium interface between superfluid and hcp 4He is partially faceted, showing that at least some of it is atomically smooth. This conclusion is also consistent with the behavior of the crystal during melting and growth. The surface tension alphaLS on the rounded part of the interface is found to be independent
Experimental measurements of infrared transmittance are reported, which show that the computer co... more Experimental measurements of infrared transmittance are reported, which show that the computer code LOWTRAN-4 predicts too high a transmittance in the region 4.3 to 5.5 microns, and that the discrepancy is dependent on the water-vapor content. We have carried out experiments at various ranges up to 45 km in order to vary the precipitable water amount over a wide range, and, from the results, we have deduced that the anomalous transmittance results from an incorrect estimate of the continuum absorption, while the spectral component is substantially correct.
During the last two decades, optical stellar interferometry has become an important tool in astro... more During the last two decades, optical stellar interferometry has become an important tool in astronomical investigations requiring spatial resolution well beyond that of traditional telescopes. This book, first published in 2006, was the first to be written on the subject. The authors provide an extended introduction discussing basic physical and atmospheric optics, which establishes the framework necessary to present the ideas and practice of interferometry as applied to the astronomical scene. They follow with an overview of historical, operational and planned interferometric observatories, and a selection of important astrophysical discoveries made with them. Finally, they present some as-yet untested ideas for instruments both on the ground and in space which may allow us to image details of planetary systems beyond our own.
Publisher Summary This chapter reviews various experiments that have been performed on the helium... more Publisher Summary This chapter reviews various experiments that have been performed on the helium surface and indicates their significance in terms of simple theoretical models. The helium surface is unique in being the only solid–liquid interface that exists over a wide continuous range of temperatures, so that the physical mechanisms of crystal growth and equilibrium can be investigated as a function of temperature. In any other material the temperature range over which this is possible is limited by the triple point on one side and the steepness of the melting curve on the other. Other significant factors contributing to the importance of the 4He surface are in particular the high inherent purity of the system and the fact that, at temperatures below 1.8 K, the fluid phase is superfluid. The mechanisms involved in atomic movements in solid helium have been reviewed. The dominant process of atomic motion appears to be quantum tunneling into vacancies. This process is temperature independent and so the time constants for structural changes in helium do not become asymptotically infinite as the temperature falls.
Page 1. JOSA COMMUNICATIONS Communications are short papers. Appropriate material for this sectio... more Page 1. JOSA COMMUNICATIONS Communications are short papers. Appropriate material for this section includes reports of incidental research results, comments on papers previously published, and short descriptions of theoretical and experimental techniques. ...
A mechanical manostat is described which enables the forced evaporation rate from a helium cryost... more A mechanical manostat is described which enables the forced evaporation rate from a helium cryostat to be controlled by the pressure measured immediately over the helium rather than at some remote point outside the cryostat. A temperature stability somewhat better than that of conventional designs has been achieved, particularly when the gas flow rate is not too small.
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