(latest first)
 
Electrooptic Fabry-Perot Filter: Development for the Study of Solar Oscillations, C.H.Burton, A.J.Leistner and D.M.Rust, Applied Optics, 26, 2637-2642 (1987)
Observations of nonradial solar oscillations require Doppler velocity measurement at many points over the photosphere with a velocity resolution better than 1 m/s. An attractive form of imaging spectrophotometer for such a task utilizes a thin, solid, electrically tunable Fabry-Perot interference filter or etalon made of an electrooptic material such as lithium niobate (LiNbO/sub 3/). The problems to be overcome in producing such an etalon for an imaging spectrophotometer are discussed and practical solutions demonstrated on the basis of measurements made on prototype devices.
(Author's note : the fabrication of this freestanding single crystal lithium niobate etalon (less than 250 microns thick, 50 mm in diameter and uniformly thick to better than lambda/100) represents a tour de force of optical fabrication measurement science and art).
 
A Tunable, Solid, Fabry-Perot Etalon for Solar Seismology,
D.M.Rust, C.H.Burton and A.J.Leistner, Soc. Photo-Opt. Inst. Eng. Conf Proc. 627 (1986)
A solid etalon has designed and fabricated from a 50-mm diameter wafer of optical-quality lithium niobate. The finished etalon has a free spectral range of 0. 325 nm at 588 nm. The parallel faces are coated with silver, and the central 15-mm aperture of the etalon has a finesse of 18.6.
The reflective faces double as electrodes, and application of voltage will shift the passband. This feature was used in a servo circuit to stabilize the passband against temperature and tilt-induced drifts to better than three parts in 10SUP9.
The etalon will be incorporated into a servo-controlled, tunable filter at the APL Solar Observatory. Because of its large aperture and high acceptance angle, it does not require that the host telescope or the filter be scanned mechanically in the course of normal solar measurements. (Edited author abstract) 11 refs.
 
Fast Ion Conduction in the Presence of a Lattice Phase Transition,
D.Bingham and C.H.Burton, Phys. Stat. Sol.(b), 130, 483-487 (1985)
A mixed pseudo-spin /sup 1///sub 2/ model of ionic conduction in the presence of a displacive phase transition of the lattice is derived from a consideration of the microscopic forces acting on the migrating ions. A phonon-mediated interaction between the ions entering into the lattice transition and the mobile ions results in a number of phase transitions in the mobile ion order parameter (S/sup z/). These are correlated with the ionic conductivity. A search is suggested for a material displaying the required properties and some possible advantages of such a material are discussed.
 
An Improved Polarizing Michelson Interferometer for the Far Infrared
C.H.Burton, D.Bingham, L.B.Whitbourn and J.A.How, Infrared Physics, 25, 575-577 (1985)
An improved design for a simple polarizing Michelson interferometer which can result in a doubling in the detected signal, is presented. The improved design has been used to measure the transmittance of fused quartz over the frequency range 300-1000 GHz
 
Analysis of Multi-Component Gas Mixtures by Correlation of Infrared Spectra
D.Bingham and C.H.Burton, Applied Spectroscopy, 38, 705-709 (1984)
A simulation study and an experimental investigation of the effect of noise and resolution in the determination of polar gas pressures in gas mixtures has been performed. The pressures were obtained by a procedure which correlates the polar gas infrared spectra and describes band absorptance phenomenologically. For single-polar-component binary mixtures, the partial pressure may be found accurately over a wide range of resolution. Low resolving powers are favored with noisy spectra. Polar gas partial pressures were also extracted from quaternary mixtures, with an uncertainty of less than 5% over a wide range of resolving power. Improvements to and limitations of the technique are discussed. 8 refs.
 
Spin Orientation and Exchange Interactions in (Fe,Co)C12
M.C.K.Wiltshire, B.D. Howes and C.H.Burton, J. Mag. and Mag. Matls., 34 PtIII, 1465- (1983)
The far infrared spectrum of FeCl/sub 2/:Co shows a localised mode from whose position a set of Fe-Co exchange parameters has been determined Mossbauer spectra of the mixtures Fe/sub 1-x/Co/sub x/Cl/sub 2/ have been measured and their analysis yields a variation of iron-spin orientation consistent with calculations using these parameters
 
The Effective Size of Mercury Lamps in the Far Infrared
D.Bingham and C.H.Burton, Infrared Physics, 23, 293-294 (1983)
The authors have measured the relative distributions of radiance of two mercury discharge lamps across their length and width as a function of the maximum frequency detected. In the far-infrared region there are contributions to the radiant flux from the lamp envelope and the discharge. The full width at half-maximum (FWHM) of the discharge contribution is 4.0 mm, whilst the envelope contribution FWHM is 10.5 mm.
 
Far Infrared Absorption and Localized Magnetic Modes In Fec12:Co And Coc12:Fe
M.C.K.Wiltshire and C.H.Burton, J. Phys. C.: Solid St. Phys, 15, 5649-5655 (1982)
The far-infrared absorption spectra of FeCl/sub 2/:Co and of CoCl/sub 2/:Fe have been measured. The FeCl/sub 2/:Co spectra show a localised magnetic impurity mode below the host antiferromagnetic resonance (AFMR), whilst CoCl/sub 2/:Fe has just a broadened AFMR. Using the equation-of-motion simulation technique with a single set of Fe-Co exchange parameters derived previously, the qualitative features of the spectra are reproduced. By adjusting the next-nearest-neighbour anisotropic exchange, which is otherwise undetermined, good agreement has been obtained between the calculated and measured spectra.
 
Far Infrared Photothermal Ionization Spectroscopy of Impurities in Germanium
C.H.Burton, Jnl. Electrical and Electronics Engineering Aust. 1,14-16 (1981)
Far infrared (FIR) photothermal ionisation spectroscopy (PTIS) is a powerful technique for detecting and identifying electronic impurities in semiconductors at concentration levels orders of magnitude smaller than those obtained ( approximately=10/sup 10/ cm/sup -3/) by state-of-the-art methods of semiconductor purification and crystal growth.
The basis of the PTIS technique is explained and some results for impurities in germanium are presented
 
Search for Intervalence Tunnelling in Mixed-Valence Compound U-(Pyrazine)-Bis(Pentaamineruthenium) Pentabromide
Elmars Krausz, Clive Burton and John Broomhead, Inorg. Chem. 20, 434-435 (1981)
 
A Polarising Michelson Interferometer for the Far Infrared And Millimetre Regions
C.H.Burton and Y.Akimoto, Infrared Physics 20,115-120 (1980)
A polarizing Michelson interferometer for the far-infrared and millimeter regions is described. It uses a simple mechanical drive to attain high-resolution spectra with excellent frequency accuracy, as evidenced by measurements of the rotational parameters for N2O, for which the D parameter is measured with an uncertainty of plus or minus 190 Hz, comparable with the accuracy of microwave techniques. (Author's note : This instrument has become the commercially produced instrument of choice for broad band spectroscopy in the far- infrared and instruments of this type have been used a number of times in space especially in important studies of the anisotropy of cosmic background radiation).
 
Multiple-Sample Wheel for Far Infrared Dichroism Measurements
C.H.Burton, Infrared Physics 20,115 (1980)
It is common practice in the far-infrared (FIR) transmission spectroscopy of solids to place several samples in a rotating sample 'wheel' which is immersed in the same liquid helium pool as the FIR detector. The author describes a multiple sample wheel which also allows dichroism studies to be performed in a simple and precise manner.
 
Variable Temperature FIR-Optical Cryostat with Unique Features
C.H.Burton, Cryogenics 641-643 (1980)
Describes a convenient cryostat for optical and far infrared transmission and photoconductivity studies at temperatures in the range 5 to 300K.
Up to four samples can be loaded in a cell and inserted into the cryostat from above without disturbing large metal seals or optical tails. Thermal contact between the heat sink and the cell is made automatically during the cooling process. The thermal link between the heat sink and liquid cryogen reservoir is varied by means of a modified thermosyphon. Even samples which are poor thermal conductors can be controlled in temperature within +or-10 mK by an exchange gas in the sample cell.
 
Non-Planar Wire Polarizers for the Far Infrared
C.H.Burton, Applied Optics 18, 420-422 (1979)
Examines the advantages offered by nonplanar polarizers at shorter wavelengths and proposes some novel uses for them. As a simple example an unconventional form of polarizing interferometer is considered in which the beam splitter consists of parallel wires defining the surface of a parabolic cylinder. As a second potential application a form of far IR mixer with mixing element is described. The desired approximate matching of the wavefronts from the local oscillator and the lens is achieved by the use of a polarizer.
 
Far Infrared Spectra of Symmetric Aliphatic Ketones C13-C27
C.H.Burton, Spectrochemica Acta 35A, 717-724 (1979).
Far infrared spectra (3 cm-1 to 400 cm-1) are presented for a range of symmetric aliphatic ketones (13 to 27 carbon atoms) at cryogenic temperatures. The predominant FIR absorption bands observed are due to motions of either or both the carbon skeleton and the molecules within the crystal unit cell.
A novel means of visualizing the point and crystal symmetries of interest is presented.
It is concluded that earlier simplified theories of the FIR spectra for such compounds, based on much more limited spectral data, are quite inadequate in both character and precision.
 
Linear and Nonlinear A/D, D/A, A/A Conversions Using the Dual Slope Principle
C.H.Burton, K.G.Weir and G.J.Bowden, IEEE Trans. Instrum. Meas. IM-24, 201-205 (1975)
New methods for precise linear and nonlinear A/D, A/A, and D/A transformations, based on the principle of the dual-slope conversion are proposed. These methods enable multiplication, exponential and logarithmic conversion, determination of nth roots, and the solution of polynomial equations to be performed during the conversion cycle.
 
Cone Channel Optics
C.H.Burton, Infrared Phys. 15,157-159 (1975)
An expression is derived for the solid angle of acceptance for any point in the mouth of a condensing cone optic.
 
Linear and Non-Linear Conversions Using the Dual Slope Principle
K.G.Weir C.H.Burton and G.J.Bowden, J. Phys. E. 8 71-79 (1975)
Some of the possible conversion devices which may be constructed using a few basic components and novel extensions of the dual slope principle are discussed. These devices are flexible and conceptually simple and may in certain applications offer advantages of convenience or economy compared with the conventional use of linear AD or DA converters coupled with a computing facility. The accuracy of the analogue processes described here is inherently determined by integrator and clock stability as for the DSDVM. Comparator errors which cause inaccuracies in some of these processes can be cancelled by using more sophisticated schemes.
(Author's note : these novel methods of AD and DA transformations were later used in a number of Hewlett Packard instruments.
Improvements in integrated circuit fabrication technology enabled them to be replaced for some purposes by 16 and 20 bit AD and DA devices. However it is worth noting that the nonlinear devices considered in this paper were capable of 0.1% resolution over a 5 decade range without gain switching networks and with excellent statistics. This corresponds to about 26 bit performance.)
 
Accurate Measurements of Junction FET Noise at Audio Frequencies
C.H.Burton, J. Phys. E: Sci. Inst. 7 338-340 (1974)
A method of measuring the equivalent voltage and current noise of a junction FET amplifier input stage at frequencies below about 20 kHz is described.
The method does not require a calibrated electronic noise generator or a knowledge of the total system gain or bandwidth.
 
The Intensity of the Dielectric Absorption in Alkali Halides Containing Divalent Cations
C.H.Burton and J.S.Dryden, J.Phys.C: Solid St. Phys., 3, 523-529 (1970)
The intensity of the dielectric absorption arising from the rotation of divalent ion-vacancy pairs in alkali crystals has been measured over a range of concentrations in the crystals NaCl:Ca/sup 2+/, NaCl:Mn/sup 2+/, KCl:Sr/sup 2+/ and LiF:Mg/sup 2+/ and found to agree with the value calculated from simple theory. In NaCl:Mn/sup 2+/ (and in some other systems) the absorption is slightly broader than a Debye curve. This is discussed in terms of the relative occupancy by vacancies of nearest neighbour and next nearest neighbour sites to the impurity ions.
 
Pressure Broadening Effects in Mixtures of Methyl Chloride and Non-Polar Gases at Microwave Frequencies
C.H.Burton, J.H.Noon, W.B.Lasich and R.W.Parsons, Aust.J.Phys.19 283-295 (1966)
Absorption measurements using 3 cm microwave resonant cavity techniques have been performed on binary mixtures of methyl chloride and five non-polar gases (CO2, Ar, N2, He, H2) at pressures up to 4 atm. The results have been analyzed in terms of the pressure-broadening theory of Van Vleck and Weisskopf, modified to include the effects of many-body collisions and a distribution of line widths.
Microwave collision diameters have been calculated for various gases. Agreement is found with other workers in that the values for hydrogen and helium are less than kinetic values. It has been established that measured collision diameters do not vary systematically with the mix ratio of the polar and non-polar constituents a reported in the literature.
 
The Accurate Measurement of the Q of a Resonant Cavity at 10 Gc/S
C.H.Burton, W.B.Lasich, J.H.Noon and R.W.Parsons, Proc.IREE.Australia 389-390 (1964)
A simple method for measuring the Q of a cavity electromagnetic resonator is described. A Q value in excess of 20,000 was measured at a frequency of 10 Gc/s to an accuracy of 2% by a method which does not involve a highly stabilized oscillator. It involves the use of a digital reading counter-type frequency meter which permits rapid measurement of the width of the cavity resonance curve. (Note in proof - this work used a state-of-the-art 100 MHz digital counter designed and constructed by the author)
Collision Broadening in the Inversion Spectrum of Methyl Chloride at Pressures up to Ten Atmospheres C.H.Burton, W.B, Lasich, J.H.Noon and R.W.Parsons, Aust.J.Phys.17 175-183 (1964)
The power absorption coefficient alpha of microwaves of wavenumber 0.333 cmsup-1 by methyl chloride at 33.7 deg C has been studied at pressures up to 2 atm and the results are compared with theoretical predictions. Discrepancies which have previously been attributed to rotational transitions between low-lying rotational states are shown to be due to three-body collisions. The collision diameter for pressure broadening of the inversion transition in methyl chloride is found to be 8.6 Angstrom; this is significantly larger than the figure of 7.2 Angstrom reported by earlier workers who neglected the effect of three body collisions.
 
The Refractive Index of Methyl Chloride at 10 Gc/S
C.H.Burton, W.B.Lasich, J.H.Noon and R.W.Parsons, Aust.J.Phys.16 434-438 (1963)
The dielectric behaviour of gases in an electromagnetic field has been studied theoretically by Van Vleck and Weisskopf (1945). They found expressions for the contributions to the absorption coefficient alpha and the refractive index n at a frequency nu arising from transitions between quantum states j and i. If nu is much less than the natural frequency nusubij associated with the transition, and if the line width is also small compared with the transition frequency, the refractive index should rise linearly with pressure. This theoretical prediction is verified by the experimental work of this paper to an accuracy of 2 parts in a million.
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