Reflected Intensity Distribution Research Articles

Measurement of Cold Neutron Spectrum with Liquid Mirror Reflection

Making use of the wavelength dependency of the critical angle for the total reflection of neutrons, the possibility of determining the energy spectrum of cold neutrons by means of a liquid mirror is examined. A carbon tetrachloride mirror, combined with a pair of fine slits, are used for the measurement of the angular distribution of the reflection intensity of beryllium filtered neutrons. For determining the correction required to account for non-reflected neutrons detected by the counter, the direct beam component is measured by disturbing the liquid mirror surface with small ripples generated by an ultrasonic vibrator submerged in the liquid, and the value obtained with this clouded mirror is subtracted from that determined with the clear undisturbed liquid mirror. The experimental results qualitatively show good agreement with those obtained with a helical-slot neutron velocity selector, and further reveal even better resolution than possible with the latter method, in the cold neutron energy region.

Off-Specular Peaks in the Directional Distribution of Reflected Thermal Radiation

Experiments have been performed which demonstrate that the directional distribution of reflected thermal radiation for moderate to large angles of incidence is not intermediate to the specular and diffuse limits as commonly assumed. Indeed, for such angles of incidence on roughened surfaces, maxima in the reflected intensity distribution occur at polar angles larger than the specular angle. In some cases, the intensity of this off-specular maximum is three or four times the intensity in the specular-ray direction. The materials studied were aluminum, nickel, copper, a nickel-copper alloy, and magnesium-oxide ceramic, thereby encompassing both metals and nonmetals. Controlled surface roughnesses of 0.23 to 5.8 microns were employed over a wavelength range extending from 0.5 to 6 microns. The angle of incidence was varied from 10 to 75 deg, while reflected radiation was collected in the plane of incidence at polar angles ranging from 0 to 89 deg. The experimental results are arranged on the basis of a surface-roughness-to-wavelength ratio, σm/λ. Certain trends of the off-specular peak with incident angle and σm/λ are noted.

Lorentz Polarization Absorption Corrections in the X-Ray Precession Method

The effect of absorption in the x-ray precession method cannot be separated from the Lorentz factor except for special cases. Consequently, a combined Lorentz polarization absorption correction 1/(LPA) is required. The angular coordinates of the camera motion which are needed to discuss absorption are defined and then expressed in terms of reciprocal lattice coordinates. It is shown that all precession reflections fall into five classes in their dependence on these angular variables. Using this classification, the degree of anisotropy in the intensity distribution of reflections from cylindrical specimens is estimated. A procedure for automatic computation of 1/(LP) has been expanded to compute 1/(LPA) for cylindrical specimens.

Reflection of Sound from Randomly Rough Surfaces

A study of the reflection of underwater sound from nonperiodic, pressure release surfaces is reported. The Eckart theory for wave reflection from rough surfaces has been adapted (with some modifications) to the experimental work. A portion of the investigation was directed toward a study of the dependence of the intensity reflected in the specular direction on angle of incidence, radiation wave number and the statistics of the reflecting surface. Secondly, a method is illustrated for determination of the rms amplitude and the correlation function of the reflecting surface from an analysis of the reflected intensity distribution. The radiation wavelength, in this case, must be much larger than the rms roughness amplitude.

Phase Condition for Light Incident Normally on a Semireflecting Film

It is shown that for a semireflecting film whose reflection and transmission factors are reiρ and teiτ, the conservation of energy requires that the angle ρ−τ must lie between cos−1(A/2rt) and cos−1(−A/2rt) where A=1−r2−t2. The corresponding condition for an asymmetrical film is derived. The effect of this phase condition on multiple beam reflection fringes and filters is studied theoretically. It is possible to set an upper limit to the error incurred in the calculation of reflected intensities on the usual assumption that ρ−τ=π/2. Expressions are found for the maximum and minimum intensities with ρ−τ at its limit. It is extablished that a necessary condition for the reflected intensity distribution to become transmission-like is that r+t⩽1.

Multiple-Beam Interferometry: Intensity Distribution in the Reflected System

The intensity distribution within the reflected fringe system from a multiple-beam interferometer employing silvered reflecting surfaces is discussed in its dependence upon the reflectivities and phase conditions at the reflecting surfaces. Using the Fizeau fringes of equal thickness localized on the zero order Feussner surface, the reflected intensity distribution is examined experimentally as the reflection coefficients of the interferometer surfaces vary between 4% and 90%. In the range of low reflectivities, when the silverings used showed marked colours, the changes in the reflected system lead to the measurement of a phase quantity related to the optical constants of the silver in the form of the thin film. Also in this range, the reflected fringes have a symmetrical form which is of use in the examination of sources of low intensity. In the range of high reflectivities, the conditions for the use of the reflected fringes in topographical investigation are discussed. The findings apply to fringes of equal chromatic order as well as to Fizeau fringes in reflection.