Study of light collection as a function of scintillator surface roughness

The variation of pulse-height spectra was observed under the consecutive treatment of CsI:Tl plane scintillators by different abrasives – with increase of the abrasive grain size the double peaks of the total absorption transferred into the single peaks with acceptable resolution. The light collection simulation of the differently treated surfaces was performed to interpret the experimental results. In simulation the surface relief was represented as a set of micro-facets with slope distribution functions extracted from the experimentally measured reflectance distribution functions. The behavior of the simulated pulse-height spectra in the vicinity of the total absorption peak under the assumption of uniform scintillation distribution in the scintillator volume was in a good agreement with experimental results for different surface treatment conditions. From pulse-height spectrum simulations for different positions of the point light source it was determined that the double peaks in experimental and simulated spectra had been caused by the scintillations in different scintillator areas. The decrease of the light output and the resolution improvement occurred under the input surface treatment of the plane scintillator by the larger abrasive was caused by the increase of the average pass length of light to the output detector window and by the decrease of the difference of this value for the various scintillator areas, respectively.     

Sputtering yields for light ions as a function of angle of incidence

The sputtering yield of Ni, Mo, and Au have been measured at oblique angles of incidence for H⁺-, D⁺-, and⁴He⁺-ion irradiation in the energy region from 1 to 8 keV. The yields were determined from the weight loss of the targets. For Ni and Mo the dependence of the sputtering yield on the angle of incidence was found to be much stronger for H⁺- and D⁺-ion than for⁴He⁺-ion irradiation. In all cases the maximum in the yield was found at angles of incidence ϑ≧80°, where ϑ is the angle measured from the surface normal. Furthermore the ratio of the maximum yield to the yeild at normal incidence increases with increasing surface binding energy of the target material as well as with increasing ion energy in the energy region inveestigated. The results are discussed qualitatively in view of a model for the sputtering mechanism for light ions.     

Cathodoluminescence of ruby as a function of angle of incidence

The effect is explained in terms of an increase in efficiency with angle of incidence. Inclined excitation is proposed as a method of preventing charging of the surface.We are indebted to Professor V. L. Levshin for discussions, to A. G. Dvchinnikov for assistance in making the attachment, and to Yu. V. Khrushchev for assistance in the experiments.     

The trapping of potassium atoms by a polycrystalline tungsten surface as a function of energy and angle of incidence

The trapping probability of potassium atoms on a polycrystalline tungsten surface has been measured as a function of the angle of incidence and as a function of the energy of the incoming atoms. Below an energy of 1 eV the trapping was complete; above 20 eV only reflection occurred. The trapping probability increased with increasing angle of incidence. The measurements are compared with a simple model of the fraction of atoms initially trapped. The model, a one-dimensional cube model including a Boltzmann distribution of the velocities of oscillating surface atoms, partially explains the data. The trapping probability as a function of incoming energy is well described for normal incidence, justifying the inclusion of thermal motion of the surface atoms in the model. The angular dependence can be explained in a qualitative way, although there is a substantial discrepancy for large angles of incidence, showing the presence of surface structure.     

Acoustic field imaging by light reflection at the free surface of a liquid

In this paper we present a novel technique for acoustic field imaging. This technique is based on reflection of a collimated laser beam at the free surface of a liquid. The reflected beam becomes phase modulated by the acoustic wave as in acoustical holographic systems. We do not use a reference acoustical beam for holographic reconstruction but we observe this phase modulation using dark-field techniques. It gives a measurement of the acoustic field power as a function of the position. The authors have built an optical imaging system and carried out experiments with piezocomposite transducers. The technique presented in this work is able to give fast quantitative information about the performance of individual ceramic rods of the piezocomposite.     

Biomolecule desorption yields as a function of the angle of incidence of fast heavy ions

A time-of-flight mass spectrometer that allows variation of the angle of incidence of the primary ion beam in desorption experiments has been developed. It has been used with heavy-ion beams of MeV energies from the Uppsala EN-tandem accelerator in order to study the yield of molecular ions from samples of ergosterol, glycylglycine and cesium iodide. The general behaviour of the angular distributions is that the yield increases sharply when oblique incidence is approached. The shape of the angular distribution for ergosterol ions is found to depend on the stopping power of the primary ion. The results are discussed in terms of thermal spike models for the desorption process.     

Generation of terahertz radiation during reflection of femtosecond laser pulses from a metal surface

The features of terahertz radiation generated upon oblique incidence of a femtosecond laser pulse on a metal surface are investigated theoretically. We propose a Cherenkov-type generation mechanism associated with excitation of low-frequency surface currents by a p-polarized optical field. The nonlinear surface currents and corresponding electrodynamic characteristics of low-frequency radiation are calculated analytically and by numerical simulation using the hydrodynamic model. The features of Cherenkov generation of terahertz radiation are analyzed, and techniques are proposed for increasing efficiency.     

The relationship of angle resolved light scattering from surface optical resonances to the surface enhanced Raman effect

For a given mildly rough Ag surface, the angle resolved pattern bears the same shape for elastic light scattering, for Raman scattering from adsorbed pyridine or cyanide, or for the luminescence background. This result suggests that surface enhanced Raman scattering is closely related to topographically related surface optical resonances.     

Sxaps spectra of pyrolytic graphite as a function of the angle of incidence of the incoming electrons

Soft X-ray appearance potential (SXAPS) spectra of pyrolytic graphite as a function of the angle of incidence of the incoming electrons have been measured to obtain information about surface plasmon excitation. Plasmons can be coupled with a core hole and two slow electrons above the Fermi level or with a fast incoming electron. In the last case angular dependent plasmon excitation can be observed. Coupling with the fast incoming electron is observed, but band structure effects cannot be neglected to explain the observed structure. Measurements were performed on clean and hydrogen-contaminated pyrolytic graphite. A signal increase over the whole spectrum was observed after hydrogen contamination, probably due to a rearrangement of the surface lattice structure. Bombardment of the surface with electrons of 2 keV gave a decrease in spectral intensity probably due to surface damage.     

Laser thermal response of a finite slab as a function of the laser pulse parameters

This paper deals with the problem of heating a finite slab using laser radiation in relation to the parameters characterizing the laser pulse, namely: q_max(W/m²), the maximum laser power density, t₀ the time interval required to reach q_max and t_d, the pulse time duration. The pulse shape q(t) is suggested in the form: q(t)=βq_max(t/t_d)(1-(t/t_d))exp-B(t-t₀/t_d), where β and B are parameters. Fitting with published experimental pulse [Ready JF. Effects due to absorption of laser radiation. J Appl Phys 1965;36:462–68] is made. Fourier series expansion technique is considered to solve the problem. The critical time required to initiate melting t_m is estimated for four metallic elements and five semiconductors, namely: Al, Cu, Ag, Au (aluminum, copper, silver, and gold), cadmium sulfide, germanium, silicon, alpha beryllium oxide, and silicon carbide. Five pulses with different characteristic parameters are considered.Computations revealed that the thermal response of the targets is highly affected by q_max and t_o, while the pulse time duration is less effective in determining the value of t_m. Moreover, it is revealed that the relation between t_m and the melting temperature for the same laser pulse is nonlinear for the considered targets under the indicated conditions.     

Charging potential of dielectrics and insulated conductors as a function of the angle of incidence of an electron beam

The cardinal characteristics of the charging of dielectric and ungrounded metal targets within radiation by medium-energy electrons (0.5–10 keV) have been studied theoretically and experimentally as a function of the angle of incidence of the electron beam. The coefficients of electron emissions and the second critical energy of primary (radiating) electrons, E _2C , have been determined as a function of the angle of incidence α when the targets are not being charged.     

Use of a light beam to probe the cell surface in vitro

An optical nondestructuve microprobe technique is proposed to examine cell surfaces in vitro. Use is made of the phenomenon of total internal reflection to achieve spatially restricted interaction between a light beam and the peripheral zone of a substrate-adherent population of cells. With the help of a suitable optical model, the technique can provide fundamental information on the molecular organization of the cell membrane from measurements made on living cells. Variations of both the intensity and polarization ellipse of the reflected beam carry information about changes in the cell surface that can be induced by any stimulus to which the cells are subjected. This promises to have important applications such as the detection of normal-to-malignant cell transformations.     

Shadowing function with single reflection from anisotropic Gaussian rough surface. Application to Gaussian, Lorentzian and sea correlations

In this paper, the monostatic (transmitter and receiver are located at the same place) and bistatic (transmitter and receiver are distinct) statistical shadowing functions from an anisotropic two-dimensional randomly rough surface are presented. This parameter is especially important in the case of grazing angles for computing the bistatic scattering coefficient in optical and microwave frequencies. The objective of this paper is to extend the previous work (Bourlier C, Berginc G and Saillard J 2002 Waves Random Media 12 145-74), valid for a one-dimensional surface, to a two-dimensional anistropic surface by considering a joint Gaussian process of surface slopes and heights separating two points of the surface. The monostatic average (statistical shadowing function average over the statistical variables) shadowing function is then performed in polar coordinates with respect to the incidence angle, the azimuthal direction and the surface height two-dimensional autocorrelation function. In addition, for a bistatic configuration, it depends on the incidence angle and azimuthal direction of the receiver. For Gaussian and Lorentzian correlation profiles and practically important power-type spectra such as the Pierson-Moskowitz sea roughness spectrum, the numerical solution, obtained from generating the surface Gaussian elevations (Monte Carlo method), is compared with the uncorrelated and correlated models. The results show that the correlation underestimates the shadow slightly, whereas the uncorrelated results weakly overpredict the shadow and are close to the numerical solution.     

Femtosecond laser-induced surface structures to significantly improve the thermal emission of light from metals

Extraordinary thermal emission properties of the metallic surface microstructures induced by femtosecond lasers are investigated in both experiment and theory. Within the spectral range of 4–17 μm, the measured maximum thermal emissivities at different temperatures enhance significantly to about 100%. Especially for the coral-like surface structure, the improved thermal emission behaviors can extend largely over the whole spectrum rather than happening at some distinctive wavelengths. Moreover, the enhancement factor of the thermal emissivity is observed to depend on the wavelength and the idiographic morphology of the microstructures. This phenomenon can be understood well by equivalent recognizing the SPP field coupling assisted transmission of blackbody radiation through the microstructured interfaces, and the finite-difference time-domain simulations elucidate the underlying physical pictures.     

Interference wedge properties relevant to laser applications: transmission and reflection of restricted light beams

The optical properties of the interference wedge are analysed for the case of restricted laser beam illumination. By further development of Brossel's method, equations describing this case are derived and used to calculate the reflected and transmitted beam profiles for typical intracavity laser beam diameters (0.2–0.6 mm) for Gaussian and uniform intensity distributions. In particular, the experimentally observed formation of bright fringes outside the beam impact area at resonant wavelengths is explained. some useful dependencies concerning the wedge reflection and transmission for laser applications are obtained and experimentally demonstrated.     

Using Raman spectroscopy to monitor surface finish and roughness of components manufactured by selective laser sintering

Selective laser sintering (SLS) is an additive manufacturing process used to realise fully functional component manufacture. Numerous parameters are used in the process to control variables such as laser power, scan speed, laser spot size and overlap of scan vectors. All of these parameters can dramatically alter the sintering process and therefore final component properties. This paper presents how Raman spectroscopy intensity effects, caused by the surface roughness of the components produced, can be used to monitor the degree of sintering between particles in the SLS process. Copyright © 2010 John Wiley & Sons, Ltd.