Radiation Of Different Wavelengths Research Articles

Electric fields of a laser spark produced by radiation with various parameters

An experimental investigation was made of the spatiotemporal structure of electric fields of a laser spark produced by radiation of different wavelengths (0.53, 1.06, and 10.6 μm), pulse durations (microsecond, nanosecond, and subnanosecond), and intensities (I=109 — 1013 W cm-2. The distribution of the fields near a spark corresponded to a quadrupole configuration of charges in a plasma, consisting of two oppositely directed dipoles in the region of the leading and trailing plasma fronts. The relationships governing the spatial evolution of the quadrupole potential structure were established as a function of the pulse duration and radiation intensity. In particular, the conditions for the relative dominance and degeneracy of the component dipoles were found. Typical dipole moments were determined for various radiation parameters. The amplitude of the fields outside the spark was influenced mainly by a geometric factor related to the transverse dimensions of the plasma. Moreover, at high intensities (I≥1013 W cm-2) this influence was supplemented by a contribution of a nonlinear mechanism dependent on the radiation wavelength and causing considerable changes in the amplitude and structure of the fields.

Laser-assisted photochemical wastewater treatment

Existing UV-emitters on the basis of mercury arc lamps have a quantum yield which is too low in the spectral range 1 < 250 nm to be of interest for most photolytic decomposition reactions. At present the only radiation sources available in that spectral range are excimer lasers or excimer lamps. Here we present a method based on an excimer laser. Its intense pulsed radiation could be a powerful alternative to common mercury lamps. As model substances dyes for colouring textiles and wastewaters of dyehouses containing also auxiliary materials were used. The waters were treated with laser radiation of different wavelengths (193 nm - ArF, 248 nm - KrF) frequently under addition of hydrogen peroxide or ozone as oxidizers. It was found that with the 193 nm radiation at the same energy dose and a substantially lower amount of added oxidizers the decolourization effect was greater than at 248 nm. The reduction of TOC was also faster. The HPLC spectra of the reaction products at the two laser wavelengths showed good agreement, so that the advantage of the shorter-wavelength radiation is the simplier achievement of the activation energies necessary for oxidation or decomposition reactions.

Laser-assisted photochemical wastewater treatment

Existing UV-emitters on the basis of mercury arc lamps have a quantum yield which is too low in the spectral range 1 < 250 nm to be of interest for most photolytic decomposition reactions. At present the only radiation sources available in that spectral range are excimer lasers or excimer lamps.Here we present a method based on an excimer laser. Its intense pulsed radiation could be a powerful alternative to common mercury lamps.As model substances dyes for colouring textiles and wastewaters of dyehouses containing also auxiliary materials were used. The waters were treated with laser radiation of different wavelengths (193 nm -ArF, 248 nm -KrF) frequently under addition of hydrogen peroxide or ozone as oxidizers.It was found that with the 193 nm radiation at the same energy dose and a substantially lower amount of added oxidizers the decolourization effect was greater than at 248 nm. The reduction of TOC was also faster. The HPLC spectra of the reaction products at the two laser wavelengths showed good agreement, so that the advantage of the shorter-wavelength radiation is the simp1ier achievement of the activation energies necessary for oxidation or decomposition reactions.

Transient mass transport mechanism during continuous laser irradiation of metals and the synergetics of arc-augmented laser melting

A new mechanism of mass transport in a melt, active in the course of a transition from thermocapillary convection to melting of a metal, is considered. The existence of convective flows of the melt, whose pattern differs from that of thermocapillary convection, is pointed out. It is shown that the effect in question occurs more generally and it probably applies during continuous irradiation of melts and liquids by laser radiation of different wavelengths. The characteristic features of the melting of metals in the course of arc-augmented laser interaction are explained by the new mechanism.

Hyalomma truncatum (Acari; Ixodidae): evidence for the inability of adult ticks to discriminate between colours

Behavioural investigations into the perception and differentiation of coloured objects by unfed adult Hyalomma truncatum ticks revealed that silhouettes of blue, green, red and yellow colour, under illumination by a sun-simulating waveband spectrum, are perceived by the ticks and responded to equally by a directed response. Two green or dark grey rectangles each with a luminance contrast ratio of 5:1 against the white wall of the test arena in combination with an overlapping, equally sized dark grey or green target were consistently reached by ticks in a ratio of 2:1. Since the outer targets were occupied by the double number of ticks compared with the central silhouette this shows that the response is independent of the colour of the object. Investigations into target perception under monochromatic radiation of different wavelength ranges which were evenly adjusted in their irradiances revealed that ticks responded equally to a black target irradiated by blue, green, yellow and red light of wavelengths 428-472, 517-563, 549-591 and 606-654 nm, respectively. These results indicate the lack of true colour vision in H. truncatum.

Spectroscopic investigation of Pr 3+ luminescence in Sr xBa 1− xNb 2O 6 crystal

Energy levels of Pr 3+ in Sr x Ba 1− x Nb 2O 6 (SBN) crystal are determined by absorption spectroscopy. The broad band fluorescence spectrum is identified by exciting Pr 3+ with laser radiation of different wavelengths, and by phase-resolved spectroscopy. The lifetime of the excited state 3P 0 is measured at various temperatures. Calculations of the transition rates of spontaneous radiation and radiationless relaxation demonstrate that the decay of 3P 0 state is dominated by a multiphonon relaxation.

Wavelength-Specific Upregulation of Keratin mRNA Expression in Response to Ultraviolet Radiation

Keratin intermediate filaments are heteropolymers of coexpressed type I and type II protein chains, whose expression is tightly linked to the differentiation status of the keratinocyte. Epidermal basal keratinocytes coexpress keratins K5 and K14, whereas suprabasal keratinocytes downregulate K5 and K14 and begin to coexpress keratins K1 and K10. Using both isotopic and non-isotopic in situ hybridization, we have investigated the changes in expression of the messenger RNA species encoding the K5/K14 and K1/K10 keratin pairs in response to ultraviolet radiation. Here we report that following irradiation, the mRNA species encoding both keratin pairs is upregulated in a wavelength-specific manner, and that the link between the pattern of keratin mRNA expression and the differentiation status of the keratinocyte is disrupted. Forty-eight hours following ultraviolet B exposure, the amount of detectable mRNA encoding all four keratins studied had increased. Following UVA irradiation, the K1 and K10 signal increased to a much lesser extent than following ultraviolet B, whereas no change in the amount of mRNA encoding the K5/K14 pair was observed. Only two samples were examined following ultraviolet C exposure, but in both, increased K5/K14 signal, but not suprabasal K1/K10 signal, was observed. We suggest that the observations reported here may reflect important qualitative changes involved in photoadaptation of the epidermis, and provide further molecular markers of the different biological effects of ultraviolet radiation of different wavelengths.

Wavelength-dependent fading of artists' pigments

AbstractThe effect of visible radiation of different wavelengths on the deterioration of several fugitive artists' pigments and dyed textiles has been assessed. For red and yellow pigments, damage decreases as the wavelength increases. The relationship between wavelength and colour change for blue pigments and for ISO blue wool standards nos. 1-3 is less straightforward: radiation in the blue region is not necessarily the most damaging for these colorants. The deterioration caused by particular wavelengths depends on the energy of the radiation and the spectral absorbance properties of the colorant. The implications of the results on the selection of light sources and the use of blue wool standards to assess damage to museum collections are discussed.

Surface electric field‐induced Raman spectroscopy from adsorbate and substrate modes

AbstractRaman spectroscopy due to electric fields at surfaces, which manifests itself as surface‐enhanced Raman scattering (SERS) from adsorbate modes, and as electric field‐induced Raman scattering (EFIRS) from substrate modes, is discussed. In SERS experiments with benzene adsorbed on small Ni/SiO2 and Pt/SiO2 clusters, using exciting radiation of different wavelengths, we observed not only very strong peaks of the normally Raman active vibrational modes but also normally infrared‐active and some inactive modes. Although the frequencies of the modes are only slightly shifted with respect to liquid benzene, the relative intensites of the Raman lines are considerably changed and in addition they are dependent on the excitation wavelength. The observation of metal‐carbon vibrations indicates a strong interaction between the adsorbate and the metal atoms. Therefore, in addition to the electric field, a metal‐molecule electronic charge transfer may be responsible for the enhancement mechanism.EFIRS is based on the symmetry‐forbidden scattering from the longitudinal optical (LO) substrate phonon. It allows the detection of the static electric field in the surface region of semiconductor substrates, which originates from electronic band bending. By EFIRS the band bending can be monitored at surfaces and interfaces for coverages from submonolayer up to more than 100 monolayers, depending on the overlayer material. Here, the Sb/GaAs(110) interface is treated as an example. Considerable band bending dynamics is observed for overlayer thicknesses up to 100 monolayers. Simultaneous analysis of the overlayer structure by Raman scattering from the Sb vibration modes allows the interpretation of the band bending dynamics.

Dynamic sweating response of man to infrared irradiation in various spectral regions

In an attempt to detect differences in the thermal effect of infrared irradiation of different wave-lengths, transient sweating response to infrared irradiation in various spectral regions was examined. In Series 1, the ventral or dorsal surface of the nude subject was irradiated repetitively for a period of 4 min (2 min on, 2 min off) by each of three kinds of infrared heaters with main emissivity in 'near-infrared' (NIR; 0.7-2.8 microns), 'intermediate-infrared' (MIR; 1.5-5.8 microns), and 'far-infrared' (FIR; 2.8-25 microns) regions. The sweating response on a non-irradiated area tended to be the greatest with MIR, while the magnitude of the sweating response on the irradiated area showed no consistent differences among various wavelengths. The results infer that MIR stimulated cutaneous thomoreceptors most effectively, while its direct effect on local sweat gland activity was minimal. In Series 2, the effects of 9-12 min irradiations in more restricted ranges of wavelength were compared by the combination of the three kinds of heaters with filters (translucent to wavelength ranges of 1.3-2.7, 2.7-3.5, 3.6-8.0 microns, respectively). The sweating response on a remote area was predominantly greater with the range of 2.7-3.5 microns than with the other wavelength ranges, while the local effect on sweating was minimal with this range. The results of Series 2 reinforce those of Series 1, indicating that the degree of stimulation of cutaneous thermoreceptors and of direct thermal effect on sweat gland activity differ with spectral regions incident on the skin, thus affecting local and remote effects on the sweating response.

New opportunities for soliton transformation in fiber-optic elements

A new method is proposed for the transformation of optical pulses, including solitons, in fiber-optic elements such as a loop–mirror and a Mach–Zehnder interferometer. The method is based on phase cross modulation accompanying a nonlinear interaction between a pulse and cw radiation of different wavelength.

Effects of laser radiation of different wavelengths on an obstacle in vacuum

An analysis is made of the effects of monochromatic radiation with different photon energies on an aluminum obstacle in vacuum. Allowance is made for lateral expansion of the resultant plasma. It is shown that under steady-state conditions the dependences of the plasma parameters on the laser radiation wavelength are relatively weak and nonmonotonic.

Electronic spectra of 8-azaguanine in solution: Evidence for double-well potential surfaces and effect of dissolved oxygen

Electronic absorption and fluorescence spectra of 8-azaguanine in aqueous solution have been studied. Relative intensities of the two peaks observed in absorption are found to change with time. This result can be interpreted in terms of the double-well potential surfaces of the molecule as has been done earlier for guanine. Like guanine, 8-azaguanine also forms a complex with oxygen dissolved in the solution on irradiation in the absorption region and this makes the1∑ g + -3∑ g - transition of oxygen in the complex allowed by dipole selection rule. The peak of 8-azaguanine fluorescence when excited by radiations of different wavelengths upto 305 nm lies near 400 nm. This fluorescence differs appreciably from that of guanine and can be interpreted as mainly arising from the second triplet excited state of the molecule which may be populated by intersystem crossing from the first singlet excited state.

Investigations on the Photoconductive Properties of Crystalline Astacin in a Sandwich Cell

Dark and photoconduction in astacin crystal in a sandwich cell has been studied as a function of applied field and temperature. The results suggest that a single discrete trapping level is involved in charge carrier generation and the dominant trapping level is different for dark and photoconduction. Space charge limited current theory has been used to evaluate various transport parameters. Linear excitation light intensity dependence of photocurrent suggests that the photo generation process is one photon process and is trap limited. Blue shift of the photoconduction action spectrum of astacin compared to its optical absorption spectrum with illumination throgh the positive electrode has been attributed to the difference in the rate of recombination of charge carriers at the surface and in the bulk when produced by radiation of different wavelengths.

Wavelength dependence for the induction of bacteriophage lambda by antitumor agent gilvocarcin V.

AbstractThe wavelength dependence for the induction of a lambda‐lacZ fusion phage of E. coli by photo‐activated gilvocarcin V was determined using a spot test or a quantitative assay for the lacZ gene product. Suspensions of bacteria and chemical were exposed to radiation of different wavelengths in the region 313‐546 nm, using a double grating monochromator. The prophage induction profiles generated were similar to the absorption spectrum of gilvocarcin V in this region, with a peak near 400 nm. The radiation fluence and chemical concentration required for threshold levels of prophage induction exhibited a nearly reciprocal relationship. These results have implications for the therapeutic use of gilvocarcins as antitumor agents.

Study of local atomic order in a ternary CuNiZn alloy using anomalous scattering of synchrotron radiation

Synchrotron radiation diffuse scattering intensity measurements have been made on Cu 0.47Ni 0.29Zn 0.24 single crystal quenched from 870 K by using a monochromatic beam of various wavelengths near the K absorption edges of the elements. By observing the intensity difference between the diffuse scatterings measured by radiation of different wavelengths (due to anomalous scattering effects), four partial intensities arising from the three kinds of interatomic correlation and the thermal vibration of atoms were separated. It has been found that the nearest neighbor pairing of unlike atoms exists in NiZn and ZnCu but a correlation of the opposite sense occurs in CuNi, consistent with the ordering energies predicted by De Rooy et al.

Optically-Induced, Room-Temperature Oxidation of Gallium Arsenide

AbstractRoom-temperature, optically-induced oxidation of the gallium arsenide surface has been studied with laser radiation of different wavelengths. It was found that deep-ultraviolet light is much more effective in enhancing oxidation than near-ultraviolet or visible light. The growth rate of the oxide was also found to be drastically increased by the presence of chemisorbed water molecules on the surface.

Absorption and scattering of laser radiation of different wavelengths by plasma

A numerical investigation was made of the interaction of high-power laser radiation with a plasma, taking into account classical, resonant, and anomalous absorption mechanisms, as well as stimulated Brillouin scattering and specular reflection. The proposed model ensures a qualitative and quantitative agreement of the reflection coefficients, the radiation scattering spectra, and the plasma temperature with the results of experiments performed using an apparatus with an Nd3+ laser operating at the wavelengths 1.06, 0.53, and 0.35 μ in a wide range of power densities from 1013 to 3×1015 W/cm2 .

The saturation of monochromatic lights obliquely incident on the retina.

Foveal dark-adaptation undertaken to test the hypothesis that the excitation of rods causes the desaturation of 'yellow' lights in a 1 degree field traversing the margin of the pupil, fails to exclude that possibility. The desaturation is largest for a 1 degree outside diameter annular test, is still measurable with a 0.5 degree circular disk, but disappears for a 0.29 degree disk. The supersaturation of obliquely incident 501.2 nm test light follows the opposite pattern; it disappears with an annulus and is largest for a 0.29 degree circular field. It is unlikely that rods replace short-wave sensitive cones in the trichromatic match of an obliquely incident test with normally incident primaries. If rods as well as all three cones species are involved, the matches might not be trichromatic in the strong sense. Grassmann's law of scalar multiplication was tested and shown not to hold for the match of an obliquely incident test with normally incident primaries, though it remains valid whenever, both primaries and test strike the retina at the same angle of incidence (independent of that angle). The result in section 3 (above) cannot be due to rod intrusion. It persists (and becomes more conspicuous) on backgrounds (4.0 log scotopic td) which saturate rods. Moreover obliquely incident 'yellow' lights remain desaturated in intervals in the dark after a full bleach, whilst the test field is below rod threshold. The amount of desaturation does not differ appreciably from that normally found. The assumption of the unified theory of Alpern, Kitahara & Tamaki (1983) that the outer segments of only a single set of three cone species (with acceptance angles wide enough to include the entire exit pupil) contain the visual pigments absorbing both the normally incident primaries and the obliquely incident test is disproved by these results. Failure of Grassmann's law is most conspicuous under the conditions for which the changes in saturation upon changing from normal to oblique incidence are greatest and least when the saturation changes are the smallest. Either all unified theories of the Stiles-Crawford effects are wrong or all the effects of oblique incidence operate at a stage in the visual process at which the effects of radiation of different wave-lengths are no longer compounded by the simple linear laws.

Time of appearance of a plasma due to action of laser radiation of different wavelengths on an aluminum target in air

The problem of appearance of a plasma in air above an aluminum target irradiated with neodymium or CO2 laser pulses is solved numerically. The published experimental data are shown to agree with the results of calculations carried out assuming evaporation of the target, reduction in the thermal conductivity of the surface layer, and absorption in the vapor. A rectangular pulse and thermally insulated layers 1 μ thick are assumed in the derivation of the dependence of the time of the onset of evaporation and of the time of appearance of a flash on the density of the radiation flux in the range of 0.5–100 MW/cm2. It follows from these calculations that the threshold of plasma formation is not greatly affected by variation of the laser radiation wavelength from 1.06 to 10.6μ.