Characteristics of microwave photoconductivity of natural diamond in the spectral range 200–250 nm

Mechanically polished plates of natural diamond of the IIa and Ia types were investigated by the microwave photoconductivity (MW PC), conventional (direct-current or, more precisely, low-frequency) photoconductivity (LF PC), and optical-absorption techniques. It is shown that the polycrystalline structure of the samples and high spatial inhomogeneity of the impurity defect distribution provide differences in MW PC and LF PC spectra. It is assumed that nonequilibrium holes in the illuminated diamond are trapped by the crystallite boundaries, while free electrons “oscillate” within the crystallites during their lifetime. The influence of chemical and mechanical treatment on the LF and MW PC is demonstrated.     

Fluorescence intensity and anisotropy decay of the 4′,6-diamidino-2-phenylindole-DNA complex resulting from one-photon and two-photon excitation

We examined the emission spectra, intensity decays, and anisotropy decays of the DNA-4,6-diamidino-2-phenylindole (DAPI) complex resulting from one- and two-photon excitation of fluorescence. Similar lifetimes and correlation times were recovered from the frequency-domain data. However, the initial anisotropies of DAPI for one- and two-photon excitation revealed different angles between the absorption and the emission oscillators, 17.8 and 23.8°, respectively. This suggests the presence of two overlapping transitions in DAPI with different one- and two-photon cross sections for absorption.     

Calculation of the 1s–2s two-photon excitation cross-section in atomic hydrogen

The two-photon excitation cross-section of atomic hydrogen is calculated using explicit summation over intermediate states within the framework of dipole approximation. The matrix element for two-photon excitation is transformed into finite sums, consisting of the product of a radial and angular part. Nine intermediate states are employed in the calculation of the transition matrix element. The two-photon excitation cross-section obtained for the transition 1s ²S_1/2–2s ²S_1/2in atomic hydrogen is a good agreement with the literature.     

Estimation and analysis of the parameters of a field spectroradiometer covering the spectral range 350–2500 nm

We describe selection of an optical layout for a spectroradiometer for rapid field diagnostics of the status of agricultural and forest vegetation, soils, and other objects over a broad spectral range (350–2500 nm), and we present calculations of the basic operating parameters of the spectroradiometer. The spectroradiometer makes it possible to make measurements of the absolute values of the spectral radiance and the relative characteristics of reflected radiation for both individual components of plants as well as for plants as a whole and plant communities.     

Absorption spectra of benzene-isooctane mixtures in the wavelength range 1620–1820 nm

Experimental absorption spectra of benzene, isooctane, and their mixtures are obtained in the wavelength range λ = 1620–1820 nm in which the first overtones of vibrational frequencies of CH, CH₂, and CH₃ hydrocarbon groups are located. Positions of fundamental absorption bands of benzene are refined. Absorption spectra of benzene-isooctane mixtures are shown to intersect in a narrow area near λ ≈ 1695 nm. The main maximum of benzene absorption at λ = 1671.5 ± 0.5 nm, where the influence of isooctane absorption is practically absent, is proposed for determining the content of benzene in benzene-isooctane mixtures. A linear calibration curve for λ = 1671.5 nm that encompasses the full range of benzene concentrations (0–100%) is presented. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 631–634, September–October, 2008.     

Magnetic anisotropy in 5d transition metal–porphyrin molecules

Single molecule magnets(SMMs) with large magnetic anisotropy energy(MAE) have great potential applications in magnetic recording.Using the first-principles calculations,we investigate the MAE of 5 d transition metal-porphyrin-based SMMs by using the PBE and PBE+U with different U values,respectively.The results indicate that W-P,Re-P,Os-P,and Ir-P possess the considerably large MAE among 5 d TM-P SMMs.Furthermore,the MAE of 5 d TM-P can be facilely manipulated by tensile strain.The reduction of the absolute value of MAE for Ir-P molecule caused by tensile strain makes it easier to implement the writing operation.The decreasing of the occupation number of minority-spin channels of Ir-d_(x~2-y~2) orbital leads the MAE to decrease when the tensile strain increases.     

Choosing optical materials for diagnostics of the solar atmosphere in the wavelength range of 6–60 nm

We present our calculations for the reflection characteristics of multilayer mirrors for a series of wavelengths in the interval of 6–60 nm. Interest in these wavelengths is due to preparations for prolonged studies of the Sun within Russia’s ARCA project. For each structure, we suggested a relationship of material layer thicknesses in the period that ensures the optimum reflection coefficient for high spectral selectivity.     

Improvement of spectral resolution by using the excitation dependence of dipole–dipole interaction in a dense atomic gas

We have studied the selective reflection from the interface between a dense rubidium (Rb) atomic vapor and a transparent dielectric. A remarkable narrowing of the spectrum, which can be used to improve the resolution of spectroscopy of dense media, has been demonstrated. This narrowing results from the reduction of the dipole–dipole interaction between atoms when the Rb vapor is excited by a strong pump laser. By using this technique, we have resolved the hyperfine structure of the Rb D₂ line, which is hidden by collisional broadening. PACS 32.70.Jz; 42.50.Ct; 34.80.Dp     

Narrow-band extreme-ultraviolet laser radiation tunable in the range 90.5–95 nm

Tunable, narrowband extreme ultraviolet radiation in the range 90.5–95 nm with only limited intensity variations is produced by frequency-tripling ultraviolet light from a frequency-doubled dye laser in a gas-jet of xenon. Acetylene gas is found to be an efficient medium for third-harmonic generation in this wavelength range as well. The extreme-ultraviolet radiation is applied in a spectroscopic study of the b ¹ II _u , v=6–8 and v=10–12, o ¹ II _u , v=0 and b¹ _u ⁺ , v=9 states of molecular nitrogen. From linewidth measurements a value k _p=6×10¹⁰ s^–1 for the predissociation rate of the b ¹ II _u , v=11 state is deduced.     

Photolysis of NO2 at multiple wavelengths in the spectral region 200–205 nm

A study of the photodissociation dynamics of NO₂ in the 200–205 nm region using resonance enhanced multiphoton ionization (REMPI) in conjunction with the velocity map imaging technique is presented. We chose this region because it allowed the use of a single laser to photodissociate the NO₂ molecule and probe both the O(¹D₂) fragment using (2+1) REMPI via the 3p'¹P₁ state at 2 ×205.47 nm and the 3p'¹F₃ state at 2 ×203.5 nm, and the O(³P_J) fragments using (2+1) REMPI via the P_J states around 2 ×∼200 nm. Translational energy and angular distributions are extracted from the O(¹D) and O(³P) product images. A growth in the population of highly excited vibrational levels of the NO X(²Π) co-fragment is found as the dissociation wavelength decreases. These are compared with similar trends observed previously for other triatomic O-atom containing molecules. Detailed information on the electronic angular momentum alignment of the ¹D₂ state is obtained from analysis of the polarization sensitivity of the O(¹D) images using the two resonant intermediate states. The angular dependence of the potential energy in the exit channels is examined using long-range quadrupole-dipole and quadrupole-quadrupole interaction terms, from which molecular-frame multipole moments of the total angular momentum of the recoiling O atoms have been calculated. Comparison with the experimentally derived multipole moments is used to help provide insight into the dissociation mechanism.     

Electron excitation of hydrogen atom by ions impact in the energy range 20–1000 keV/amu

We have calculated the electron excitation cross sections of hydrogen atom by the impact of protons, alpha particles and He⁺ ions using the boundary corrected continuum intermediate state approximation in the intermediate and high energies. The calculated results are compared with other theoretical and experimental results. The angular influence of excitation to the H atom at the intermediate energy is also discussed. The distortion effects due to the projectile charges in reactions of electron excitation to bound states of the target H atom are shown in the intermediate and high collision energy.     

Performance of a polarizer using synthetic mica crystal in the 12–25 nm wavelength range

To develop polarizer functioning in the extreme ultraviolet (EUV) and soft X-ray region, the polarization performance of synthetic mica has been investigated theoretically with a simulation code using Fresnel equations and optical constants from the Henke database. The reflectance of synthetic mica crystal for s and p polarization was measured to investigate its polarization performance in a home-made synchrotron radiation soft X-ray polarimeter at beamline 3W1B, Beijing Synchrotron Radiation Facility (BSRF...     

New self-developing photopolymers for holographic recording in the 500–700 nm range

The methods of sensitization in the visible spectral region of self-developing photopolymeric materials on the basis of oligoether- and oligourethane acrylates have been investigated. As a result of the choice of the initiating system and modification of the monomer component of the base FPK-488, new FPK-520 and FPK-650 compositions have been obtained that provide holographic recording in the 500–700 nm range. The compositions developed can be used to record holographic optical elements (gratings, lenses) as well as for holographic interferometry and in pattern recognition systems. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 29–33, January–February, 2000.     

Photosensitivity of mercurous chloride single crystals in 280–400 nm spectral region

The paper deals with the dependence of emission intensities of Hg₂Cl₂ luminescence observed at 78 K on the previous room-temperature exposure of the samples to monochromatic light (280–400 nm). The spectral dependence of the Hg₂Cl₂ photosensitivity was determined from the variation of the emission intensities. The photosensitivity peaks were found at the excitonic absorption near 300 nm, at the absorption band of mercury excimers (Hg₂)^* near 330 nm and at the excitation band of the infrared emission near 360 nm. The relative concentration of the photolytically released mercury can be determined from the ratio of emission intensities of bands peaked at 503 nm and 399 nm.     

Cathodoluminescence of monoclinic Li3AlF6 crystals in the spectral region of 150–600 nm

Cathodoluminescence (CL) of monoclinic LiAF crystals was studied in the spectral (150–600 nm) and temperature (78–302 K) ranges using both the steady-state CL and pulse CL (PCL) techniques. Three CL emission bands were found in the spectral range of 150–600 nm. The dominant complex CL band at 350 nm obeys the Mott law (E = 0.072 eV and ω = 750). On heating, the 172 and 208–212 nm CL bands vary in intensity non-monotonically. At T = 78 K, the CL decay kinetics comprises three components: a dominant fast exponential component with a lifetime of 750 ns, and two low-intensity components with the lifetimes of 20 and 240 μs. The last two components were fitted by a second order hyperbolic law. Time-resolved PCL spectra were recorded using time-windows corresponding to the PCL decay components. Paper discusses the reasonable interpretation of the CL emission bands.     

Four-photon polarization spectroscopy of water and its isotopic molecules in the spectral range between 0 and 50 cm<Superscript>–1</Superscript>

By the method of saturation of absorption of counterpropagating light waves, the gas-phase spectrum of SiF₄ is obtained without Doppler broadening of spectral lines. In the frequency range of the generation of a low-pressure CO₂ laser (the 9.4-μm band), multiplets of the superfine structure (associated with tunneling transitions between the states of rotation about the equivalent symmetry axes of the SiF₄ molecule) of the spectrum were observed. Weak satellites were observed in the vicinity of the multiplets. Some of the satellites were interpreted as resonances formed by the collisional transfer of the three-photon Bennett holes and peaks.     

Vacancy generation in silicon in the temperature range 100–633 K under electron irradiation

The processes of radiation defect formation in Si with 1 MeV electron irradiation in the temperature range 100–633 K have been investigated. It is established that the generation efficiency of vacancies λ_V increases with temperature, then starts to saturate at temperatures of 250 K and finally stays constant at T>300 K. It is shown that at high temperatures, the λ_V dependence can be caused by the additional scattering of “hot” interstitial atoms on acoustical and optical phonons, the numbers of which increase with the temperature. An explanation, based on the creation of quasi-molecule of “hot” interstitial and lattice atoms, is proposed.     

Pion-Nucleus potentials in the energy range of 0–80 MeV

Data for the elastic scattering of 30–80 MeV positive and negative pions by a wide range of nuclei is analysed with an Ericson-Ericson MSU type optical potential. By use of consistent sets of data for π⁺ and π⁻ and of experimental results for total reaction cross sections we obtain for the first time optical potentials that describe well all the data without the need of introducing non-standard charge-dependent effects.     

Phase evolution of the reemitted field in the semiconductor quantum wells under the femtosecond pulse train intersubband excitation

Property of the phase of the reemitted field in the semiconductor quantum wells (QWs) excited by femtosecond pulse train is investigated. It is shown that the phase evolution of the reemitted field is controlled by the relative phase between the successive pulses of the incident train. For all the odd pulses excitation, the reemitted field is from out-of-phase to in-phase, then again to out-of-phase with the incident pulses, whereas for all the even pulses excitation, the situation is the opposite, i.e., it is from in-phase to out-of-phase, then again to in-phase with the incident pulses.