Structure of Thermal Radio Emission from the Atmosphere in the Middle Part of the Submillimeter Wavelength Range

We present the results of theoretical studies of the structure of thermal radio emission from the Earth's atmosphere in the middle part of the submillimeter wavelength range (wave numbers 1/ 20–50 cm^-1). Absorption spectra of the atmosphere, heights at which the radiation is formed, and other physical factors, which determine the features of the inverse problems of remote sensing in the band considered, are analyzed.     

Excited state absorption of Ti3+:YAlO 3 ⋆

Spectroscopic properties and excited-state absorption (ESA) of Ti³⁺ doped YAlO₃ are investigated in detail. The fluorescence band is centered at 623 nm with a room-temperature lifetime of 11.4 s and a quantum efficiency nearby one. Till now laser action could not be detected because of strong excited-state absorption into a charge transfer band located 45 500 cm^–1 above the Ti³⁺ ground state. At the Ar-laser pump wavelength the ESA cross-section is determined to be _ESA=1×10^–18 cm². This value is a factor of 44 higher than the ground-state absorption cross-section. Consequently the pumping efficiency is decreased by one or two orders of magnitude. The Ti:YAlO₃ results are compared with the spectroscopic data of Ti:Al₂O₃.Dedicated to Prof. Dr. Herbert Welling on the occasion of his 60th birthday     

Absorption of subpicosecond ultraviolet laser pulses in high-density plasma

The absorption of 250 fs KrF laser pulses incident on solid targets of aluminum, copper and gold has been measured for normal incidence as a function of laser intensity in the range of 10¹²–10¹⁴ W cm^–2 and as a function of polarization and angle of incidence for the intensity range of 10¹⁴–2.5×10¹⁵ W cm^–2. As the intensity increases from 10¹² W cm^–2 the reflectivity at normal incidence changes from the low-intensity mirror reflectivity value to values in the range of 0.5–0.61 at 10¹⁴ W cm^–2. For this intensity maximum absorption of 63–80% has been observed for p-polarized radiation at angles of incidence in the range of 54°–57°, increasing with atomic number. The results are compared with the expected Fresnel reflectivity from a sharp vacuum-plasma interface with the refractive index given by the Drude model and also to numerical calculations of reflectivity for various scale length density profiles. Qualitative agreement is found with the Fresnel/Drude model and quantitative agreement is noticed with the numerical calculations of absorption on a steep density profile with normalized collision frequencies, v/, in the range of 0.13–0.15 at critical density and normalized density gradient scale lengths, L/₀, in the range of 0.018–0.053 for a laser intensity of 10¹⁴ W cm^–2.At 2.5×10¹⁵ W cm^–2 a small amount of preplasma is present and maximum absorption of 64–76% has been observed for p-polarized radiation at angles of incidence in the range of 45°–50°.Dedicated to Prof. Dr. Rudolf Wienecke on the occasion of his 65^th birthdayOn leave from: Department of Electrical Engineering, University of Alberta, Edmonton, T6G 2G7, Canada     

Electronic spectrum of cobalt doped rubidium zinc sulphate hexahydrate

Optical absorption spectrum of Co²⁺ doped rubidium zinc sulphate hexahydrate has been investigated both at room and at liquid nitrogen temperatures. The gross features of the observed spectrum are characteristic of octahedral symmetry associated with spin-orbit interaction. The interelectronic repulsion (B, C), crystal field (Dq) and spin-orbit () parameters which give a good fit to the observed band positions areB = 860 cm^–1,C = 3870 cm^–,Dq = 980 cm^–1,= 500 cm^–1. The non-ligand bands observed in the spectrum are attributed to vibrational modes of water molecule.The authors are thankful to the Council of Scientific and Industrial Research, New Delhi (India) for financial support.     

The UV absorption spectrum of the phenyl radical isolated in solid argon

Phenyl radicals have been generated by photodecomposition of nitrosobenzene isolated in solid argon at 12 K. In this medium the origin of the first UV absorption band of nitrosobenzene corresponding to theS ₀ S ₂ transition is found at 30260 cm^–1. Excitation with an excess energy of 2200 cm^–1 results in very efficient photodissociation. The fragments NO and phenyl are stable for many hours. Annealing of the sample above 35 K led to partial recombination and recovery of the absorption spectrum of nitrosobenzene. The UV spectrum of the phenyl radical was obtained in the wavenumber range 25000–45000 cm^–1, apparently without contamination by other species. It shows sharp lines at 25220, 33880, and 34820 cm^–1 and two broader maxima at 38360 and 41060 cm^–1. Of these only the line at 34820 cm^–1 had been assigned to the phenyl radical in earlier work. These data are compared to recent molecular orbital calculations.Dedicated to Prof. F. P. Schäfer on the occasion of his 65th birthday.     

Photoinduced Oxidation of Diphenylbisanthene and Its Spectral Manifestations

The absorption and fluorescence spectra of diphenylbisanthene (DPB) in n-octane and benzene at 300 and 77 K have been investigated. The appreciable Stokes shift of the fluorescence band (180 cm^–1 in n-octane and 440 cm^–1 in benzene) points to the nonplanar character of the aromatic skeleton of DPB, which has been confirmed by results of the optimization of the molecule geometry by the AMI quantum-mechanical method. It has been found that spectral manifestations of the products of photoinduced transformations of DPB molecules are observed in the UV region (200–350 nm), and it has been shown that the observed photochemical process is two orders of magnitude less effective than for diphenylhelianthrene. On the basis of the experimental data and the results of the quantum-chemical calculations of the electronic spectra of molecules of DPB and endoperoxides (ZINDO/S method), it has been concluded that the end products of DPB phototransformations are its endobiperoxides in which —O—O— groups are added to the phenyl-substituted benzene rings of the aromatic skeleton.     

FTIR and Raman spectroscopic study of Fenugreek (<Emphasis Type="Italic">Trigonella foenum graecum L.</Emphasis>) seeds

The composition of Fenugreek seeds in the form of powder, ash, and oil is investigated through FTIR and FT Raman spectra measurements. The results indicate that Fenugreek seeds (powder) are rich in proteins. Fats (lipids) and starch are present in small amounts in the seeds. The FTIR absorption bands of seed powder appeared at: 3365 cm^–1 assigned as N-H stretching vibrations (amide A of protein), 1657 cm^–1 (C=O, amide I), 1540 cm^–1 (N-H bending vibration, amide II), and 1240 cm^–1 (N-H bending, amide III). In the FT Raman spectra the band at 1661 cm^–1 is ascribed to amide I (C=O) of proteins while the band at 1080 cm^–1 indicates the starch. The fenugreek oil Fourier transform infrared absorbance ratios A(3009 cm^–1)/A(2924 cm^–1), A(3009 cm^–1)/A(2854 cm^–1), and A(3009 cm^–1)/A(1740 cm^–1) were considered for measuring the iodine values. These ratios (0.3609, 0.4916, and 0.4129) revealed that the iodine value of fenugreek oil is higher than that of other oils. On the other hand, the ash of fenugreek is very rich in phosphate compounds. The spectra showed absorption bands at frequencies 1082, 1000, 618, and 566 cm^–1, and the FT Raman spectrum showed a strong absorbance band at 793 cm^–1, which is due to phosphate compounds. It could be concluded that the inorganic part of fenugreek consists mainly of phosphate compounds. The Fenugreek seed contains proteins, fat, fiber, and ash, which is in complete harmony with AACC, 1980.__________Published in Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 1, pp. 106–110, January–February, 2005.     

Estimation of the Optimum Concentration Interval of the Contents of Praseodymium, Neodymium, Europium, Holmium, and Erbium in a Solution

Based on the electronic absorption spectra of Pr³⁺, Nd³⁺, Eu³⁺, Ho³⁺, and Er³⁺ ions in 1 M aqueous solutions of chloric acid, calibration graphs have been constructed in a concentration of metals–optical density of a solution format for different frequencies. The band for praseodymium was used at 22,520 cm^–1, for neodymium at 17,380, 13,480, and 12,560 cm^–1, for europium at 25,380 cm^–1, for holmium at 18,580 and 15,580 cm^–1, and for erbium at 39,160, 26,480, and 19,160 cm^–1. The errors in determining the concentration of the indicated elements as a function of their content have been calculated. It is shown that for perchloric solutions of praseodymium it is possible to correctly determine its contents within the concentration range 0.1–1.5% at a frequency of 22,520 cm^–1; for neodymium the ranges are 0.4–1.0, 0.3–1.0, and 0.5–1.0% at 17,380, 13,480, and 12,560 cm^–1, respectively; for europium 0.4–1.5% at 25,380 cm^–1; for holmium — 0.2–1.5 and 0.4–1.5% at 15,580 and 18,580 cm^–1, and for erbium the range is 0.4–1.0% at frequencies of 39,160, 26,480, and 19,160 cm^–1.     

Experimental investigation of infrared fluorescence of molecular gases under the action of CO2-laser radiation

In the paper, the experimental investigation is carried out of the IR fluorescence of organic substances of different classes in the range 600–3000 cm^–1 under the action of the continuous radiation of a CO₂ laser with a power of 40 W/cm². The procedure is given for obtaining the fluorescence spectra. For all the substances investigated, the magnitudes of the effective absorption cross section were determined experimentally at the generation frequency of the laser. Fluorescence is observed only in the case when _v 0; if _v 0, fluorescence is absent. It is shown that the fluorescence intensity depends significantly on the magnitude of the absorption cross section at the laser frequency. A comparison of the fluorescence and absorption spectra shows that only vibrations allowed in the IR region appear in the emission; in a number of cases, a sharp increase of the fluorescence intensity of certain overtones and compound vibrations is observed: when the frequencies are multiples of the laser emission.Translated from Izvestiya Uchebnykh Zavedenii, Fizika, No. 3, pp. 50–53, March Vysshikh 1979.     

Sum-frequency generation at electrochemical interfaces: Cyanide vibrations on Pt(111) and Pt(110)

We use optical sum-frequency generation to investigate the stretching vibrations of cyanide (CN^–) molecules chemisorbed from aqueous electrolytes on single-crystalline Pt(111)- and Pt(110)-electrode surfaces. For clean and well-ordered Pt(111) electrodes, a single vibrational band between 2080 and 2150 cm^–1 with a nonlinear frequency dependence on the potential is observed and assigned to the CN stretching vibration of chemisorbed cyanide. A second band between 2145 and 2150 cm^–1 with very weak potential dependence appears on a surface which was subjected to oxidation-reduction cycles and is attributed to cyanide associated with a microscopically disordered surface. This assignment is supported by preliminary results for a Pt(110) single-crystal electrode. On a well-ordered (110) surface a single and potential-dependent cyanide vibration between 2070 and 2112 cm^–1 is observed. After oxidation of the cyanide and readsorption, this band is replaced by a higher frequency band at 2144 cm^–1 which is essentially not potential-dependent. Occasionally, additional vibrational bands at lower frequencies not reported in corresponding IR studies are observed on Pt(111).Paper presented at the 129th WE-Heraeus-Seminar on Surface Studies by Nonlinear Laser Spectroscopies, Kassel, Germany, May 30 to June 1, 1994     

Electron emission from insulator and semiconductor surfaces by multiphoton excitation below the optical damage threshold

The shape of acoustic pulses excited in crystalline silicon during absorption of Nd³⁺ YAG laser radiation was studied as a function of incident light intensity. It was revealed that the amplitude of the dilatation wave is saturated while the duration of the compression pulse is shortened. A theoretical model is suggested which explains the above experimental facts by a decrease in the time of Auger recombination for nonequilibrium carriers with an increase in their concentration for higher intensity of the optical excitation. The value of the Auger constant obtained from the experiment is 5×10^–31 cm⁶s^–1.     

Transient absorption and laser output of YAG : Nd

YAG : Nd grown under 98% Ar 2% H₂ protective atmosphere free of nitrogen or hydrocarbons showed after UV irradiation broad absorption peaked at 1·9×10⁴ cm^–1 which disappeared relatively slowly at room temperature. It was more intensive in oxygen treated samples than in those annealed in hydrogsn. Transient absorption suppresses laser output by the increase of absorption at 0·94×10⁴ cm^–1 (1064 nm) and, particularly in CW mode, by the anomalous rod deformation. YAG : Nd containing Fe ions (2·10^–4 wt%) showed no transient absorption.     

A study of the luminescence of glasses activated with holmium

The absorption and luminescence of glasses activated with holmium were studied at room temperature and at low temperatures in the region of 4300–30 000 cm^–1. Using the position of the absorption and luminescence bands, the energy levels and the transition scheme were plotted for the trivalent holmium ion in glass. The influence of the glass composition, of the activator concentration, and of the temperature upon the shape, position, intensity, and lifetime of the 5000 cm^–1 band (⁵I₇⁵I₈) were studied. From the temperature dependence of this band, the scheme for the splitting of the (⁵I₇ and (⁵I₈ holmium levels in glass was obtained.In conclusion, we express our thanks to P. P. Feofilov for this interest.     

Low-Temperature Midinfrared Absorption in GaSe

We report the measurement of the temperature dependence of the absorption spectra of - GaSe over the temperature range 300 K to 5 K. Measurements have been made for both the e-ray (polarized parallel to the crystals c-axis) and the o-ray (polarized perpendicular to the c-axis), over the spectral range 4000 to 10 cm^–1. Nine absorption lines at 417, 440, 499, 546, 891, 945, 1015, 1093, 1270 cm^–1 were recorded at 300 K for the e- ray spectra. Some of these lines were identified using the results of a modified single layer, linear chain model of GaSe. The lines at 417, 440 and 499 cm^–1 were assigned to local impurity absorption originating from N, Mg and O, respectively. The weak lines at 945, 1015 and 1093 cm^–1 were assigned to hole transitions from the acceptor levels to the top of the valence band. Two absorption lines at 891 cm^–1 and 1270 cm^–1 were assigned to hole transitions from the quasi-local acceptor levels to the double degenerate valence sub-bands ₅ or ₆. The origin of lines recorded in the far IR absorption spectra at 20, 37 cm^–1 and 362 cm^–1 were also identified.     

Electronic absorption in silicate mineral of copper

The electronic absorption spectrum of chrysocolla, a silicate mineral of copper, has been studied at room and liquid air temperatures. The observed bands were satisfactorily explained as belonging to Cu²⁺ ion subjected to tetragonal and spin-orbit fields. A good fit between the theoretical and observed band positions was obtained for the following crystal field parameters:Dq=–1400 cm^–1 Ds=–3000 cm^–1 Dt=–800 cm^–1 =–800 cm^–1     

Intensity distribution in the rotational structure of the electron-vibrational bands of nitrogen

The intensity distribution was measured for the rotational lines of the N₂ molecule in the radiation of a glow discharge in the pure gas, at pressure 0.1–5 torr, or with argon, at a total pressure of 2 torr, at a current of 40 mA. The distribution found lags behind a Boltzmann distribution in the 0–3 band (corresponding to the C³-B³ transition; the second positive system) over the pressure range 0.1–2 torr and in the 1–4 band (the C³-B³ transition; second positive system) at a pressure of 0.1 torr. In the N₂ + Ar mixture there is selective amplification of the J=25, 26 rotational lines.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 17–21, September, 1970.     

Photoconductivity of highly excited A IV B VI thin films

We report the results of picosecond photoconductivity measurements in photosensitive electrolytically deposited PbS and vacuum evaporated PbTe polycrystalline films. We determine Auger recombination to be the prevailing carrier recombination mechanism in highly excited PbTe and PbS films and found Auger coefficients _A5×10^–28 cm⁶ s^–1 for PbTe and _A5.3×10^–29 cm⁶ s^–1 for PbS for carrier concentration changes N>10¹⁸ cm^–3. The results indicate that the low mobility values are controlled by intergrain carrier scattering. We have studied the thermal annealing influence on picosecond photoconductivity of the films.     

A contribution to the infrared spectrum of the metaborate ion BO′2 isolated in the alkali halide lattice

The paper deals with the vibration spectrum of the monomer metaborate ion BO₂ substituted in the lattice of some alkali halides belonging to the isotopes¹⁰B,¹¹B,¹⁶Oand¹⁸O. The measurements of the BO₂ spectra performed on KBr over the range of temperatures 27°C to 470°C proved the existence of the band ₃+2₂–2₂. Some theoretical relations in the spectra have been verified. It has been shown that the wave number of the bond B = O lies in the range 2120 to 1940 cm^–1 and that of the bond B-O in the range 1490 to 1170 cm^–1.The authors wish to thank Dr. A. Bohun of the Institute of Solid State Physics, Czechosl. Acad. Sci. for stimulating discussions and Dr. Trnka of the same Institute for the preparation of the doped single crystals of NaCl and RbCl. Thanks are also due to the employees of the firm Perkin-Elmer, Überlingen. German Federal Republic, for some measurements of infrared spectra made on the 225 type spectrometer.     

Submillimeter BWO spectroscopy of solids

The potentialities of submillimeter spectroscopy (3–30 cm^–1) based on backward wave oscillators for studying solids are discussed. The scope of the research on this problem made at the Institute of General Physics of the USSR Academy of Sciences is outlined.