Synchrotron radiation for long wavelength spectroscopy

A fundamental radiometric measurement has been carried out in the spectral region 1–140 cm^–1 which demonstrates the higher brightness of the synchrotron radiation source at Daresbury Laboratory over a high pressure mercury arc lamp source. Comparison of the output powers from the SRS and the mercury lamp revealed that the SRS has a particular advantage in the region where the wavelength of the emitted photon becomes very longer. The gain factor of the SRS at 10 cm^–1 was at least 10 times of the mercury lamp at a storage ring current of about 90 mA.A single period wiggler is considered to be a favorable device which will provide a higher level of photon fluxes from an electron storage ring in the long wavelength region.     

The spectral narrowing of a high-power flashlamp-pumped dye laser by injection of external narrow-band radiation

A method of increasing the injection-locking efficiency by external narrow-band radiation relying on a space-frequency separation in a nonlinear absorber (spectral contraster) placed into the high-power dye-laser cavity is proposed. It is shown that this method permits an increase of the energy conversion efficiency into a narrow-band line ( 10^–3 nm) up to 90% with a laser output energy of about 1 J and a pulse duration of more than 1 µs.     

Generation and amplification of nanosecond pulses by iodine lasers

Results are reported of experimental investigations of high-power photodissociation iodine laser pumped by lamps and by radiation from high-current electric discharges. The basic parameters of the working medium, the parameters of both lamp-pumped and discharge-pumped lasers, and methods of shaping of a short pulse with diffraction directivity of the radiation are investigated. The possibility of effective amplification of a short pulse by an iodine amplifier pumped with an open high-current discharge is demonstrated. An iodine laser generating a pulse of duration I nsec, divergence 10^-4 rad, and energy 100 J at a contrast 10⁸ and 300 J at a contrast 10²–10³ is described.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Akademii Nauk SSSR, Vol. 125, 46–103, 1980.     

Diffraction radiation of ultrarelativistic particles passing through a slit in a tilted screen

Diffraction radiation generated by relativistic particles passing through a slit in a tilted screen is proposed for nondestructive particle beam diagnostics. For ultrarelativistic particles with the Lorentz factor γ≫1, simple relations are derived for the field strength of diffraction radiation from a slit in a tilted perfectly conducting plane. It is shown that the total radiation loss is proportional to γ. The effect of the initial beam divergence on the angular distribution pattern of diffraction radiation is pointed out. A principal possibility of determining a beam divergence smaller than γ^-1 is demonstrated when measuring the angular distribution of radiation with a constant wavelength. Tomsk Polytechnical University. Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 4, pp. 56–61, April, 2000.     

The factor of nonparaxial Hermite–Gaussian beams and related problems

On the basis of the second-order moment of the power density and in the use of the series expansion, the expressions for the beam width, far-field divergence angle and M² factor of nonparaxial Hermite–Gaussian (H–G) beams are derived and expressed in a sum of the series of the Gamma function. The theoretical results are illustrated with numerical examples. The M² factor of nonparaxial H–G beams depends not only on the beam order m, but also on the waist-width to wavelength ratio w₀/λ. The far-field divergence angles of nonparaxial H–G beams with even and odd orders approach their upper limits θ_max=63.435 and 73.898, respectively, which results in M²<1 as w₀/λ→0. For the special case of m=0 our results reduce to those of nonparaxial Gaussian beams. Some problems related to the characterization of the nonparaxial beam quality are also discussed.     

Intense, broadband, pulsed I-R source at the national synchrotron light source

We describe a broadband (1 m–1 mm) synchrotron radiation infrared source, pulsed each 20–180 nseconds and delivering about 10¹⁵ photons/sec/1% bandpass into f10 optics. The source size is diffraction limited. This source is thus 100–1000 times brighter than a 2000°K black body, very stable and capable of being used for calibration.Work supported by the U.S. Department of Energy.     

Far-infrared spectroscopy by synchrotron radiation at the UVSOR Facility

At the UVSOR Facility, Institute for Molecular Science, the practical use of the synchrotron radiation as a far-infrared light source has started. A spectroscopic system has been constructed at the beam line BL6A1 of UVSOR storage ring, which covers the wavenumber region from 5 to 250 cm^–1. The cross sectional diameter of the light beam at the sample position is as small as 3 mm with the angular divergence of about 100 mrad. The system has been made mainly for the transmission and reflection measurements of small samples with small angular divergence by the use of the high brightness of the synchrotron radiation. Examples of observed transmission and reflectivity spectra are shown.     

Ground-state depleted solid-state lasers: principles, characteristics and scaling

A novel class of rare-earth-doped solid-state lasers is described. The ground-state depleted laser is pumped by an intense (more than tens of kW cm^–2) narrow-band (less than a few nm) laser source and is characterized by: (1) an unusually low laser ion doping density (5 to 10×10¹⁸ion cm^–3), (2) an unusually large fractional excited population inversion density (4 to 8×10¹⁸ ion cm^–3, or >75%), (3) a gain element that is optically thick at the pump wavelength and (4) a gain element that has a substantially uniform gain distribution due to a bleaching of the pump transition at the pump intensity utilized. These features enable efficient room-temperature operation of rare-earth-ion laser transitions terminating on the ground manifold. The relationships between laser parameters (cross-sections, saturation fluences and fluxes, bleaching wave velocities, etc.) are given and laser performance scaling relationships are presented and discussed.     

Effect of electron irradiation on the properties of germanium-doped gallium arsenide

The Hall effect, electrical conductivity (77–370 K), and photoluminescence spectra (77 K) are studied in single-crystals of nuclearly doped GaAs (NDG) and GaAs doped with Ge by the metallurgical method after irradiation by electrons (E= 1 MeV, D=1.1·10¹⁵–3.8·10¹⁸ cm^–2). Initial electron concentrations were n= 1.7·10¹⁷ cm^–3 and n₀=2.6·10¹⁷ cm^–3 respectively. In the GaAs doped during crystal growth by the Czochralski method the degree of compensation related to the amphoteric impurity Ge is higher (K=0.8) than in the NDG (K=0.4) for identical initial electron concentration. It was established that the rate of charge carrier removal in GaAs is lower than in NDG, while radiation defects are more thermostable in NDG. The energy spectrum of radiation defects and radiating recombination centers, and the basic steps in reestablishment of electrophysical and optical properties in GaAs and NDG are similar, i.e., they do not depend on the method of germanium doping.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 82–86, April, 1991.     

Angular divergence of forwards and backwards emission from an FIR laser,using a pyroelectric vidicon

The angular divergence of FIR radiation at 66 μm and 116 μm from a D₂O cell pumped by single mode pulsed CO₂ laser is obtained, in both forward and backward directions. The forward emission, in similarity with SRS at other wavelengths, emerges with divergence close to the diffraction limit in some cases. The backward emission, probably dominated by ASE, has a greater divergence and at high filling pressures appears to break up into speckles.     

High-power end-pumped CW Nd:GdVO4 laser formed with a flat–flat cavity

Formed with a flat–flat resonator, a diode-laser-array end-pumped CW Nd:GdVO₄ laser at 1.06 μm, capable of generating 8.6 W of TEM₀₀ output power with optical conversion efficiency of 43% and slope efficiency of 48%, has been developed. The laser beam was nearly diffraction limited, with the beam quality factor measured to be M²=1.22. Under the conditions of multi-mode operation, the laser was able to produce 11.2 W of low-order transverse mode radiation (M²<2) at the incident pump power of 22 W, giving an optical conversion efficiency of 51%, and a slope efficiency of 55%.     

Effect of the Radiation Power Density on the Sensitivity of a Diamond Detector

This paper presents the results of an experimental study of the sensitivity of a detector made of natural diamond of the IIa type as a function of the power density of the radiation of a pulsed xenon lamp. It has been shown that the sensitivity of the detector depends on the power density of the xenon lamp radiation and equals about (1–6)·10^–4 A/W. A monotonic decrease in sensitivity of the detector during a radiation pulse has been detected. The minimum resistance of the diamond crystal with an irradiated face of area 3 mm², placed 7 mm away from the axis of the xenon lamp, was 300 , which corresponds to a specific conductivity of 2.2 ^–1·m^–1.     

A simple technique for generating single-mode nanosecond pulses of 10.6 μm radiation

A technique for generating short pulses of 10.6 μm radiation is presented. This technique produces pulses of 10⁻⁹−10⁻⁸ s duration of single-mode radiation with diffraction-limited divergence of the beam and good extraction efficiency of the energy stored in the cavity.     

Anomalous scattered light correlator

The space-time correlation function of the scattered radiation intensity of atoms situated in an external field is investigated. This function includes contributions of the normal +E^–> and anomalous –E–> complex field amplitude correlator. These correlators have components due to scattering by density fluctuations and to collective, diffraction effects. The spatial structure of these correlators is studied and the conditions for the measurement of the anomalous correlator are derived. The temporal properties of the anomalous correlator and the effect of Doppler broadening on the correlation properties of scattered radiation are also considered. The investigation of the anomalous correlator is of interest in high-resolution spectroscopy and may also be useful in the study of nonresonant media.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 70–73, February, 1982.     

Two-Photon Raman scattering and high excitation luminescence in ZnTe

Two-Photon-Raman Scattering (TPRS) and the luminescence of ZnTe are investigated when the samples are highly excited with a tunable narrow-band dye-laser. In luminescence, one observes emission bands due to the well-known inelastic exciton-exciton scattering at intermediate excitation intensities, and the recombination radiation of an electronhole plasma (EHP) at the highest excitation levels. For the first time, TPRS is reported in ZnTe. From the change in the TPRS lines in magnetic fields up to 10T we deduce a diamagnetic shift of 1.2°10^–2 meV/T² of the free longitudinal exciton. This value is in good agreement with results obtained by other authors from reflection spectroscopy.     

Dislocation structure of kcl crystals grown with vibration of the melt

Summary The amplitude at all frequencies was 0.04 mm. Three crystals were grown at each frequency, with seeds of dislocation density D = 6 × 10⁴ cm^–2. Figure 1 shows the frequency dependence of the final D. Each point in Figs. 1 and 2 is the mean from 50 measurements (50 fields of view). At all frequencies except 180 Hz, D was 2–4 times less than that without vibration, while at 100 and 160 Hz it was less by nearly an order of magnitude.The effects of amplitude (0.02 to 0.2 mm) were examined at 100 Hz, the minimum D occurring at 0.1 mm (Fig. 2). At 0.04–0.08 mm, D was less by a factor 3–4 than for crystals grown without vibration, while at 0.1 mm it was less by an order of magnitude, being 2 × 10^–4 cm^–2. The size of the etch pits on crystals grown at amplitudes up to 0.1 mm did not differ from that for crystals grown at rest, but above 0.1 mm the size increased, by more than a factor 3 at 0.2 mm. Figure 3 illustrates these effects.Optimal vibration reduces D by improving the growth conditions (reduction of temperature gradients by mixing, more uniform impurity distribution).     

ВЛИЯНИЕ ПЛАСТИЧЕСКОЙ ДЕФОРМАЦИИ НА ХАРАКТЕР ЭКСТИНКЦИИ И ОСТАТОЧНЫЕ ИСКАЖЕНИЯ РЕШЕТКИ ЧИСТОГО ПОРОШКОВОГО АЛЮМИНИЯ

The integrated intensities and widths of the X-ray diffraction lines of pure powder aluminium (99·99%) were measured after annealing above the recrystallization temperature and once more after the following plastic deformation at room temperature.An analysis of the values measured for the integrated intensities of the diffractions shows that, in the annealed state and in states after plastic deformation by grinding in an organic liquid medium, the primary extinction of this substance predominates. The corresponding magnitude of the mosaic blocks is 4×10^–4 cm and the minimum dislocation density calculated from it is 2×10⁷ cm^–2. On the other hand, an analysis of a sample of unannealed fillings from the same material shows that both kinds of extinction — primary and secondary — play equalroles.Measurement of the (420) diffraction line widths showed that plastic deformation at room temperature leads to a clear broadening of the diffractions in spite of the process of recovery intensively taking place. An interpretation of these broadenings by micro stresses in the region of individual grains led to values of the mean stress function of 7–8×10⁸ dyne cm^–2. This value is compared with the yield point and the corresponding values of the stored energy are calculated. The hypothesis is put forward that the maintenance of these stresses in the grains is due to the oxide envelope surrounding the grains.For plastically deformed samples the diffraction broadening led to maximum dislocation densities of the order of 2×10¹⁰–3×10¹⁰cm^–2 and thus to maximum stored energy values of the order of 1×10^–2 to 2×10^–2 cal/g.     

Nuclear spin lattice relaxation of58CoFe and60CoFe measured by the thermal cycling method

Thermal cycling of thin foil samples is used to measure nuclear spin lattice relaxation of dilute⁵⁸Co and⁶⁰Co in iron at polarizing fields up to 1.3 T. The relaxation rates for the two isotopes differ by a factor of 7.1; the good agreement between the high field values for ² C ₂, (2.93±0.15)·10¹⁵ K·s^–1·T^–2 (⁵⁸Co) and (3.01±0.06)·10¹⁵K·s^–1·T^–2 (⁶⁰Co) verifies the reliability of the experimental method. An enhancement factor model is introduced and shown to give an excellent reproduction of the observed field dependence of the relaxation.     

The application of a raman-shifted tunable KrF excimer laser for laser-induced fluorescence combustion diagnostics

Four wavelength extensions have been investigated by stimulated Raman scattering in hydrogen or deuterium gas of the 248 nm fundamental output of a narrow-band tunable KrF excimer laser. They have been used to acquire laser-induced fluorescence spectra of NO and OH in flames at atmospheric pressure. NO is detected in relatively high rotational states within the -band electronic system at 225 nm. OH was excited at 291.5 nm in the (1–0), at 313 nm in the (1–1) and at 268.5 nm in the predissociative (3–1) band of the ²–² electronic band system, respectively. Prospects of 2D imaging for concentration and temperature measurements in flames using these wavelength extensions are discussed.     

Temperature dependence of a lattice defect induced electric fieldgradient at181Ta in Pt

By implantation of¹⁸¹Hf ions radiation damage is produced in platinum. Subsequent annealing of the samples leads to the trapping of a unique defect at the probe atoms. The temperature dependence of the resulting electric field gradient eq(T) is measured by use of the TDPAC-method. Assuming a relation eq(T)=eq(0)·(1–B·T ^3/2) one findsB=(1.9±0.7)×10^–6 K^–3/2. This low value is of the same magnitude as the corresponding values for¹¹¹Cd in various locally distorted cubic metals.