Time-Resolved Vacuum Ultraviolet Spectroscopy of Er<Superscript>3+</Superscript> Ions in the SrF<Subscript>2</Subscript> Crystal

The photoluminescence and photoexcitation spectra as well as the luminescence decay kinetics of Er³⁺ ions in the visible ultraviolet and vacuum ultraviolet (VUV) regions have been studied by the method of low-temperature, time-resolved VUV-spectroscopy on excitation by synchrotron radiation. In the VUV spectral region of the luminescence of SrF₂:1% Er³⁺, the 146.5-nm band with a time of decay of less than 0.6 nsec was revealed together with the well-known emission band at 164.3 nm (decay constant in the microsecond range). Its possible nature is discussed. The specific features of the formation of photoexcitation spectra of the f-f and f-d transitions in the Er³⁺ ion are considered. Competition between the processes of excitation of f-f and d-f luminescence has been revealed. It manifests itself in the inverse relationship of their photoexcitation spectra in a range of energies of incident photons that are close to the position of the 4fⁿ⁻¹5d configuration levels. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 4, pp. 519–523, July–August, 2005.     

Full tunability of laser femtosecond high-order harmonics in the ultraviolet spectral range

We demonstrate experimentally the full tunability of a coherent femtosecond source in the whole ultraviolet spectral region. The experiment relies on the technique of high-order harmonic generation driven by a near-infrared parametric laser source in krypton gas. By tuning the drive wavelength in the range between 1100 to 1900?nm, we generated intense harmonics from near to extreme ultraviolet. A number of photons per shot of the order of 10⁷ has been measured for the first harmonic orders. Many novel scientific prospects are expected to benefit from the use of such a table-top tunable source.     

The search for the existence of <Superscript>229m</Superscript>Th at IGISOL

An overview of preparatory work aiming at the identification of the low-lying 7.6 eV isomer in ²²⁹Th through a measurement of its hyperfine structure is presented. A ²³³U recoil gas cell has been developed and has undergone several iterations in order to improve the efficiency of extracting a low-energy beam of ²²⁹Th⁺ ions. Spectroscopic studies on stable ²³²Th have been carried out to establish an efficient laser ionization scheme. The latter will be applied in connection with the gas cell in order to improve the extraction efficiency by accessing the neutral atomic fraction. In addition to that of the ²²⁹Th ground state, the hyperfine structure of the isomer can then be determined either by collinear laser spectroscopy on the extracted and accelerated ions or by direct in-source/in-jet high-resolution Resonance Ionization Spectroscopy (RIS). The first experiments using high-resolution RIS have been performed and isotope shifts of ²²⁸Th, ²²⁹Th and ²³⁰Th relative to ²³²Th were measured on an atomic 7s ² → 7s7p ground-state transition at 380.42 nm. A template of the ground-state hyperfine structure of ²²⁹Th has been established for a 261.24 nm UV transition. This is an important step towards identification of the isomeric state.     

Atmospheric ultraviolet and red-infrared flashes from Universitetsky-Tatiana-2 satellite data

Millisecond ultraviolet (240–400 nm) and red-infrared (610–800 nm) flashes were detected in the nighttime atmosphere with the scientific payload installed onboard the Universitetsky-Tatiana-2 micro-satellite. Flashes with various numbers of photons, from 10²⁰ to 10²⁶, were detected within the atmospheric area 300 km in diameter observed by the detector. The flashes differ in duration and temporal profile: from single short flashes ～1 ms in duration to flashes with a complex profile more than 100 ms in duration. Different global geographic distributions are observed for flashes with different numbers of photons. Flashes with fewer than 10²² photons are distributed uniformly over the Earth’s map. Flashes with more than 10²² photons are concentrated near the equator and above the continents. Series of flashes were observed in one turn of the satellite when flying not only over thunderstorm regions but also over cloudless ones. The flash number distribution has been derived from the ratio of the numbers of red-infrared and ultraviolet photons. As applied to discharges in the upper atmosphere, whose glow is dominated by the emission in the first and second positive systems of molecular nitrogen bands (1PN₂ and 2PN₂), this distribution is equivalent to the flash altitude distribution in the atmosphere. The observed ratio of the numbers of photons in red-infrared and ultraviolet flashes agrees with the calculated one for electric discharges at altitudes higher than 50 km. In-orbit measurements of the charged particle flux (with a threshold energy for electrons of 1 MeV) provide no evidence for a synchronous occurrence of an ultraviolet flash and a burst in the particle flux in the orbit.     

利用单光子和双光子共振电离增强He原子谐波强度

理论研究了He原子在吸收紫外光子后对高次谐波的强度的影响。结果表明：当紫外光光子能量满足He原子基态与激发态的单光子和双光子共振跃迁时,谐波强度有超过2个数量级的增强。当紫外光光子能量满足He原子基态与激发态的多光子共振跃迁时,谐波强度增强明显减弱。分析电离几率表明,单、双光子共振电离在紫外共振电离中起主要作用,因此导致谐波强度的明显增强。同时,在啁啾调频场的作用下谐波截止能量也明显延伸,可以获得一个强度较高的谐波光谱连续区。选取该谐波连续区可获得脉宽为40 as的孤立脉冲。     

Generation of tunable picosecond pulses in the medium infrared by down-conversion in AgGaS2

Picosecond pulses from a mode-locked Nd:YAG laser and a traveling-wave dye laser are mixed in an AgGaS₂ crystal to generate pulses at the difference frequency. The dye laser is tunable between 1200 nm and 1460 nm resulting in a tuning range of the parametric pulses from 3.9 μm to 9.4 μm. The spectral bandwidth is quite narrow. A value of Δ?=6.5 cm^-1 was measured which is constant over the whole tuning range. Several percent of the Nd:YAG laser photons are converted to infrared photons. Pump pulses of 21 ps give parametric pulses of 8 ps.     

A review of visible-range Fabry–Perot microspectrometers in silicon for the industry

This review presents microspectrometers in silicon for the industry for measuring light in the visible range, using the Fabry–Perot interferometric technique. The microspectrometers are devices able to do the analysis of the individual spectral components in a given signal and are extensively used on spectroscopy. The analysis of the interaction between the matter and the radiated energy can found huge applications in the industrial sector. The microspectrometers can be divided on three types, determined by the dispersion element or the used approach and can be found microspectrometers based on prisms, gratings interferometers. Both types of microspectrometers can be used to analyze the spectral content ranging from the ultraviolet (UV, below 390 nm), passing into the visible region of the electromagnetic spectrum (VIS, 390–760 nm) up to the infrared (IR, above 760 nm). The microspectrometers in silicon are versatile microinstruments because silicon-compatible techniques can be used to assembly both the optical components with the readout and control electronics, thus resulting high-volume with high-reproducibility and low-cost batch fabrications. A compensation technique for minimizing the scattered light effects on interferometers was implemented and is also a contribution of this paper. Fabry–Perot microspectrometers for the visible range are discussed in depth for use in industrial applications.     

氮团簇离子注入单晶硅的光致发光谱研究

氮团簇离子N⁺₁₀注入单晶硅直接诱发其表层转化为纳米晶结构, 导致光学性质发生显著变化. 在250—320nm波段的紫外光激励下,在330—500nm光区出现明显的光发射带,并在360nm附近产生强度极高、单色性良好的发射峰,其强度达到N⁺注入试样或基底的5倍,是N⁺₂注入试样的1.5倍. 在可见光区的730nm附近和近红外区的830nm附近也出现发光带. 所有上述发光都非常稳定,可长时间保持其发 关键词： 光致发光 团簇离子注入 硅单晶 纳米晶结构     

Wavelength‐dependent amplitude of Teflon Raman lines

Raman and other spectroscopy systems operating in the deep ultraviolet (DUV) spectral region below 250 nm lack scattering standards. Such standards are particularly important for experiments that use multiwavelength excitation and/or when results are compared across different experiment platforms. Teflon has been used as an external standard in the visible and near‐IR spectral regions and has been suggested for use in the ultraviolet (UV). Comparison of the relative amplitudes of prominent Teflon Raman lines indicates a significant effect on line ratios when the excitation wavelength is below 250 nm. This dependence on excitation wavelength has been commented on previously and attributed to pre‐resonance effects, but no detailed examination had been undertaken to date. We present the results of a study of Teflon Raman line ratios obtained from closely spaced excitation wavelengths in the DUV from 210 to 320 nm. The 731 cm⁻¹ line is identified as well suited for a standard. Electronic transition energies associated with resonance of principal Teflon Raman lines are obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

Penning ionization electron spectroscopy and photo-electron spectroscopy of molecular solids. II. Ammonia and water

The Penning ionization electron spectra (PIES) and ultraviolet photoelectron spectra (UPS) of ammonia and water molecules condensed on a cold metal substrate have been measured using thermal He*(2³S, 2¹S) metastable atoms and He(I) (58.4 nm) photons. The shifts of the observed positions of the PIES peaks relative to those of the UPS peaks in the condensed phase are roughly equal to the corresponding shifts in the gas phase. The relative intensities of the 3a₁ and 1e orbital peaks are reversed in the PIES and UPS for both gaseous and condensed ammonia; the origin of this reversal is interpreted as the difference between the interactions with metastable atoms and photons. On the other hand, the relative intensities of the 3a₁ orbital peak in the PIES and UPS for condensed water decrease as compared to the gas-phase spectra. This implies participation of the 3a₁ orbital of water in the hydrogen bonding.     

Spectral response of radiochromic gel detector in the near-ultraviolet region (200–400 nm)

Tissue-equivalent radiochromic gel detector is sensitive in the regions of ultraviolet radiation (UVR) and gamma and X-rays. This study aims to investigate the spectral response and other optical properties of the ferrous sulphate, xylenol orange and gelatin (FXG) radiochromic gel dosimeter at particular UVR wavelengths. A total of nine monochromatic wavelengths were selected in the range of 240–400 nm with an increment of 20 nm. The FXG spectral response was estimated from the variation of spectral absorbance at 560 nm resulting from 1 h exposure to UVR beam at each chosen wavelength. Experimental results show that the FXG responsivity depends on the wavelength of the radiation and the optical path in the gel material. UVC and UVB photons have relatively higher photochemical effect than UVA; however, UVA penetration is deeper. Investigations showed that the FXG gel response is relatively constant between 240 and 320 nm, but it varies rapidly with wavelength in the UVA range and takes a minimal value at 360 nm. UVR spectral absorbance curves for different gel sample thicknesses were examined. The experiment showed that 6 mm of neutral gelatin or FXG gel samples was capable of absorbing >99.7% of the beam in the UV range of 240–290 nm.     

In-source laser spectroscopy developments at TRILIS—towards spectroscopy on actinium and scandium

Resonance Ionization Laser Ion Sources (RILIS) have become a versatile tool for production and study of exotic nuclides at Isotope Separator On-Line (ISOL) facilities such as ISAC at TRIUMF. The recent development and addition of a grating tuned spectroscopy laser to the TRIUMF RILIS solid state laser system allows for wide range spectral scans to investigate atomic structures on short lived isotopes, e.g., those from the element actinium, produced in uranium targets at ISAC. In addition, development of new and improved laser ionization schemes for rare isotope production at ISAC is ongoing. Here spectroscopic studies on bound states, Rydberg states and autoionizing (AI) resonances on scandium using the existing off-line capabilities are reported. These results allowed to identify a suitable ionization scheme for scandium via excitation into an autoionizing state at 58,104 cm^???1 which has subsequently been used for ionization of on-line produced exotic scandium isotopes.     

Single and double ionization of neon 2s- and 2p-subshells by proton and electron impact

Absolute single and double ionization cross sections of neon 2s- and 2p-subshells for proton (40–900 keV) and electron impact (0.2–10 keV) have been measured using photon spectroscopy in the spectral range of the vacuum ultraviolet. Cross sections for double ionization decrease more rapidly with increasing impact energy than cross sections for single ionization. No definite asymptotic energy dependence of a Bethe-Fano-plot could be found for double ionization in contrast to single ionization. The experimental results are compared with theoretical predictions of the shake-off model and Gryzinski's classical binary encounter theory. Better agreement is found with the latter, indicating that successive binary collisions have to be considered as a strong mechanism for double ionization by protons or electrons of the investigated energy range. Comparison is made with other experimental results for double ionization by photon impact or capture ionization by proton impact.     

稀土元素铕(Fu)的单光子共振和双光子共振激光增强电离光谱

本文首次报道稀土元素铕(Eu)的激光增强电离光谱.用紫外可调谐激光器检测到EuI 287.779um,EnI 287·887nm,EuI 289.254nm,Eul 289.303nm,EuI 289.383nm的单光子共振激光增强光谱.用可见区可调谐染料激光器检测到EuI的双光子共振激光增强电离光谱.对铕(Eu)原子激发和离化机理进行了讨论.稀土元素铕的检测限达10ng/ml.     

Spectroscopic studies of laser-produced plasmas formed in CO and CO2 using 193, 266, 355, 532 and 1064 nm laser radiation

The wavelength dependence of laser-produced breakdown in air, CO and CO₂ has been studied using the four Nd:YAG harmonics (266 nm, 355 nm, 532 nm and 1064 nm) and the ArF-excimer laser (193 nm). Breakdown thresholds at these wavelengths are reported for air, CO and CO₂. A significant reduction in the breakdown thresholds for both CO and CO₂ is apparent when comparing 193 nm with the four Nd:YAG harmonics. This reduction is attributed to the resonance-enhanced two-photon ionization of metastable carbon atoms generated in the laser focus at the ArF-laser wavelength. In addition to reporting breakdown thresholds, the laser-produced plasmas in CO and CO₂ are characterized in terms of plasma temperatures and electron densities which are measured by time-resolved emission spectroscopy. Electron densities range from 9 × 10¹⁷ cm^–3 to 1 × 10₁₇ cm^–3. Excitation temperatures range from 22 000 K at 0.2 µs to 11 000 K at 2 µs. Ionization temperatures range from 22 000 K at 0.1 µs to 16 000 K at 2 µs. Evidence is presented to indicate that, like ArF-laser-produced plasmas, Nd:YAG-laser-produced plasmas formed in CO and CO₂ are in or near a state of Local Thermodynamic Equilibrium (LTE) soon after their formation.     

Two photon luminescence with ultraviolet excitation of trivalent praseodymium

In the fluorides YF₃ and α-NaYF₄, the trivalent praseodymium ion shows a two photon luminescence in which one ultraviolet photon (?210 nm) is converted into two visible photons.     

19 fs shaped ultraviolet pulses

We report the generation of shaped tunable ultrashort ultraviolet pulses with full control over the spectral phase and amplitude. The output of a noncollinearly phase-matched optical parametric amplifier is shaped in phase and amplitude by a liquid-crystal spatial light modulator. The resulting structured visible pulses are transferred into the ultraviolet by sum-frequency mixing with strongly chirped 775 nm pulses. Single, double, and triple pulses at 344 nm with subpulses as short as 19 fs are explicitly demonstrated. The method can easily be adapted to arbitrarily shaped pulses throughout the 295-370 nm range.     

Proton and electron impact on molecular and atomic oxygen: I. High resolution fluorescence spectra in the visible and VUV spectral range and emission cross-sections for dissociative ionisation and excitation of

Molecular oxygen O₂ was dissociated in collisions with protons and electrons in the intermediate velocity range (p⁺-energies: 17-800 keV, e^--energies: 0.2-2 keV). Fluorescence from excited atomic and singly ionised fragments and from singly ionised molecules was detected in the VUV and in the visible and near UV spectral range. Highly resolved spectra are presented for the VUV (46-131 nm) and the near UV/visible (340-605 nm) spectral range. Absolute emission cross-sections have been determined for dissociative ionisation and excitation leading to fluorescence in the VUV. Results are compared with published data. Received 9 September 1999 and Received in final form 15 December 1999     

Absorption,excitation and fluorescence spectra of thallium activated cesium bromide

Absorption, excitation and fluorescence spectra of T1⁺ doped cesium bromide have been investigated at various thallium concentrations. At very low thallium concentration two absorption bands are obtained at 225 nm and 264 nm. With rise of thallium concentration additional absorption bands are obtained at 230, 244, 258, 270 and 285 nm. A single bell-shaped fluorescence band at 357 nm in the ultraviolet region is obtained at low thallium concentration. Two additional visible fluorescence bands appear at 440 and 540 nm with rise in thallium content. The excitation spectra for ultraviolet emission band and visible emission bands are found to be different. Accordingly the ultraviolet emission band is attributed to the characteristic A emission in T1⁺ ion and the visible bands are attributed to dimer centers havingD _4h site symmetry.     

Resonant interaction of femtosecond radiation with a cloud of cold <Superscript>87</Superscript>Rb atoms

The resonant interaction of ⁸⁷Rb atoms in a magneto-optical trap with femtosecond laser radiation in the spectral range 760–820 nm has been investigated experimentally. It has been demonstrated that femtosecond laser radiation with a spectral width of 10 nm interacts with an atomic ensemble as a set of spectrally narrow modes and as an ionizing laser field simultaneously. The dynamics of trap loading in the presence of ionization by femtosecond radiation has been studied, and the 5D _5/2 level population produced by an additional weak laser field has been measured.