Frequency-doubled Dye Laser Research Articles

One-dimensional energy transfer in GdCl3

We report the observation of the intrinsic fluorescence of anydrous gadolinium trichloride GdCl3 when laser light is absorbed into the first excited state 6P7/2. With the aid of a frequency doubled pulsed dye laser, we are able to analyze carefully the excitation and emission spectra as well as the decay times over a range of temperatures including that at which the material undergoes a ferromagnetic transition at 2.2 K. At 4.4 K and above, experiments at low excitation density (N0<1014 excited ions/cm3) show that the intrinsic and the impurity induced trap fluorescence dynamics are well described in terms of a fast diffusion and trapping model. When the excitation density is increased anti-Stokes fluorescences appear efficiently; they are assigned to the 6D9/2, 6I7/2→8S7/2 transitions. High excitation density effect on the intrinsic decay as well as the decay of the anti-Stokes fluorescence are nicely reproduced by a theoretical model involving mainly an exciton–exciton annihilation process. Moreover, an excited state absorption mechanism contributes notably to the anti-Stokes fluorescence intensity at t=0 with increasing the excitation density. In the ferromagnetic phase of GdCl3, at 1.5 K, the one-dimensional nature of the exciton diffusion (8S7/2↔6P7/2) is confirmed by the ‘‘incoherent’’ exciton decay analysis using an appropriate model recently developed by Cibert et al. Finally a diffusion length spreading over 2500 visited Gd3+ normal sites is evaluated, knowing the hopping time as a function of the nearest neighbor interactions (nn) in the crude approximation of an ideal two level system in a linear chain of atoms.

Comparative photon statistics of several ultraviolet laser systems determined by transient two-photon absorption

The photon statistics of several different laser systems operating at 226 nm are probed by measuring absolutely the fluorescence following two-photon absorption in atomic oxygen. The integrated fluorescence, obtained by scanning the laser frequency through the two-photon resonance, is theoretically shown to be proportional to G(2) (0) σ0(2). The second-order intensity-correlation function at time zero, G(2)(0), characterizes the laser, and σ0(2) is a fundamental atomic property. Measurement of the integrated fluorescence permits determination of the relative value of G(2) (0) for each laser. The assumption that G(2)(0) = 1 for one of the lasers, a single-frequency source, allows G(2)(0) for the other lasers to be placed on an absolute scale. The values thereby obtained range from 0.8 ± 0.2 to 3.2 ± 0.4. Different values are obtained when the radiation is generated by frequency mixing or Raman shifting of the same frequency-doubled visible dye laser, suggesting that frequency-conversion processes have a significant effect on G(2)(0).

Laser-induced fluorescence of the B1Π- X1Σ + band system of the isotopic lithium hydrides

Resonance fluorescence series in the B 1Π- X 1Σ + band system of the isotopic lithium hydrides were observed for the first time. Six series of 7LiD and eight of 6LiH were excited by a frequency-doubled dye laser pumped by a frequency-doubled YAG laser. These observations have provided experimental data to compare with previous theoretical transition probabilities (W. T. Zemke, K. R. Way, and W. C. Stawalley, J. Chem. Phys. 69, 402–408 (1978)). Excellent correspondences between the observed fluorescence intensities and the theoretical results have been realized.

Stark-effect studies in xenon autoionizing Rydberg states using a tunable extreme-ultraviolet laser source.

The Stark spectra of autoionizing Rydberg states of Xe converging to the second ionization limit 5${p}^{5}$ $^{2}P_{1/2}$ have been investigated as a function of applied electric field over the range 26--2362 V/cm. Single-photon excitation from the Xe ground state was achieved using coherent radiation near 92.5 nm, generated by frequency tripling the pulsed output of a frequency-doubled dye laser in a free jet of rare-gas atoms. For the lowest electric field only the ns' and nd' series were observed. As the electric field was increased the np' series appeared because of the mixing of wave functions with different l values. Further increase of the electric field caused the appearance of hydrogenlike Stark manifolds. The Stark spectrum was simulated in a two-step procedure with no adjustable parameters. Using a jl-coupling basis set the Hamiltonian matrix was diagonalized to determine the energy levels and corresponding eigenfunctions for a given electric field strength. The intensities and line shapes were then calculated using the formalism developed by Fano for a many-discrete-level--single-continuum configuration interaction. This treatment was sufficient to reproduce the positions, widths, and shapes of most observed features. At field strengths between 1000 and 2000 V/cm, however, an additional modulation structure with a spacing of about 2.7 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ appeared on top of the \ensuremath{\Vert}M\ensuremath{\Vert}=1 autoionizing resonances, which could not be explained by our simple theoretical model.

Frequency-domain measurements of the rotational dynamics of the tyrosine groups of calmodulin.

We used frequency-domain fluorometry to determine the intensity and anisotropy decay kinetics of tyrosine residues in calmodulin and its fragments. Excitation was provided by a continuous ultraviolet laser source, a frequency-doubled rhodamine 6G ring dye laser, whose output was externally modulated to 200 MHz. Both the intensity and anisotropy decays were found to be multiexponential and dependent upon temperature and solution conditions. By examination of calmodulin fragments we determined that energy transfer between the two tyrosine residues reduces the steady-state anisotropy values by about 20%. Additionally, the frequency-domain anisotropy decays indicate local torsional motions of the tyrosine residues, as well as significant individual motions of the two domains of calmodulin.

Distribution of beryllium concentrations and fluxes in the Tokamak UNITOR

The use of beryllium as a wall and limiter material is investigated in the small Tokamak UNITOR. The transport of neutral and ionized beryllium released from poloidal limiter is studied both experimentally and numerically. The numerical simulation is based on an impurity transport algorithm in cylindrical geometry. It comprises anomalous diffusion as well as ionization; recombination via charge exchange processes is included for highly ionized beryllium atoms. The code yields the spatial distribution of the various ionization states with densities up to 4% of the electron density ne and fluxes up to 1019 m-2s-1. The contribution of beryllium to Zeff is evaluated to be well below 1. The spatial and temporal distribution of neutral beryllium is measured by laser induced fluorescence. For this purpose, the Be I resonance line at 234.9 nm is pumped by a frequency doubled dye laser. These measurements yield the densities as well as the fluxes of neutral beryllium released from the limiter. The experimental results reveal that besides sputtering additional erosion mechanisms are of importance.

Attaining the wavelength range 189?197 nm by frequency mixing in?-BaB2O4

Wavelengths in the range from 188.9 to 197 nm have been obtained by type-I sum frequency generation (SFG) in β-BaB2O4. The fundamental beams were supplied by pulsed dye lasers one of which tuned between 780 and 950 nm and the other frequency-doubled at 497 nm. The possibility of shifting the excimer wavelength 248.5 nm to the excimer wavelength 193 nm has been demonstrated, replacing the frequency-doubled dye laser by KrF excimer lasers of different beam properties.

Quenching of the translationally hot and thermalized NH(c 1Π) radicals by HN 3

The cross section for the quenching of NH(c 1Π, ν = 0) by HN 3 was measured by using a pulsed laser technique. A single rotational level of NH(c 1Π, ν = 0) was formed by exciting NH(a 1Δ, ν = 0) with a frequency doubled dye laser. NH(a 1Δ) was produced by photolyzing HN 3 with a XeCl excimer laser. The time profiles of the NH(c-a) fluorescence were measured at various pressures of HN 3. Experiments were performed both in the presence and in the absence of He buffer gas. In the absence of He, the NH radicals were found to be translationally hot; the average velocity was 3800±600 m s −1. The quenching cross sections for the translationally hot and thermalized NH(c) radicals by HN 3 were determined to be (28±5) × 10 −16 and (85±3) × 10 −16 cm 2, respectively. No rotational level dependence could be observed in the quenching of the hot NH(c) radicals.

On the intercombination line 4s 24p 2 P-4s4p 2 4 P in the spectrum of neutral gallium

Hyperfine structure and natural radiative lifetimes have been measured of different components of the intercombination transition in the Ga I spectrum. The gallium atoms, in an atomic beam, are excited by the light of a frequency doubled pulsed dye laser and observed by their fluorescent light. The lifetimes and the hfs are observed and compared with the corresponding transitions in indium. A theoretical interpretation using Cowan's code is given.

Laser excitation of the muonium 1S-2S transition.

We present evidence for the excitation of the two-photon Doppler-free $1S\ensuremath{-}2S$ transition in muonium. Thermal muonium atoms were produced in vacuum by a 27.5-MeV/c pulsed positive-muon beam incident on a powdered Si${\mathrm{O}}_{2}$ target. Transitions were induced by the light from a frequency-doubled pulsed dye laser and were detected by photoionization of the $2S$ state. The $1S(F=1)\ensuremath{\rightarrow}2S(F=1)$ transition frequency is within 300 MHz of the QED prediction.

Atomic arsenic detection by ArF laser-induced fluorescence

Arsenic atoms sputtered from gallium arsenide wafers or arsenic-doped n-type silicon wafers have been detected in argon plasmas using the laser-induced fluorescence technique (LIF). Two methods of LIF detection were employed. One used a tunable, frequency-doubled dye laser to pump a metastable transition of atomic arsenic at 228.81 nm. The second technique used the broadband output of an ArF excimer laser to pump a ground-state transition of As at 193.76 nm.

Isotope shift and hyperfine structure of stable platinum isotopes

Isotope shift (IS) and hyperfine structure (hfs) measurements have been performed on seven lines of the platinum I spectrum with interference as well as laser fluorescence spectroscopy. In the latter case a frequency-doubled single-mode cw dye laser was applied. The IS of190Pt with a natural abundance of only 0.01% was determined to beδν 190, 192=−38.65(8) mK in theλ306.47 nm transition. The IS parameters and the effective hfs integrals in the configuration (5d+6s)10 were determined in intermediate coupling by a least squares fit of the IS and hfs data with eigenvectors obtained from the platinum fine structure (fs). The results are compared with theoretical values and yield improvedδ〈r 2〉 data.

Generation of 50 ps 308 nm pulses by means of truncated stimulated brillouin scattering

A frequency doubled dye laser system, incorporating a single longitudinal mode oscillator, followed by a single stage XeCl amplifier has yielded truncated stimulated Brillouin scattering (TRUBS) pulses of ≈50 ps duration and is potentially capable of providing significantly shorter pulses.

Shock-tube study of pressure broadening of the A2∑ + - X2Π (0,0) band of OH by Ar and N 2

A rapid-tuning, frequency-doubled ring dye laser was used to make fully-resolved lineshape measurements of OH generated behind reflected shock waves in H 2-O 2-Ar and H 2-O 2-N 2 mixtures. Values of the collisional linewidth were deduced by fitting the observed lineshapes to Voigt profiles. Lines corresponding to transitions with lower-state rotational quantum numbers ranging from 1.5 to 17.5 in the A 2∑ + - X 2Π (0,0) band near 307 nm were probed in order to evaluate a possible J″-dependence in the observed broadening. The temperature range investigated was 1400–4100 K. The collisional broadening parameter, 2γ, was measured at fixed temperature and did not exhibit a strong dependence on the rotational quantum number for either Ar or N 2. The temperature dependence of 2γ for specific J″-values was measured and fit to a power law with an average value of the temperature exponent of 0.8 for both species.

Three exponential fluorescence decay of horse liver alcohol dehydrogenase revealed by iodide quenching.

Abstract— The time resolved fluorescence decay of horse liver alcohol dehydrogenase was measured using a frequency doubled picosecond dye laser and time‐correlated single‐photon counting detection. A flow‐cell technique is described which eliminates the photodegradation artifacts which commonly occur with laser excitation. A procedure is introduced which uses fluorescence quenching to reveal minor fluorescence lifetime components. The decay of the unquenched tryptophanyl fluorescence could be described by a double exponential decay law, but experiments conducted in the presence of iodide ion showed that the fluorescence decay must be more complex than this. A model is presented in which the fluorescence decay consists of three exponential components, only two of which are susceptible to quenching by iodide ion. Several possibilities are presented for the origin of this minor decay component, the most reasonable of which is that it arises from conformational heterogeneity in the solvent‐exposed tryptophanyl residue.

Conformational dynamics of the anticodon loop in yeast tRNAPhe as sensed by the fluorescence of wybutine

Conformational and dynamic properties of the anticodon loop of yeast tRNAPhe were investigated by analyzing the time resolved fluorescence of wybutine serving as a local structural probe adjacent to the anticodon GmAA on its 3' side. The influence of Mg2+, important for stabilizing the tertiary structure of tRNA, and of the complementary anticodon s2UUC of E. coli tRNA2Glu were investigated. Fluorescence lifetimes and anisotropies were measured with ps time resolution using time correlated single photon counting and a mode locked synchronously pumped and frequency doubled dye laser as excitation source. From the analysis of lifetimes (tau) and rotational relaxation times (tau R) we conclude that wybutine occurs in various structural states: one stacked conformation where the base has no free mobility and the only rotational motion reflects the mobility of the whole tRNA molecule (tau = 6 ns, tau R = 19 ns), an unstacked conformation where the base can freely rotate (tau = 100 ps, tau R = 370 ps) and an intermediary state (tau = 2 ns, tau R = 1.6 ns). Under biological conditions, i.e. in the presence of Mg2+ and neutral salts, wybutine is found in a stacked and immobile state which is consistent with the crystallographic picture. In the presence of the complementary codon however, as exemplified by the E. coli-tRNA2Glu anticodon, our analysis indicates that the codon-anticodon complex exists in an equilibrium of structural states with different rotational mobility of wybutine. The conformation with wybutine freely mobile is the predominant one and suggests that this conformation of the codon-anticodon structure differs from the canonical 3'-5' stack.

Two-photon spectra of TlCl

Two-photon spectra with UV radiation from a frequency-doubled pulsed dye laser were recorded for TlCl. A new high-lying electronic state was identified which has symmetry 0 + and predissociates strongly to give the atomic state 7s 2S 1 2 of Tl. The line positions of the two-photon transitions are determined by the fine structure of the known AX transition, showing that the two-photon process is stepwise with the state A as a real intermediate. The fine structure due to the new state E0 + shows up by the envelope of the recorded spectrum. A model to extract this information out of the structure of the observed spectrum is presented. Finally, superfluorescence was observed on most of the molecular two-photon transitions giving the green light of the atomic transition 7s 2S 1 2 → 6p 2P 3 2 of Tl. Our observed resonance structure of exciting the superfluorescence should be included in describing photodissociation lasers such as of T1I.

Lifetime measurements of selectively excited rovibronic levels of SO2

With a frequency doubled single mode cw dye laser, pulse modulated with a Pockels cell, lifetimes of selectively excited rovibronic levels of SO2 molecules in a collimated molecular beam have been measured. Under collision-free conditions single exponential decay curves were found for all observed levels. Their radiative lifetimes scatter considerably for the different levels. For the Clements band ‘‘E’’ a mean unperturbed lifetime of about 8 μs was found while for the band at λ=322.6 nm the average lifetime was 30 μs. Possible perturbations are discussed and experimental evidence is given which explains the causes of the greatly differing lifetimes.

Laser spectroscopy of perturbed states of BaO in the region above 32 000 cm−1

The excitation spectrum of BaO in the region above 32 000 cm −1 was investigated with a frequency-doubled pulsed dye laser. We have observed fully developed rotational structures of the C 1 Σ + - X 1 Σ + transition. The analysis of the vibrational states v ′ = 0 through 7 leads to a large number of perturbations. This spectroscopic information in combination with the observation and rotational analysis of transitions to several new electronic states allows a systematic summary, which gives more than eight electronic states in the investigated region. Besides the known states B , C , D and c , we find four new bound states, designated by E , F , G , and H . For all states molecular constants are given. The discussion of possible molecular electron configurations leads to classifications of the molecular electronic states. Our results on the vibrational levels v ′ = 0 to 3 are in reasonable agreement to the optical-optical double resonance work of R. A. Gottscho, P. S. Weiss, and R. W. Field [ J. Mol. Spectrosc. 82 , 283–309 (1980)], but show several new details.

Vibronic band structure in the 270–330 nm photodissociation spectrum of (CO)+2

The photodissociation spectrum (CO)+2 →hν CO++CO has been obtained in the near UV from 270–330 nm at 300 K in a fast flow reactor. Mass selected CO+ photofragments are detected following excitation with a frequency doubled pulsed dye laser. The spectrum exhibits a long progression of predissociative vibronic bands spaced by 475±20 cm−1, in contrast to the unstructured visible spectra of other dimer cations. Preliminary ab initio SCF calculations can qualitatively explain the unusual transparency of (CO)+2 in the visible.