Laser Spectroscopic Methods Research Articles

Laser spectroscopy of atoms in superfluid helium for the measurement of nuclear spins and electromagnetic moments of radioactive atoms

A new laser spectroscopic method named “OROCHI (Optical RI-atom Observation in Condensed Helium as Ion catcher)” has been developed for deriving the nuclear spins and electromagnetic moments of low-yield exotic nuclei. In this method, we observe atomic Zeeman and hyperfine structures using laser-radio-frequency/microwave double-resonance spectroscopy. In our previous works, double-resonance spectroscopy was performed successfully with laser-sputtered stable atoms including non-alkali Au atoms as well as alkali Rb and Cs atoms. Following these works, measurements with 84−87Rb energetic ion beams were carried out in the RIKEN projectile fragment separator (RIPS). In this paper, we report the present status of OROCHI and discuss its feasibility, especially for low-yield nuclei such as unstable Au isotopes.

Study of electronic absorption spectrum of hafnium monobromide molecule in the 550–800 nm region

The electronic absorption spectrum of the HfBr molecule in the 550–800 nm region is studied using the intracavity laser spectroscopy method. The HfBr molecules are produced in plasma formed during a pulse electric discharge in the vapor mixture of hafnium tetrabromide with hydrogen or ammonium. The discharge tube with the mixture is placed in a dye laser cavity. The spectrum recording is conducted with the help of a diffraction spectrograph (resolution power 240000). The high sensitivity of the intracavity method makes it possible to reveal the presence of twenty new bands in the HfBr spectrum with partially resolved rotational structure. By analogy with the HfCl spectrum, the HfBr bands are assigned to the 2Δ3/2–X2Δ3/2 transition. Analysis of the bands is conducted and molecular constants are determined for the ground and excited states:ωe'' = 255.07 cm–1, ωeωe''= 0.86 cm–1, ωe'= 238.31 cm–1, ωeωe'= 1.1 cm–1, B'' = 0.04251 cm–1, B' = 0.04025 cm–1.

Geographic and seasonal variation of dissolved methane and aerobic methane oxidation in Alaskan lakes

Abstract. Methanotrophic bacteria play an important role oxidizing a significant fraction of methane (CH4) produced in lakes. Aerobic CH4 oxidation depends mainly on lake CH4 and oxygen (O2) concentrations, in such a manner that higher MO rates are usually found at the oxic/anoxic interface, where both molecules are present. MO also depends on temperature, and via methanogenesis, on organic carbon input to lakes, including from thawing permafrost in thermokarst (thaw)-affected lakes. Given the large variability in these environmental factors, CH4 oxidation is expected to be subject to large seasonal and geographic variations, which have been scarcely reported in the literature. In the present study, we measured CH4 oxidation rates in 30 Alaskan lakes along a north-south latitudinal transect during winter and summer with a new field laser spectroscopy method. Additionally, we measured dissolved CH4 and O2 concentrations. We found that in the winter, aerobic CH4 oxidation was mainly controlled by the dissolved O2 concentration, while in the summer it was controlled primarily by the CH4 concentration, which was scarce compared to dissolved O2. The permafrost environment of the lakes was identified as another key factor. Thermokarst (thaw) lakes formed in yedoma-type permafrost had significantly higher CH4 oxidation rates compared to other thermokarst and non-thermokarst lakes formed in non-yedoma permafrost environments. As thermokarst lakes formed in yedoma-type permafrost have been identified to receive large quantities of terrestrial organic carbon from thaw and subsidence of the surrounding landscape into the lake, confirming the strong coupling between terrestrial and aquatic habitats and its influence on CH4 cycling.

Prospects for laser spectroscopy, ion chemistry and mobility measurements of superheavy elements in buffer-gas traps

Laser spectroscopic methods are reviewed which are of potential interest for the investigation of atomic and ionic level structures of superheavy elements. The latter are defined here as the trans-fermium elements with Z>100 for which no experimental atomic or ionic level structure information is known so far, and which cannot be bred in high flux nuclear power reactors via successive neutron capture. The principles of suitable laser spectroscopic methods are described, and illustrated by examples of real experiments. The addressed methods include single-ion spectroscopy in Paul traps, laser-induced fluorescence spectroscopy (LIF), radiation-detected optical pumping (RADOP), radioactive decay-detected resonance ionization spectroscopy (RADRIS), and ion-guide-detected resonance ionization spectroscopy (IGRIS). With the exception of the first all take advantage of a storage of the ions or atoms in so-called buffer-gas traps.The developed experimental methods can, in principle, also be employed for studying ion-chemical reactions with gas admixtures like O2 as well as for performing ion mobility measurements. Both provide complementary information on the electronic structure of superheavy ions. First attempts on this road of research are reviewed as well.

Measurement of the hyperfine splitting of 133Cs atoms in superfluid helium

We have been developing a new nuclear laser spectroscopy method named “OROCHI” (Optical RI-atom Observation in Condensed Helium as Ion-catcher). OROCHI utilizes superfluid helium (He II) not only as an efficient stopping medium of highly energetic ions but also as a host matrix of in-situ atomic laser spectroscopy. Using these characteristic of He II, we produce atomic spin polarization and measure Zeeman and hyperfine structure (HFS) splitting using laser-RF (radio frequency) / MW (microwave) double resonance method. From the measured energy splittings, we can deduce nuclear spins and moments. So far, we have conducted a series of experiments using both stable (85,87Rb, 133Cs, 197Au, 107,109Ag) and unstable isotopes (84,86Rb) to confirm the feasibility of OROCHI method, especially observing Zeeman resonance and determining nuclear spins. The measurement of HFS splitting of atoms introduced into He II is indispensable to clarify the nuclear properties by deducing nuclear moments as well as the study of nuclear spins. For this purpose, we perform a precision measurement of HFS of 133Cs atoms immersed in He II using laser ablation technique. In this paper, we describe the result of the experiment.

Application of R-ICOS laser spectroscopy technique for measurement of absorption in optically dense media

The integral R-ICOS method of three-beam diode laser spectroscopy allows extending the dynamic range of measurements of the absorption coefficient of particles in a medium compared to the conventional ICOS (CEAS) integral absorption technique in an external optical cell. The application of the method for optically dense media is discussed.

Applications of absorption spectroscopy using quantum cascade lasers.

Infrared laser absorption spectroscopy (LAS) is a promising modern technique for sensing trace gases with high sensitivity, selectivity, and high time resolution. Mid-infrared quantum cascade lasers, operating in a pulsed or continuous wave mode, have potential as spectroscopic sources because of their narrow linewidths, single mode operation, tunability, high output power, reliability, low power consumption, and compactness. This paper reviews some important developments in modern laser absorption spectroscopy based on the use of quantum cascade laser (QCL) sources. Among the various laser spectroscopic methods, this review is focused on selected absorption spectroscopy applications of QCLs, with particular emphasis on molecular spectroscopy, industrial process control, combustion diagnostics, and medical breath analysis.

Laser spectroscopy and chemometric study of the specific features of air exhaled by patients with lung cancer and chronic obstructive pulmonary disease

The specificity of exhaled air spectra in the range from 9.2 to 10.6 µm for patients with lung cancer and chronic obstructive pulmonary disease has been analyzed by laser spectroscopy and chemometrics methods. The informativeness of the absorption spectra of exhaled air is compared with that of clinical analysis data.

Laser spectroscopy methods for probing highly charged ions at GSI

We describe two opposite and partly complementary experimental approaches for performing high-precision laser spectroscopy of dipole-forbidden transitions in highly charged ions. We report on the wavelength determination of the ground state hyperfine transitions in hydrogen-like and lithium-like bismuth ions confined in the experimental storage ring at GSI. Direct comparison of the experimental results with theoretical predictions reveals an agreement of the specific hyperfine-structure splitting difference $\Delta ^{\prime }E$ within the 1- σ confidence interval of the experimental value. Additionally, we discuss an experimental strategy based on ion manipulation and cooling in a cylindrical open-endcap Penning trap to further increase the precision of the previous measurement. Trapping and laser cooling of external produced singly charged magnesium ions is demonstrated. This represents a first step towards sympathetic cooling of simultaneously confined ion species in order to perform laser spectroscopy measurements on highly charged ions nearly at rest. These measurements will offer new prospects in the field of laser-based tests of quantum electrodynamics in strong electric and magnetic fields.

Precision measurement of laser RF double resonance spectra with an effective compensation of residual magnetic field

We have been developing a novel laser spectroscopy method-“OROCHI” for radioisotopes trapped in superfluid helium. This new method is expected to determine nuclear spins and moments of exotic nuclei by precise measurement of Zeeman and hyperfine splitting of atoms using laser double resonance method. Its feasibility has been confirmed by means of a series of experiments with various stable atoms in superfluid helium, while the accuracy of experimental results is found strongly affected by external magnetic field. In order to obtain reliable and accurate results for atomic spectra with “OROCHI” method, based on laser RF double resonance spectroscopy of on-line experiment, we performed off-line test experiments for \(^{85,87}\)Rb in helium buffer gas. In this test experiment, we used three mutually orthogonal coils to effectively compensate for laboratory residual magnetic field and subsequently observed precise laser RF double resonance spectra of atoms which affords us accurate nuclear spin value. By comparison of those results, we could make clear the effect of residual magnetic field on experimental results. The details of “OROCHI” method and test experiments are presented.

Structure and Hydrogen-Bonding Ability of Estrogens Studied in the Gas Phase

The structures of estrogens (estrone(E1), β-estradiol(E2), and estriol(E3)) and their 1:1 hydrogen-bonded (hydrated) clusters with water formed in supersonic jets have been investigated by various laser spectroscopic methods and quantum chemical calculations. In the S1-S0 electronic spectra, all three species exhibit the band origin in the 35,050-35,200 cm(-1) region. By use of ultraviolet-ultraviolet hole-burning (UV-UV HB) spectroscopy, two conformers, four conformers, and eight conformers, arising from different orientation of OH group(s) in the A-ring and D-ring, are identified for estrone, β-estradiol, and estriol, respectively. The infrared-ultraviolet double-resonance (IR-UV DR) spectra in the OH stretching vibration are observed to discriminate different conformers of the D-ring OH for β-estradiol and estriol, and it is suggested that in estriol only the intramolecular hydrogen bonded conformer exists in the jet. For the 1:1 hydrated cluster of estrogens, the S1-S0 electronic transition energies are quite different depending on whether the water molecule is bound to A-ring OH or D-ring OH. It is found that the water molecule prefers to form an H-bond to the A-ring OH for estrone and β-estradiol due to the higher acidity of phenolic OH than that of the alcoholic OH. On the other hand, in estriol the water molecule prefers to be bound to the D-ring OH due to the formation of a stable ring-structure H-bonding network with two OH groups. Thus, the substitution of one hydroxyl group to the D-ring drastically changes the hydrogen-bonding preference of estrogens.

Laser Spectroscopy of Ba+ Ions in Liquid He: Towards the Detection of Majorana Fermion Surface State in Superfluid 3He-B

We propose an experimental technique that can be applied to search for the Majorana fermion surface state in superfluid 3He-B. Our proposal uses the electron spin of the Ba+ ion as a sensitive probe for the surface excitations, that can be manipulated and monitored by the methods of laser spectroscopy. We discuss the advantages and challenges of the proposed experimental approach and present the progress report of our project up to date.

Quantum Cascade Laser Spectrometry Techniques: A New Trend in Atmospheric Chemistry

Since the first demonstration in 1994, progress in the development of quantum cascade lasers (QCLs) has been breathtakingly rapid. Various techniques based upon novel QCLs have attracted much interest from researchers working in science and engineering disciplines (atmospheric environmental monitoring, chemical analysis, industrial process control, medical diagnostics, applications of life science, etc.) over the course of approximately the last two decades. Some background and recent advances in the development of QCLs are discussed together with a brief outline of a few representative atmospheric chemical species and their spectral features, as well as a short summary of terahertz-QCL. Among the various laser spectroscopic methods, the focus in this review is directed toward selected applications of QCL absorption spectroscopic techniques, which are commonly used to measure atmospheric trace gases, with particular emphasis on ground-based eddy covariance measurements, isotope measurements, and airborne-platform atmospheric measurements.

Collisional shift and broadening of the 2p-2sspectral lines in muonic helium ions

In connection with the recently proposed Lamb-shift experiments at Paul Scherrer Institute in ${\ensuremath{\mu}}^{\phantom{\rule{0.16em}{0ex}}4}{\mathrm{He}}^{+}$ and ${\ensuremath{\mu}}^{\phantom{\rule{0.16em}{0ex}}3}{\mathrm{He}}^{+}$ by using the laser-spectroscopy method, the pressure shift and width of the $2p$-$2s$ spectral lines in muonic-helium ions were studied in the present paper within the fully quantum-mechanical close-coupling approach. The calculations of the $S$ matrix as well as of the energy-dependent shift and width were made for collisional energies $E={10}^{\ensuremath{-}5}--1$ eV. The shift and width averaged over energy were obtained for target temperatures up to 350 K. It is shown that the fine-structure effect does not exceed a few percent. The isotopic effect is very small and can be neglected for the shift at $T\ensuremath{\ge}150$ K, contrary to the width, for which the isotopic effect becomes much more pronounced at $T\ensuremath{\ge}150$ K. At density $N=2.4145\ifmmode\times\else\texttimes\fi{}{10}^{18}$ atom/cm${}^{3}$ corresponding to the target pressure 100 mbar ($T=300$ K) the predicted values of the shifts are equal to 35 (50) MHz for ${\ensuremath{\mu}}^{\phantom{\rule{0.16em}{0ex}}3}{\mathrm{He}}^{+}$ and 33 (35) MHz for ${\ensuremath{\mu}}^{\phantom{\rule{0.16em}{0ex}}4}{\mathrm{He}}^{+}$ respectively for upper (lower) values of the $2p$-$2s$ energy-level separation. At the same conditions the values of the widths are equal to 2.4 (13.6) MHz for ${\ensuremath{\mu}}^{\phantom{\rule{0.16em}{0ex}}3}{\mathrm{He}}^{+}$ and 2.0 (3.0) MHz for ${\ensuremath{\mu}}^{\phantom{\rule{0.16em}{0ex}}4}{\mathrm{He}}^{+}$.

Case study: in vivo stress diagnostics by spectroscopic determination of the cutaneous carotenoid antioxidant concentration in midwives depending on shift work

Laser spectroscopic methods, for instance resonance Raman spectroscopy and reflectance spectroscopy, permit us for the first time to investigate the antioxidative status in human skin non-invasively by measurement of carotenoid concentration. The individual antioxidant concentration of the human skin is determined by the nutritional habits, on the one hand, and by stressors, such as shift work, on the other. Due to the disturbance of the circadian rhythm and melatonin secretion, shift work is associated with, inter alia, insomnia and gastrointestinal disorders. The study at hand was the first to determine the cutaneous antioxidant concentration of midwives using reflectance spectroscopy and to relate the results to shift work. Seven midwives took part in the study. An LED-based compact scanner system was used for non-invasive measurements of carotenoids in human skin. The measuring principle is based on reflection spectroscopy. The study at hand suggests that the cutaneous antioxidative status may be adversely affected by shift work. Despite numerous international strategies of programmes available which invite people to eat more healthily, there are only a few measures aiming at stress reduction and management. In this field the use of reflectance spectroscopic investigation methods could play an essential role in the future.

Novel nuclear laser spectroscopy method using superfluid helium for measurement of spins and moments of exotic nuclei

We have been developing a novel nuclear laser spectroscopy method “OROCHI” for determining spins and moments of exotic radioisotopes. In this method, we use superfluid helium as a stopping material of energetic radioisotope beams and then stopped radioisotope atoms are subjected to in situ laser spectroscopy in superfluid helium. To confirm the feasibility of this method for rare radioisotopes, we carried out a test experiment using a 85Rb beam. In this experiment, we have successfully measured the Zeeman resonance signals from the 85Rb atoms stopped in superfluid helium by laser-RF double resonance spectroscopy. This method is efficient for the measurement of spins and moments of more exotic nuclei.

The possibility of using femtosecond IR spectroscopy to determine the composition of molecules in the gas phase

The possibility of using one method of femtosecond laser spectroscopy, IR pump-probe, is considered for analyzing the molecular composition of gas. The measured intramolecular relaxation time of the vibrational energy is proposed as an individual characteristic of molecules. A number of compounds of different classes having the molecular chromophore group C=O are investigated. It is shown that the characteristic relaxation times of the corresponding analytical signals in the resonant exciting of C=O vibrations are significantly different for different molecules (ten or more), making it possible to identify molecules in mixtures by means of temporal selection. The linear dependence of the analytical signal on the vapor pressure of the investigated compounds and the energy fluence of the exciting radiation is revealed. It is shown that the analytical signal is not dependent on the pressure of the buffer gas (nitrogen) up to 1 atm.

The in-gas-jet laser ion source: Resonance ionization spectroscopy of radioactive atoms in supersonic gas jets

New approaches to perform efficient and selective step-wise resonance ionization spectroscopy (RIS) of radioactive atoms in different types of supersonic gas jets are proposed. This novel application results in a major expansion of the in-gas laser ionization and spectroscopy (IGLIS) method developed at KU Leuven. Implementation of resonance ionization in the supersonic gas jet allows to increase the spectral resolution by one order of magnitude in comparison with the currently performed in-gas-cell ionization spectroscopy. Properties of supersonic beams, obtained from the de Laval-, the spike-, and the free jet nozzles that are important for the reduction of the spectral line broadening mechanisms in cold and low density environments are discussed. Requirements for the laser radiation and for the vacuum pumping system are also examined. Finally, first results of high-resolution spectroscopy in the supersonic free jet are presented for the 327.4nm 3d104s 2S1/2→ 3d104p 2P1/2 transition in the stable 63Cu isotope using an amplified single mode laser radiation.

Increasing of the Signal-To-Noise Ratio in Precision Spectroscopy

Is considered the possibility of increasing the signal / noise ratio in one of the main methods of laser spectroscopy without Doppler broadening – the method of saturated absorption. The colliding beam of laser radiation in a multimode regime is expected to be used. Interaction of counter propagating modes with different frequencies will increase the number of gas atoms effectively interact with the field and, consequently, the value of a narrow resonance line shape. It is shown that the photon noise, which is essentially unavoidable, signal / noise ratio can be increased in a time where – the number of modes. For other noise (power fluctuations of the radiation, noise, photo detector, etc.) the magnitude of the signal / noise ratio may increase again

Laser Spectroscopic Study of Cold Host–Guest Complexes of Crown Ethers in the Gas Phase

A laser spectroscopic study on the structure and dynamics of cold host-guest inclusion complexes of crown ethers (CEs) with various neutral and ionic species in the gas phase is presented. The complexes with neutral guest species are formed by using supersonic free jets, and those with ionic species are generated with electrospray ionization combined with a cold 22-pole ion trap. For CEs, various sizes of 3n-crown-n ethers (n=4, 5, 6, and 8) and their benzene-substituted species are used. For the guest species, water, methanol, ammonia, acetylene, and phenol are employed as neutral guest species, and for charged guest species, alkali metal cations are chosen. The electronic and vibrational spectra of the complexes are measured by using various laser spectroscopic methods; electronic spectra for the neutral complexes are measured by laser-induced fluorescence. Discrimination of different species such as conformers is performed by ultraviolet-ultraviolet hole-burning spectroscopy. The vibrational spectra of selected species are observed by infrared-ultraviolet double-resonance (IR-UV DR) spectroscopy. For the ionic complexes, ultraviolet photodissociation and IR-UV DR spectroscopy are applied. The complex structures are determined by comparing the observed spectra with those of possible structures obtained by density functional theory calculations. How the host CEs change their conformation or which conformer prefers to form unique inclusion complexes are discussed. These results reveal the key interactions for forming special complexes leading to molecular recognition.