Laser Spectroscopic Methods Research Articles

Four-wave mixing spectroscopy of the photo-elastic scattering resonance in Nd:YVO4 crystal

A new method of non-linear laser spectroscopy based on four-wave scattering of pump laser radiation into the probe laser cavity is suggested and realized. As a result of intracavity amplification there is an opportunity to investigate weak narrow resonances of different types including the resonances of photo-elastic scattering in optical materials and laser crystals. A theory describing this phenomenon is suggested and experiments with narrowband (1 MHz linewidth) tunable continuous-wave diode laser were carried out. It is shown that the four-wave scattering of pump laser radiation into the cavity of the probe laser can be used for measurement of dispersion of photo-elastic constants in solid and liquid dielectrics.

Low-frequency spectroscopy of four-photon scattering in aqueous solutions of biopolymers

The novel method of nonlinear laser spectroscopy -- low frequency spectroscopy of four-photon scattering of laser radiation was applied to detect a considerable growth of ortho-H2O spin isomer and also H2O2 molecule concentration in a hydrate layer at the interface between water and DNA, denatured DNA molecules and alpha-chymotrypsin. Spectra of rotational resonances of ortho/para-H2O spin isomers were observed in aqueous solutions of different biopolymers and also in distilled water in the range from zero to 100 cm(-1) with the spectral resolution of 0.05-0.1 cm(-1). The fitting of four-wave mixing spectra shows notable growth of the H2O2 concentration and rotational line's amplitude by a factor of approximately 3 in DNA solutions due to denaturizing. Besides, we studied the four-photon scattering spectra of alpha-chymotrypsin aqueous solutions at protein concentrations between 0 and 20 mg/cm(3) in the range of +/- 7 cm(-1). We found that the velocity of sound in the protein aqueous solution measured by the shift of the Mandelstam-Brillouin scattering spectrum components was a cubic dependence on the protein concentration and reached the value of about 3000 m/s at 20 mg/cm(3).

Simultaneous fluorescence and breakdown spectroscopy of fresh and aging transformer oil immersed in paper using ArF excimer laser

HV transformers are taken into account as the heart of the power distribution system. The on-line monitoring based on the oil analysis offers a rapid diagnostic technique to detect the probable faults. In fact, the transformer malfunctions can be detected using UV laser spectroscopic methods. Here, a novel technique is presented based on simultaneous laser induced fluorescence (LIF) and laser induced breakdown (LIB) spectroscopy for hyper sensitive identification of the oil degradation. Oil is mainly degraded due to the internal transformer faults such as overheating and partial discharge. The spectroscopic characteristics of oil in paper substrate were obtained due to ArF laser irradiation. It was shown that the amplitude of fluorescence signal increases when the oil suffers aging and degradation. A couple of additional characteristic carbon and Hα emissions appear in the corresponding breakdown spectra too.

Structures of (3n-Crown-n)-Phenol (n = 4, 5, 6, 8) Host-Guest Complexes: Formation of a Uniquely Stable Complex for n = 6 via Collective Intermolecular Interaction.

Structures of crown-phenol 1:1 host-guest complexes, 3n-crown-n [12C4(n = 4), 15C5(n = 5), 18C6(n = 6), 24C8(n = 8)], in the gas phase have been studied by various laser spectroscopic methods. The S1-S0 electronic spectra identified 3, 2, 1, and 2 isomers for the complexes of 12C4, 15C5, 18C6, and 24C8, respectively, suggesting that only 18C6-phenol forms one uniquely stable complex. The IR spectra in the phenolic OH and CH stretch regions indicate that these complexes form the O···HO hydrogen bond, and the benzene ring is involved in the complex formation. Theoretical analysis with molecular mechanics and density functional theory calculations also supports one considerably stable isomer for 18C6-phenol. The most stable 18C6-phenol isomer is largely stabilized through collective intermolecular interaction consisting of O···HO hydrogen bond, CH···π, and O···HC(aromatic) so that phenol is inserted into the cavity of a particular conformation of 18C6 like a "lock and key".

Absolute frequency measurement for the emission transitions of molecular iodine in the 982 — 985 nm range

We report high-precision frequency measurements of the separate hyperfine structure (HFS) components of the emission B — X system transitions of 127I2 molecules in the 982 — 985 nm range. To resolve the HFS of the emission lines, advantage was taken of the method of three-level laser spectroscopy. The function of exciting radiation was fulfilled by the second harmonic of a cw Nd : YAG laser, and the probe radiation in the 968 — 998 nm range was generated by an external-cavity diode laser. The output Nd : YAG laser frequency was locked to an HFS component of theabsorption transition and the probing laser radiation to the emission transition component. When both frequencies were locked to HFS components with a common upper level, the output diode laser frequency was precisely equal to the emission transition frequency. The output frequency of the thus stabilised diode laser was measured with the help of a femtosecond optical frequency synthesiser based on a Ti : sapphire laser. We present the results of the absolute frequency measurements of 20 HFS components belonging to six vibrational — rotational transitions of the B — X system of iodine [R56(32 — 48)a1, P58(32 — 48)a1, P85(33 — 48)a1, R87(33 — 48a1, R88(33 — 48)a10] and all 15 components of the R86(33 — 48) line. The relative measurement uncertainty is equal to 7×10-10 and is determined by the frequency instability of the diode laser radiation.

A porewater-based stable isotope approach for the investigation of subsurface hydrological processes

Abstract. Predicting and understanding subsurface flowpaths is still a crucial issue in hydrological research. We present an experimental approach to reveal present and past subsurface flowpaths of water in the unsaturated and saturated zone. Two hillslopes in a humid mountainous catchment have been investigated. The H2O(liquid) – H2O(vapor) equilibration laser spectroscopy method was used to obtain high resolution δ2H vertical depth profiles of pore water at various points along two fall lines of a pasture hillslope in the southern Black Forest, Germany. The Porewater-based Stable Isotope Profile (PSIP) approach was developed to use the integrated information of several vertical depth profiles of deuterium along transects at the hillslope. Different shapes of depth profiles were observed in relation to hillslope position. The statistical variability (inter-quartile range and standard deviation) of each profile was used to characterize different types of depth profiles. The profiles upslope or with a weak affinity for saturation as indicated by a low topographic wetness index preserve the isotopic input signal by precipitation with a distinct seasonal variability. These observations indicate mainly vertical movement of soil water in the upper part of the hillslope before sampling. The profiles downslope or at locations with a strong affinity for saturation do not show a similar seasonal isotopic signal. The input signal is erased in the foothills and a large proportion of pore water samples are close to the isotopic values of δ2H in streamwater during base flow conditions indicating the importance of the groundwater component in the catchment. Near the stream indications for efficient mixing of water from lateral subsurface flow paths with vertical percolation are found.

Near IR TDLS study of HF first overtone line shape. I. Experimental results

The HF first overtone vibration-rotational absorption spectral line profile (the transition 0–2 R(0)) broadened by Ar (mixture HF: Ar = 1: 150, T = 295 K, P = 10−300 mm Hg) is studied by the method of near IR diode laser spectroscopy. A tunable distributed feedback fiber diode laser was used as a radiation source in a two-channel spectrometer (λ ∼ 1.284 μm, spectral tuning range Δν = 1.5−2.0 cm−1, the output radiation power is 15 mW, the spectral half-width of lasing lines is ∼ 5 MHz). The broadening and shifting coefficients of the considered HF line are determined, using traditional Voigt, Rautian, and Galatry spectral profiles.

包接錯体のレーザー分光

Laser spectroscopic study has been carried out for host-guest encapsulation complexes formed in supersonic jets and electrospray ionization cold 22 ion trap. The examined hosts include benzene-substituted 18-crown-6-ethers and calix[4]arene, and for the guest species rare gas atoms, neutral molecules and alkali metal cations have been chosen. Various laser spectroscopic methods are applied: for the neutral complexes the electronic spectra are observed by laser-induced fluorescence (LIF), mass-selected resonance enhanced multiphoton ionization (REMPI) and ultraviolet-ultraviolet hole-burning (UV-UV HB) spectroscopy. The vibrational spectra are observed by infrared-ultraviolet double resonance (IR-UV DR) and fragment detected infrared photodissociation (IRPD) spectroscopy. For the ionic complexes, ultraviolet photodissociation (UVPD) and IR-UV DR spectroscopy has been applied. The obtained results are analyzed by density functional theory and first principles electronic structure calculations. We discuss how the host molecule changes its conformation or which conformer is preferred for forming stable encapsulation complex as well as the key interactions, leading to the molecular recognition.

Laser spectroscopies for elemental and molecular analysis in art and archaeology

Spectroscopic methods using laser sources have significantly improved our capacity to unravel the chemical composition of works of art and archaeological remains. Lasers enhance the performance of spectroscopic techniques which require intense light sources and specific analytical protocols assuring a microanalytical approach for analysis has been established. This review focuses on laser spectroscopic methods used in the field of cultural heritage diagnostics. Emphasis in this work is given to the analytical capabilities of laser-based techniques for elemental and/or molecular analysis and in-situ use, spatial resolution and microanalysis. Analytical methods are classified according to the elemental (LIBS, LA–ICP–MS) and molecular (LIF/LIDAR, time-resolved absorption spectroscopy, laser desorption ionization mass spectrometry) information they yield. For non-destructive laser-induced fluorescence (LIF/LIDAR) and time-resolved fluorescence spectroscopy, imaging applications are described. The advantages provided by combined complementary techniques including but not limited to LIBS–LIF–Raman and LIBS–XRF are presented, as are recent improvements in terms of chemical imaging. Advances and applications of THz spectroscopy, non-linear spectroscopy and imaging are outlined. Finally, laser spectroscopies are described for investigations of different materials and works of art which include Bronze Age ceramics, Minoan archaeological remains, Ancient Roman buildings, Renaissance wall paintings and sculptures, and manuscripts containing iron gall inks and colorants.

Using the method of laser spectroscopy in the evaluation of the therapy effectiveness in patients with severe bronchial asthma

Because of the shortcomings of existing methods of assessment of inflammation activity in the airways, the method of laser optic-acoustic spectroscopy of patients expired air considered using for this purpose. This method can be used to indirectly evaluate the activity of inflammation in the airways and as an additional criterion for the effectiveness of basic treatment in patients with asthma.

Measurement of the absorption line profiles of water vapour isotopomers at 1.39 μm using the methods of diode laser spectroscopy

The issues related to high-precision measurement of the absorption line profiles of water vapour and its isotopomers using the methods of diode laser spectroscopy in the near IR range aimed at the analysis and detection of greenhouse gases are considered. The absorption line shape of H216O is investigated as a function of pressure of different buffer gases. The influence of the instrument function of the diode laser (DL) on the precision of measuring the line profile is studied. From fitting the profile of Doppler-broadened H216O absorption line to a model profile the lasing line width of the DL with a fibre pigtail is determined. The frequencies and intensities of absorption lines of water isotopomers H216O, H217O, H218O, and HDO are measured in the range of DL oscillation. Analytical spectral regions are chosen for distant probing of water vapour using an airborne lab.

Photon detection from stopped 87Rb atoms injected into superfluid helium for a new nuclear laser spectroscopy of rare radioisotopes

We have been developing a new nuclear laser spectroscopic method "OROCHI" for determining spins and moments of exotic RIs. This is a method based on the combination of superfluid helium as a stopper of radioactive isotope (RI) beam and in-situ laser spectroscopy of RI atoms. This unique method will enable us to measure nuclear spins and electromagnetic moments of extremely low yield RI (less than 1 particle per second). To confirm the feasibility of this method for rare radioisotopes, we carried out the first on-line experiment with a 87Rb beam, aiming at evaluating the minimum beam intensity required for the measurement. The LIF (Laser Induced Fluorescence) photons from the 87Rb atoms stopped in He II are successfully observed in the on-line experiment. The obtained LIF intensity is nearly consistent with the intensity calculated from the photo-absorption cross section of atoms in He II.

Isolated Monohydrates of a Model Peptide Chain: Effect of a First Water Molecule on the Secondary Structure of a Capped Phenylalanine

The formation of monohydrates of capped phenylalanine model peptides, CH(3)-CO-Phe-NH(2) and CH(3)-CO-Phe-NH-CH(3), in a supersonic expansion has been investigated using laser spectroscopy and quantum chemistry methods. Conformational distributions of the monohydrates have been revealed by IR/UV double-resonance spectroscopy and their structures assigned by comparison with DFT-D calculations. A careful analysis of the final hydrate distribution together with a detailed theoretical investigation of the potential energy surface of the monohydrates demonstrates that solvation occurs from the conformational distribution of the isolated peptide monomers. The distribution of the monohydrates appears to be strongly dependent on both the initial monomer conformation (extended or folded backbone) and the solvation site initially occupied by the water molecule. The solvation processes taking place during the cooling can be categorized as follows: (a) solvation without significant structural changes of the peptide, (b) solvation inducing significant distortions of the backbone but retaining the secondary structure, and (c) solvation triggering backbone isomerizations, leading to a modification of the peptide secondary structure. It is observed that solvation by a single water molecule can fold a β-strand into a γ-turn structure (type c) or induce a significant opening of a γ-turn characterized by an elongated C(7) hydrogen bond (type b). These structural changes can be considered as a first step toward the polyproline II condensed-phase structure, illustrating the role played by the very first water molecule in the solvation process.

Isotope-shift measurements of stable and short-lived lithium isotopes for nuclear-charge-radii determination

Changes in the mean square nuclear charge radii along the lithium isotopic chain were determined using a combination of precise isotope shift measurements and theoretical atomic structure calculations. Nuclear charge radii of light elements are of high interest due to the appearance of the nuclear halo phenomenon in this region of the nuclear chart. During the past years we have developed a laser spectroscopic approach to determine the charge radii of lithium isotopes which combines high sensitivity, speed, and accuracy to measure the extremely small field shift of an 8-ms-lifetime isotope with production rates on the order of only 10 000 atoms/s. The method was applied to all bound isotopes of lithium including the two-neutron halo isotope $^{11}\mathrm{Li}$ at the on-line isotope separators at GSI, Darmstadt, Germany, and at TRIUMF, Vancouver, Canada. We describe the laser spectroscopic method in detail, present updated and improved values from theory and experiment, and discuss the results.

Realtime Stable Isotope Monitoring of Natural Waters by Parallel-Flow Laser Spectroscopy

A parallel-flow H(2)O(liquid)-H(2)O(vapor) equilibration and laser spectroscopy method provides a new way to monitor the hydrogen and oxygen stable isotopic composition of water from rivers or lakes or in hydrologic tracer tests in real time. Two custom-built equilibrator devices and one commercial membrane device were tested to determine if they could be used to convert natural water samples (lakes, rivers, groundwater) to a H(2)O gas phase for continuous online δ(18)O and δD isotopic analysis by laser spectroscopy. Both the commercial minimodule device and the marble-filled equilibrator produced water vapor in isotopic equilibrium with the flowing liquid water, suggesting that unattended field measurement using these devices is possible. Oxygen isotope disequilibrium was indicated using the minimodule device at low temperatures.

Principle of remote control over the presence of dissolved gases in water media

We propose a method that allows one to carry out a remote estimation of small concentrations of gases dissolved in water at large depths. The method is based on modulation laser spectroscopy combined with the application of a fiber-optical communication line. We demonstrate specific features and advantages of the method of modulation laser spectroscopy for the spectral analysis in aqueous media with large attenuation. We develop the structural scheme of a measuring system, whose main components are a one-mode fiber-optical communication line, a laser diode with tuning frequency, and a gauge in the form of a hollow ellipsoidal mirror reflector. The principle of self-focusing of radiation in the gauge is considered. The expedience of the use of modulation laser spectroscopy and a measuring system in the solution of problems of the analysis of aqueous media is evaluated.

Observation of carbon and oxygen isotopic compositions of CO2 at an urban site in Nagoya using Mid-IR laser absorption spectroscopy

We report the application of Mid-IR laser spectroscopy to differentiation of CO 2 sources. High-frequency isotopic CO 2 measurements (δ 13 C and δ 18 O) in urban air in Nagoya allow for the contributions of anthropogenic and biogenic CO 2 sources to be differentiated. The laser spectroscopic method, using a Mid-IR quantum cascade laser, provides us with the advantage of higher temporal resolution of the data compared to traditional isotope ratio mass spectroscopy. The relative contribution of CO 2 sources in Nagoya was found to be roughly 0.42, 0.33 and 0.25 for natural combustion, gasoline combustion and biogenic respiration in the spring, but with large short-term (hourly) variations dependent on wind direction, and long-term variations dependent on heating demand and biological seasonality. ► Mid-IR laser spectroscopy was applied for differentiation of CO 2 sources in urban air. ► High-frequency isotopic CO 2 measurements (δ 13 C and δ 18 O) were performed. ► Relative contribution of CO 2 sources showed short-term and seasonal variations. ► Relative contribution of CO 2 sources changed in different atmospheric conditions. ► A quantum cascade laser was used for the Mid-IR laser spectroscopy.

High-sensitivity near-field laser microscopy

We propose a new method of laser spectroscopy, which combines high subwavelength space resolution, high sensitivity, and spectral resolution. The method is based on using a fiber laser near the generation threshold instead of a fiber optical near-field microscope. The near-field subwavelength aperture in the “active” fiber is employed for probing. Absorption on the objects under consideration (atoms, molecules, nanostructure, etc.) leads to the failure of oscillations in the fiber laser. We make a computer simulation of the system under consideration and analyze the method’s sensitivity.

ChemInform Abstract: High Resolution Spectroscopy Below the Doppler Width

Microscopic insights into elementary molecular processes are only feasible through the observation of unique quantum states and the study of their couplings and time-dependent behavior. In the case of larger chemically relevant molecules, the corresponding transitions lie so close that they mostly overlap and lead to band structures. For example, electronic band spectra of large molecules cannot be resolved into single lines even by high resolution UV-spectrometers. The reason for this is the Doppler broadening, arising from the random velocity of the molecules in the gas phase. In this article, we want to demonstrate that modern laser spectroscopic methods make it possible to overcome this “Doppler barrier” and to resolve the line structure in band spectra. The selective excitation of unique quantum states yields precise information on the mechanisms responsible for energy redistribution in molecules. Energy redistribution processes represent a crucial first step preceding chemical reactions, which they influence decisively. Very high resolution spectroscopy elucidates the influence of molecular rotation on the energy redistribution. Through Coriolis forces in rotating molecules, vibrations can couple, causing a flow of energy from the selectively excited vibrations to the many other vibrational degrees of freedom. Weak interactions, namely van der Waals interactions and hydrogen bonding, determine the structure of large molecules (biomolecules) and supermolecular systems. Weak intermolecular interactions, given their selectively resolved quantum states, can be analyzed and understood at the microscopic level. “Doppler-free spectroscopy” with its resulting line spectra furnishes information on the structure, including bond lengths, of van der Waals complexes. With this information, Doppler-free spectroscopy provides the model parameters indispensable for the quantitative description of complex systems.

Laser spectroscopy of Ag and Au atoms immersed in superfluid helium and its applications to investigate nuclear structures

We have been developing a new nuclear laser spectroscopic method “OROCHI” for determining spins and moments of exotic RIs. It is the method based on the combination of superfluid helium as a stopper of radioactive isotope (RI) beam and in situ laser spectroscopy of RI atoms. This unique method will enable us to measure nuclear spins and electromagnetic moments of extremely low yield RI (less than 1 particle per second). For applying this method to stable Ag and Au isotopes, we have measured optical absorption spectra of these elements. Optical pumping of those atoms has also been attempted with pumping lasers tuned to the measured absorption lines. Details of this laser spectroscopy method in He II “OROCHI” and the development for applying OROCHI to Ag and Au atoms are presented.