High-resolution Diode Laser Spectroscopy Research Articles

Zeeman Effect of Sm Atoms by High-Resolution Diode-Laser Spectroscopy

High-resolution atomic-beam diode-laser spectroscopy in Sm I has been performed. Zeeman spectra have been measured for the three optical transitions at different external magnetic fields and well resolved at the magnetic fields of stronger than 6.0 mT. Using the known precise Landé -factors of the ground multiplet, the Landé -factors of the upper 4f66s6p   and levels have been determined, and their precision has been improved compared with the reference values.

Pore size assessment based on wall collision broadening of spectral lines of confined gas: experiments on strongly scattering nanoporous ceramics with fine-tuned pore sizes

Wall collision broadening of absorption lines of gases confined in porous media is a recently opened domain of high-resolution spectroscopy. Here, we present an experimental investigation of its application for pore size assessment. We report on the manufacturing of nanoporous zirconia ceramics with well-defined pore sizes fine-tuned from 50 to 150 nm. The resulting pore structure is characterized using mercury intrusion porosimetry, and the optical properties of these strongly scattering materials are measured using femtosecond photon time-of-flight spectroscopy (transport mean free paths found to be tuned from 2.3 to 1.2 μm as the pore size increase). Wall collision line broadening is studied by performing near-infrared (760 nm) high-resolution diode laser spectroscopy of confined oxygen molecules. A simple method for quantitative estimation of the pore size is outlined and shown to produce results in agreement with mercury intrusion porosimetry. At the same time, the need for improved understanding of wall collision broadening is emphasized.

Wall-collision line broadening of molecular oxygen within nanoporous materials

Wall-collision broadening of near-infrared absorption lines of molecular oxygen confined in nanoporous zirconia is studied by employing high-resolution diode-laser spectroscopy. The broadening is studied for pores of different sizes under a range of pressures, providing new insights on how wall collisions and intermolecular collisions influence the total spectroscopic line profile. The pressure series show that wall-collision broadening is relatively more prominent under reduced pressures, enabling sensitive means to probe pore sizes of porous materials. In addition, we show that the total wall-collision-broadened profile strongly deviates from a Voigt profile and that wall-collision broadening exhibits an additive-like behavior to the pressure and Doppler broadening.

Non-equilibrium thermodynamics of the gas–liquid interface: measurement of the Onsager heat of transport for nitrous oxide at the surface of water

The Onsager heat of transport, Q*, for nitrous oxide at the surface of water has been measured by using high-resolution diode-laser spectroscopy to monitor the partial pressure of N2O as a function of the temperature difference across a 5-mm vapour gap above the water surface. The metal surface above the vapour gap was conditioned with ammonia prior to the measurements, to enable efficient thermal accommodation at that surface, which allowed the temperature difference to be as large as 15 K. We find Q* = –6.6 ± 0.85 kJ mol–1, so that Q*/RT is –2.9 at T = 275.15 K. These experiments are a necessary preliminary to a planned series of measurements of Q* for CO2 at the surface of simulated sea water.

Line strength and collisional broadening studies of hydrogen sulphide in the 1.58 μm region using diode laser spectroscopy

High resolution diode laser spectroscopy has been applied to the detection of hydrogen sulphide at ppm levels utilizing different transitions within the region of the ν1 + ν2 + ν3 and 2ν1 + ν2 combination bands around 1.58 µm. Suitable lines in this spectral region have been identified, and absolute absorption cross sections have been determined through single-pass absorption spectroscopy and confirmed in the Doppler linewidth regime using cav- ity enhanced absorption spectroscopy (CEAS). The desire for a sensitive system potentially applicable to H2S sens- ing at atmospheric pressure has led to an investigation on suitable transitions using wavelength modulation spec- troscopy (WMS). The set-up sensitivity has been calculated as 1.73 × 10 −8 cm −1 s 1/2 , and probing the strongest line at 1576.29 nm a minimum detectable concentration of 700 ppb under atmospheric conditions has been achieved. Further- more, pressure broadening coefficients for a variety of buffer gasses have been measured and correlated to the intermolec- ular potentials governing the collision process; the H2S-H2S dimer well depth is estimated to be 7.06 ± 0.09 kJ mol −1 .

Temperature dependence of pressure broadening and shifts of acetylene at 1550 nm by He, Ne, and Ar

Pressure broadening and shift coefficients for the ν1+ν3 band of 12C2H2 have been measured for He, Ne, and Ar at a temperature of 195 K using high resolution diode laser spectroscopy. The pressure broadening and shifts follow patterns with rotational assignment that are similar to those at room temperature but are generally larger in magnitude. The change in magnitude is qualitatively described by assuming, for each transition, a constant cross section for pressure broadening or shifting. Better agreement may be obtained for pressure broadening coefficients by using empirically determined temperature exponents; better agreement still is obtained from close coupling calculations of the pressure broadening cross sections.

Characterization of the supersonic expansion in the vacuum interface of an inductively coupled plasma mass spectrometer by high-resolution diode laser spectroscopy

The supersonic expansion in the first vacuum stage of an inductively coupled plasma mass spectrometer has been characterized by laser-induced fluorescence of metastable argon atoms in the expansion. Atom velocities and temperatures were determined from Doppler shifts and linewidths, respectively, in the excitation spectra of the argon atoms. Shock structures characteristic of a supersonic expansion, the barrel shock and the Mach disk, were manifest as bimodal velocity distributions. The terminal velocities reached by the atoms were characteristic of conditions in the plasma source upstream from the entrance to the vacuum interface.

Helium- and argon-broadening coefficients of phosphine lines in the ν2 and ν4 bands

Pressure broadening of phosphine lines by helium and argon at room temperature has been experimentally investigated by high-resolution diode-laser spectroscopy. The broadening coefficients are measured for 38 transitions of PH 3 in the Q R branch of the ν 2 band and in the P P and R P branches of the ν 4 band. The recorded lines with J values ranging from 3 to 14 and K from 0 to 10 are located between 1062 and 1094 cm −1. The retrieval of the collisional widths is carried out by fitting each spectral line with a Voigt profile, a Rautian profile and a speed-dependent Rautian profile. The latter model provides larger broadening coefficients than the Voigt model. They are also calculated on the basis of a semiclassical model involving the atom–atom Lennard–Jones potential. The theoretical results are in reasonable agreement with the experimental data and reproduce the J and K dependencies of the broadenings.

Measurement of the Hyperfine Structure and Zeeman Shift in Y I by High-Resolution Diode-Laser Spectroscopy

High-resolution laser spectroscopy has been performed using a tunable diode laser to measure the hyperfine structure (hfs) and Zeeman shift of two transitions in Y I. The hfs constants A of 89Y were determined for the 4d5s22D3/2 and 2D5/2 levels, and 4d5s5p4F3/2 and 4F5/2 levels; the A values of the 4F3/2 and 4F5/2 were determined for the first time. Using circular polarizations, the Zeeman spectra were selectively measured and the g factors were determined for the 4d5s5p4F3/2 and 4F5/2 levels.

Photo-acoustic measurements of gas and aerosol absorption with diode lasers

The results of designing multipurpose high-sensitive photo-acoustic (PA) detectors and their application to high-resolution diode laser spectroscopy of molecular gases, gas analysis, and aerosol absorption measurements are summarized in this paper. The hardware and software of the diode laser spectrometer with a Helmholtz resonant PA detector providing an absorption sensitivity limit of better than 10 −7 W m −1 Hz −1/2 are described. A procedure is proposed for an experiment involving the measurements of the rotational structure of hot vibrational bands of molecules. The results of the application of the nonresonant PA cell with temporal resolution of signals to measurements of weak nonresonant absorption of gases and soot aerosols are presented, and the possibility of creating a broad-band PA laser diode aerosol-meter is discussed.

Measurements of the Hyperfine Structure and ΔF=+2 Transitions in Eu I by High-Resolution Diode-Laser Spectroscopy

High-resolution atomic-beam laser spectroscopy in Eu I has been performed using a tunable diode laser. The hyperfine structure (hfs) and isotope shift of the 4 f 7 6 s 2 8 S 7/2 –4 f 7 6 s 6 p 10 P 9/2 transition at 686.45 nm have been measured. The hfs constants A and B of 151 Eu and 153 Eu have been determined for the upper state 4 f 7 6 s 6 p 10 P 9/2 , and the hyperfine anomaly has been derived. The Δ F =+2 transitions, normally forbidden, have been induced by applying a magnetic field of approximately 1 G. Their intensity dependences on the magnetic field strength and on the hfs splittings agreed with the first-order perturbation theory, which considers the mixing between the closely lying hfs levels in the ground state.

Results of small-signal gain measurements on a supersonic chemical oxygen iodine laser with an advanced nozzle bank

High-resolution diode laser spectroscopy has been used to probe the gain in the active medium formed by an advanced supersonic chemical oxygen iodine laser (COIL), ejector nozzle bank. The probe beam was directed through the medium at 90/spl deg/ (normal) to the flow velocity and at an angle of 27.5/spl deg/ away from normal incidence. Analysis of the small-signal gain spectrum allowed for the determination of the gain, average gas velocity, static pressure, and temperature. The dependence of gain, temperature, and gas velocity on the primary nitrogen molar flow rate and basic hydrogen peroxide temperature was obtained. A maximum small-signal gain of 7 /spl times/ 10/sup -3/ cm/sup -1/, average gas velocity of 575 m/s, static temperature of 172 K were measured for flow rates of 270 mmole/s of primary nitrogen, 39.2 mmole/s of chlorine, 11 mmole/s of secondary nitrogen, and 0.8 mmole/s of iodine. Estimation of the static pressure in the flow core from spectroscopic data is very close to the static sidewall pressure. The role of transverse velocity components in the gas flow and their effect on the interpretation of gain profiles is discussed.

Amplification and gas-dynamic parameters of the active oxygen—iodine medium produced by an ejector nozzle unit

The gain, the temperature, and the absolute velocity of the supersonic active oxygen—iodine medium produced by an ejector nozzle unit were determined by the technique of high-resolution diode laser spectroscopy. The gain in the active medium is formed at less than 44 mm from the nozzle unit for an absolute flow velocity ν ≈ 600 m s-1. Upon dilution of oxygen by primary nitrogen in the ratio of 1 : 6.9, the gain of the active medium amounts to 7×10-3 cm-1, the temperature of the active medium to 200 K, the absolute flow velocity to 580 m s-1, and the pressure to 58 Torr. As the dilution is increased to 1 : 13.5, the gain reduces to 4.5×10-3 cm-1, the temperature lowers to 180 K, the velocity of the active medium increases to 615 m s-1, and the pressure increases to 88 Torr. The increase in the initial content of water vapour in the oxygen flow results in an increase in the temperature and a decrease in the gain of the active medium.

Specific Mass Shift in Gd I and Dy I

High-resolution diode-laser spectroscopy has been performed on atomic beams of natural Gd and Dy. Isotope shifts of the even-mass isotopes have been measured for two transitions in Gd I and one transition in Dy I. Specific mass shifts, as well as field shifts, have been derived for transitions of 4 f 7 5 d 6 s 2 –4 f 7 6 s 2 6 p in Gd I, and 4 f 10 6 s 2 –4 f 9 5 d 6 s 2 in Dy I; the specific mass shift is much larger than the normal mass shift. It has been found that the specific mass shift of the 4 f 10 6 s 2 –4 f 9 5 d 6 s 2 transition in Dy I is about one order of magnitude larger than that of the 4 f 7 5 d 6 s 2 –4 f 7 6 s 2 6 p transition in Gd I. This shows that the specific mass shift, related to the correlation effect between electrons, strongly depends on the orbital angular momentum of electrons.

Temperature dependence of the collision broadeningof the 2P1/2 — 2P3/2 line of atomic iodine

The temperature dependence of the collision broadening of the spectrum of the 2P1/2 → 2P3/2 line of atomiciodine is determined in the 220 — 347 K range by the techniqueof high-resolution diode laser spectroscopy. The collision widthin an oxygen—nitrogen medium depends on temperature as(300 K/T)γ, where γ=0.87 ± 0.13.

Diode Laser Spectroscopy in the 9.8-μm ν14Band of Benzene: II. Self-, Air-, and Noble-Gas Broadening Coefficients

High-resolution diode laser spectroscopy was applied to measure broadening coefficients in the 9.8-μm ν14band of benzene, C6H6. Self-broadening was investigated at 295 and 344 K for 73 lines between 1017.31 and 1045.85 cm−1with 9 ≤J″≤ 66 and 1 ≤K″≤ 66. The measured self-broadening coefficients at room temperature vary from 0.12 to 0.22 cm−1/atm (HWHM), whereas at 344 K the self-broadening coefficients are in an interval between 0.07 cm−1/atm to 0.16 cm−1/atm. The Anderson–Tsao–Curnutte (ATC) theory was used to deduce the benzene quadrupole moment and theb0parameter from mean values of the broadening coefficients at room temperature. It could be shown that the ATC theory is able to describe the quantum number dependence and the absolute values of the self-broadening coefficients with sufficient accuracy. The collision partner dependence of the broadening coefficients was measured for threeQ-branch lines in benzene mixtures with air, N2, He, Ne, Ar, Kr, and Xe. The results are compared with similar experiments with NO2and SO2absorption lines with the outcome that the qualitative change of the broadening coefficients with changing collision partner is similar for all three molecular gases. Air broadening was measured for additional five lines at both temperatures mentioned above. The experimental setup and the data treatment are described in Part I of this article (J. Mol. Spectrosc.,184,433).

Diode Laser Spectroscopy in the 9.8-μm ν14Band of Benzene

High-resolution diode laser spectroscopy was applied to measure absolute line intensities in the 9.8-μm ν14band of benzene12C6H6. A new data treatment had to be developed to derive single line parameters from the strongly overlapped lines. This procedure includes a self-deconvolution and an adapted fit technique for complete pressure series. The obtained data set contains absolute line intensities of 73 lines between 1017.31 and 1045.85 cm−1with 9 ≤J″ ≤ 66 and 1 ≤K″ ≤ 66. These results for individual lines formed the basis for the calculation of the vibrational bandstrengthSV0of the ν14band consideringl-type resonance. In contrast to previous values derived from bandshape integration the deduced value ofSV0= (17.0 ± 1.4) cm−2/atm at 295 K is not affected by difference band lines.

High-resolution diode-laser spectroscopy on a fast beam of metastable atoms for detecting very rare krypton isotopes

A fast krypton ion beam with an energy of 10 keV is transferred through a mass filter and neutralized in a Rb- (or Cs-) vapour charge exchange cell. The emerging beam of metastable Kr atoms of a selected Kr isotope is collinearly irradiated with a tunable cw GaAlAs diode laser at 811 nm. The spectrum of the 1s5–2p9 transition covers ∼ 10 GHz and consists of one line each for the five stable isotopes of Kr with even mass number and 15 hyperfine structure lines of83Kr. The individual lines are recorded by detecting the fluorescence signal perpendicular to the beams. Photons are guided to the PM tube by diffuse reflection from a high reflectance thermoplastics light collector. Up to 20 photons per atom are emitted by cycling between the two states during the flight time of 1.2 µs through the detector. The observed absorption linewidth of 100 MHz is a combination of laser linewidth and energy uncertainty in the fast atomic beam. In order to achieve maximum isotope selectivity the beam energy has to be adjusted in such a way that the Doppler shifted lines of all isotopes form an optimum pattern for detecting the very rare isotopes81Kr and85Kr in natural environmental samples.

Diagnostics of the active medium of a waveguide CO 2 laser: Vibrational distributions and plasma-chemical processes

High-resolution diode laser spectroscopy has been used to study the active medium of a waveguide CO 2 laser. Detailed rotational and vibrational distributions of the CO 2 molecules in a capillary glow discharge plasma have been obtained over a wide range of experimental conditions. Influences exerted by plasma-chemical processes on the rates of excitation and deactivation of the molecular vibrations in the discharge plasma have been investigated. The results of this study make it possible to construct a satisfactory kinetic model of the active medium of the waveguide CO 2 laser.

High resolution diode laser and heterodyne spectroscopy with applications toward remote sensing

The recent developments of IR heterodyne and high resolution spectroscopy at the University of Cologne are presented. By using an impedance matched HEMT amplifier together with newly developed HgCdTe-mixers very low noise temperatures of 2100 K (DSB, corrected) have been achieved, which is only 50% above the quantum limit. In addition, very broad banded detection of the heterodyne signals was obtained with a 1.4 GHz, 2000 channel acousto-optical spectrometer. First results with a tuneable infrared diode laser as local oscillator have been obtained. For the interpretation of atmospheric absorption signals laboratory measurements of pressure effects are made using infrared diode laser spectroscopy with very high frequency resolution by frequency stabilization of the laser, and very low noise data acquisition by signal averaging methods.