S. te Lintel Hekkert

On-line laser photoacoustic detection of ethene in exhaled air as biomarker of ultraviolet radiation damage of the human skin

The exhaled air and volatile emission by the skin of human subjects were analyzed for traces of ethene (C2H4) by means of CO2 laser photoacoustic trace gas detection. Due to the extreme sensitivity of the detection system (6 part per trillion volume, 6:1012), these measurements could be performed on-line and noninvasively. Exhaled ethene was used as a biomarker for lipid peroxidation in the skin of human subjects exposed to ultraviolet (UV) radiation from a solarium. A change in the ethene concentration was already observed in the exhaled air after 2 min. Adaptation of the skin to UV exposure and direct skin emission could also be observed.

Wide single-mode tuning of a 3.0-3.8-mu m, 700-mW, continuous-wave Nd : YAG-pumped optical parametric oscillator based on periodically poled lithium niobate

A new optical parametric oscillator (OPO) for the mid-infrared wavelength region of 3-3.8mum with an idler output power of up to 1.5 W has been developed. The singly resonant OPO is pumped by a single-mode, 10-W, continuous-wave Nd:YAG laser and consists of a bow-tie ring cavity with a fan-out periodically poled lithium niobate crystal and a low-finesse intracavity air-spaced etalon. The single-frequency idler output can be continuously tuned over 24 GHz with 700-mW power by tuning of the pump laser. The tuning was demonstrated by recording of an absorption line of ethane with photoacoustic spectroscopy.

LASER PHOTOACOUSTIC TRACE GAS DETECTION, AN EXTREMELY SENSITIVE TECHNIQUE APPLIED IN BIOLOGICAL RESEARCH

The use of infrared laser based photo-acoustic trace gas detection equipment in biological research is discussed on the basis bf two examples. A CO2 laser based photo-acoustic trace gas detection system is employed to follow the time-dependent pattern of the nitrogen fixation process by the cyanobacteria Nodularia Spumigena on a one-minute time scale. Due to the high sensitivity of the detection system for ethylene (detection limit 6 part per trillion; 6.10(12)), the fixation process can be followed on-line in a flow-through system. Following a 50 h dark incubation period, the bacteria show nitrogen fixation only after a certain illumination period, indicating lack of carbohydrates needed to start the nitrogen fixation. [KEYWORDS: CO-LASER; PLANTS; ACETALDEHYDE; SPECTROSCOPY; ADAPTATIONS; CO2-LASER; RESPONSES; ETHYLENE; ECOLOGY; ANOXIA]

Multiphoton multi laser spectroscopy of the ν3 mode of SF6 in a molecular beam

Abstract Results are presented of measurements utilizing two counter propagating CO 2 waveguide lasers interacting simultaneously with SF 6 molecules in a molecular beam. 95 new two-photon transitions were observed and assigned, for combinations of two different CO 2 laser lines. Especially transitions to levels of E g vibrational symmetry provide new information on the parameters of the Hamiltonian because previous one-colour measurements could barely access these levels. Still no transitions were found to levels with A 1g vibrational symmetry. Some results are presented on three- and four-photon transitions.

Calculation of two-photon transitions in SF6, fit to measured frequencies

Abstract Two-photon transitions of the ν 3 band of SF 6 have been fitted utilizing two different representations of the Hamiltonian. The strong transitions predicted around the 10P16 CO 2 laser line can all be observed within 3 MHz from the calculated frequencies. For the other measured spectral regions (i.e. the regions around the 10P14, 10P18 and 10P20 CO 2 laser lines), we are less certain of the assignment of the two-photon transitions, because in these regions almost no strong lines are predicted. The constants utilized to produce the best fit of the two-photon transitions are presented.

Differential cross sections for state specific reactive scattering of Na–SF6→NaF–SF5

Double‐differential cross sections for the interaction of Na(3 2S) and Na(3 2P) with SF6 have been measured in crossed beam experiments for center of mass collision energies between 0.25 and 1.75 eV. In comparison with recently reported experiments the reaction with vibrationally excited SF6 is found to be more effective than the one with electronically excited Na. Results from an ab initio CASSCF calculation with Na in the ground state and the 3P state are presented. The experimental findings and the results from the calculation lead us to two different models for the reaction in the ground state and the excited state: While the well known harpooning model is verified for the ground state the reactive collisions with excited Na are mediated by nonadiabatic (nonreactive) transitions to the ground state surface. For these transitions the vibrational motion of SF6 is much more efficient than the relative motion in the collision.

Multiphoton multi laser excitation of SF6 in a molecular beam

Abstract Multiphoton experiments on SF6 in a molecular beam are performed utilizing cw CO2 waveguide lasers. In this paper the emphasis will be on the non-spectroscopic aspects. (i) The saturation dip in one-photon transitions is measured. (ii) To investigate which rotational states participate in the multiphoton process, an intra cavity laser is used as a pump laser, followed by a waveguide laser. Only hot band transitions seem to be depleted. (iii) With the aid of two counter-propagating CO2 waveguide laser beams, new spectral regions were entered to investigate two-photon transitions. In this way it is also possible to investigate three- and more-photon transitions, because of the higher intensity (two lasers) and smaller intermediate detunings (two colours).

Differential cross sections for elastic and reactive collisions between Na and multiple photon excited SF6

Abstract Differential cross sections for collisions of Na and SF 6 from beam experiments are presented. The SF 6 is vibrationally excited to the 5 v 3 level with a CO 2 laser. Enhancement of reactive scattering is detected for different energies (0.25 eV, 1.04 eV and 2.70 eV) and at laboratory angles between 10 and 75 deg. The amount of elastically scattered Na from excited SF 6 always decreases in comparison with ground state scattering. The experiments show that the reaction is more efficient if vibrational energy is put into SF 6 as compared with exciting Na electronically.

The ΔV=2 CO laser: Photoacoustic trace gas detection

In order to improve the detection limit of biologically interesting gas, a ΔV=2 CO laser operating between 2.8 and 3.8 μm is developed; 165 laser lines divided over 24 bands have been observed with maximum intracavity power of 11 Watt. The fingerprints of ethane, pentane and ethylene have been measured in a dilute mixture using nitrogen as buffer gas. The detection limits of C2H4, C2H6, C5H12 in N2 are 2 ppb, 0.4 ppb and 0.5 ppb, respectively (S/N=1).

Laser photoacoustic ethene detection from human air as on-line biomarker for lipid peroxidation

Trace gas emission from human lungs or skin can be an indication of specific physiological processes inside the body. The advantage of studying these molecular gases is that they can be performed on-line, non-invasively and quickly, when using detectors with the appropriate sensitivity. To determine whether ethene could be used as an on-line biomarker for lipid peroxidation, the exhaled air of human subjects was analyzed by means of laser-based trace gas detection.