F. J. M. Harren

Photoacoustic trace gas detection of ethane using a continuously tunable, continuous-wave optical parametric oscillator based on periodically poled lithium niobate

A 1.2 W, continuous-wave, continuously-tunable, singly-resonant optical parametric oscillator (OPO) (idler tuning range 3.0–3.8 μm), pumped by a 10 W continuous-wave Nd:YAG laser, is used in combination with a photoacoustic cell for the detection of ethane. An intracavity solid-state etalon (thickness 400 μm) was used to stabilize the OPO cavity and could be used to mode-hop tune the idler wavelength over 10 cm−1. The usefulness of the system was demonstrated by determining a detection limit for ethane down to 10 parts per trillion. The selectivity was achieved by making a 24 GHz wide pump laser scan over the ethane absorption line at 2996.9 cm−1, after which a Lorentzian fit determined the total area of the absorption signal. Both area value and peak value proved to be linearly depending on the ethane concentration.

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.

Continuous-wave operation of a single-frequency optical parametric oscillator at 4–5 μm based on periodically poled LiNbO 3

We present a cw, Nd:YAG-pumped singly resonant single-frequency narrow-linewidth high-power optical parametric oscillator with idler tuning from 3.7 to 4.7 μm . In this spectral range the absorption of the idler wave in the LiNbO3 crystal is significant, causing the oscillation threshold to increase with a subsequent decrease in output power from 1.2 W at 3.9 μm to 120 mW at 4.7 μm . The optical parametric oscillator’s cavity was stabilized and mode-hop tuned with a rotatable solid etalon but with a subsequent reduction in idler power of as much as 50%. We demonstrated the usefulness for spectroscopy by recording the photoacoustic spectrum of a strong CO2 absorption, using a 24-GHz continuous idler scan.

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]

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).

A CO laser based photoacoustic system applied to the detection of trace gases emitted by conference pears stored at high CO2 and low O2 levels

The photoacoustic (PA) spectra of five gaseous molecules were measured using a CO laser based PA detector. The data for two of these molecules were compared with literature. The spectra were used in a multi-component analysis of trace gas emission by Conference pears stored at high CO2 and low O2 levels.

Sensitive and fast trace gas detection by means of OPO-based cw cavity ring down spectroscopy

A 2 W, continuous-wave, widely and continuous tunable, singly frequency, mid-infrared optical parametric oscillator is used in combination with cavity ring down spectroscopy for the fast and sensitive detection of trace gases.

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.