Henrik Ahlberg

Analysis of errors caused by optical interference effects in wavelength-diverse CO2 laser long-path systems.

The measurement errors in a CO2 laser differential absorption system caused by optical interference effects are analyzed. Major sources of errors are identified and design suggestions to improve the system accuracy are made. The effects of temperature changes, short measurement paths, and spectral features of the measured species are taken into account.

Imaging Q-switched CO2 laser radar with heterodyne detection: design and evaluation

A Q-switched CO2 laser radar with heterodyne detection has been designed and evaluated. A simplified theory has been used to optimize the Q-switched laser for high-resolution ranging. The return signal statistics from diffuse, glint, and topographical targets have been investigated, and statistical distributions have been fitted to the experimental data. Detection of specific targets in laser radar images using range gating has also been studied.

Evaluation of distributed Bragg reflector lasers for high-sensitivity near-infrared gas analysis

Three-section distributed Bragg reflector (DBR) lasers emit- ting in the 1.5-mm wavelength region are characterized for use as a light source in a spectrometer for gas analysis. The three-section DBR lasers facilitate a wide, continuous tuning range while preserving the output power at a constant level. Typical characteristics for three-section DBR lasers and potentials and limitations of these lasers in gas-monitoring applications are discussed. A fiber optic system for high-sensitivity gas detection using wavelength-tunable DBR lasers is also presented.

Gas monitoring using semiconductor lasers operating in the 2 μm wavelength region

Abstract Measurements of ammonia (NH3) and carbon dioxide (CO2) using a Fabry–Perot strained layer quantum well laser operating at 1.94 μm have been made. Fourier-transform infrared (FTIR) measurements, in the 1.4–2.1 μm region, were also made in order to compare the strength of different absorption bands of NH3 and CO2. The FTIR measurements showed that the absorption line intensities for NH3 and CO2 in the 2 μm wavelength region were up to two orders of magnitude stronger than the line intensities in the 1.5 μm region. An NH3 sensitivity of 3 ppm·m, at atmospheric pressure, using 1 Hz detection bandwidth, is demonstrated using wavelength modulation spectroscopy and second harmonic detection. Furthermore, the sensitivity for NH3 was estimated at 0.03 ppm·m in the 2 μm region.

Measurements of electric field strength in gas insulated high-voltage components using infrared diode laser absorption spectroscopy

Measurements of electric field strength in gas insulated high-voltage components using a tunable diode laser spectrometer have been made. The method utilizes the linear Stark effect in a trace gas molecule (nitric oxide) introduced in the insulating gas (sulfur-hexafluoride). Polarization effects make it possible to monitor the local electric field as to both magnitude and direction. Changes in the sparking potential due to the introduced trace gas have been investigated.

Industrialized high-sensitivity fiber optic near-IR diode-laser-based gas analysis system

An industrialized computer-controlled fiber optic laser diode gas analysis system is described. A unique signal processing scheme completely eliminates both non-gas-related transmission variation and long-term drift. Sensitivities better than 1 ppm(DOT)m and 200 ppm(DOT)m is routinely achieved for field-installed systems for ammonia and oxygen, respectively. due to the superior selectivity of laser diodes, interference effects from coexisting gases, such as water vapor in ammonia measurements, are easily avoided.

CO2 laser long-path measurements of diffuse leakages from a petrochemical plant.

Ethylene plume profile measurements and mass flow estimations of diffuse ethylene leakages from a petrochemical plant have been performed with a computer-automated CO2 laser long-path absorption instrument. The total ethylene mass flow was estimated using a trace gas method. Comparative measurements were also performed.

Advanced semiconductor laser structures for gas analysis spectroscopy

ding/core interface, depending on the energy flux in the interface region. We discuss these results in terms of colour center formation and of possible thermal or stress-induced effects. In conclusion, careful choice of coupling conditions is necessary for UV-laser based fiber optical sensors to avoid undesirable photodegradation. Selection of laser parameters like laser energy and repetition rate for a given application has to take into account the dependence of fiber transmission on these parameters.

High Tc superconducting IR detectors from Y-Ba-Cu-O thin films

A thin-film high-Tc superconducting multielement optical detector made of Y-Ba-Cu-O has been designed and evaluated using optical pulses from a diode laser (830 nm) and a Q-switched CO2-laser (10.6 microns). Different thin films have been tested. A laser deposited film showed the strongest response amplitude for short pulses and responded to an ultrafast, 50 ps wide pulse. Comparisons between dR/dT and response as a function of temperature indicated, however, a bolometric response.

Spatially resolved measurements of electric field distributions in gas-insulated high voltage components using a CO 2 laser probe beam

A new optical method for spatially resolved measurements of high electric field strengths in gas-insulated high voltage components is presented. The method utilizes the parity mixing phenomenon and the Stark effect in a trace gas (NH(3)) added to the insulating gas (SF(6)). The change in the optical properties of the trace gas when exposed to the electric field is probed using a CO(2) laser. Measurements on different electric field distributions have been made and compared to theoretical calculations using the finite element method. The use of the Stark effect is briefly reviewed, and methods for extending the range of measurements and further increasing the resolution are discussed.