Stefan Lundqvist

Generation of single‐mode picosecond pulses by injection locking of an AlGaAs semiconductor laser

We report on the generation of picosecond single‐mode optical pulses with 1‐GHz repetition rate. Single‐mode operation is obtained by injection locking a modulated multimode buried optical guide laser with a single‐mode channel substrate planar master laser. The power ratio of the dominant mode to the total emitted power is improved from less than 0.07 without to more than 0.9 with injection locking. Detection is performed with an autocorrelator using second‐harmonic generation in a nonlinear crystal. A pulsewidth of 58 ps is obtained assuming a Gaussian pulse shape. Moreover, the substructure of spikes caused by multimode operation is strongly suppressed when the laser is injection locked.

Measurements of pressure-broadening coefficients of NO and O3 using a computerized tunable diode laser spectrometer.

Foreign-gas broadening coefficients have been measured for selected lines of ozone in the 9.2-microm region and for several R -branch lines of nitric oxide in the 5.4-microm region using a computerized tunable diode laser spectrometer. The data analysis showed the importance of fitting a Lorentzian line shape out to several times the halfwidth to obtain a correct value of the broadening coefficient. The measured broadening coefficients of nitric oxide were in good agreement with those obtained by Abels and Shaw. The results of the analysis of eleven lines in the nu(1) band and five lines in the nu(3) band of ozone show a transition-dependent broadening coefficient. The average value of the foreign-gas broadening coefficients for the measured nu(1) and nu(3) lines are 0.075 and 0.073 cm(-1) atm(-1), respectively.

Generation of tunable single-mode picosecond pulses from an AlGaAs semiconductor laser with grating feedback

Widely tunable single‐mode picosecond pulses have been obtained from a buried optical guide AlGaAs semiconductor laser operated with external grating feedback. Intensity autocorrelation measurements show single‐mode 30‐ps pulses. A tuning range of 20 nm, corresponding to more than 70 different laser frequencies, was easily achieved.

Differential reflectance of natural and man-made materials at CO 2 laser wavelengths

The differential reflectance of several naturally occurring and man-made materials at CO(2) laser wavelengths is determined. The computer-controlled measurement system has two CO(2) lasers and determines the differential reflectance of each material by measuring the ratio of the reflected signals at two wavelengths simultaneously. These results can be used to improve the accuracy of air pollution measurement systems which derive their return signals from topographic targets.

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.

Temporal coherence properties of picosecond pulses generated by GaAlAs semiconductor lasers for directly modulated and frequency stabilized optical communication systems

The temporal coherence properties of picosecond pulses from GaAlAs semiconductor lasers have been studied by measuring first- and second-order autocorrelation functions with a Michelson interferometer. The time-bandwidth product and chirp have been evaluated for several different laser structures and frequency stabilization schemes. Time-bandwidth products from 1.2 for a CSP laser to 3.6 for a TJS laser were obtained with operating conditions representative of high-speed communication systems. Computer simulations based on the rate equations have been used to model the temporal coherence during the pulse and they show good agreement with our measurements. The results show that it is important to select the appropriate laser structure and stabilization scheme in applications where the temporal coherence is significant for system performance.

Air pollution monitoring with a Q-switched CO 2 -laser lidar using heterodyne detection

A differential absorption lidar (DIAL) using a Q-switched CO(2) laser and a heterodyne receiver has been developed. The DIAL system is highly automated with computer-controlled laser-line selection and signal processing. The transmitter operates at a pulse-repetition frequency of 20 kHz and has an average output power of 1.8 W. A wideband HgCdTe detector is used together with a high speed adding buffer to detect the return signals. The system has been used in a field experiment to monitor ethylene emission from a petrochemical factory.

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.