Rapid laser-wavelength modulation spectroscopy used as a fast temperature measurement technique in hydrocarbon combustion.

A fast temperature measurement technique is described which is suitable for use in dynamic reacting gases, particularly in situations which involve hydrocarbon-air combustion. Temperature is determined from the relative intensity of a pair of fully resolved absorption lines probed with a rapid-tuning single-frequency laser. Demonstration of the technique using 300-micros scans across the R(1) (7) and R(1)(11) lines in the (0, 0) band of the A(2)Sigma(+) ? X(2)II system of OH present in the postflame gases above a CH(4)-air flat-flame burner is reported. Fluorescence monitoring of the absorption spectra was used to provide improved spatial resolution. Temperatures inferred from simultaneous absorption and fluorescence measurements showed good agreement with radiation-corrected thermocouple scans.

Temperature measurements in shock tubes using a laser-based absorption technique.

A laser-based technique for monitoring temperature in shock tube flows is reported. The method employs a rapid-tuning ring-dye laser to record the fully resolved absorption spectrum of the R(1)(7) and R(1)(11) lines of OH near 306.5 nm. The temperature is inferred from the ratio of the peak absorption coefficients of the two lines. Comparisons with calculated reflected shock temperatures show agreement within +/-3% for the 1300-3500 K range.

Laser-induced fluorescence technique for velocity field measurements in subsonic gas flows.

A nonintrusive optical technique is reported for multiple-point velocity measurements in subsonic flows. The technique is based on the detection of fluorescence from a Doppler-shifted absorption line of seeded iodine molecules excited at a laser frequency fixed in the wing of the line. Counterpropagating laser sheets are used to illuminate the flow, in the present case a nitrogen round jet, thereby eliminating the need for an unshifted reference signal. The fluorescence is detected simultaneously at 10,000 points in a plane of the flow using a 100 x 100 element photodiode-array camera. The velocity at each point is computed from four successive camera frames, each recorded with a different beam direction. The measured mean velocities between 5 and 50 m/sec agree well with data from the literature.

Beam deflection in a pulsed chemical laser amplifier.

Analyses and experiments have been performed to investigate deflection of a Gaussian beam propagating through an amplifying medium possessing a strong transverse gain gradient. The analysis includes effects due to dispersion and gain steering. The experiments were performed in a high power pulsed chemical laser amplifier using a cw frequency stabilized laser as a source. Time dependent beam deflection due to the interaction of the gain gradient with the finite radius of curvature of the propagating beam was observed.