Lidar for remote measurement of ozone in the exhaust plumes of launch vehicles.

Large quantities of chlorine and alumina particles are injected directly into the stratosphere by the current fleet of launch vehicles. Environmental concerns have been raised over the impact of the rocket exhaust on the ozone layer. Recently differential absorption lidar (DIAL) was selected for remote sensing of ozone density within the plumes of Titan IV launch vehicles. The application of DIAL to this very challenging problem is described, and an implementation of UV-ozone DIAL is discussed that holds promise for this application.

Iron Boltzmann factor LIDAR: proposed new remote-sensing technique for mesospheric temperature.

We describe a new LIDAR technique for middle atmospheric temperature measurement. The proposed LIDAR exploits the Fe layer in the 80-100-km altitude region. Absolute temperatures are inferred by the use of the Maxwell-Boltzmann relationship from the ratio of LIDAR returns from mesospheric Fe atoms excited at 372 and 374 nm, corresponding to the ground-state resonance line and a thermally populated resonance line, respectively. The wavelengths of the new LIDAR are favorable for capturing Rayleigh signals from the middle atmosphere. A simulation indicates that a complete temperature profile from 30 to 100 km can be acquired with the proposed LIDAR by monitoring simultaneously the Rayleigh signals and the Fe fluorescence returns excited by the same transmitter pulse.

Passive Fraunhofer-wavelength atomic filter at 422.7 nm.

We have demonstrated 25% internal photon conversion efficiency of a new passive atomic filter. The signal wavelength matches an intense Fraunhofer line at 422.7 nm, thereby offering enhanced sunlight rejection. A quasimolecular interaction promotes rapid energy transfer between the 4p (1)P(1) level and the 4p (3)P(J) level of neutral calcium for wavelength shifting of 422.7-nm light into 657.3-nm emission. We discuss augmentation of the photon conversion efficiency by radiation trapping.

422.7-nm atomic filter with superior solar background rejection.

A novel atomic resonance filter with powerful solar background rejection is proposed. The filter wavelength matches the g Fraunhofer line at 422.7 nm. Atomic filtering occurs within the singlet manifold of neutral calcium. Superior sunlight discrimination arises mainly from two factors: overlay with an intense Fraunhofer line and signal levels devoid of fine and hyperfine structures. The new filter should exhibit high throughput and low noise.

Proposed Fraunhofer-wavelength atomic filter at 534.9 nm.

A new atomic filter is proposed. It operates at 534.9 nm. The new filter offers two important advantages for openchannel laser communications. First, its wavelength matches the output of the frequency-doubled Nd:BEL laser. Second, the filter overlays a solar Fraunhofer line, thereby offering intrinsic sunlight suppression. Ultranarrowband optical filtering takes place within the singlet manifold of neutral-calcium vapor. Excellent filter properties are deduced from spectroscopic examination of the atomic system. A novel feature of the new filter is the potential for greater-than-unity internal photon conversion.

Solar background rejection by a pressure-broadened atomic resonance filter operating at a Fraunhofer wavelength.

We have calculated the solar background rejection of the Mg atomic resonance filter operating at the b(1) Fraunhofer wavelength (518.4 nm) as a function of the pressure-broadened filter linewidth. For pressure broadening induced by the noble gases the solar background rejection decreases from 93% at a 0.002-nm bandwidth to 82-84% at a 0.02-nm bandwidth. Solar background rejection was insensitive to buffer gas and was optimum for the noble gas with the smallest shift-to-broadening ratio.

Experimental demonstration of internal wavelength conversion in the magnesium atomic filter.

We describe what is to our knowledge the first experimental demonstration of internal wavelength conversion in the metastable Mg atomic filter. The filter operates at a Fraunhofer line, thereby offering intrinsic solar background rejection. Incoming green Fraunhofer photons (518 nm) are absorbed by metastable Mg atoms in an oven cell and are converted into UV (384-nm) photons. We observed a green-to-UV conversion efficiency of greater than 50%.

Water-vapor continuum CO2 laser absorption spectra between 27 degrees C and -10 degrees C.

Water continuum CO2 laser absorption spectra are reported for temperatures between 27 and -10 degrees C. The continuum is found to possess a negative temperature coefficient. The results obtained suggest that the magnitude of this temperature coefficient increases with increasing water pressure and decreasing temperature. The temperature coefficients between 27 and 10 degrees C for air mixtures containing 3.0- and 7.5-Torr water vapor are -2.0 +/- 0.4 and -2.9 +/- 0.5%/ degrees C, respectively. For mixtures with 3.0-Torr water the 10-0 degrees C temperature coefficient is -7.7 +/- 0.2%/degrees C. The temperature and water pressure dependencies observed for the continuum suggest that while both collisional broadening and water dimer mechanisms contribute to the continuum, the dimer mechanism is more important over this temperature range.

Carbon dioxide laser absorption spectra and low ppb photoacoustic detection of hydrazine fuels.

Absorption cross-section data are reported for the toxic rocket fuels hydrazine, monomethylhydrazine, and unsymmetrical dimethylhydrazine (UDMH), as well as for their selected air oxidation products dimethylamine, trimethylamine, and methanol at up to seventy-eight CO(2) laser wavelengths each. These data are important for the assessment of the capability of CO(2) laser-based spectroscopic techniques for monitoring low levels of hydrazine-fuel vapors in the ambient air. Interference-free detection sensitivities of <30 ppb have been demonstrated for UDMH using a laboratory photoacoustic detection system.

Harmonic saturated spectroscopy for improved atomic detection.

A novel method for improved cw laser-induced atomic fluorescence detection that we call harmonic saturated spectroscopy takes advantage of the nonlinear response of an optically saturated atomic system to reject background sources of interference. A reduction in background and an improved SNR are demonstrated for sodium detection in an air-acetylene flame. The dependence of the harmonic signal on intensity, excitation waveform, and depth of modulation was also investigated.