Ultrashort Laser Pulse Uses In Environmental Monitoring

Abstract

Abstract Recent advances in laser technology have led to the production of coherent optical pulses having duration in the picosecond (10− 12 second) regime. These time intervals are comparable to or shorter than the phase memory times associated with many atomic systems. This allows the pulse to propagate through a medium such as the atmosphere unattenuated. Ultrashort pulses of particular wavelengths might propagate through clouds unattenuated. Hence ultrashort light pulses might be used to "see" through clouds. The reflection of ultrashort laser pulses might also be used to sense sea state from very high altitudes. Since light travels only 0.03mm in one picosecond these pulses could also be used to measure distances of many miles to a thousandth-of-an-inch. I. Introduction Laser sensing techniques have been developed that allow monitoring at very great distances. Recent advances in the development of ultrashort laser pulses have now greatly expanded the possible uses of lasers in environmental monitoring. Laser systems have now generated pulses in the picosecond (10− 12 seconds) regime. Analytical studies based on experimental evidence show that these ultrashort pulses might propagate through most atmospheric conditions with no or very low loss. This phenomena is called self-induced transparency. Also, since light travels only 12 one-thousandth of an inch in one picosecond, these laser pulses can be used to resolve distances to 6 one-thousandth of an inch over a range of many miles. This would allow monitoring of movement--fast or slow--accurately. Also, using range gating techniques atmospheric monitoring could be done at desired altitudes very accurately. The power reqUirements for such systems would be significant but such laser systems have been built with power outputs in the terawatt (10−12) regime. In this paper the propagating phenomena of ultrashort, called self-induced transparency will be discussed as applied to " seeing " through clouds. The pulse shape and time of flight measurements as applied to reflections from surfaces will also be discussed. Finally, atmospheric monitoring using Raman backscattering and range gating techniques will be considered. II. Self-Induced Transparency Recent advances in laser technology have led to the production of coherent optical pulses haying durations in the picosecond (1012 seconds) regime. Such time intervals are comparable to or shorter than the phase memory times associated with many atomic systems. The high frequency polarization induced in a medium by such a pulse can therefore retain a definite phase relationship with the incident pulse. The novelty of the effects that may occur as a result of the coherent response of a medium to an optical pulse has been brought out quite strikingly by the recent discovery covery of self-induced transparency.