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We consider the optimum design of photon-counting microlaser altimeters operating from airborne and spacebome platforms under both day and night conditions. Extremely compact Qswitched microlaser transmitters produce trains of low energy pulses at multi-kHz rates and can easily generate subnanosecond pulsewidths for precise ranging. To guide the design, we have modeled the solar noise background and developed simple algorithms, based on Post-Detection Poisson Filtering 0aDPF), to optimally extract the weak altimeter signal from a high noise background during daytime operations. Practical technology issues, such as detector and/or receiver dead times, have also been considered in the analysis. We describe an airbome prototype, being developed under NASA's Instrument Incubator Program, which is designed to operate at a 10 kHz rate from aircratt cruise altitudes up to 12 km with laser pulse energies on the order of a few microjoules. We also analyze a compact and power efficient system designed to operate from Mars orbit at an altitude of 300 km and sample the Martian surface at rates up to 4.3 kHz using a lwatt laser transmitter and an 18 cm telescope. This yields a Power-Aperture Product of 0.24 W-m 2, corresponding to a value almost 4 times smaller than the Mars Orbiting Laser Altimeter (0.88 W-m2), yet the sampling rate is roughly 400 times greater (4 kHz vs 10 Hz).Relative to conventional high power laser altimeters, advantages of photon-counting laser altimeters include: (1) a more efficient use of available laser photons providing up to two orders of magnitude greater surface sampling rates for a given laser power-telescope aperture product; (2) a simultaneous two order of magnitude reduction in the volume, cost and weight of the telescope system; (3) the unique ability to spatially resolve the source of the surface return in a photon counting mode through the use of pixellated or imaging detectors; and (4) improved vertical and transverse spatial resolution resulting from both (1) and (3). Furthermore, because of significantly lower laser pulse energies, the microaltimeter is inherently more eyesafe to observers on the ground and less prone to internal optical damage, which can terminate a space mission prematurely.https://ntrs.nasa.gov/search

The general equations describing Q-switched laser operation are transcendental in nature and require numerical solutions. This greatly complicates the optimization of real devices. In this paper, we demonstrate that, using the mathematical technique of Lagrange multipliers, one can derive simple analytic expressions for all of the key parameters of the optimally coupled laser, i.e., one which uses an optimum reflector to obtain maximum laser efficiency for a given pump level. These parameters (which include the optimum reflectivity, output energy, extraction efficiency, pulsewidth, peak power, etc.) can all he expressed as functions of a single dimensionless variable z , defined as the ratio of the unsaturated small-signal gain to the dissipative (nonuseful) optical loss, multiplied by a few simple constants. Laser design tradeoff studies and performance projections can he accomplished quickly with the help of several graphs and a simple hand calculator. Sample calculations for a high-gain Nd :YAG and a low-gain alexandrite laser are presented as illustrations of the technique.