ABSTRACT
A coherent three-dimensional (angle-angle-range) lidar imager using a master-oscillator-power-amplifier concept and operating at a wavelength of 1.5 microm with chirp-pulse compression is described. A fiber-optic delay line in the local oscillator path enables a single continuous-wave semiconductor laser source with a modulated drive waveform to generate both the constant-frequency local oscillator and the frequency chirp. A portion of this chirp is gated out and amplified by a two-stage fiber amplifier. The digitized return signal was compressed by cross correlating it with a sample of the outgoing pulse. In this way a 350-ns, 10-microJ pulse with a 250-MHz frequency sweep is compressed to a width of approximately 8 ns. With a 25-mm output aperture, the lidar has been used to produce three-dimensional images of hard targets out to a range of approximately 2 km with near-diffraction-limited angular resolution and submeter range resolution.
ABSTRACT
An Er:Yb codoped fiber amplifier chain for the generation of pulses for coherent lidar applications at a wavelength near 1.5 microm is reported. The final 1.8-m-long power amplification stage had a 50-microm core diameter and yielded a 23-dB energy gain, resulting in 0.29-mJ, 100-ns pulses at a repetition rate of 4 kHz with no Brillouin scattering and an M2 of 2.1.
ABSTRACT
A method for the remote detection and identification of liquid chemicals at ranges of tens of meters is presented. The technique uses pulsed indirect photoacoustic spectroscopy in the 10-microm wavelength region. Enhanced sensitivity is brought about by three main system developments: (1) increased laser-pulse energy (150 microJ/pulse), leading to increased strength of the generated photoacoustic signal; (2) increased microphone sensitivity and improved directionality by the use of a 60-cm-diameter parabolic dish; and (3) signal processing that allows improved discrimination of the signal from noise levels through prior knowledge of the pulse shape and pulse-repetition frequency. The practical aspects of applying the technique in a field environment are briefly examined, and possible applications of this technique are discussed.
ABSTRACT
The antenna and the Doppler estimation characteristics of a coherent pulsed lidar intended for short-range aerosol backscatter applications have been analyzed. The system used fiber-optic interconnects and operated at a wavelength of 1.548 microm. The range dependence of the signal for various bistatic and monostatic antenna configurations has been determined. The system operated in a low-pulse-energy, high-pulse-repetition-rate mode, and the Doppler estimates from the return signal were achieved with a multipulse accumulation procedure. The expected performance of the accumulation in this low-photocount regime was compared with the data obtained from the system, and a reasonable level of agreement was demonstrated.
