| Popis: |
The Army Research Laboratory (ARL) has developed a three dimensional (3D) imaging ladar based on an amplitude modulated laser for which the frequency of the amplitude modulation (AM) is linearly increased and/or decreased with time (i.e., chirped). The frequency chirped waveform is a standard radar and coherent ladar waveform for high resolution ranging and Doppler frequency shift measurement. ARL first demonstrated the use of this waveform with laser amplitude modulation and optical direct detection for high range resolution 3D imaging ladar. The Doppler frequency shift measurement capability of the AM direct detection ladar had been known previously, but had not been demonstrated until recently. This paper contains the first report of an experimental demonstration of the capability of an AM direct detection ladar to measure the frequency and amplitude of surface vibrations via the phase/frequency modulation induced on the return waveform by the surface motion. In addition, we present data demonstrating the measurement of line-of-sight translational velocities via the Doppler shift of the chirped AM waveform using the same apparatus. We first briefly describe the operating principles of ARL's chirped AM ladar for range and translational Doppler measurement with references to previous papers. We then present the classic theory for vibration induced phase/frequency modulation to explain the operating principles of the AM direct detection ladar vibrometer. We then describe the experimental demonstration of the AM direct detection ladar vibrometer, including descriptions of the experimental setup, data processing and analysis methods, and results. |
