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Analysis of noncooperative targets using a diode-pumped Nd:YAG microchip laser with frequency-shifted optical feedback

I. A. PAUN1,* , E. LACOT2

Affiliation

  1. Politehnica University of Bucharest, Romania
  2. University Joseph Fourier Grenoble, France

Abstract

It is described an experimental setup with a diode-pumped Nd:YAG microchip laser with frequency-shifted optical feedback and we present an experimental study of the characteristics of the reinjected laser, which we use for determining the reflectivity of noncooperative targets. It is demonstrated the very high sensitivity of this laser to frequency-shifted optical feedback. In order to shift the frequency of the output laser beam, we use two acousto-optic modulators. It is shown experimentally that the reinjection of a frequency-shifted beam into the laser cavity induces fluctuations of the laser output intensity and spectra. The laser output presents a strong amplification and also irregular spiking oscillations. By observing the amplification of the laser signal for different relaxation frequencies and frequency-shifts, the maximum amplification was obtained when the frequency-shift corresponded to the relaxation frequency of the laser in the absence of feedback. In this case, the response of the laser cavity to the optical reinjected field is maximized. The laser output in the presence on frequency-shifted optical feedback consists of alternative stable output and chaotic pulsation. The power spectrum of the laser with optical feedback contains the typical relaxation frequency and also the shifted frequency. The high sensitive response to optical feedback makes this laser very useful in practical applications. Based on the existing experimental methods and theoretical models, we show that the reflectivity of noncooperative targets can be determined and we also calculate the ultimate sensitivity of the technique. All the experimental results are in good agreement with the theoretical models..

Keywords

Microchip laser, Frequency-shift, Optical feedback, Noncooperative target.

Submitted at: Nov. 2, 2006
Accepted at: April 15, 2007

Citation

I. A. PAUN, E. LACOT, Analysis of noncooperative targets using a diode-pumped Nd:YAG microchip laser with frequency-shifted optical feedback, Journal of Optoelectronics and Advanced Materials Vol. 9, Iss. 4, pp. 1065-1070 (2007)