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A long-range and variable focus phase-conjugation experiment in shallow water

A second phase-conjugation experiment was conducted in the Mediterranean Sea in May 1997 extending the results of the earlier time-reversal mirror experiment [Kuperman et al., J. Acoust. Soc. Am. 103, 25–40 (1998)]. New results reported here include (1) extending the range of focus from the earlier result of 6 km out to 30 km, (2) verifying a new technique to refocus at ranges other than that of the probe source [Song et al., J. Acoust. Soc. Am. 103, 3234–3240 (1998)], and (3) demonstrating that probe-source pulses up to 1 week old can be refocused successfully.