A two-dimensional heterodyne detection technique based on the frequency-synchronous detection method [Jpn. J. Appl. Phys. 39, 1194 (2000)] is demonstrated for full-field optical coherence tomography. This technique, which employs a pair of CCD cameras to detect the in-phase and quadrature components of the heterodyne signal simultaneously, offers the advantage of phase-drift suppression in interferometric measurement. Horizontal cross-sectional images are acquired at the rate of 100 frames/s in a single longitudinal scan, with a depth interval of 6 microm, making the rapid reconstruction of three-dimensional images possible.

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We present a new approach to improving the longitudinal resolution of optical coherence tomography by optimal synthesis of several LED's. The search for an optimal synthesis of several low-coherence sources involves solution of an inverse problem, and an optimization algorithm is introduced that is used to arrange the parameters of light sources to effectively reduce the width of the center peak and inhibit the sidelobes simultaneously. Good coincidence between the experimental result and theoretical expectation is found.

Novel propagation effects of coherent short light pulses have been studied in connection with a resonant interaction with a two-level system such as in ruby 1 and gaseous SF 6 2 " 4 and Rb. 5 Selfinduced transparency (SIT) due to a one-photon resonant transition was first investigated by Recently, coherent two-photon propagation in which twice the propagating frequency is resonant with a two-level system has also been analyzed, 6 * 7 though the experimental study has not been reported yet. We wish to present here the first observation and theoretical analysis of a new type of coherent propagation of two different-frequency optical pulses causing a two-photon transition in a gaseous three-level system. The present model excludes two simultaneous transitions in double resonance.The basic effect of coherent two-photon propagation can by analyzed in the limit of two different-frequency plane waves given as E.Low-loss, coherent two-photon propagation and pulse breakup with peak amplification are observed resulting from two-photon resonant self-induced transparency of different-, frequency optical pulses interacting with a three-level system in potassium vapor. Theoretical analysis yielding new area equations for two different-frequency pulses with computer solutions agrees well with the observed results.