Investigation of highly scattering media using near-infrared continuous wave tunable semiconductor laser

The principle of frequency modulated continuous wave radar (FMCW) has been applied to optical frequencies. By tuning the wavelength of a semiconductor laser with time, high resolution imaging in scattering media is possible. The spatial resolution depends mainly on the tuning range of the laser. Several tuning principles to be used in optical FMCW are discussed. As a coherent detection scheme with small bandwidth is used, low noise and high dynamic range are expected. The basic theory is outlined and experimental results are presented. Nonlinear tuning characteristics that degrade the resolution are discussed and interferometric methods enhancing system characteristics are proposed.

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