We investigated the wavelength dependence of imaging depth and clearness of structure in ultrahigh-resolution optical coherence tomography over a wide wavelength range. We quantitatively compared the optical properties of samples using supercontinuum sources at five wavelengths, 800 nm, 1060 nm, 1300 nm, 1550 nm, and 1700 nm, with the same system architecture. For samples of industrially used homogeneous materials with low water absorption, the attenuation coefficients of the samples were fitted using Rayleigh scattering theory. We confirmed that the systems with the longer-wavelength sources had lower scattering coefficients and less dependence on the sample materials. For a biomedical sample, we observed wavelength dependence of the attenuation coefficient, which can be explained by absorption by water and hemoglobin.

Ultrahigh-resolution, high-penetration-depth optical coherence tomography (OCT) by use of an all-fiber supercontinuum source at 1.7 µm was demonstrated. A Gaussian-like supercontinuum with 358 nm bandwidth at a center wavelength of 1.7 µm was generated by an ultrashort-pulse Er-doped fiber laser system. A longitudinal resolution of 3.3 µm in tissue, with a sensitivity of 95 dB, was achieved. In vitro ultrahigh-resolution imaging of biological tissues was also demonstrated. To the best of our knowledge, this is the first demonstration of ultrahigh-resolution OCT in the 1.7 µm-wavelength region.

Abstract:We developed a high power supercontinuum source at a center wavelength of 1.7 μm to demonstrate highly penetrative ultrahighresolution optical coherence tomography (UHR-OCT). A single-wall carbon nanotube dispersed in polyimide film was used as a transparent saturable absorber in the cavity configuration and a high-repetition-rate ultrashort-pulse fiber laser was realized. The developed SC source had an output power of 60 mW, a bandwidth of 242 nm full-width at half maximum, and a repetition rate of 110 MHz. The average power and repetition rate were approximately twice as large as those of our previous SC source [20]. Using the developed SC source, UHR-OCT imaging was demonstrated. A sensitivity of 105 dB and an axial resolution of 3.2 μm in biological tissue were achieved. We compared the UHR-OCT images of some biological tissue samples measured with the developed SC source, the previous one, and one operating in the 1.3 μm wavelength region. We confirmed that the developed SC source had improved sensitivity and penetration depth for low-water-absorption samples. tomographic imaging of human tissue at 1.55 μm and 1.81 μm using Er-and Tm-doped fiber sources," J.

The dispersion cancellation observed in Hong-Ou-Mandel (HOM) interference between frequency-entangled photon pairs has been the basis of quantum optical coherence tomography and quantum clock synchronization. Here we explore the effect of phase dispersion on ultranarrow HOM dips. We show that the higher-order dispersion, the linewidth of the pump laser, and the spectral shape of the parametric fluorescence have a strong effect on the dispersion cancellation in the high-resolution regime with several experimental verifications. Perfect dispersion cancellation with a linewidth of 3 μm is also demonstrated through 25 mm of water.

A Michelson interferometer based on the Linnik microscope configuration has been constituted and applied to the measurement of lubricant spreading on diamond-like-carbon (DLC) surface. Performing image processing on the fringe patterns formed by the interferometer, the lubricant thickness, as well as the spreading behavior can be investigated. This method provides complete line profiles in two dimensions and permits direct observation of the spreading phenomena, in contrast to the conventional point-by-point scanning method. To improve the measurement accuracy, a fringe following technique and a noise suppression technique were introduced. The fringe following technique successfully prevented a fringe shift over the visual field and thus suppressed the pseudo phase shift caused by a fringe shift. The spatially fixed noise due to non-uniform laser beams and flaws in optical components was also efficiently suppressed by the noise compensation method. From the calculation of multiple beam interference in a stratified medium, it is found that reduction in sensitivity due to additional reflections from underlayers is effectively prevented if the lubricant is observed through a glass disk using reflections on the back surfaces of the glass and lubricant, instead of being observed on a disk using the front surface reflections. Utilizing this advantage, a novel scheme was employed to give maximum sensitivity in which lubricant was coated on the back side of a glass disk whose front surface was coated with non-reflecting film and whose back surface was sputtered with the proper thickness of DLC. The enhanced resolution attained by the new scheme was experimentally confirmed by observing lubricant on the back surface of the glass disk and the front surface of a magnetic disk.