We demonstrate Optical-Resolution Photoacoustic Microscopy (OR-PAM), where
the optical field is focused and scanned using Digital Phase Conjugation (DPC)
through a multimode fiber. The focus is scanned across the field of view using
digital means, and the acoustic signal induced is collected by a transducer.
Optical-resolution photoacoustic images of a knot made by two absorptive wires
are obtained and we report on resolution smaller than 1.5{\mu}m across a
201{\mu}m by 201{\mu}m field of view. The use of a multimode optical fiber for
the optical excitation part can pave the way for miniature endoscopes that can
provide optical-resolution photoacoustic images at large optical depth.Comment: 10 pages, 3 figure
After a review of the basic concepts of slow and fast light, recent advancements based on nonlinear wave-mixing processes are described. As a nonlinear medium, the authors focus on a liquid crystal light valve showing that it allows obtaining a large control of the group delay, with a maximum fractional delay of 1, and a deceleration of light pulses down to group velocities as small as 0.2 mm/s. A theoretical model accompanies the observations and accounts for them in the general framework of two-wave mixing in the light valve. At the end, a high-sensitivity interferometer is presented as an example of slow light applications.Two-wave mixing in a liquid crystal light valve: the input pulse is sent together with a pump; at the output several diffraction orders are obtained with different group delays. From [28].
Abstract:In this paper we demonstrate the enhancement of the sensing capabilities of glass capillaries. We exploit their properties as optical and acoustic waveguides to transform them potentially into high resolution minimally invasive endoscopic devices. We show two possible applications of silica capillary waveguides demonstrating fluorescence and opticalresolution photoacoustic imaging using a single 330 μm-thick silica capillary. A nanosecond pulsed laser is focused and scanned in front of a capillary by digital phase conjugation through the silica annular ring of the capillary, used as an optical waveguide. We demonstrate optical-resolution photoacoustic images of a 30 μm-thick nylon thread using the water-filled core of the same capillary as an acoustic waveguide, resulting in a fully passive endoscopic device. Moreover, fluorescence images of 1.5 μm beads are obtained collecting the fluorescence signal through the optical waveguide. This kind of silica-capillary waveguide together with wavefront shaping techniques such as digital phase conjugation, paves the way to minimally invasive multi-modal endoscopy.
Programmable spectral phase modulation of femtosecond pulses by use of a nonpixelated spatial light modulator is reported. This light valve, based on the optical addressing of a continuous layer of liquid crystal, allows the operation of spectral phase modulation when optical frequency components are spatially dispersed within a grating-and-lenses pulse-shaping apparatus. Characterization and feedback control of this device were determined by use of spectral interferometry. Demonstrations of the capabilities of this device are given in the spectral and the temporal domains, and recompression of chirped pulses was performed.
We present an original technique for coherent beam combining of an array of fiber amplifiers based on self-adaptive digital holography. In this method, the phase errors between the fibers of the array are compensated by using the diffracted phase-conjugated -1 order of a digital hologram. The proposed method is compatible with a large number of fibers and simply implemented with a CCD detector matrix and a spatial light modulator. This concept is analyzed and experimentally demonstrated with three polarization-maintaining passive fibers at 1.06 microm.
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