Photoacoustic imaging is a new, rising imaging technique which combines high penetration depth with a good image contrast. It is demonstrated for the first time that remote photoacoustic sensing by speckle-analysis can be performed in the MHz-sampling range using a low-resolution diode array by showing experimental results. Phantoms and ex-vivo samples are measured in transmission-mode. In addition, the detection sensitivity of the new system is estimated. The new technique might help in future to broaden the applications of photoacoustics in special applications like wound imaging, endoscopy or guiding laser surgeries.
In previous work we demonstrated a new method for shaping of pulsed IR (λ=1.55μm) laser probe beam in silicon. The shaping was done by a second pump pulsed laser beam at 0.532μm and 17ns pulse width which simultaneously and collinearly, illuminates the silicon surface with the IR beam. Following the Plasma Dispersion Effect (PDE), and in proportion to its spatial intensity distribution, the pump laser beam shapes the point spread function (PSF) by controlling the lateral transmission of the IR probe beam. In this paper we report on improvement by factor of 10 in the PSF of the probe beam. We use for the pump beam a pico-second laser at wavelength of 775nm. The use of shorter pulse width for the pump laser allows us to reduce the PSF of the probe beam to diameter of ~2μm, so far, which is smaller by factor of 10 from what we had before. Also, the penetration depth of the 775 nm pump beam in silicon is ~10μm compeer to ~1μm for the 0.532μm laser, which allows probe beam shaping inside the silicon. The use of the shaped probe beam in laser scanning microscopy allows imaging and wide range of contactless electrical measurements in silicon integrated circuits (IC) for failure analysis purposes. We propose this shaping method to overcome the diffraction resolution limit in silicon microscopy on and deep under the silicon surface depending on the wavelength of the pump laser and its temporal pulse width.
Optical wavefront shaping is one of the most effective techniques in focusing light inside a scattering medium. Unfortunately, most of these techniques require direct access to the scattering medium or need to know the scattering properties of the medium beforehand. Through our scheme we develop a novel concept in which both the illumination and the detection is on the same side of the inspected object and the imaging process is a real time fast converging operation that does not require to capture large plurality of images. We model the scattering medium being a biological tissue as a Matrix having mathematical properties matched to the physical and biological aspects of the sample. In our adaptive optics scheme, we aim to estimate the scattering function and thus to encode the intensity of the illuminating laser light source using DMD (Digital Micromirror Device) with an inverse scattering function of the scattering medium, such that after passing its scattering function a focused beam is obtained. We optimize the pattern to be displayed on the DMD using Particle Swarm Algorithm (PSO). As first proof of concept we show validation via numerical MATLAB simulations where we obtain a focused spot behind a scattering medium in amplitude modulation scheme.
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