Sharper and dipper laser beam shaping for super-resolved imaging in silicon

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.