Direct observation of self-focusing near the diffraction limit in polycrystalline silicon film

Abstract

We present direct observation of self-focusing near the diffraction limit by measuring the beam-spot size with a scanning fiber probe tip. We have used the polycrystalline silicon film, which exhibits a reverse-saturation (Im χ(3)≈8×10−3 esu) and self-focusing (Re χ(3)≈2×10−2 esu), as measured by the conventional z-scan method with He–Ne laser. It is observed that the beam radius of about its wavelength becomes smaller as the input laser intensity is increased, which indicates that the self-focusing effect dominates over the reverse saturation in the 300-nm-thick sample.

Nonlinear absorption and refraction in crystalline silicon in the mid‐infrared

“…There are several possible factors, apart from experimental uncertainties, that could account for discrepancies between values obtained by different authors using nominally identical experiments. The first factor is the use of a simplified model to fit the experimental z‐scan data . When this model is a good approximation even for relatively large values of nonlinear phase change.…”

Dispersion of silicon nonlinearities in the near infrared region

“…͑2͒ reduces to the on-axis transmittance. 14,16 In our experiments, we use an aperture transmittance of S = 0.5. By using the previously deduced values of ␤ T and w 0 in Eqs.…”

“…To go beyond the commonly used on-axis transmittance, 14,16 we derive the following form for D r and D i :…”

Selective Tuning of Silicon Photonic Crystal Cavities via Laser-Assisted Local Oxidation

“…The temperature-dependent absorption may lead to self-amplification of the heating. Also, there might be some nonlinear optical effects [11]. In experiments, we observed that 50 mW input powers can lead to rapid oxidation and melting of the silicon slab in just a few seconds.…”