Nanocrystalline silicon optomechanical cavities.

Silicon on insulator photonics has offered a versatile platform for the recent development of integrated optomechanical circuits. However, there are some constraints such as the high cost of the wafers and limitation to a single physical device level. In the present work we investigate nanocrystalline silicon as an alternative material for optomechanical devices. In particular, we demonstrate that optomechanical crystal cavities fabricated of nanocrystalline silicon have optical and mechanical properties enabling non-linear dynamical behaviour and effects such as thermo-optic/free-carrier-dispersion self-pulsing, phonon lasing and chaos, all at low input laser power and with typical frequencies as high as 0.3 GHz.

Lifetimes of confined acoustic phonons in ultrathin silicon membranes.

We study the relaxation of coherent acoustic phonon modes with frequencies up to 500 GHz in ultrathin free-standing silicon membranes. Using an ultrafast pump-probe technique of asynchronous optical sampling, we observe that the decay time of the first-order dilatational mode decreases significantly from ~4.7 ns to 5 ps with decreasing membrane thickness from ~194 to 8 nm. The experimental results are compared with theories considering both intrinsic phonon-phonon interactions and extrinsic surface roughness scattering including a wavelength-dependent specularity. Our results provide insight to understand some of the limits of nanomechanical resonators and thermal transport in nanostructures.

Dispersion engineering of photonic crystal waveguides with ring-shaped holes.

The geometry of photonic crystal waveguides with ring-shaped holes is optimized to minimize dispersion in the slow light regime. We found geometries with a nearly constant group index in excess of 20 over a wavelength range of 8 nm. The origin of the low dispersion is related to the widening of the propagating mode close to the lower band gap edge.

Intervalley-scattering-induced electron-phonon energy relaxation in many-valley semiconductors at low temperatures.

We report on the effect of elastic intervalley scattering on the energy transport between electrons and phonons in many-valley semiconductors. We derive a general expression for the electron-phonon energy flow rate at the limit where elastic intervalley scattering dominates over diffusion. Electron heating experiments on doped n-type Si samples with electron concentrations (3.5-16.0) x 10(25) m(-3) are performed at sub-Kelvin temperatures. We find a good agreement between the theory and the experiment.

Detection of fetal QRS-complexes by external methods.

A new method is presented for detection of the QRS complexes and the fetal heart rate from the fetal magnetocardiogram and from the fetal electrocardiogram. In the method, the amplitude, the polarity and the shape of the QRS complex are tested. By using the described equipment it is possible to detect all consecutive heart beat intervals from a fetal electrocardiogram with less than 1% error in timing. When an external fetal electrocardiogram was used for testing, generally slightly over 10% of the QRS complexes were lost since they were simultaneous with the maternal complexes. In addition, complexes were also lost due to noise.