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Gain and phase dynamic characteristics in the compressive, unstrained and tensile strained InGaAs-InGaAsP quantum well (QW) semiconductor optical amplifiers (SOAs) are theoretically investigated via a detailed model. Based on the calculation of energy band structure, the effects of compressive and tensile strain on the differential gain and the derivative of refractive index change are investigated. It is demonstrated that the compressive strained QW SOA shows the fastest gain recovery rate and the largest phase change. That is because the SOA has the characteristics of the largest differential gain and the smallest derivative of refractive index change. In addition, the ultrafast recovery process due to the carrier heating effect can be enhanced significantly in the tensile strained QW SOA.

In order to study experimentally the ultrafast (

Picosecond transient grating experiments in sodium and iodine vapors, involving the 3S → 3P and X → B transitions respectively, are discussed. Population gratings in sodium demonstrate that the technique can be used to measure velocity distributions in the gas phase. It is shown that the time dependent transient grating signal is related to the Fourier transform of the velocity distribution. Similar experiments on iodine illustrate the effect of state changing collisions on the grating signal. In addition, the sodium experiments are used to illustrate a new type of time domain high resolution spectroscopy. When the grating excitation pulses have perpendicular polarizations, a polarization grating, rather than the usual population grating, is formed. Diffraction from the sodium polarization grating shows large time dependent oscillations in the diffraction efficiency. These oscillations yield the ground state and excited state hyperfine frequencies (1.77 GHz and 189 MHz, respectively). The results suggest that polarization grating spectroscopy can have applications in other areas, such as molecular rotational dynamics.

We combine a scanning near-field microscope (SNOM) with a time-resolved detection scheme to measure the mode dynamics of InGaN laser diodes emitting at 405 nm. Observed phenomena are filaments, mode competition, near-field phase dynamics, near-field to far-field propagation, and substrate modes. In this article we describe in detail the self-built SNOM, specialized for these studies. We also provide our recipe for SNOM tip preparation using tube etching. Then we compare the mode dynamics for a 3 μm narrow and a 10 μm wide ridge waveguide laser diode.