Lasing microbottles

Lasing of an optical microbottle resonator at predetermined resonant wavelengths is feasible via spatial engineering of the pump laser beam

Observation of Wave Packet Distortion during a Negative-Group-Velocity Transmission

In Physics, causality is a fundamental postulation arising from the second law of thermodynamics. It states that, the cause of an event precedes its effect. In the context of Electromagnetics, the relativistic causality limits the upper bound of the velocity of information, which is carried by electromagnetic wave packets, to the speed of light in free space (c). In anomalously dispersive media (ADM), it has been shown that, wave packets appear to propagate with a superluminal or even negative group velocity. However, Sommerfeld and Brillouin pointed out that the “front” of such wave packets, known as the initial point of the Sommerfeld precursor, always travels at c. In this work, we investigate the negative-group-velocity transmission of half-sine wave packets. We experimentally observe the wave front and the distortion of modulated wave packets propagating with a negative group velocity in a passive artificial ADM in microwave regime. Different from previous literature on the propagation of superluminal Gaussian packets, strongly distorted sinusoidal packets with non-superluminal wave fronts were observed. This result agrees with Brillouin's assertion, i.e., the severe distortion of seemingly superluminal wave packets makes the definition of group velocity physically meaningless in the anomalously dispersive region

Opium, Guns and Communist Party of Burma: The Chinese Community of Kokang in Northern Myanmar

The early work of Brattain and Bardeen [1] demonstrated that under illumination, a semiconductor surface develops a potential which can be measured with non-contact, capacitive coupling. Since then, the surface photo-voltage (PV) effect has received sporadic experimental as well as theoretical considerations. A number of experiments have been reported (with and without contacts) which make use of both dc and ac surface PV (see, for example, Ref. 5). In the latter form, the incident light is modulated at frequencies ranging from a few Hz to a few MHz. Both the dc and ac embodiments of the surface photo-voltage effect have been used to study various minority and majority carrier transport mechanisms in the presence of various degrees of inversion (or accumulation) of the semiconductor surface