Investigation of Time–Frequency Features for GPR Landmine Discrimination

Ground-penetrating radar (GPR) is capable to detect plastic antipersonnel landmines as well as other subsurface targets. In order to reduce false alarms, an option of automatic landmine discrimination from neutral minelike targets would be very useful. This paper presents a possibility for such discrimination and analyzes it experimentally. The authors investigate time-frequency features of an ultrawideband (UWB) target response for the discrimination between buried landmines and other objects. The discrimination method includes the extraction of an early-time target impulse response, its time-frequency transformation, and the extraction of time-frequency features based on a singular value decomposition of the transformed image. In order to take into account the changes in the UWB target signals, the experimental conditions are completely controlled to focus on the behavior of the target's response with respect to its depth and the horizontal position of the GPR above it. The dependence of the features on the GPR bandwidth is analyzed as well. The Mahalanobis distance is used as a criterion for optimal discrimination. The obtained results define the best features and conditions when the landmine discrimination is successful. For comparison, the discriminant power of the proposed features has been tested on a dataset, acquired during a field campaign in Angola     

A temperature-stable semiconductor laser based on coupled waveguides

The design of a stripe semiconductor laser with a composite waveguide formed of two tunneling-coupled waveguides, one of which is narrow and contains the active medium and the other of which is wide and forms the optical mode is considered. It is shown that temperature stabilization of the lasing wavelength can be attained with such a semiconductor laser design. Stabilization of the wavelength can be brought about by lasing in antiresonance conditions of coupling of two waveguides; these conditions arise in a narrow range of wavelengths that depends on temperature only slightly. Calculations performed at the parameters characteristic of the InAlGaAsP laser system show that it is possible to reduce the temperature dependence of the lasing wavelength by a factor of 3 in the temperature range with the width of 60 K.     

Effect of carrier dynamics and temperature on two-state lasing in semiconductor quantum dot lasers

It is analytically shown that the both the charge carrier dynamics in quantum dots and their capture into the quantum dots from the matrix material have a significant effect on two-state lasing phenomenon in quantum dot lasers. In particular, the consideration of desynchronization in electron and hole capture into quantum dots allows one to describe the quenching of ground-state lasing observed at high injection currents both qualitatevely and quantitatively. At the same time, an analysis of the charge carrier dynamics in a single quantum dot allowed us to describe the temperature dependences of the emission power via the ground- and excited-state optical transitions of quantum dots.