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Journals and Conferences
Femtosecond and nanosecond laser-induced breakdown spectroscopy (LIBS) were used to study trinitrotoluene (TNT) deposited on aluminum substrates. Over the detection wavelength range of 200-785 nm, we have observed emission from CN and C(2) molecules as the marker for the explosive with femtosecond LIBS. In contrast, the signal for nanosecond LIBS of TNT is… (More)
High-speed free-space optical communication systems have recently used fiber-optic components. The received laser beam in such a system must be coupled into a single-mode fiber at the input of the receiver module. However, propagation through atmospheric turbulence degrades the spatial coherence of a laser beam and limits the fiber-coupling efficiency. We… (More)
Non-uniform lateral current distribution in quantum cascade (QC) lasers is investigated, as a result of stimulated-optical-emission-assisted electron transport, the rate of which depends on the local photon density and is comparable to the longitudinal optical (LO) phonon scattering rate. A microscopic model based on rate equations is built to study the… (More)
We analyze the temperature dependence of the transparency current density in mid-infrared quantum cascade lasers and assess its contribution to measured threshold current density for a laser with low voltage defect.
The localization of electron wavefunctions due to interface roughness in a quantum cascade heterostructures is investigated by observing the electroluminescence spectra. Localization is more prominent in heterostructures with designed extended states.
Ultrafast pulsed lasers find application in a range of spectroscopy and sensing techniques including laser induced breakdown spectroscopy (LIBS), coherent Raman spectroscopy, and terahertz (THz) spectroscopy. Whether based on absorption or emission processes, the characteristics of these techniques are heavily influenced by the use of ultrafast pulses in… (More)
We use a density-matrix framework to evaluate the wallplug efficiency of mid-infrared quantum cascade lasers. We assess the limitations to maximum current and internal efficiency, imposed by injection coupling and current leakage, respectively.
We present an analytical model that shows that reflection from a rough surface causes a Gaussian frequency roll-off for the spectral magnitude of a terahertz wave and reduces the signal-to-noise ratio of terahertz time-domain spectroscopy. The parameter that determines the width of the frequency roll-off is the standard deviation of the surface height… (More)