Lasing and sharp line emission in the 1.55-μm wavelength region is demonstrated from ensembles and single InAs
quantum dots (QDs) embedded in InGaAsP on InP (100) by metalorganic vapor phase epitaxy (MOVPE). Wavelength tuning of the QDs is achieved through the insertion of ultra-thin (1-2 monolayers) GaAs interlayers underneath the
InAs QDs. To increase the active volume widely-stacked QD layers are identically reproduced. Closely-stacked QDs
reveal unpolarized emission from the cleaved side due to vertical electronic coupling which is important for polarization
insensitive semiconductor optical amplifiers. Fabry-Perot narrow ridge-waveguide lasers implementing five layers of
widely-stacked QDs as gain medium operate in continuous wave mode at room temperature with low threshold current,
low transparency current density of 6 A/cm2 per QD layer, and low loss of 4.2 cm-1, which are accompanied by a 80 nm
wide gain spectrum. Device performance does not suffer from sidewall recombination in deeply-etched QD lasers which
possess similar threshold currents as shallowly-etched ones and do not deteriorate with time. This allows the fabrication
of mono-mode and compact devices with small bending radii, as demonstrated by the operation of a QD ring laser with
40-GHz free spectral range. Micro-PL of single QDs exhibits sharp exciton-biexciton emission around 1.55 μm
persisting to temperatures above 70 K; the prerequisite for single photon sources working at liquid nitrogen temperature
for fiber-based quantum information and cryptography systems.
Potential application of elementary excitation in semiconductor quantum dot to quantum computation is discussed. Construction of scalable hardware and all optical implementation of logical gate that exploits discrete nature of electron-hole states and their well concentrated oscillator strenth for ultrafast gate operation are proposed. Rabi population oscillation of an excitonic two-level system in an isolated single InxGa1-xAs quantum dot is manifested by a quantum wave function interferometry in time domain, demonstrating a long lived coherence of zero-dimensional excitonic states and revealed the coherent population flopping under strong optical field. A phase-sensitive coherent gate operation on single-dot exciton qubit is demonstrated.
Recently, much attention has been focused upon generation of ionized particles from solid target by coulomb explosion using high intensity and ultrashort pulse laser since the high intensity electric field can easily ionize to the maximum charge of the element. This paper reports the generation of molecular carbon ions and decrease of multiple charged ions in case of irradiation of low power nanosecond laser pulse prior to femtosecond laser pulse. The changes in the ion current waveform have been analysed by time of flight measurement with 76.4cm of drift section. This observed waveform was interpreted using energy conservation law.
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