137 research outputs found
Three-Dimensionally Confined Optical Modes in Quantum Well Microtube Ring Resonators
We report on microtube ring resonators with quantum wells embedded as an
optically active material. Optical modes are observed over a broad energy
range. Their properties strongly depend on the exact geometry of the microtube
along its axis. In particular we observe (i) preferential emission of light on
the inside edge of the microtube and (ii) confinement of light also in
direction of the tube axis by an axially varying geometry which is explained in
an expanded waveguide model.Comment: 5 pages, 4 figure
Growth and optical characterization of indirect-gap AlxGa1âxAs alloys
Nonintentionally doped AlxGa1âxAs layers with 0.38 x 0.84 were grown on (100) GaAs substrates by liquid phase epitaxy (LPE) under near-equilibrium conditions. The crystalline quality of the samples was studied by photoluminescence at 2 K and room temperature Raman spectroscopy. The peculiar behavior in the photoluminescence intensities of the indirect bound exciton line and the donorâacceptor pair transition is explained from the evolution of the silicon donor binding energy according to the aluminum composition. It was also possible to observe the excitonic transition corresponding to the AlxGa1âxAs/GaAs interface, despite the disorder and other factors which are normally involved when growing high-aluminum-content layers by this technique. Furthermore, Raman measurements show the quadratic variations of longitudinal optical phonon frequencies with aluminum concentration in good agreement with previous experimental results. In this work we show that high quality indirect-gap AlxGa1âxAs samples can be grown by LPE under near-equilibrium [email protected]
Sub-nanosecond Pulse Generation from a Two-section Laser-thyristor: Theoretical Analysis
We have developed a theoretical model of a two-section laser-thyristor. It is shown that using a 4 ”m weakly doped p-base can increase blocking voltage up to 50 V, which makes it possible to generate 2 ns 10 A current pulses. It is demonstrated that the proposed device utilizes passive Q switching to generate high-power short optical pulses that account for up to 80% of output power. By picking the optimal passive section length, we have achieved optical pulses of âŒ30 ps full width at half maximum (FWHM) and âŒ100 W peak power.
Keywords: pulsed laser, semiconductor N-p-N-i-P heterostructure, laser-thyristor, dynamic model of pulsed lase
Low-temperature tapered-fiber probing of diamond NV ensembles coupled to GaP microcavities
In this work we present a platform for testing the device performance of a
cavity-emitter system, using an ensemble of emitters and a tapered optical
fiber. This method provides high-contrast spectra of the cavity modes,
selective detection of emitters coupled to the cavity, and an estimate of the
device performance in the single- emitter case. Using nitrogen-vacancy (NV)
centers in diamond and a GaP optical microcavity, we are able to tune the
cavity onto the NV resonance at 10 K, couple the cavity-coupled emission to a
tapered fiber, and measure the fiber-coupled NV spontaneous emission decay.
Theoretically we show that the fiber-coupled average Purcell factor is 2-3
times greater than that of free-space collection; although due to ensemble
averaging it is still a factor of 3 less than the Purcell factor of a single,
ideally placed center.Comment: 15 pages, 6 figure
Highâspeed photoconductivity and infrared to visible upâconversion in GaP lightâemitting diodes
In GaP:N (Zn,Te) lightâemitting diodes extrinsic photoconductivity and infrared to visible upâconversion have been investigated by short laser pulses at 10âÎŒm wavelength. A time constant of the order of 1 ns was observed indicating that free infrared excited hole to bound donor recombination yields the fast response
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