Topic
Spontaneous emission
About: Spontaneous emission is a research topic. Over the lifetime, 12855 publications have been published within this topic receiving 323684 citations.
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TL;DR: In this paper, a large spontaneous emission factor (β∼0.97) was reported by fitting the L-L curve with the rate equations, based on high Q/V nanobeam cavities.
Abstract: Photonic crystal lasers operating at room temperature based on high Q/V nanobeam cavities have been demonstrated. We reported a large spontaneous emission factor (β∼0.97) by fitting the L-L curve with the rate equations.
125 citations
TL;DR: In this paper, the population inversion on some specific atomic transitions can be created using very weak incoherent pumping, which may be useful in principle for generation of high-frequency and/or high power laser light.
Abstract: A four-level atom, driven by a coherent field, is considered. We show that under certain conditions complete quenching of spontaneous emission is possible. Hence the population inversion on some specific atomic transitions can be created using a very weak incoherent pumping. We investigate the physics of the effect using bare and dressed states. The proposed scheme may be useful, in principle, for generation of high-frequency and/or high power laser light.
124 citations
TL;DR: In this article, single pass gain was measured in N2 laser pumped exciplex 4-Methylumbelliferone (4-MU) and rhodamine 6G dye lasers using a technique developed by Silfvast and Deech for high gain pulsed metal vapor lasers.
Abstract: Single pass gain has been measured in N2 laser pumped exciplex 4‐Methylumbelliferone (4‐MU) and rhodamine 6G dye lasers using a technique developed by Silfvast and Deech for high‐gain pulsed metal vapor lasers. The gain is measured by comparing the intensities of amplified spontaneous emission in single and double cell lengths with the maximum unsaturated single‐pass gain being limited by the saturation of the spontaneous emission. Maximum unsaturated gains on the order of 20 dB/cm were measured for both dyes. The gain was found to vary linearly with pump power. The technique was also used to measure the variation of gain with wavelength for a given pump power. The maximum gain for exciplex 4‐MU occurred at the fluorescence peak, whereas for rhodamine 6G it was shifted to a longer wavelength due to ground‐state reabsorption. By fitting the measured gain versus wavelength to the theory, it was possible to deduce the fractional excited singlet population in the rhodamine 6G solution.
124 citations
TL;DR: In this paper, a detailed quantitative analysis of the light extraction and loss mechanisms in high-efficiency GaAs-AlGaAs surface-textured thin-film light-emitting diodes (LEDs) is presented based on a Monte Carlo simulation.
Abstract: We present a detailed quantitative analysis of the light extraction and loss mechanisms in high-efficiency GaAs-AlGaAs surface-textured thin-film light-emitting diodes (LEDs). The analysis is based on a Monte Carlo simulation. Most input parameters, including scattering of photons at the textured surface, sub-bandgap absorption, and absorption at the metal mirror are obtained from experiments or from literature. The simulation also takes into account the effect of photon recycling and the realistic geometry of the diodes. The only remaining fitting parameter is the internal quantum efficiency, which is deduced to be about 80% at room temperature for the experimentally realized 850-nm LEDs with an external quantum efficiency of 44%. The analysis shows further that the most important loss mechanism is reabsorption in the active layer, and in particular in those parts of the active layer that are not electrically pumped. This conclusion is also valid for other types of high-efficiency LEDs. We could furthermore verify the validity of the Monte-Carlo simulation results by conducting experiments at low temperatures, where nonradiative recombination processes are reduced, resulting in the internal quantum efficiency approaching unity. The measured external quantum efficiency at 90 K is 68%, which is close to the theoretically predicted efficiency for a perfect active layer. The results demonstrate that the light extraction from surface-textured LEDs is fully understood and can be quantitatively modeled by a simple raytracing algorithm.
124 citations
TL;DR: In this paper, a theory of the intrinsic linewidths of laser output of single-mode quantum-cascade (QC) lasers in mid-infrared and terahertz (THz) ranges is developed.
Abstract: We have developed a theory of the intrinsic linewidths of laser output of single-mode quantum-cascade (QC) lasers in mid-infrared and terahertz (THz) ranges. In the theoretical treatment, the concept of an effective coupling efficiency of spontaneous emission, given by a fractional rate of spontaneous emission coupled into a lasing mode to total nonlasing relaxation, is introduced to clarify a hidden reason for the narrowness of the linewidths. A narrow linewidth (12-kHz) reported with a frequency-stabilized 8.5- distributed-feedback QC laser is successfully interpreted in terms of an extremely small effective coupling efficiency of spontaneous emission, caused by ultrafast nonradiative scatterings. The present theory predicts the presence of a minimum ldquolinewidth floorrdquo in a high-injection-current region and the independence of linewidth on detuning between gain-peak and emission wavelengths. The theoretical treatment is expanded to derive the further modified Schawlow-Townes formula including the line-broadening by black body radiation in a THz QC laser. The linewidth of a THz QC laser is predicted to be considerably broadened by black body radiation.
123 citations