Orbital order parameter inLa 0.95 Sr 0.05 MnO 3
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The temperature dependence of the electron-spin resonance in ${\mathrm{La}}_{0.95}{\mathrm{Sr}}_{0.05}{\mathrm{MnO}}_{3}$ has been investigated and analyzed in the paramagnetic regime across the orbital ordering transition. From the temperature dependence and the anisotropy of linewidth and g value the orbital order can be unambiguously determined via the mixing angle of the wave functions of the ${e}_{\mathrm{g}}$ doublet. The linewidth shows a similar evolution with temperature as resonant x-ray scattering results.Keywords:
Laser linewidth
As the laser linewidth arises under the influence of spontaneous emission, it is of considerable interest to find effects that decrease it. In this paper it is considered the effect of cooperative atomic interactions on the linewidth of a single-mode laser. It can be shown by suitably generalizing the Scully-Lamb theory that the cooperative effects tend to decrease the natural linewidth of the laser at high intensities. Considering the interaction of two-two- level atoms with a single-mode quantized field and the effect of cooperative atomic interactions it was obtained an expression for the natural linewidth of the system. Based on the theoretical models we obtain the numerical results for the laser linewidth as a function of the cooperation parameter. We then present a set of graphs by suitably plotting these data and we discuss the results.
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The lasers used in coherent transmission systems need to produce output that has a narrow spectral linewidth, and this means that their rebroadening and linewidth floor have to be reduced. Spatial. hole burning has been suggested to cause rebroadening and to elevate the linewidth floor [1,2], and we have previously reported that a 56-kHz linewidth can be achieved by using a corrugation-pitch modulated structure to suppress spatial hole burning [3].
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We propose and demonstrate experimentally a laser source whose linewidth is adjustable independently of its other characteristics. This source can be used to test whether a particular laser would be suitable in a system, without the need to purchase several different lasers. It also has the advantage that the linewidth is generated digitally so it is extremely stable over time. We demonstrate a dialed-linewidth emulator between 256 kHz to 150 MHz. The narrowest linewidth shown by this technique is the original linewidth of the semiconductor laser source used in the setup. We also investigate the effect of driving our modulator into its nonlinear range.
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The spectral linewidth Δv of a vertical cavity surface-emitting laser was measured for the first time. The linewidth measured by a delayed self-homodyne method was 50 MHz at an output power of 1.4 mW under room-temperature CW operation. The linewidth we obtained was quite narrow in spite of the short cavity configuration of the SE laser. This narrow linewidth is attributed to the high-reflectivity mirrors. The measured linewidth is in good agreement with theoretical values.
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Microcavity laser linewidth behavior close to the threshold transition region is investigated through high-resolution linewidth measurements. A local maximum is found for the linewidth of lasers operating slightly above threshold. The increase in laser linewidth close to threshold is explained by the effective contribution of the linewidth enhancement factor (alpha) to the laser linewidth. The Fokker-Planck model of laser noise is then solved using the eigenfunction expansion method to fit to the measured linewidth data. The behavior of the measured linewidth agrees with the model with an extracted linewidth enhancement factor (alpha) ranging between 3.5 and 5.0.
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The linewidth floor of a DFB laser observed in the linewidth/optical output power relation is an unresolved issue. It is found experimentally that the linewidth floor and linewidth rebroadening occurs in conjunction with spatial hole-burning along the lasing axis. Tailoring the current distribution along the lasing axis by using a three-terminal DFB laser can reduce the linewidth floor.
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Abstract The spectral linewidth for a semiconductor laser diode coupled to two external cavities (known as a three-cavity laser diode) is studied in the article. A closed-form expression for the linewidth of this laser is derived by analyzing the number of photons in the laser cavity. It is found that, because of the optical feedback provided by the external cavities, the photon lifetime becomes longer than that of a solitary Fabry-Perot (FP) laser, hence reducing the value of the spectral linewidth. Our theoretical investigations reveal that the linewidth of a three-cavity laser can be reduced further by using external mirrors with high reflectivities and using anti-refection (AR) coatings on the laser diode facets. We have also studied the effects of uncertainties in the linewidth enhancement factor a due to optical feedback and found that such uncertainties have negligible effects on the validity of our results.
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Multiple quantum well distributed feedback laser diodes (MQW-DFB-LDs) are attractive as narrow linewidth light sources for coherent optical communications use. Although narrow spectral linewidth operations have been reported in long wavelength MQW-DFB-LDs[1], the design for further linewidth reduction has not been clarified yet. This paper reports that negative detuning as well as threshold carrier density reduction are extremely important for narrow linewidth operation. The narrowest ever achieved 250kHz spectral linewidth was obtained, based on the experimental characterization of linewidth enhancement factor a.
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A sub-MHz (467 kHz) spectral linewidth for a tunable twin-guide distributed feedback laser is achieved for the first time. The linewidth is kept to less than 9 MHz during a continuous tuning range of 2 nm. The measured linewidth can be expressed separately by a power-dependent term and a power-independent term. The linewidth during tuning is separated into two terms experimentally for the first time. The power-dependent term conforms to the estimated linewidth during tuning. The experimental results indicate that linewidth broadening during tuning is mainly caused by the power-independent factor.
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We experimentally show that a distributed feedback interband cascade laser exhibits a linewidth broadening factor around 2.5, an intrinsic linewidth down to 13 kHz, and a total spectral linewidth as narrow as 284 kHz.
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