Low-frequency intensity noise in semiconductor lasers

The low-frequency intensity noise at 25 MHz of a Fabry-Perot semiconductor laser is measured as a function of injection current. All the measurements are taken at room temperature and the laser is operated with a commercial current source (the conditions under which laser diodes are often used). At the highest injection current of twice threshold, the intensity noise is 5.5 dB above the shot-noise limit. When the longitudinal side mode suppression of the laser is 20 dB or larger, the intensity noise is modeled adequately by an expression derived from the single-mode, small-signal, linearized, semiclassical rate equations. All the parameters used in the theory are derived or referenced.     

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爱立信IMS weShare业务有20%的开发与用户视觉体验相关(用户界面、图标、标签以及进度条),其它的80%则主要致力于设备间的系统.与此相对比,用户的体验则完全(100%)有赖于其可接触的事物.     

Simple method for measuring frequency chirps with a Fabry-Perot interferometer

A simple method for measuring the frequency-chirped response of lasers is presented. This method relates the deviation from the Lorentzian line shape of the transmission of a Fabry-Perot interferometer to the frequency chirp of the laser and allows a direct measurement of the frequency chirp. Two chirps produced by an external-cavity laser diode with an intracavity electro-optic crystal were measured. The first measurement was of a linear chirp of 800 MHz occurring in a time of 12.3 mus, and the second measurement was of eight repeated 800-MHz linear chirps each occurring in 337 mus. Agreement between the measured and the expected frequency-chirped response of the laser is shown.     

Detecting mode hopping in semiconductor lasers by monitoringintensity noise

Mode-hopping semiconductor lasers exhibit intensity fluctuations which are correlated to the level of mode-hopping activity. It is shown that these fluctuations occur at a level that is easily measured and that mode hopping can be detected with a p-i-n photodiode and an AC voltmeter having microvolt sensitivity. A plot of intensity fluctuations versus laser case temperature and injection current displays periodicities in the conditions under which mode hopping occurs. These regularities are explained in terms of the peak gain wavelength passing the longitudinal mode wavelength as temperature changes. The occurrence of mode hopping is determined by junction temperature (which determines the relationship of the gain peak with longitudinal mode structure) and injection current (which determines mode-hopping frequency). The junction temperature is itself a function of case temperature and injection current. The stability map shows that precise control of the operating parameters is not sufficient to avoid mode hopping. It is necessary to have these parameters set properly     

Stimulated rotational Raman scattering in CO2-pumped para-H2

Stimulated rotational Raman scattering in a 300 K multipass cell filled with para-H2with a single-mode CO2pump laser was studied using a single-mode OPO as a probe laser at the Stokes frequency for the So(0) transition. Amplification and pump depletion are examined as a function of incident pump energy. For an incident CO2pump laser energy of 1.5 J, a photon conversion efficiency of 47 percent is observed.     

High-power deuterium Raman laser at 632 nm

We demonstrate a continuous-wave deuterium Raman laser that generates more than 160 mW of Stokes output power despite severe thermal effects. This output power represents nearly an order-of-magnitude increase over any previously reported continuous-wave Raman laser and is the first such system to our knowledge that uses deuterium gas as the Raman medium. The high output power is achieved through careful consideration of the electronic feedback design, frequency actuators, and pump-laser intensity noise.     

Exploring minimal scenarios to produce transversely bright electron beams using the eigen-emittance concept

Next generation hard X-ray free electron lasers require electron beams with low transverse emittance. One proposal to achieve these low emittances is to exploit the eigen-emittance values of the beam. The eigen-emittances are invariant under linear beam transport and equivalent to the emittances in an uncorrelated beam. If a correlated beam with two small eigen-emittances can be produced, removal of the correlations via appropriate optics will lead to two small emittance values, provided non-linear effects are not too large. We study how such a beam may be produced using minimal linear correlations. We find it is theoretically possible to produce such a beam, however, it may be more difficult to realize in practice. We identify linear correlations that may lead to physically realizable emittance schemes and discuss promising future avenues.     

Differential immunological aberrations in patients with primary and secondary Sj?gren''s syndrome

PURPOSE: To evaluate the dependence of fine particle dose charge (FPD charge) generated from powder inhalers on physico-chemical properties of the inhalation powder, inhaler type, deaggregation mechanism, dose number and/or retained powder. METHODS: Electrostatic charges were determined on micronized powders and aerosolized fine particle doses withdrawn from two, high efficiency, multidose powder inhalers, Turbohaler and prototype Dryhaler. The behavior of terbutaline sulfate, budesonide, albuterol (sulfate and base), beclomethasone dipropionate and lactose was assessed before and after aerosolization. RESULTS: Both inhalers conferred triboelectric FPD charges during aerosolization in the range -400 pC through +200 pC. Specific charges (charge/unit mass) on the fine particle doses of budesonide from Dryhaler were significantly less than those from Turbohaler (p < 0.01). Electrostatic charges on the potentially respirable cloud of terbutaline sulfate generated by Bricanyl Turbohaler were positive and/or negative and unpredictable. With Pulmicort Turbohaler, FPD charges on budesonide were always positive. Dryhaler was used to determine the chemical dependence of fine particle triboelectrification during the aerosolization of pure materials. A triboelectric series was constructed from the Dryhaler results ranking the powders from positive to negative as budesonide > lactose > albuterol sulfate > terbutaline sulfate > or = albuterol > or = beclomethasone dipropionate. CONCLUSIONS: While there was no evidence of FPD charge dependence upon dose number with either inhaler, FPD charges were dependent upon the powder under investigation, as well as the construction and deaggregation mechanism of the inhaler. The specific charge on the fine particle dose of budesonide from Turbohaler corresponded to approximately 200 electronic charges per particle, a value which is known to affect both total and regional aerosol deposition in the human lung. Electrostatic charge effects may be important determinants of aerosol behavior and should not be neglected.     

Characterization and comparison of noise generation forquasi-resonant and pulsewidth-modulated converters

A buck converter with a given output filter is operated with pulse-width modulated and quasi-resonant switching schemes at the same nominal load and switching frequency. Electromagnetic interference generated by the natural switching action of the converter is examined by spectral analysis. Interference caused by excitation of parasitic elements is examined experimentally. Quasi-resonant converters are found to have a lower switching frequency harmonic bandwidth than the equivalent pulse-width modulated converter, even with switching frequency control. The most significant parasitic responses are the turn-on current and turn-off voltage of the catch diode and the gate current of the MOSFET. A significant decrease in radiated and conducted noise occurs when the gate drive voltage rise and fall times are increased, which is possible without loss of efficiency using quasi-resonant switching     

Development of a high spectral resolution lidar based on confocal Fabry-Perot spectral filters

The high spectral resolution lidar (HSRL) instrument described in this paper utilizes the fundamental and second-harmonic output from an injection seeded Nd:YAG laser as the laser transmitter. The light scattered in the atmosphere is collected using a commercial Schmidt-Cassegrain telescope with the optical receiver train first splitting the fundamental and second-harmonic return signal with the fundament light monitored using an avalanche photodiode. The second-harmonic return signal is mode matched into a tunable confocal Fabry-Perot (CFP) interferometer with a free spectral range of 7.5?GHz and a finesse of 50.7 (312) at 532?nm (1064?nm) placed in the optical receiver for spectrally filtering the molecular and aerosol return signals. The light transmitted through the CFP is used to monitor the aerosol return signal while the light reflected from the CFP is used to monitor the molecular return signal. Data collected with the HSRL are presented and inversion results are compared to a co-located solar radiometer, demonstrating the successful operation of the instrument. The CFP-based filtering technique successfully employed by this HSRL instrument is easily portable to other arbitrary wavelengths, thus allowing for the future development of multiwavelength HSRL instruments.