Pulse duration

About: Pulse duration is a research topic. Over the lifetime, 19429 publications have been published within this topic receiving 286507 citations.

Subpicosecond, freely propagating electromagnetic pulse generation and detection using GaAs:As epilayers

Abstract: Using GaAs epilayers with arsenic precipitates (GaAs:As) as the photoconductive material in a broad‐band optoelectronic terahertz beam system, we have generated and detected freely propagating, subpicosecond electromagnetic pulses. The receiver signal gave a measured integrated pulse width of 0.71 ps. Fast photoconductive rise times have been achieved which are characteristic of good mobility GaAs. In addition, the material exhibits a short ‘‘effective’’ carrier lifetime of several ps due to the embedded, closely spaced (about 20 nm) arsenic precipitates.

Laser interaction with dental soft tissues: What do we know from our years of applied scientific research?

Abstract: A variety of lasers are used for many oral soft tissue procedures. Each dental laser has specific parameters giving a wide range of operation. Lasers such as the carbon dioxide, argon and diode operate in continuous wave, while Nd:YAG, Er:YAG, Ho:YAG, and Er,Cr:YSGG are free-running pulsed lasers with high peak power and very short pulse duration. Laser tissue interaction is basically a photothermal effect and the biologic effect is dependent on the laser operating parameters, such as emission wavelength, power, emission mode, pulse duration, energy/pulse, energy density, duration of exposure, total energy and tissue characteristics. This article reviews current knowledge of laser parameters, laser-tissue interaction and applied preclinical and clinical safety and effectiveness scientific support.

Pulse repetition rate up to 92 GHz or pulse duration shorter than 110 fs from a mode-locked semiconductor disk laser

Abstract: A semiconductor disk laser based on an InGaAs/AlGaAs quantum-well gain medium was mode-locked by a fast semiconductor saturable absorber mirror. By high-order harmonic mode-locking a 92 GHz pulse train was obtained with a pulse duration of <200 fs. In order to achieve fundamental mode-locking, too strong saturation of the semiconductor elements had to be avoided. In a single-pulse regime, pulses shorter than 110 fs were generated at a wavelength of 1030 nm.

Time-gating improves the spatial resolution of STED microscopy.

Abstract: Stimulated-emission depletion (STED) microscopy improves image resolution by encoding additional spatial information in a second stimulated-decay channel with a spatially-varying strength. Here we demonstrate that spatial information is also encoded in the fluorophore lifetime and that this information can be used to improve the spatial resolution of STED microscopy. By solving a kinetic model for emission in the presence of a time-varying STED pulse, we derive the effective resolution as a function of fluorophore lifetime and pulse duration. We find that the best resolution for a given pulse power is achieved with a pulse of infinitesimally short duration; however, the maximum resolution can be restored for pulses of finite duration by time-gating the fluorescence signal. In parallel, we consider time-gating in the presence of a continuous-wave (CW) STED beam and find that time-gating produces theoretically unbounded resolution with finite laser power. In both cases, the cost of this improved resolution is a reduction in the brightness of the final image. We conclude by discussing situations in which time-gated STED microscopy (T-STED) may provide improved microscope performance beyond an increase in resolution.

Impulsive noise measurements and characterization in a UHF digital TV channel

Abstract: This paper presents the results of a study covering measurement and characterization of the wide-band impulsive noise present in a digital TV radio channel. Measurements were conducted at a frequency of 762 MHz in different outdoor and indoor environments using vertical and horizontal polarization. The measurement system was built on commercial equipment only. The calibration process, which is an important stage of this kind of measurements, is described. To analyze the measurements the impulsive noise has been modeled as a pulse train where the pulse amplitude, pulse duration and elapsed time between pulses are considered random variables. It has been found that the pulse duration and elapsed time between pulses is not dependent on the antenna polarization while the pulse amplitude is, especially in the case of the noise generated by a fluorescent lamp. It has also been found that the pulse duration of the noise measured in the outdoor environments presents some clustering features and is correlated with the pulse amplitudes. This correlation may be caused by a RF noise bandwidth that is larger than the bandwidth of the measurement system. The noise in busy streets presents larger pulse durations, larger amplitude, and shorter elapsed time between pulses that the noise measured in a pedestrian area. Several statistical tests have been done to find the distribution function that best fits these random variables. Power Rayleigh, lognormal, exponential, Poisson, and Gamma distributions have been tested. According to the assessment carried out, none of the distribution functions is adequate to model the pulse amplitudes or the elapsed time between pulses, while the pulse duration seems to be Gamma distributed.