China
Africa
Explore chapters and articles related to this topic
Continuous-Wave Silica Fiber Lasers
Published in Johan Meyer, Justice Sompo, Suné von Solms, Fiber Lasers, 2022
Johan Meyer, Justice Sompo, Sune von Solms
The other notable influence is the energy levels broadening. In Erbium-doped media, emission and absorption transitions occur between sublevels resulting from Stark levels. The emission and absorption lines are therefore non-continuous but made of distinct transitions. The homogeneous and inhomogeneous broadening of the sublevels determines the transition widths. Inhomogeneous broadening occurs because of the host electrical field's variation from site to site. Homogeneous broadening, on the other hand, is produced by internal mechanisms that are not a function of the ion site such as thermal fluctuations or intrinsic level lifetimes. Figure 5.4 shows the emission and absorption cross-section as a function of wavelength near 1550 nm for the Al-Ge silica glass. At high concentration, Erbium-doped glasses are plagued by detrimental effects due to ion-ion interactions. The most notable are energy transfer, excited-state absorption, and up-conversion. These are mainly due to the tendency of Erbium ions to cluster in glass hosts. The consequence of these effects is luminosity quenching which reduces fiber laser efficiency and increases the lasing threshold. One solution to address this issue is to use phosphate glass instead of simple silica glass because Erbium ions are more soluble in phosphate glass than silica glass.
Semiconductor lasers
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
Jayanta Mukherjee, J. Stephen Sweeney
A few things are worth noticing from the plots in Figure 11.11a. The gain spectrum is narrower than the spontaneous emission spectrum with a peak at lower energy than the latter. The peak for both shifts to higher energies (shorter wavelengths) with increasing carrier density (band-filling) at a constant temperature (300 K). Both have an asymmetric profile dictated by the density of states and carrier distribution functions. The effect of homogeneous broadening leads to a broadening of the spectra as expected, a reduction in peak value and some sub-band-gap gain and spontaneous emission. The optical transparency point also moves to higher energies with increasing carrier density. If we track the variation of the integrated (total) spontaneous emission and the peak gain with carrier density (Figure 11.11b), we find that that the total spontaneous emission has a stronger nonlinear dependence on carrier density compared to peak gain (which is sublinear). Thus, the total spontaneous emission is generally modeled as BN2, where B is taken as constant for a material (bimolecular recombination coefficient) while the gain is assumed to linearly depend on carrier density as
Absorption Spectroscopy and Its Implementation
Published in Helmut H. Telle, Ángel González Ureña, Laser Spectroscopy and Laser Imaging, 2018
Helmut H. Telle, Ángel González Ureña
In general, the “line broadening” factors are classified into two categories: homogeneous and inhomogeneous line broadening factors. Homogeneous broadening refers to the case in which the contribution to the linewidth is the same for all atoms (or molecules), while inhomogeneous broadening refers to the situation where that contribution is not the same for every atom or molecule. In the latter case, the functional dependence is related to a particle property, like, for example, the particle velocity that differs for individual particles. As key examples for the two broadening mechanisms, natural (homogeneous) and Doppler (inhomogeneous) line broadening will be discussed in more detail.
Improved analytical model for Rayleigh–Brillouin scattering spectrum in gases
Published in Journal of Modern Optics, 2019
Hang Ji, Hang Wu, Yin Yu, Yingbiao Cheng, Jiaqi Xu, Kun Liang
According to the broadening theory, the scattering spectrum is not described by an ideal Dirac function in the frequency domain, as the spectral line widens. For a gas medium, line broadening is mainly divided into homogeneous broadening caused by collisions and inhomogeneous broadening. In low-density gases, the molecular distance is larger, and collisions are less. In this case, spectral broadening mainly consists of the Doppler broadening generated by molecular random motion, and the spectral shape has a characteristic Gaussian profile. As the density or pressure increases, the frequency of collisions increases, the impact of collision broadening will be greater. When collision broadening is larger than the Doppler broadening, the profile of the spectral line is close to Lorentzian. As a result of the two broadening effects, the RBS spectrum is evaluated as the convolution of Gaussian and Lorentzian distributions.