The double barrier separate confinement heterostructure (DBSCH) design aimed at reduction of vertical beam divergence and increase of catastrophic optical damage (COD) level for high power laser diodes (LDs) operation is presented. Insertion of thin, wide-gap barrier layers at the interfaces between waveguide and cladding layers of SCH gives an additional degree of freedom in design making possible more precise shaping of the optical field distribution in the laser cavity. By comparison with the large optical cavity (LOC) heterostructure design it has been shown that the low beam divergence emission of DBSCH LDs can be attributed to the soft-profiled field distribution inside the cavity. This soft mode profile seems to determine narrow laser beam emission rather than the field distribution width itself. The potential problem with the soft-profiled but relatively narrow (at half-maximum) mode distribution is a lower COD level. Widening of the mode profile by the heterostructure design corrections can increase it, but care must be taken to avoid excessive decrease of confinement factor (Γ). As a result it is shown that DBSCH design is possible, where the low beam divergence and high COD level is achieved simultaneously. Wide stripe gain-guided LDs based on GaAsP/AlGaAs DBSCH SQW structures have been manufactured according to the design above. Gaussian-shaped narrow directional characteristics are in relatively good agreement with modelling predictions. Vertical beam divergences are 1315o and 1718o FWHM for design versions experimentally investigated. Threshold current densities of the order of 350270 Acm-2 and slope efficiencies of 0.95 and 1.15 W/A have been recorded for these two versions, respectively. Optical power at the level of 1 W has been achieved. The version with lower beam divergence proves to be more durable. Higher optical power levels are to be obtained after heterostructure doping optimisation.
Since the second half of the 20th century many cities in Poland lose population and the rate is more than likely to increase in future. The determinants that have the greatest impact on the process of shrinking cities are those related to economic transformation and restructuring of the so called traditional industry and consequences of the second demographic transition. In general, it can be distinguished a few main drivers for shrinkage of cities: transformation, suburbanization, demographic change (e.g. falling birth rates, outmigration in rural depopulation areas), environmental pollution. Shrinkage is a varied phenomenon because of its multidimensional, multiscalar and multitemporal character. But the multifacted character of these processes renders their recognition and estimation difficult. The purpose of the article is to identify the sorts of shrinking cities and to presents method of measuring this process. This paper presents the differentiation of shrinking cities process in Poland on the basic of selected empirical indicators. A detailed analysis was conducted in cities with more than 100 thousand inhabitants in the period of 2000–2017.