Results of studying stripe quantum cascade lasers emitting at room temperature in the spectral range of 4.8 µm are presented. Power characteristics and turn-on dynamics of the lasers upon pulse pumping are studied. The performed investigations demonstrate the presence of a significant heating of the active region during the pump pulse.

We demonstrate the experimental study of the axial intensity distribution of a quasi-Bessel beam with a droplet structure of the central core, formed by an axicon with the round-tip, and the results of the theoretical calculations. We show that the period of ‘droplet’ quasi-Bessel beam is determined by the shape of the surface rounding and the angle at the top of the axicon lens and depends on the distance to it. The analysis of this dependence makes it possible to restore the shape of the round-tip of the axicon without 3D scanning.