Rok Petkovšek

This paper presents a laboratory experiment designed to help undergraduate engineering students distinguish between the general principle of energy conservation and the conditional conservation of mechanical energy. Using the accessible system of a vertically bouncing ball, the experiment employs temporal measurements of successive rebound intervals. From these measurements, students determine the coefficient of restitution and quantify mechanical-energy loss during impacts without relying on fitting procedures or image analysis. The experiment is configured to minimize the influence of air resistance through the choice of small, relatively dense balls and modest release heights, ensuring that energy dissipation is dominated by non-conservative processes during the collision. The activity was implemented on a large scale with approximately 400 first‐year students across two study programs. Student results exhibit a high degree of reproducibility, with clear distinctions between rigid and soft impact surfaces. The experiment proved robust, conceptually transparent, and well aligned with the learning objective of clarifying the limitations of mechanical‐energy conservation. Its simplicity, scalability, and strong diagnostic value make it a valuable addition to introductory physics laboratory curricula.

One of the hallmarks of a versatile laser is the ability to generate pulses on demand. In this work, we demonstrate a self-stabilizing pulse on demand fiber laser with passive gain control through an implemented gain-clamped oscillator that generates an idler beam that is filtered out from the amplifier output. The amplification gain is defined by the losses in the oscillator, while the pump power determines the maximum repetition rate for stable amplification. The temporal dynamics of the system are analyzed in the context of gain switching theory to determine the maximum frequency at which the stable amplified pulses can be obtained at the output. As a proof of principle, the range from single pulses to repetition rates over 100 kHz is demonstrated with constant pulse energies. For arbitrary seeding of gain clamping oscillator, a laser diode-based seeder with a pulse duration down to 60 ps and repetition rates of up to 200 MHz is used. The high temporal resolution of the seed is also used to investigate the temporal dynamics of the population inversion in the gain clamped amplifying fiber after a single pulse passage. The presented approach is suitable for fiber preamplifier systems where low power signals consisting of arbitrarily spaced pulses need to be amplified to an appropriate level prior to high power amplification.