Three experiments with 18‐ to 35‐month‐old children (n = 169) studied toddler–caregiver interactions when being confronted with another person in need. In particular, we explored whether toddlers would request their caregiver to help a needy other when they are not able to help themselves. Children observed another person who needed help to accomplish a task, but were either not able to provide help as the object was out of reach (Experiment 1) or because an obstacle prevented children from interacting with the other person (Experiments 2, 2b). The experiments revealed the same developmental trend with 2.5‐year‐olds selectively involving their caregiver to help the needy other. The results are interpreted in terms of toddlers’ motivation to see others helped and with respect to their developing ability to actively involve others to regulate their emotions.

Spin-controlled lasers are highly interesting photonic devices and have been shown to provide ultrafast polarization dynamics in excess of 200 GHz. In contrast to conventional semiconductor lasers their temporal properties are not limited by the intensity dynamics, but are governed primarily by the interaction of the spin dynamics with the birefringent mode splitting that determines the polarization oscillation frequency. Another class of modern semiconductor lasers are high-𝜷 emitters, which benefit from enhanced light-matter interaction due to strong mode confinement in low-mode-volume microcavities. In such structures, the emission properties can be tailored by the resonator geometry to realize for instance bimodal emission behavior in slightly elliptical micropillar cavities. This attractive feature is utilized to demonstrate and explore spin-lasing effects in bimodal high-𝜷 quantum dot micropillar lasers. The studied microlasers with a 𝜷-factor of 4% show spin-laser effects with experimental polarization oscillation frequencies up to 15 GHz and predicted frequencies up to about 100 GHz, which are controlled by the ellipticity of the resonator. These results reveal appealing prospects for very compact, ultrafast, and energy-efficient spin-lasers and can pave the way for future purely electrically injected spin-lasers enabled by short injection path lengths.

We investigate and compare the intensity and polarization dynamics in a vertical-cavity surface-emitting laser (VCSEL) with a monolithically integrated, electrically controlled birefringence tuning mechanism. The influence of the bias current on the polarization dynamics is investigated over a large range of birefringence values. Bias current tuning toward low values and simultaneous maximization of the resonance frequency is an important strategy to optimize the spin-VCSEL toward energy-efficient operation. A polarization dynamics resonance tuning range from a few GHz up to the maximum frequency of 36 GHz was achieved, and polarization dynamics at maximum frequency are demonstrated at minimum bias current and at high temperatures of approximately 70 °C. We propose a strategy for data communication with low energy consumption and low cooling effort.

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