† These authors contributed equally to this work Solution-processed organic-inorganic lead halide perovskites have recently emerged as promising gain media for tunable semiconductor lasers. However, optically pumped continuous-wave lasing at room temperature -a prerequisite for a laser diode -has not been realized so far. Here, we report lasing action in a surface emitting distributed feedback methylammonium lead iodide (MAPbI3) perovskite laser on silicon substrate, at room temperature under continuous-wave optical pumping. This outstanding performance is achieved because of the ultra-low lasing threshold of 13 W/cm 2 , which is enabled by thermal nanoimprint lithography that directly patterns perovskite into a high Q cavity with large mode confinement, while at the same time improves perovskite's emission characteristics. Our results represent a major step toward electrically pumped lasing in organic and thin-film materials, as well as the insertion of perovskite lasers into photonic integrated circuits for applications in optical computing, sensing and on-chip quantum information.Since the advent of silicon (Si) photonics, the field of photonic integrated circuit (IC) has progressed significantly over the last few decades [1]. While many photonic components have the potential to be inserted into future electronic-photonic ICs on Si, a critical component -an efficient chip-scale laser on Si -has not been realized because of Si's indirect bandgap. Although III-V/Si lasers formed via wafer bonding of III-V onto Si substrate have been the main candidate, the low yield and high manufacturing cost restrict their further development as light sources for electronic-photonic ICs [2]. An alternative gain medium that is Si compatible is solution-processed organic semiconductors. Although organic lasers cannot compete with inorganic III-V lasers in many performance metrics, they do offer several advantages such as easy wavelength tunability,

Metal halide perovskites have emerged as promising gain materials for on-chip lasers in photonic integrated circuits. For these to become commercially relevant as economical on-chip light sources, a clear onset of quasi-continuous wave (quasi-CW) and, eventually, continuous wave (CW) lasing at room temperature or Peltier-cooling accessible temperatures from directly patterned perovskite cavities is a critical milestone that must be achieved. Herein, through directly patterning with nanoimprint lithography and encapsulation of the cavity with a thin layer of polycarbonate (PC), quasi-CW lasing from CH 3 NH 3 PbBr 3 (MAPbBr 3 ) is demonstrated up to 260 K. The PC layer is also shown to effectively encapsulate the surface defects of MAPbBr 3 and protect devices from environmental hazards. Through the combined analysis of the crystal quality, degradation process during optical pumping, defect encapsulation, and laser performance, room temperature CW lasing from directly patterned perovskite cavities should be within reach.

A special class of anisotropic media -hyperbolic metamaterials and metasurfaces (HMMs) -has attracted much attention in recent years due to its unique abilities to manipulate and engineer electromagnetic waves on the subwavelength scale. Because all HMM designs require metal-dielectric composites, the unavoidable metal loss at optical frequencies inspired the development of active HMMs, where gain material is incorporated to compensate the metal loss. Here, we experimentally demonstrate an active type II HMM that operates at vacuum wavelengths near 750 nm on a silicon platform. Different from previous active HMMs operating below 1 𝝁𝒎 , the dielectric constituent in our HMM is solely composed of gain medium, by utilizing solution-processed and widely tunable metal-halide perovskite gain. Thanks to the facile fabrication, tunability and silicon compatibility of our active HMM, this work paves the way towards HMM's integration into on-chip components, and eventually, into photonic integrated circuits.

in absorption in the vicinity of 83 nm. Predissociative widths as narrow as 0.3 cm have been measured, and profile analyses based on the theory of Pano are performed on these predissociated states. The importance of overlap integrals in the predissociation of B" is shown, and the absorption cross section o = (7.2 +0. 7) &(10 " cm' for the B"~X(2,0) is determined. Anomalous behavior observed in the D (v = 5) states of 0, is analyzed in terms of an accidental perturbation by the D" (v = 0) states.

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