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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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DOE OSTI2020

Controlled Assembly of Upconverting Nanoparticles for Low-Threshold Microlasers and Their Imaging in Scattering Media

Micron-sized lasers fabricated from upconverting nanoparticles (UCNP) coupled to whispering gallery mode (WGM) microresonators can exhibit continuous-wave anti-Stokes lasing useful for tracking cells, environmental sensing, and coherent stimulation of biological activity. The integration of these microlasers into organisms and microelectronics requires even smaller diameters, however, which raises threshold pump powers beyond practical limits for biological applications. To meet the need for low lasing thresholds and high fidelity fabrication methods, we use correlative optical and electron microscopy to uncover the nanoparticle assembly process and structural factors that determine efficient upconverted lasing. We show that 5 μm microspheres with controlled submonolayer UCNP coatings exhibit, on average, 25-fold lower laser thresholds (1.7 ± 0.7 kW/cm 2 ) compared to the mean values of the lowest threshold UCNP lasers, and variability is reduced 30-fold. WGMs are observed in the upconversion spectra for TiO 2 -coated microspheres as small as 3 μm, a size at which optical losses had previously prevented such observations. Finally, we demonstrate that the WGM signatures of these upconverting microlasers can be imaged and distinguished through tissue-mimicking phantoms. These advances will enable the fabrication of more efficient upconverting lasers for imaging, sensing, and actuation in optically complex environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Air-Stable Room-Temperature Quasi-2D Tin Iodide Perovskite Microlasers

Quasi-2D tin iodide perovskites (TIPs) are promising lead-free alternatives for optoelectronic applications, but achieving stable lasing remains challenging due to their limited environmental stability. Here, we report air-stable, room-temperature lasing from quasi-2D TIP microcrystals as small as 4 μm. Incorporation of the organic spacer 5IPA3 significantly enhanced the stability of these materials compared with previously reported TIPs. Lasing was observed from both dielectric (n = 4) and plasmonic (n = 3 and n = 4) TIP microlasers. Under picosecond pumping, lasing was sustained for over 108 pump pulses in ambient conditions. These results represent a significant step toward practical photonic applications of tin-based perovskites.

crystals↗

DOE OSTI2021

Laser particles with omnidirectional emission for cell tracking

The ability to track individual cells in space over time is crucial to analyzing heterogeneous cell populations. Recently, microlaser particles have emerged as unique optical probes for massively multiplexed single-cell tagging. However, the microlaser far-field emission is inherently direction-dependent, which causes strong intensity fluctuations when the orientation of the particle varies randomly inside cells. Here, we demonstrate a general solution based on the incorporation of nanoscale light scatterers into microlasers. Two schemes are developed by introducing either boundary defects or a scattering layer into microdisk lasers. The resulting laser output is omnidirectional, with the minimum-to-maximum ratio of the angle-dependent intensity improving from 0.007 (-24 dB) to > 0.23 (-6 dB). After transfer into live cells in vitro, the omnidirectional laser particles within moving cells could be tracked continuously with high signal-to-noise ratios for 2 h, while conventional microlasers exhibited frequent signal loss causing tracking failure.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2022

Solid-state laser refrigeration of core-shell polystyrene microspheres

Microlaser designs based on the coupling of whispering gallery modes (WGMs) with the upconversion processes which take place within lanthanide-doped nanoparticles (UCNPs) have been demonstrated and shown to have many valuable qualities, such as high Q factors and low lasing thresholds. One obstacle that these microlaser designs still face is the challenges caused by photothermal heating of the gain medium, which could be solved through the design of a radiation balanced microlaser. In this work, WGM microresonators composed of 5 µm diameter polystyrene spheres are fabricated with a layer of Yb3+-doped NaYF4 UCNPs in order to test if the anti-Stokes cooling properties of the UCNPs can cool the microresonator and its environment under laser irradiation. We find via calibrated mean fluorescence spectroscopy that the UCNPs can cool their local environment by as much as 23 °C and significantly reduce the heating of the aqueous environment surrounding the microresonator, showing promise for inclusion in a design for a radiation balanced microlaser.

whispering gallery modes, optical refrigeration, m↗

DOE OSTI2023

Aggregation‐Induced Stimulated Emission of 100% Dye Microspheres

Dyes with aggregation-induced emission (AIE) properties have gained interest due to their bright luminescence in solid-state aggregates. While fluorescence from AIE dyes is widely exploited, relatively little is known about aggregation-induced stimulated emission. Here, stimulated emission of tetraphenylethene (TPE)-based organoboron AIE dyes, TPEQBN, in thin films and in microcavity lasers is investigated. Using femtosecond pump–probe spectroscopy, gain coefficients up to 230 cm -1 at 500 nm are measured. Using rate equations, concentration- and pump-dependent gain dynamics as well as laser build-up dynamics are analyzed. During laser oscillation, radiative stimulated emission allows high instantaneous quantum yield greater than 90% to be achieved. Solid-state microspheres made of 100% AIE dyes are fabricated via microfluidic emulsion and solvent evaporation method. Coupled with high gain and high refractive index of 1.76, microspheres as small as 2 µm in diameter show lasing by nanosecond pumping with a threshold of ≈10 pJ µm –2 . Polymer coated, but not bare, microspheres are internalized by live cells and generate narrowband cavity-mode emission from within the cytoplasm. This work shows the potential of AIE dyes as laser materials.

36 MATERIALS SCIENCE↗