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Whispering gallery mode microlasers are highly sensitive refractive index sensors widely explored for biophotonic and biomedical applications. Microlaser excitation and collection of the emitted light typically utilize microscope objectives at normal incidence, limiting the choice of the oscillation plane of the modes. Here, a platform that enables the excitation of microlasers from various directions using an optically manipulated micromirror is presented. The scheme enables precise sensing of the environment surrounding the microlasers along different well‐controlled planes. The capability of the platform to perform a time‐resolved experiment of dynamic sensing using a polystyrene probe bead orbiting the microlaser is further demonstrated. [ABSTRACT FROM AUTHOR]

Multiplexed, specific, and sensitive detection of antigens is critical for the rapid and accurate diagnosis of disease and the informed development of personalized treatment plans. Here, it is shown that polymer microsphere lasers can be used as photonic sensors to monitor and quantify direct surface binding of biomolecules via changes in the refractive index. The unique spectral signature of each individual laser can be used to find their size and effective refractive index which adds a new encoding dimension when compared to conventional fluorescent beads. Antibody‐functionalized microlasers selectively detect protein binding, as demonstrated for Immunoglobulin G and C‐reactive protein, and have the ability to resolve different stages of the multilayer surface modification. Moreover, by continuously monitoring single lasers, the possibility of real‐time monitoring of binding dynamics between antigens in solution phase and the immobilized antibodies is demonstrated. For multiplexed detection, the microlasers are employed in a flow cytometer configuration, with fast spectral detection and identification of microlasers with and without antigen binding. It is envisioned that by combining microlasers with well‐established surface modification chemistries and flow geometries, the multiplexing ability of microbead immunoassays can be strongly increased while also opening avenues for single‐cell profiling within heterogeneous cell populations. [ABSTRACT FROM AUTHOR]

Fluorescent proteins have emerged as an attractive gain material for lasers, especially for devices requiring biocompatibility. However, due to their optical properties, integration with distributed feedback (DFB) resonators is not readily achievable. Here, a DFB laser with enhanced green fluorescent protein (eGFP) as the gain material is demonstrated by incorporating a thin (65 nm), high refractive index (n = 2.12) ZrO2 interlayer as waveguide core. Deposition of ZrO2 via atomic layer deposition yields a smooth and conformal film as required to minimize optical losses. Lasing emission is obtained from 2D second‐order DFB eGFP lasers at pump power densities above 56.6 kW cm–2 and a wavelength tuning range of Δλ = 51.7 nm is demonstrated. Furthermore, it is shown that in contrast to conventional organic DFB lasers, both transverse electric (TE) and transverse magnetic (TM) modes are accessible. The effective refractive index of these modes can be predicted accurately through optical modelling. Using far‐field imaging, the laser beam profile is studied and TE and TM modes are distinguished. [ABSTRACT FROM AUTHOR]

We demonstrate an evanescently pumped water-based optofluidic distributed feedback (DFB) laser with a record low pump threshold of ETH = 520 nJ. The low threshold results from an optimized mode shape, which is achieved by a low refractive index substrate, and from the use of a mixed-order DFB grating. Investigating the photonic band structure via angular dispersion analysis both above and below lasing threshold allows us to measure the refractive index of the liquid gain layer and to determine the device parameters such as the waveguide core layer thickness. We show that it is possible to tailor the divergence of the lasing emission by varying the number of second order grating periods used for outcoupling. [ABSTRACT FROM AUTHOR]