Spherical Microlaser Research Articles

Pneumatically Tunable Droplet Microlaser

AbstractAn ideally flexible laser may function in unison with minute fluctuations in nature. Lasers made solely from liquids are promising toward this end, but they are intrinsically unstable and have been inapplicable to steady operation under ambient conditions unless they are enclosed in a tailored container or a matrix to prevent the evaporation of the liquid. Here, a simple methodology is reported to form a self‐standing spherical microlaser that is composed fully of liquid and operates steadily even under atmosphere. The robustness and spherical morphology of the droplets are achieved by using ionic liquid as the liquid medium and gently casting the droplets on a substrate covered with hydrophobic nanoparticles to enhance the metastability of the contact angle. The resulting droplets are highly robust and work as efficient long‐lasting laser oscillators. The lasing wavelength is sensitively shifted when the droplets are subjected to a faint breeze or moisture, which is associated with the deformation of the droplet. The morphological and optical responses of the droplet under gas convection are consistently supported by aerodynamic and electromagnetic simulations. The droplets are readily scalable with an inkjet printer without the need for any further treatments.

Au nanoparticle concentration study in hybrid plasmonic microlasers.

In this paper, the concentration effects of Au nanoparticles placed in dye-doped polymeric spherical microlasers are investigated. The microlasers (average diameter of ∼293µm) are made with a mixture of UV curable polymer named Norland Blocking Adhesive (NBA) and Rhodamine 6 G. Four different ratios (between the Au nanoparticles and the NBA solutions) are investigated here, namely, 1000, 2000, 3000, and 4000 ratios. The Au nanoparticles (size of ∼5nm) are randomly scattered within the microlaser. The light is collected via a multimode optical fiber, ending to a spectrometer/CCD camera. It is found that the 3000 ratio case exhibited the lowest energy threshold value and the highest photonic emission slope. The 4000 ratio (lowest concentration) exhibited a behavior that was very similar to a microlasers with no Au particles. In terms of longevity of the laser modes, the 3000 ratio case exhibited the most stable emission, although the laser mode disappeared at an earlier time. The emission of the 2000 ratio case dropped drastically after a few seconds but increased after that before dropping again; in this case, the TE and TM laser modes were found to be in competition with each other due to the partial overlapping of the plasmonic emission with some of the resonant cavity modes and due to the thermal expansion effect. The quality factor was found to be of the same order of magnitude for all cases (∼104). Ultimately, this work allows us to select the optimum microlaser's configuration in terms of Au nanoparticle concentration as well as laser mode emission and longevity for different mechanical and biomedical sensing applications.

Embedded Spherical Microlasers for In Vivo Diagnostic Biomechanical Performances

Abstract In this article, we propose to use spherical microlasers that can be attached to the surface of bones for in vivo strain monitoring applications. The sensing element is made of mixing polymers, namely, PEGDA-700 (Sigma Aldrich, St. Louis, MO) and Thiocure TMPMP (Evan Chemetics, Teaneck, NJ) at 4:1 ratio in volume doped with rhodamine 6G (Sigma Aldrich, St. Louis, MO) laser dye. Solid-state microlasers are fabricated by curing droplets from the liquid mixture using ultraviolet (UV) light. The sensing principle relies on morphology-dependent resonances; any changes in the strain of the bone causes a shift of the optical resonances, which can be monitored. The specimen is made of a simulated cortical bone fabricated with photopolymer resin via an additive manufacturing process. The light path within the resonator is found to be about perpendicular to the normal stress' direction caused by a bending moment. Therefore, the sensor measures the strain due to bending indirectly using the Poisson effect. Two experiments are conducted: 1) negative bone deflection (called loading) and 2) positive bone deflection (called unloading) for a strain range from 0 to 2.35 × 10−3 m/m. Sensitivity values are ∼19.489 and 19.660 nm/ε for loading and unloading experiments, respectively (percentage difference is less than 1%). In addition, the resolution of the sensor is 1 × 10−3 ε (m/m) and the maximum range is 11.58 × 10−3 ε (m/m). The quality factor of the microlaser is maintaining about constant (order of magnitude 104) during the experiments. This sensor can be used when bone location accessibility is problematic.

On the Performance of Intracavity Gas Sensors Based on Whispering-Gallery Microlasers

We analytically investigate the performance of whispering gallery mode (WGM) spherical microlasers for gas sensing based on intra-cavity absorption. Using a simple model we estimate the response of a compact optical gas sensor based on these microlasers. We use detection of carbon dioxide by an Er:ZBLAN mid-IR microlaser with a relative intensity noise (RIN) of - 110 dB/Hz as an example, and show that using a commercial mid-IR photodetector, the limit of detection (LOD) for the resulting sensing system is about 5 ppm. We also investigate the impact of using a fiber optical amplifier on the LOD for different values of RIN. The numerical calculations and the presented approach can be applied to analyze the performance of any intracavity sensor based on WGM microlaser.

Power scaling of narrow-linewidth mid-IR spherical microlasers

We provide experimental demonstrations on power scaling of the mid-IR Er:ZBLAN microlaser by three orders of magnitude while maintaining the linewidth below 50 pm. In the reported laser source an optimized Er:ZBLAN spherical microlaser is efficiently coupled to a home-made high-gain Er-Pr:ZBLAN fiber amplifier to generate near 1 mW at 2.71 µm.

Spectral and Modal Properties of a Mid-IR Spherical Microlaser

Whispering gallery mode (WGM) lasers are well-known for their small sizes, low thresholds and narrow linewidths, and have been the subject of research and development for more than two decades. However most of the initial reports and studies have focused on near-IR and visible WGM microlasers. Recent advances in the synthesis, doping and processing of high quality mid-IR transparent glasses have provided the means to extend the wavelengths of these microlasers to the mid-IR range. In this paper, we present a detailed characterization of a compact and low-cost mid-IR spherical WGM microlaser based on heavily doped Er:ZBLAN glass operating near 2.7 um with an estimated linewidth less than 1.1 MHz. We describe experimental results on observed single-mode and multimode spectra, thermal tuning, and polarization characteristics of such microlasers. Using a simple analysis of spherical microresonator modes and including considerations of pump and laser mode overlap we provide guidelines for optimized microlaser design.

Optically tunable/switchable omnidirectionally spherical microlaser based on a dye-doped cholesteric liquid crystal microdroplet with an azo-chiral dopant

This paper presents an optically wavelength-tunable and intensity-switchable dye-doped cholesteric liquid crystal (DDCLC) spherical microlaser with an azo-chiral dopant. Experimental results present that two functions of optical control - tunability of lasing wavelength and switchability of lasing intensity - can be obtained for this spherical microlaser at low and high intensity regimes of non-polarized UV irradiation, respectively. If the DDCLC microdroplet is subjected to weak UV irradiation, azo-chiral molecules may transform to the bent cis state at a low concentration rate. The effect can slightly decrease the local order of LCs and thus the helical twisting power of the CLC in the microdroplet. As a result, the CLC pitch may become slightly elongated, which will cause the gradual red-shift of both omnidirectional PBG and lasing emission of the DDCLC spherical microdroplet. In contrast, when the microdroplet is subjected to strong UV irradiation, numerous azo-chiral molecules may simultaneously change to bent cis-isomers to seriously disarrange the helical texture of the CLC, which will quickly deform the PBG and deactivate the lasing emission of the microdroplet. Prolonged irradiation of a blue beam after strong UV irradiation may cause the cis azo-chiral molecules quickly convert back rod-like trans-isomers, which may then regenerate the CLC Bragg onion and PBG structures and reactivate the lasing emission of the microdroplet. Optical control of the DDCLC spherical microlaser is realized on a scale of seconds and minutes when UV irradiation is strong and weak, respectively. The 3D DDCLC spherical microlaser is a highly promising controllable 3D micro-light source or microlaser (e.g., all-optical 3D single photon microlaser) for applications of 3D all-optical integrated photonics, laser displays, and biomedical imaging and therapy, and as a 3D UV microdosagemeter or microsensor.