Investigation Of Low-threshold Lasing Generation And Sensing Applications Based On Spherical Microcavity

Spherical whispering-gallery mode（WGM）microcavity has attracted extensive attention of researchers in various countries in the cutting-edge scientific and technological fields such as low-threshold lasers,high-sensitivity sensors,nonlinear optics,and quantum optics due to its excellent optical characteristics including ultra-high quality（Q）factor,extremely small mode volume and ultra-sensitive sensing.The basic research of microcavity has shown an explosive growth momentum and has become a research hotspot in the field of micro-nano photonics.In particular,spherical microcavities with highly symmetrical geometric structures have become one of the most promising cavities due to their ultra-high Q factor surpassing other cavity shapes and simple fabrication methods.However,limited by the cavity structure,composition materials,and application conditions,the spherical microcavity still faces many severe challenges.In terms of ultra-low threshold laser,the high excitation threshold,the inability to output for a long time,and the difficulty in obtaining single-frequency lasers are the common problems of WGMs resonators.In terms of high-sensitivity sensing,to achieve specific detection of the analyte,it is necessary to functionalize specific receptors on the surface of the cavity,and the process is cumbersome.Aiming at the above bottleneck problem,the research on low-threshold optical performance and sensing application of spherical WGM microcavity is carried out.The WGM optical properties of solid-and liquid-state active spherical microcavities and their applications in low-threshold lasers,as well as high-sensitivity sensing,are deeply studied.Using the evanescent field strong coupling mechanism,the single-mode lasing generation method based on microcavity is expanded,and the constraint relationship between the cavity size and the lasing threshold is overcome;With the help of the long-range ordered characteristics of liquid crystal（LC）molecules in soft matter,the surface disturbance is amplified into the cavity in biosensing,which greatly improves the sensing sensitivity and further enriches the microcavity sensing application system.A brief overview is as follow:1.In the aspect of the solid-state active spherical microcavity,a self-assembled core/shell quantum well（QW）WGM microsphere laser is realized based on the high optical gain colloidal QW material system and the simple drip strategy.The resulting monolithic QW-WGM microlaser has a low lasing threshold of 3.26μJ/cm².Due to the low threshold and high optical gain,the laser output intensity decays less than 9%under the excitation of strong nanosecond pulses lasting 100 minutes.In addition,the optical characteristics of the WGMs such as the polarization mode,polarization state factor,and repeatability of the microlaser were studied.Further,to achieve low-threshold single-mode lasing output,two isolated QW-WGM microlasers are integrated into a strongly coupled system.A record-breaking ultra-low threshold single frequency as low as 3.84μJ cm^-2 was achieved for the first time in the field of colloidal quantum well semiconductor materials with the help of the vernier effect mechanism laser.2.In terms of the spherical liquid active resonator,a functionalized spherical WGM liquid crystal（LC）microcavity co-doped with functional materials and fluorescent dyes is proposed.Benefiting from the high refractive index contrast between the liquid crystal cavity and the environment and the smooth cavity surface,the lasing threshold is～107μJ/cm²,which is nearly an order of magnitude lower than that of other types of liquid lasers.For the first time,it was confirmed that the spectral shift of the WGM of the LC microcavity can effectively and quantitatively monitor the biochemical reaction process.The proposed functionalized LC droplet sensor further enriches the sensing form of the WGM cavity.3.With the help of the enzymatic hydrolysis,the detection limit of urea as low as 0.1 m M was achieved,and it has the ability to detect urea in actual urine samples.Using the enzyme inhibition effect,the low concentration detection of fenobucarb and dimethoate of 0.1 pg/m L and 1 pg/m L,respectively,was achieved,which was 3 orders of magnitude better than the traditional detection scheme.The electrostatic adsorption effect between positive and negative ions was used to achieve high-sensitivity detection of heavy ions Cu（II）and discrimination of light/heavy metal ions was achieved.The detection limit of the LC microcavity for heavy ion Cu（II）is as low as 40 p M,which is nearly 6 orders of magnitude lower than the safety threshold specified by WHO.The comparative experiment results show that the WGM lasing of the LC microcavity can sharply capture the deflection signal of the LC molecules that cannot be recognized by the naked eye,which is more sensitive than the traditional LC polarization monitoring.