Single 5-nm quantum dot detection via microtoroid optical resonator photothermal microscopy

Label-free detection techniques for single particles and molecules play an important role in basic science, disease diagnostics, and nanomaterial investigations. While traditional fluorescence-based methods offer powerful tools for single molecule detection and imaging, they are limited by a narrow range of molecular probes and issues such as photoblinking and photobleaching. Photothermal microscopy has emerged as a label-free imaging technique capable of detecting individual nanoabsorbers with high sensitivity. Whispering gallery mode microresonators can confine light in a small volume for enhanced light-matter interaction and thus are a promising ultra-sensitive photothermal microscopy platform. Previously microtoroid optical resonators were combined with photothermal microscopy to detect 250 nm long gold nanorods. Here, we combine whispering gallery mode microtoroid optical resonators with photothermal microscopy to spatially detect 5 nm diameter quantum dots (QDs) with a signal-to-noise ratio (SNR) exceeding $10^4$. To achieve this, we integrated our microtoroid based photothermal microscopy setup with a low amplitude modulated pump laser and utilized the proportional-integral-derivative (PID) controller output as the photothermal signal source to reduce noise and enhance signal stability. The measured heat dissipation of these 5 nm QDs is below the detectable level from single dye molecules, showcasing the high sensitivity and discrimination capabilities of this platform. We anticipate that our work will have application in a wide variety of fields, including the biological sciences, nanotechnology, materials science, chemistry, and medicine

รายงานการวิจัยการศึกษาอะตอมเอ็กโซติกโดยวิธีทางฟังก์ชันสเตอร์เมียน

SUT1-105-48-36-10 การศึกษาอะตอมของปฏิยานภาคโปรตรอนโดยวิธีทางฟังก์ชันสเตอร์เมียน SUT1-105-48-36-11 การศึกษาอะตอมพายออนิกโดยวิธีทางฟังก์ชันสเตอร์เมียน SUT1-105-48-36-12 การศึกษาพายออเนียมโดยวิธีทางฟังก์ชันสเตอร์เมียนThis work was supported by Suranaree University of Technology in fiscal year 2005-200

Ultra-high-Q free space coupling to microtoroid resonators

Whispering gallery mode (WGM) microtoroid resonators are one of the most sensitive biochemical sensors in existence, capable of detecting single molecules. The main barrier for translating these devices out of the laboratory is that light is evanescently coupled into these devices though a tapered optical fiber. This hinders translation of these devices as the taper is fragile, suffers from mechanical vibration, and requires precise positioning. Here, we eliminate the need for an optical fiber by coupling light into and out from a toroid via free-space coupling and monitoring the scattered resonant light. A single long working distance objective lens combined with a digital micromirror device (DMD) was used for light injection, scattered light collection, and imaging. We obtain Q-factors as high as $1.6 \times 10^8$ with this approach. Electromagnetically induced transparency (EIT)-like and Fano resonances were observed in a single cavity due to indirect coupling in free space. This enables improved sensing sensitivity. The large effective coupling area (~10 ${\mu}$m in diameter for numerical aperture = 0.14) removes the need for precise positioning. Sensing performance was verified by combining the system with the frequency locked whispering evanescent resonator (FLOWER) approach to perform temperature sensing experiments. We believe that this work will be a foundation for expanding the implementation of WGM microtoroid resonators to real-world applications

Reaction of electron-positron to omega and pi mesons and rho(1450) and rho(1700) mesons in quark model

The investigation in the work of the reaction electron-positron to omega and pi0 mesons in the 3P0 nonrelativistic quark model reveals that the reaction electron-positron to omega and pi0 mesons process at the energy region from the omega and pi mesons threshold to 2.0 GeV is dominated by the two-step process in which the primary quark-antiquark pair first forms rho and rho' mesons and then the vector mesons decay into omega and pi. With rho(1450) and rho(1700) mainly in 2S and 1D states respectively, the experimental data for the cross section of the reaction electron-positron to omega and pi0 mesons are well produced in the 3P0 quark model. The work supports the argument that rho(1450) is mainly a 2S meson and rho(1700) a 1D meson.Comment: 8 pages, 2 figure

Strong interactions in pionium

Pionium is investigated in various pion-pion strong interactions which reproduce well the pion-pion scattering data. It is found that the ground-state pionium wave functions in those realistic pion-pion strong interactions are considerably different from the hydrogenlike one at small distance. One may suggest that some pion-pion interactions may need to be largely improved before applied to the pion-pion atomic system