Optical Whispering Gallery Modes for Biosensing: From Physical Principles to Applications

Description

This interdisciplinary book covers the fundamentals of optical whispering gallery mode (WGM) microcavities, light–matter interaction, and biomolecular structure with a focus on applications in biosensing. Novel biosensors based on the hybridization of WGM microcavities and localized surface plasmon resonances (LSPRs) in metal nanoparticles have emerged as the most sensitive microsystem biodetection technology that boasts single molecule detection capability without the need for amplification and labeling of the analyte. The book provides an ample survey of the physical mechanisms of WGMs and LSPRs for detecting affinity, concentration, size, shape and orientation of biomarkers, while informing the reader about different classes of biomolecules, their optical properties and their importance in label-free clinical diagnostics. This expanded and updated second edition features a new chapter that introduces the reader to advanced in vivo biosensing techniques using WGM microcavities, looking at photothermal sensing, methods for trapping neutral atoms around WGM microcavities, and practical aspects of optoplasmonic sensing. The second Edition now provides a comprehensive introduction to the use of WGM microcavities in physical sensing which includes measurements with frequency combs, macro and micro (one atom) lasers, gyroscopes, optomechanical and parity-time-symmetric sensor devices. Chapter-end problems round out this comprehensive and fundamental textbook, inspiring a host of up-and-coming physicists, bioengineers, and medical professionals to make their own breakthroughs in this blossoming new field. This textbook can be used for both introductory and advanced courses about the modern optics of optical microcavities. Preface to the Second Edition Preface to the First Edition Contents About the Authors 1 Sensing with Light 1.1 Introduction 1.2 Light Propagation in Space 1.2.1 Vector and Scalar Potentials 1.2.2 Wave Equations for Electric and Magnetic Fields 1.2.3 Boundary Conditions 1.3 Polarizability 1.3.1 Electric Dipole 1.3.2 Local Field Correction 1.3.3 Lorentz Oscillator Model 1.4 Frequency and Intensity Fluctuations of Light 1.4.1 Autocorrelation Function and Spectrum 1.4.2 Lorentzian and Gaussian Broadening 1.4.3 Phase Noise 1.4.4 Hanbury Brown–Twiss Effect 1.5 Frequency Stabilization 1.5.1 Fabry–Pérot Resonator 1.5.2 upper L upper CLC Oscillators 1.5.3 Laser Frequency Locking to Transmission Line 1.5.4 Pound–Drever–Hall Technique 1.5.5 Shot Noise 1.5.6 Optical Heterodyne and Homodyne Detection 1.5.7 Measuring the Photon Number 1.6 Optical Sensing Technologies 1.6.1 Michelson–Morley Interferometer 1.6.2 Optical Clocks 1.6.3 Single Atom Detection 1.6.4 Optical Tweezers Problems References 2 Surface Plasmon Resonance 2.1 Introduction 2.2 Plasmonics: Interaction of Light with Metals 2.2.1 Drude–Sommerfeld Model 2.2.2 Interband Transitions of Bound Electrons 2.2.3 Drude–Lorentz Model 2.3 Surface Plasmon Polaritons—SPPs 2.3.1 SPPs at Plane Interfaces 2.3.2 Excitation of SPPs 2.3.3 SPR Sensors 2.3.4 Surface Plasmon Optics 2.4 Localized Surface Plasmon Resonances—LSPRs 2.4.1 Spherical Nanoparticles 2.4.2 Energy Stored in Metal Nanoparticles 2.4.3 Nanoellipsoids 2.4.4 Mie Theory of Light Scattering 2.4.5 Numerical Methods for LSPRs 2.5 Plasmonic Coupling of Nanoparticles References 3 Whispering Gallery Modes in Optical Microcavities 3.1 Introduction 3.2 Microspheres 3.2.1 Strict Analytical Eigenmodes 3.2.2 Analytical WGM Frequencies 3.2.3 Effective Mode Volume 3.2.4 Approximate Solutions 3.2.5 Intrinsic Quality Factor 3.2.6 Excitation of WGMs 3.3 Microbottles 3.4 Microdisks 3.5 Microtoroids 3.6 Thermo-Refractive-Noise-Limited Frequency Stability References 4 Applications of WGM Microcavities in Physics 4.1 Introduction 4.2 Laser Generation 4.3 Nonlinear Frequency Conversion 4.3.1 Pockels Effect 4.3.2 Multiple-Wave Mixing 4.3.3 Second-Order Nonlinearity 4.3.4 Frequency Doubling 4.3.5 Parametric Down-Conversion 4.3.6 Third-Order Nonlinearity 4.4 Parity–Time Symmetry 4.4.1 Parity and Time-Reversal Transformations 4.4.2 Spectral Reality of Non-hermitian Hamiltonians 4.4.3 Parity–Time Symmetry in Optics 4.4.4 Observation in Experiments 4.5 Electromagnetically Induced Transparency 4.6 Optical Frequency Combs 4.6.1 Conventional Mode-Locked Combs 4.6.2 Frequency Microcombs 4.6.3 Modeling of Microcombs 4.6.4 Chip-Scale Optical Frequency References 4.7 Optomechanics 4.7.1 Classical Description 4.7.2 Acoustic Modes in Microcavities 4.7.3 Optical Measurement of Mechanical Motion 4.7.4 Optomechanical Cooling 4.8 Nanoparticle Trapping 4.9 Gyroscopes References 5 Single Molecule Sensing 5.1 Introduction 5.2 Sensing Mechanism 5.2.1 WGM Microcavity Perturbed by Single Nanoparticles 5.2.2 WGM Microcavity Perturbed by a Nanolayer 5.3 Chemical Reaction Analysis 5.3.1 Kinetics of Association and Dissociation Reactions 5.3.2 Determination of Kinetic Constants 5.3.3 Thermodynamic Analysis 5.4 Sensing Based on Passive WGM Microcavities 5.4.1 Experimental Demonstrations 5.4.2 Mode Splitting 5.5 Sensing Based on Active Microcavities 5.6 Other Schemes of Single Particle Detection 5.6.1 Optomechanical Sensing of Single Molecules 5.6.2 Exceptional Point-Based Sensor 5.6.3 Self-referenced Photonic Molecule Biosensor 5.6.4 Individual Gas Molecule Detection Using Stokes Solitons 5.7 Practical Limits of Sensing Detection 5.8 Optoplasmonic Sensors 5.8.1 LSPR Enhanced Local Electric Field 5.8.2 Detection of Microsphere–Nanorod Interaction 5.8.3 Optoplasmonic Sensing Mechanism 5.8.4 Single-Molecule Linewidth Shifts Larger Than Wavelength Shifts 5.8.5 Estimate of a Nanoparticle/Molecule's Excess Polarizability 5.8.6 Optoplasmonic Sensing Experiments 5.8.7 Detection of Nucleic Acid Hybridization 5.8.8 Detection of Ion-Nanorod Interactions 5.8.9 Detection of Protein Conformational Changes and Chemical Reactions 5.8.10 Temperature Dependence of Enzymatic Rates Reveals Thermodynamics 5.8.11 Attomolar Detection of Single Molecules 5.8.12 Characterizing Thiol Gold and Amine Gold Reactions 5.9 Comparison of Different Sensing Methods 5.10 Intracellular Sensing 5.10.1 Soft Microcavities Versus Solid Microcavities 5.10.2 Barcoding References 6 Fundamentals of Quantum Optics 6.1 Introduction 6.2 Light–Matter Interaction 6.3 Rabi Oscillation 6.4 Rabi and Ramsey Measurements 6.5 Quantization of Electromagnetic Field 6.6 Fock States 6.7 Photon Correlation Functions 6.8 Interaction Between Single Emitter and Photons 6.9 Multiple Emitters Interacting with Photons 6.10 Spontaneous Emission of Emitter in Free Space 6.11 Master Equation 6.11.1 Two-Level Emitter 6.11.2 Spin Echo 6.11.3 Dynamical Polarizability of an Emitter 6.11.4 EIT in upper Lamda-Type Emitters 6.11.5 Shelving Detection and Quantum Jumps 6.11.6 Cavity 6.11.7 Interaction-Induced Spectral Shift and Broadening 6.11.8 Diagonalization Method 6.11.9 Two-Time Correlation Functions 6.11.10 One-Emitter Laser References 7 Molecular Cavity QED 7.1 Introduction 7.2 Cavity QED 7.3 Purcell Effects 7.4 Strong Coupling Between Single Neutral Atoms and a WGM Microcavity 7.5 Trapping Atoms Around a WGM Microcavity 7.6 Molecular Emitters 7.6.1 Dipole Moment 7.6.2 Jablonski Diagram 7.6.3 Franck–Condon Principle 7.6.4 Absorption and Emission Spectroscopy 7.6.5 Beer–Lambert Law 7.6.6 Einstein Coefficients 7.6.7 Förster Resonant Energy Transfer 7.7 Molecular Cavity QED in Experiment 7.7.1 Single Molecule Interacting with Plasmonic Oscillations 7.7.2 Strong Coupling Between Molecules and Microcavities 7.7.3 Molecular Microlasers 7.7.4 Single Molecule Interacting with a Microcavity 7.8 Heisenberg-Limited Quantum Metrology 7.8.1 Heisenberg Uncertainty and Squeezed States 7.8.2 Heisenberg-Limited Phase Measurement References Appendix A Vector Calculus Appendix B Cylindrical and Spherical Coordinate Systems Appendix C Bessel Functions Appendix D Eigenmodes of Optical Fiber D.1 Wave Theory of Step-Index Fibers D.2 Linearly Polarized Modes Appendix E Split-Step Fourier Algorithm Appendix F Diagonalization of the Two-Dimensional Matrix Appendix G Solving the First-Order Linear Matrix Differential Equation Index