Spectroscopy is all about how light and matter interact. It's a powerful tool that helps us understand the world around us by looking at how atoms and molecules absorb, emit, or scatter light.
In modern optics, spectroscopy is used for everything from identifying materials to medical imaging. It's based on the idea that atoms and molecules have specific energy levels, and transitions between these levels create unique spectral fingerprints.
Principles of Spectroscopy
Principles of spectroscopic techniques
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Spectroscopy studies the interaction between electromagnetic radiation and matter
Analyzes absorption, emission, or scattering of light by atoms, molecules, or materials
Fundamental principles of spectroscopy:
Atoms and molecules have quantized energy levels
Transitions between energy levels result in absorption or emission of photons with specific energies
Photon energy is related to frequency by E=hν, where h is Planck's constant and ν is frequency
Applications in modern optics:
Characterizes and identifies materials
Analyzes chemicals and senses their presence
Monitors environmental conditions
Enables biomedical diagnostics and imaging (MRI, fluorescence microscopy)
Electromagnetic radiation-matter interactions
Absorption occurs when a photon's energy matches the energy difference between two states in an atom or molecule
Photon is absorbed, exciting the atom or molecule to a higher energy state
Emission:
Spontaneous emission: Excited atom or molecule spontaneously decays to lower energy state, releasing a photon with energy equal to the difference between states
Stimulated emission: Incoming photon stimulates excited atom or molecule to decay to lower energy state, releasing a second photon with same energy, phase, and direction as stimulating photon (lasers)
Scattering:
Elastic scattering (Rayleigh scattering): Photons scattered by atoms or molecules without change in energy (blue sky)
Inelastic scattering (Raman scattering): Photons interact with molecular vibrations or phonons, resulting in scattered photons with slightly different energies than incident photons
Energy levels and spectral transitions
Atoms and molecules have discrete, quantized energy levels
Transitions between energy levels occur when atom or molecule absorbs or emits photon with energy equal to difference between levels
Photon energy is related to wavelength by E=hc/λ, where h is Planck's constant, c is speed of light, and λ is wavelength
Spectra observed in spectroscopic techniques:
Absorption spectra: Dark lines or bands corresponding to wavelengths of light absorbed by sample
Emission spectra: Bright lines or bands corresponding to wavelengths of light emitted by sample (neon signs, fireworks)
Intensity and position of spectral lines or bands provide information about composition, structure, and properties of sample
Types of spectroscopy
Electronic spectroscopy involves transitions between electronic energy levels in atoms or molecules
Nuclear spectroscopy involves transitions between nuclear energy levels
Examples: Nuclear magnetic resonance (NMR) spectroscopy, Mössbauer spectroscopy
Spectroscopic Techniques and Applications
Principles of spectroscopic techniques
Spectroscopic techniques based on interaction between electromagnetic radiation and matter
Different techniques utilize different regions of electromagnetic spectrum (radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays)
Key applications of spectroscopic techniques in modern optics:
Determines atomic and molecular structures
Analyzes chemical composition quantitatively and qualitatively
Characterizes surfaces and interfaces
Monitors chemical reactions and processes in real-time
Enables remote sensing and imaging (satellite imagery, astronomical spectroscopy)