Lec 17 (Non-Linear Optics) Flashcards
No OCT Flashcards here, they’re in Lec 18-19
Non-linear absorption examples
- Two photon fluorescence
- Second harmonic
Non-linear phenomena definition
- Input wavelength different from output wavelength
- Caused by wavelength mixing
Non-linear optics objective
Use longer wavelengths for imaging
–> Less scattering
–> Increased penetration
Wavelength mixing definition
- Multiple, lower energy wavelengths combine to produce fewer, higher energy wavelengths
- Superposition principle no longer applies
- Caused by anharmonic oscillations
Non-linear optics objective
Use longer wavelengths for imaging
–> Less scattering
–> Increased penetration
Non-linear optical phenomena examples
- Two-photon fluorescence
- Second Harmonic Generation
Two-photon fluorescence steps
Distinctive feature: Has Stokes shift
- Two lower energy photons emitted
- Photons density higher at focal point
–> absorption energy only reached at focal point
–> absorption only occurs at focal point
Second Harmonic Generation
Distinctive feature: No Stokes shift
Point Spread Function (PSF)
Function describing intensity distribution of light at a point
Resolution limit cause
PSF at every point interferes constructively and destructively with neighbouring points
Factors affecting PSF
- Numerical aperture (NA)
- Sample frequency
Rayleigh Criterion
To obtain resolved image, minimum centres of diffraction of objects must not overlap
Numerical aperture formula
NA = n sinα
- Angle close to 90° –> NA increase
Minimum distance of separation formula
X_min = 0.61λ/NA
- λ increase –> X_min increase –> Resolution increase
- NA increase –> X_min increase –> Resolution increase
