L8 Flashcards
Longitudinal Coherence
Table of Contents, DELETE
Describe longitudinal (temporal) coherence. Wiener-Khinchin theorem. Interference of light. Types of interferometers: Michelson, Mach-Zehnder, Sagnac. Matrix method for multiple surfaces. Application to the Fabry-Perot interferometer.
Coherence of Light
What is it and what does it depend on?
- Ability for light to interfere
- Depends on the phase stability between the different light waves.
Temporal Coherence Function
context? or is it valid in absolute terms?
No dependence on absolute time t because we have a stationary wave.
Coherence Levels
- High coherence: phase difference between t and t + τ is always the same.
- Low coherence: random phase between time t and time t + τ.
Ensembles of Light Waves
-
Monochromatic light:
– Same wavelength and amplitude
– Random phase -
Random light:
– Random wavelength, amplitude and phase.
Coherence Time
FWHM of the coherence function g(τ).
Wiener–Khinchin Theorem
add context / explanations
- Stationary ensemble of light.
- Power spectral density (S): energy / frequency / area / time of the light.
- We can use the coherence G(τ) to measure the spectrum.
Michelson Interferometer
- Used to measure the coherence of light.
- Contains mirrors and a detector to observe interference patterns.
Fourier Transform Spectroscopy
Used to measure spectral properties of a light source without a traditional spectrometer.
Optical Coherence Tomography (OCT)
A technique for obtaining sub-surface images, such as in medical imaging, based on light coherence.
Gravitational Waves Interferometers
Used for the direct observation of gravitational waves. Example: LIGO with 4 km perpendicular arms.
Mach-Zehnder Interferometer
An interferometer using beam splitters and phase shifters to measure phase shifts.
Sagnac Interferometer
Used as gyroscopes for accurate rotation measurements.
