Advanced Spectroscopy Flashcards
What does LASER stand for?
Light Amplification by Stimulated Emission of Radiation
What are longitudinal modes?
Allowed frequencies or wavelengths of electromagnetic radiation that can be sustained within the optical cavity.
What is a gain profile?
The variation of the optical gain as a function of wavelength or frequency in the laser medium.
What is a wavepacket?
A vibrational superposition of vibrational wavefunctions.
Why is a free-electron laser not a real laser?
A free-electron laser is generated from coherent synchrotron radiation, not stimulated emission.
What are insertion devices?
These are components inserted into the straight sections of a storage ring in a synchrotron or linear accelerator, designed to enhance the intensity and modify the spectrum of the synchrotron radiation produced by the accelerated electrons.
What is a wavelength shifter?
A material or device that absorbs higher frequency photons and emits lower frequency photons.
What is a multipole wiggler and how does it work?
periodic high field devices used to generate enhanced flux levels (∝ no. of poles)
- multiple wavelength shifters i.e. dipole magnets w/ alternating polarity on same straight section
Intensity adds incoherently
Enhances flux
What is an undulator and how does it work?
periodic lower field devices that generate radiation at specific harmonics
- periodic arrangements of dipole magnets but the “wiggling angle” is smaller than or close to the natural photon emission angle 1/γ (lower B)
What does it mean to trap ions?
Use an electric potential minimum to confine the charged particles
How does Kerr lens mode-locking work?
Medium’s refractive index has slight intensity dependence
n(I)=n_0+n_2 I
Beam self-focuses, more pronounced for higher int
Placing aperture favours high int pulses, selectively amplifies high-intensity spikes and absorbs low-intensity light
How does mode-locking work?
Many longitudinal modes oscillating in laser cavity, a mechanism induces fixed phase relationship between modes, they constructively interfere to make one ultrashort pulse.
What is the difference between active and passive mode-locking?
Active: external modulator actively modulates losses/OPL in laser cavity
Passive: mode-locking mechanism is inherent to laser cavity i.e. saturable absorber or Kerr lens mode-locking modulator
