• Laser -- , i.e.
• Threshold for oscillations: round trip gain * loss
• Laser = Light Amplification by Stimulated Emission of Radiation.
• History of laser: A team afford, maser lasers covering a wide spectrum from far infra-red to X-ray.
• Laser market: Diode laser (semi-conductor) versus nondiode laser; material processing, medicine, communication, R&D, optical memory & entertainment.
• Radiation: material transition from excited state to ground state; candidates -- atomic transition levels, molecular vibration levels and energy bands.
Stimulated emission optical amplification with uniformity of freq.,
direction, polarization and phase (time delay) coherent.
Spontaneous emission noise
Absorption inverse of stimulated emission
• Photon energy: , h -- planck constant; E(eV) = E / q or in wavelength .
• Population inversion (): require 3-level and 4-level atomic systems for lasing.
• Pumping sources: electrical, chemical, optical, thermal, nuclear.
• CW & pulse: average power (W), peak power (W), fluence (energy density) (), intensity (average power density) (); pulse width -- FWHM or full width.
Linewidth and coherency:
conversion between freq width and wavelength width
temporal coherence -- or ;
spatial coherence -- ;
coherence measured by .
Transverse and longitudinal modes:
transverse mode -- interference pattern labeled by for
longitudinal mode -- mode spacing (free spectral range) 1/ round trip time.
• Gain profile: spectral width of gain provided by a medium > > linewidth of cavity .
Uncertainty relationship & pulse spreading:
Nyquist theorem ; .