Laser Conceptions Sept. 6, 2017

• Laser -- optical oscillator, i.e. amplifier + feedback

• Threshold for oscillations: round trip gain * loss [equation]

• Laser = Light Amplification by Stimulated Emission of Radiation.

• History of laser: A team afford, maser [equation] 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.

• Radiative processes: Stimulated emission [equation] optical amplification with uniformity of freq., direction, polarization and phase (time delay) [equation] coherent.
Spontaneous emission [equation] noise
Absorption [equation] inverse of stimulated emission

• Photon energy: [equation], h -- planck constant; E(eV) = E / q or in wavelength [equation].

• Population inversion ([equation]): 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) ([equation]), intensity (average power density) ([equation]); pulse width -- FWHM or [equation] full width.

• Linewidth and coherency: conversion between freq width [equation] and wavelength width [equation] (again FWHM) [equation];
temporal coherence -- [equation] or [equation];
spatial coherence -- [equation];
coherence measured by interferometer.

• Transverse and longitudinal modes: transverse mode -- interference pattern labeled by [equation] for laser;
longitudinal mode -- mode spacing (free spectral range) [equation] 1/ round trip time.

• Gain profile: spectral width of gain provided by a medium [equation] > [equation] > linewidth of cavity [equation].

• Uncertainty relationship & pulse spreading:
Nyquist theorem [equation]; [equation].

Laser Engineering Chapter 1

Energy level and quantum mechanics

Last Modified: Sept. 5, 2017
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