Lecture Course: Laserphysics I - Laser and Nonlinear Optics




Dr. A. Volkmer


I Introduction

-          Course objectives

-          Lasers today: Scientific and technical applications

-          Specific properties of laser light (an overview)

-          Historical review


II Absorption and emission of light

-          Two-level system (Einstein coefficients, Lorentzian line shape function and lifetime)

-          Black-body radiation (spectral mode density and energy density (Plancks formula), limiting cases and consequences for Laser operation)

-          The Laser principle (amplification by stimulated emission, amplified stimulated emission (ASE, without cavity), light amplification by stimulated emission radiation (Laser, with cavity), rate equation analysis, 3- and 4-level laser)


III Coherence properties of the radiation field

-          The phase space cell (longitudinal and transversal uncertainty of a wave packet)

-          Complex representation of light waves

-          The superposition principle (1st order coherence function, complex degree of coherence and visibility, The Wiener-Kintchine theorem)

-          Coherence of damped waves (the wave packet)

-          Photon statistics (2nd order coherence function, Bose-Einstein distribution for thermal light, Poissonian distribution for coherent laser light, sub-Poissonian distribution for non-classical light)

-          Example: Coherence of photons from a single quantum system


IV Resonators and interferometers

-          Ray matrix derivation of resonator stability criterion (paraxial ray transfer matrix approximation, ray position for periodic system, stability diagram for spherical mirror resonator)

-          Wave optics description of Gaussian beams (solution of the paraxial Helmholtz equation (TEM modes))

-          Description of Gaussian beams (confocal parameter, beam waist)

-          Axial (longitudinal) modes (resonance frequencies for Gaussian modes, mode degeneracy in a confocal symmetric resonator)

-          Interferometer (two-beam interferometer (Michelson, Mach-Zehnder, Sagnac), the Fabry-Perot interferometer)

-          Passive optical resonator (reflection and diffraction losses)

-          Active optical resonator (Laser)

-          Transversal and longitudinal mode selection

-          Mode stability (Laser intensity and frequency stabilization schemes)


V Ultrashort laser pulses

-          Generation of ultrashort laser pulses (Q-switching, active and passive mode-locking)

-          Wave-packet description of mode-locked laser pulses (group velocity dispersion, self-phase modulation)

-          Pulse compression techniques

-          Experimental characterization of ultrashort laser pulses (2nd order autocorrelation techniques, frequency-resolved optical gating (FROG))


VI Nonlinear Optics

-          Nonlinear polarization (the nonlinear wave equation)

-          Symmetry properties of the nonlinear susceptibility tensor

-          Classical anharmonic oscillator model

-          Phase-matching requirements

-          Chi(2) processes (second-harmonic and sum-frequency generation (SHG and SFG), difference-frequency generation (DFG), optical parametric amplification and oscillation (OPA and OPO), optical rectification (OR), the Pockels effect)

-          Chi (3) processes(third-harmonic generation (THG), optical Kerr-effect (self-focusing, self-phase modulation), stimulated Raman scattering (SRS), coherent anti-Stokes Raman scattering (CARS))

-          High-harmonic generation of coherent radiation


VII Types of lasers

-          Gas lasers; different excitation mechanisms (atomic gas laser (He/Ne), metal vapor laser (Cu, Pb, Au), ionic gas laser (Ar+, Kr+, Xe+, Cd+), molecular gas lasers: infrared CO2 laser; the CO laser; far-infrared (FIR) lasers: CH3Br, CH3F, H2O/D2O, HCN, excimer and exciplex superradiators / lasers, the nitrogen (N2) superradiator/laser)

-          Liquid dye (solution) lasers (continuous and pulsed operation; tunability; ultrashort pulse generation)

-          Solid state lasers (undoped crystal lasers (excitonic lasers), doped crystal and glass lasers (dopant is laser-active): Ruby (Cr3+/Al2O3); Alexandrite (Cr3+/BeAl2O4); Emerald (Cr3+/BeAl2Si6O18); Titanium-sapphire (Ti3+/Al2O3); Neodymium-YAG (Y3Al5O12); Nd-glass; Chromium-LiSAF (LiSrAlF6); Er3+: YAlO3 up-conversion laser)

-          Semiconductor lasers (injection laser diode, distributed-feedback laser diode (DFB), vertical cavity surface emitting laser diode (VCSEL), quantum well laser)

-          Other (exotic) Lasers (chemical lasers (HF-, I- laser), the Free-Electron-Laser (FEL), X-ray lasers (Se24+; table-top lasers))