Laser Beam Characterization

This handbook for the characterization of laser beams covers the theoretical background of each property, references to the respective ISO standards, experimental setups required for reliable measurements, and strengths and weaknesses of the corresponding commercial devices.

Table of Contents:
Introduction Short introduction into physical optics Ray optics Light as geometrical rays Free propagation of light rays The law of refraction Paraxial approximation, Gaussian optics Law of refraction in paraxial approximation Refraction at spherical surfaces Ray transfer matrices in one dimension Ray transfer matrices in two dimensions Separability of optical systems Separierbarkeit optischer Systeme Limits of of Gaussian optics, aberrations Wave optics Light as an electro-magnetic wave Harmonic waves, frequency, wavelength Amplitude, phase and coherence Huygens principle Collins integral (optional) Gaussian beams Definition of Gaussian beams Gaussian beam parameters and free propagation Propagations through first order optical systems Partial spatial coherence Influence of reduced spatial coherence The Wigner distribution Gaussian Schell-modell beams Moments of power density distributions Definition and meaning of first order moments Propagation of first order moments through first order systems Definition and meaning of centered, second order moments Propagation of second order moments through first order moments Definition of the variance diameter in one dimension Propagation of the variance diameter in one dimensional systems Beam propagation parameter and beam propagation ratio M2 in one dimensional optical systems Definition of the variance ellipse in two dimensions Propagation of the variance ellipse in two-dimensional optical systems Beam propagation parameters and invariants in two dimensional systems Separable beams Astigmatism and geometrical beam classification Power and Energy Detectors Calorimetric detectors Pyroelectric detectors Thermopile detectors Photo diodes Integrating spheres (Ulbricht spheres) Calibration Temporal behaviour Pulsed emission Pulse duration Pulse repetition frequency Pulse rise and delay time Continuous wave emission Noise Power density distribution Parameters of power density distributions Center of gravity Threshold diameter Radial power content diameter ("power-in-the-bucket") Linear power content diameter ("knife-edge method") Variance diameter Flatness, Steepness, Roundness Detectors for power density distributions Variable apertures ("iris aperture", "variable slit",...) Scanning Detectors (Pinhole, photo diodes) CCD-Kameras Pyro-electric cameras Measurement of power density distributions Alignment Attenuation Calibration Measurement with (CCD) cameras, choise of ROI, saturation, baseline correction, typical errors Evaluation of power density distributions Calculation of parameters Error discussion Beam propagation parameters Caustic measurements with (CCD) cameras Typical setup Required caustic range Fitting process Checking the beam symmetry Back calculation to reference plane Measurement arrangement Laboratory conditions Stability of laser parameters Minimum free aperture of optical components Pointing stability Positional stability Directional stability Detectors Wave fronts Wave front und phase distribution of coherent beams Wave front of partially coherent beams Shack-Hartmann-Sensor for wavefront measurements Determination of the beam propagation ratio with the Shack-Hartmann-Sensor Interferometric measurements of wave fronts Coherence Interferometric determination of coherence properties Superposition of beams and contrast Longitudinal (temporal) coherence Lateral (spatial) coherence Spectral properties Typical power spectra of various laser types Spectrometer Polarization States of polarization Spatially homogenous polarization Jones matrices Polarizer Relevant international standards

About the Author :
Dr. Bernd Eppich is staff scientist at the Ferdinand-Braun-Institut in Berlin since 2005, where he is responsible for laser beam characterization of diode lasers and the design of micro-optical beam forming system. He holds degrees from the Technical Universities of Karlsruhe and Berlin where he investigated design criteria for resonators, the optimization of beam quality, and theoretical and experimental aspects of laser beam characterization. He developed a metrological method for reconstructing the four-dimensional Wigner distribution, allowing for the complete characterization of partially coherent laser radiation with respect to its propagation behavior. As a member of the working team "Definitions, Test Control Units and Testing Methods" of the DIN standards committee "Precision Mechanics and Optics" he was the leading author of the international standard ISO 11146, which is an important standard concerning laser beam characteristics. After his Ph.D. Bernd Eppich worked on methods for early recognition of rheumatism and on non-invasive blood glucose measurement at the Laser- and Medizin-Technologie Berlin company. He was awarded with the Innovation Competition Prize of the German Federal Ministry of Research and Education for the "Advancement of Medical Technology" in 2000.