Abstract: A method for non-invasive measurement of the velocity of a medium selected from either a gas or a fluid at an examination location by boosting atoms and molecules of the medium into an excited atomic or molecular state with a focused first pulsed light beam in the investigation location, allowing the excited atoms and/or molecules to relax into a metastable state and then boosting the atoms and/or molecules in the metastable state into an excited atomic or molecular state with a second pulsed light beam that is weaker than the intensity of the first beam to transirradiate the investigation location and to produce a characteristic luminescence, detecting the characteristic luminescence of the selectively excited atoms and/or molecules and determining the coordinates of the investigation location and of the occurrence of the luminescence of a luminescent cloud in an image field and then calculating the velocity of the medium on the basis of the distance between the investigation location and the mid-point of th

Abstract: A frequency-doubled diode pumped solid state laser with intracavity frequency doubling comprises a lasing solid state medium with suitable reflecting coats which makes up a component part of a resonator cavity. The solid state laser further comprises at least one pumped light source constructed as a laser diode and a frequency doubling nonlinear optical element in the form of a nonlinear crystal with suitable reflective coatings which forms a further component part of the resonator cavity. This resonator cavity is formed between reflective coatings of the solid state medium and of the element. The pumped radiation is transmitted to the lasing solid state medium through optical means. At least one aperture of a material with good thermal conductivity is provided at the element and/or at the lasing solid state medium. The frequency doubling optical element is designed for phase matching at a higher temperature than the surrounding temperature.