Photonics and laser optical diagnostics for in vestigations of high-speed transient processes

摘要

The present paper gives an overview on laser optical diagnostics used for studies of fast, transient phenomena. Examples are cited, related to investigations of high power nonlinear laser radiation interacting with materials. These quasi explosively developing effects require photonic techniques with highest temporal and spatial resolution, such as provided by short-pulse and ultra-short pulsed lasers. As discussed, optical methods are useful for optimization of industrial production processes and research topics. Advantages of coherent light in classical optical methods for beam deflection or phase measurements are evaluated and compared with disadvantages, due to superimposed speckle patterns causing noise and loss of information in higher parts of spatial frequency spectra. As a major breakthrough, features of holographic three-dimensional reconstruction of optical wave-fields are emphasized. Selected examples provide a comprehensive evaluation of coherent optical diagnostic principles, as compared to non coherent techniques. Moreover, novel methods, using carreer-frequency photography are stressed in which case speckles themselves are carrying information to be measured. Further examples demonstrate the versatility and flexibility of ultra-short pulsed laser measurements down to the femtosecond-range (1 fs=10~(-15)s), whereby the Moire set-up chosen for demonstration can be substituted similarly by other optical techniques. Summarizing, it can be stated that lasers provide unique tools for highest resolution, highest accuracy measurements. Direct visualization, pump and probe techniques and other methods are adaptable to any industrial or research related requirements. As shown in the outlook, meanwhile achievable XUV attosecond pulses (1 as=10~(-18)s), generated by fs-lasers, open the door for future (so far not yet fully predictable) applications, also in the field of ultra high-speed diagnostics.