Rough surface interferometry with a two-wavelength heterodyne speckle interferometer

Two-wavelength double heterodyne interferometry using a matched grating technique

“…(9) can be simplified to Although a DHI virtually works with an effective (long) wavelength Xef, the target is illuminated by two short laser wavelengths Xi and X 2 that generate speckles on an optically rough surface. The influence of varying speckle intensities on phase error probabilities was theoretically and experimentally examined by Fercher et al 6 We found their results confirmed, but in our measurements the target distances were small and strong intensities occurred. By the choice of the integration time of the phase meter we were able to compensate for phase errors caused by temporary signal fading.…”

“…The unambiguous distance range of the DHI was 27.75 Azm and enabled measurements on machined aluminum samples. Intensity thresholding to reject phase (distance) data of signals with low amplitudes, as suggested by Fercher et al, 6 was not required in our experiments. The strong signals involved allowed us to compensate for signal fading and related phase errors by appropriate choice of phasemeter integration time while scanning.…”

“…4 Polhemus 5 demonstrated contrast modulation of interference fringes by Xef generated with two wavelengths simultaneously. A scanning two-wavelength heterodyne speckle interferometer using a krypton laser was described by Fercher et al 6 where two phasemeters are needed to finally calculate the phase of the effective wavelength.…”

White light interferometric surface profiler

“…A number of techniques have been developed to extend this range including heterodyne interferometry and multiple interferometry. [5][6][7][8][9][10] Many papers detail a wide variety of algorithms that can be used with these profilers. 3,4,11,12 However, these methods are still limited to ranges of the order of 10 m.…”

Desenvolvimento de métodos para a geração e controle da emissão em lasers aleatórios e <i>speckle</i>

“…Uma abordagem diferente foi proposta nos primeiros trabalhos sobre lasers sem cavidade ressonante [22,23], onde o cristal laser foi posicionado entre um espelho e uma superfície espalhadora. Baseamo-nos neste conceito para definir o mecanismo de realimentação espacialmente localizado, desde que o meio ativo e os elementos espalhadores estejam separados espacialmente.…”